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The dorsal raphe nucleus (DRn) receives glutamatergic inputs from numerous brain areas that control the function of DRn serotonin (5-HT) neurons. By integrating these synaptic inputs, 5-HT neurons modulate a plethora of behaviors and physiological functions. However, it remains unknown whether the excitatory inputs onto DRn 5-HT neurons can undergo activity-dependent change of strength, as well as the mechanisms that control their plasticity. Here, we describe a novel form of spike-timing-dependent long-term potentiation (tLTP) of glutamate synapses onto rat DRn 5-HT neurons. This form of synaptic plasticity is initiated by an increase in postsynaptic intracellular calcium but is maintained by a persistent increase in the probability of glutamate release. The tLTP of glutamate synapses onto DRn 5-HT is independent of NMDA receptors but requires the activation of calcium-permeable AMPA receptors and voltage-dependent calcium channels. The presynaptic expression of the tLTP is mediated by the retrograde messenger nitric oxide (NO) and activation of cGMP/PKG pathways. Collectively, these results indicate that glutamate synapses in the DRn undergo activity-dependent synaptic plasticity gated by NO signaling and unravel a previously unsuspected role of NO in controlling synaptic function and plasticity in the DRn., Competing Interests: Authors report no conflict of interest.

Neuronal pentraxin 1 (NPTX1) has been implicated in Alzheimer's disease, being present in and around dystrophic neurons in plaques, affecting glutamatergic transmission postsynaptically and mediating effects of amyloidβ. Here, we confirm the presence of NPTX1 around plaques in postmortem Alzheimer's disease brain and report that acutely applied human NPTX1 increases paired-pulse ratio at mouse CA3-CA1 hippocampal synapses, indicating a decrease in glutamate release. In contrast, chronic exposure to NPTX1, NPTX2, or NPTX receptor decreases paired-pulse ratio, mimicking some of the earliest changes in mice expressing familial Alzheimer's disease genes. The peripheral pentraxin, serum amyloid P component (SAP), causes similar synaptic effects to NPTX1. The presence of SAP on amyloid plaques in Alzheimer's disease confirms that it can enter the brain. We show that SAP and neuronal pentraxins can interact and that SAP can enter the brain if the blood-brain barrier is compromised, suggesting that peripheral pentraxins could affect central synaptic transmission via this interaction, especially in the event of blood-brain barrier breakdown., (© The Author 2017. Published by Oxford University Press.)

GABA C receptors are ligand-gated chloride channels and have important roles in some neurological functions like vision. Recent investigations demonstrated that these receptors are also expressed in the somatosensory cortex. In this study, we investigated the effect of (1,2,5,6-tetrahydropyridin-4-yl)methylphosphinic acid (TPMPA) (GABA C receptor antagonist) on the properties of the neuronal response to natural stimuli (whisker deflection) in deep layers of rat barrel cortex. Twenty-eight male Wistar rats, weighing 230-260 g, were used in this study. TPMPA (100 μmol/rat) was administered intracerebroventricularly (ICV). Neuronal responses to deflection of principal (PW) and adjacent (AW) whiskers were recorded in barrel cortex using tungsten microelectrodes. A computer-controlled mechanical displacement was used to deflect whiskers individually or in combination at 30 ms inter-stimulus intervals. ON and OFF responses for PW and AW deflections were measured. A condition-test ratio (CTR) was computed to quantify neuronal responses to whisker interactions. Our data suggest that ICV administration of TPMPA increased neuronal spontaneous activity, ON and OFF responses to PW, and/or AW deflections. However, CTR for neither ON nor OFF responses changed following TPMPA administration. The results of this study demonstrated that inhibition of GABA C receptors by TPMPA can modulate neuronal response properties in rat barrel cortex.

Key Points: Relaxin-3 is a stress-responsive neuropeptide that acts at its cognate receptor, RXFP3, to alter behaviours including feeding. In this study, we have demonstrated a direct, RXFP3-dependent, inhibitory action of relaxin-3 on oxytocin and vasopressin paraventricular nucleus (PVN) neuron electrical activity, a putative cellular mechanism of orexigenic actions of relaxin-3. We observed a Gα i/o -protein-dependent inhibitory influence of selective RXFP3 activation on PVN neuronal activity in vitro and demonstrated a direct action of RXFP3 activation on oxytocin and vasopressin PVN neurons, confirmed by their abundant expression of RXFP3 mRNA. Moreover, we demonstrated that RXFP3 activation induces a cadmium-sensitive outward current, which indicates the involvement of a characteristic magnocellular neuron outward potassium current. Furthermore, we identified an abundance of relaxin-3-immunoreactive axons/fibres originating from the nucleus incertus in close proximity to the PVN, but associated with sparse relaxin-3-containing fibres/terminals within the PVN., Abstract: The paraventricular nucleus of the hypothalamus (PVN) plays an essential role in the control of food intake and energy expenditure by integrating multiple neural and humoral inputs. Recent studies have demonstrated that intracerebroventricular and intra-PVN injections of the neuropeptide relaxin-3 or selective relaxin-3 receptor (RXFP3) agonists produce robust feeding in satiated rats, but the cellular and molecular mechanisms of action associated with these orexigenic effects have not been identified. In the present studies, using rat brain slices, we demonstrated that relaxin-3, acting through its cognate G-protein-coupled receptor, RXFP3, hyperpolarized a majority of putative magnocellular PVN neurons (88%, 22/25), including cells producing the anorexigenic neuropeptides, oxytocin and vasopressin. Importantly, the action of relaxin-3 persisted in the presence of tetrodotoxin and glutamate/GABA receptor antagonists, indicating its direct action on PVN neurons. Similar inhibitory effects on PVN oxytocin and vasopressin neurons were produced by the RXFP3 agonist, RXFP3-A2 (82%, 80/98 cells). In situ hybridization histochemistry revealed a strong colocalization of RXFP3 mRNA with oxytocin and vasopressin immunoreactivity in rat PVN neurons. A smaller percentage of putative parvocellular PVN neurons was sensitive to RXFP3-A2 (40%, 16/40 cells). These data, along with a demonstration of abundant peri-PVN and sparse intra-PVN relaxin-3-immunoreactive nerve fibres, originating from the nucleus incertus, the major source of relaxin-3 neurons, identify a strong inhibitory influence of relaxin-3-RXFP3 signalling on the electrical activity of PVN oxytocin and vasopressin neurons, consistent with the orexigenic effect of RXFP3 activation observed in vivo., (© 2017 The Authors. The Journal of Physiology © 2017 The Physiological Society.)

Choline is present at cholinergic synapses as a product of acetylcholine degradation. In addition, it is considered a selective agonist for α5 and α7 nicotinic acetylcholine receptors (nAChRs). In this study, we determined how choline affects action potentials and excitatory synaptic transmission using extracellular and intracellular recording techniques in CA1 area of hippocampal slices obtained from both mice and rats. Choline caused a reversible depression of evoked field excitatory postsynaptic potentials (fEPSPs) in a concentration-dependent manner that was not affected by α7 nAChR antagonists. Moreover, this choline-induced effect was not mimicked by either selective agonists or allosteric modulators of α7 nAChRs. Additionally, this choline-mediated effect was not prevented by either selective antagonists of GABA receptors or hemicholinium, a choline uptake inhibitor. The paired pulse facilitation paradigm, which detects whether a substance affects presynaptic release of glutamate, was not modified by choline. On the other hand, choline induced a robust increase of population spike evoked by orthodromic stimulation but did not modify that evoked by antidromic stimulation. We also found that choline impaired recurrent inhibition recorded in the pyramidal cell layer through a mechanism independent of α7 nAChR activation. These choline-mediated effects on fEPSP and population spike observed in rat slices were completely reproduced in slices obtained from α7 nAChR knockout mice, which reinforces our conclusion that choline modulates synaptic transmission and neuronal excitability by a mechanism independent of nicotinic receptor activation.

Due to their fast kinetic properties, K v 3.1 voltage gated potassium channels are important in setting and controlling firing frequency in neurons and pivotal in generating high frequency firing of interneurons. Pharmacological activation of K v 3.1 channels may possess therapeutic potential for treatment of epilepsy, hearing disorders, schizophrenia and cognitive impairments. Here we thoroughly investigate the selectivity and positive modulation of the two small molecules, EX15 and RE01, on K v 3 channels. Selectivity studies, conducted in Xenopus laevis oocytes confirmed a positive modulatory effect of the two compounds on K v 3.1 and to a minor extent on K v 3.2 channels. RE01 had no effect on the K v 3.3 and K v 3.4 channels, whereas EX15 had an inhibitory impact on the K v 3.4 mediated current. Voltage-clamp experiments in monoclonal hK v 3.1b/HEK293 cells (34 °C) revealed that the two compounds indeed induced larger currents and faster activation kinetics. They also decrease the speed of deactivation and shifted the voltage dependence of activation, to a more negative activation threshold. Application of action potential clamping and repetitive stimulation protocols of hK v 3.1b expressing HEK293 cells revealed that EX15 and RE01 significantly increased peak amplitude, half width and decay time of K v 3.1 mediated currents, even during high-frequency action potential clamping (250 Hz). In rat hippocampal slices, EX15 and RE01 increased neuronal excitability in fast-spiking interneurons in dentate gyrus. Action potential frequency was prominently increased at minor depolarizing steps, whereas more marginal effects of EX15 and RE01 were observed after stronger depolarizations. In conclusion, our results suggest that EX15 and RE01 positive modulation of K v 3.1 and K v 3.2 currents facilitate increased firing frequency in fast-spiking GABAergic interneurons., (Copyright © 2017 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Alpha-7 nicotinic acetylcholine receptor (α7-nAChR) agonists can prevent glutamate-induced excitotoxicity in cultured retinal ganglion cells (RGCs). However, the neuroprotective effects and the mechanism of action of PNU-282987, an α7-nAChR agonist, in a chronic in vivo rat glaucoma model are poorly understood. We found that elevated intraocular pressure (IOP) downregulated retinal α7-nAChR expression. Electroretinography revealed that the amplitude of the photopic negative response (PhNR) decreased in parallel with the loss of RGCs caused by elevated IOP. PNU-282987 enhanced RGC viability and function and decreased terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL)-positive signals in RGCs. Patch-clamp recordings revealed differences in the baseline frequencies and decay times of the miniature GABAergic inhibitory postsynaptic currents (mIPSCs) of RGCs between control and glaucomatous retinal slices. The results of western blotting and immunostaining showed that glutamic acid decarboxylase 65/67 and GABA deficits persisted in glaucomatous retinas and that these deficits were reversed by PNU-282987. Patch-clamp recordings also showed that PNU-282987 significantly increased the frequency and amplitude of the GABAergic mIPSCs of RGCs. The protective effects of PNU-292987 were blocked by intravitreal administration of selective GABA A receptor antagonists. The modulation of GABAergic synaptic transmission by PNU-282987 causes de-excitation of ganglion cell circuits and suppresses excitotoxic processes.

In the insect olfactory system, odor information is transferred from the antennal lobe (AL) to higher brain areas by projection neurons (PNs) in multiple AL tracts (ALTs). In several species, one of the ALTs, the mediolateral ALT (mlALT), contains some GABAergic PNs; in the Drosophila brain, the great majority of ventral PNs (vPNs) are GABAergic and project through this tract to the lateral horn (LH). Most excitatory PNs (ePNs), project through the medial ALT (mALT) to the mushroom body (MB) and the LH. Recent studies have shown that GABAergic vPNs play inhibitory roles at their axon terminals in the LH. However, little is known about the properties and functions of vPNs at their dendritic branches in the AL. Here, we used optogenetic and patch clamp techniques to investigate the functional roles of vPNs in the AL. Surprisingly, our results show that specific activation of vPNs reliably elicits strong excitatory postsynaptic potentials (EPSPs) in ePNs. Moreover, the connections between vPNs and ePNs are mediated by direct chemical synapses. Neither pulses of GABA, nor pharmagological, or genetic blockade of GABAergic transmission gave results consistent with the involvement of GABA in vPN-ePN excitatory transmission. These unexpected results suggest new roles for the vPN population in olfactory information processing.

Rationale: There is accumulating evidence for a role of GABA B receptors in depression. GABA B receptors are heterodimers of GABA B1 and GABA B2 receptor subunits. The predominant GABA B1 subunit isoforms are GABA B1a and GABA B1b . GABA B1 isoforms in mice differentially influence cognition, conditioned fear, and susceptibility to stress, yet their influence in tests of antidepressant-like activity has not been fully investigated., Objectives: Given the interactions between GABA B receptors and the serotonergic system and the involvement of 5-HT 1A receptors (5-HT 1A R) in antidepressant action, we sought to evaluate 5-HT 1A R function in GABA B1a -/- and GABA B1b -/- mice., Methods: GABA B1a -/- and GABA B1b -/- mice were assessed in the forced swim test (FST), and body temperature and hypothalamic-pituitary-adrenal (HPA) responses to the 5-HT 1A R agonist 8-OH-DPAT were determined. Brain 5-HT 1A R expression was assessed by [ 3 H]-MPPF and [ 3 H]-8-OH-DPAT autoradiography and 5-HT 1A R G-protein coupling by [ 35 S]GTP-γ-S autoradiography., Results: As previously described, GABA B1a -/- mice showed an antidepressant-like profile in the FST. GABA B1a -/- mice also demonstrated profoundly blunted hypothermic and motoric responses to 8-OH-DPAT. Furthermore, 8-OH-DPAT-induced corticosterone and adrenocorticotropic hormone (ACTH) release were both attenuated in GABA B1a -/- mice. Interestingly, [ 3 H]-MPPF and [ 3 H]-8-OH-DPAT binding was largely unaffected by genotype. [ 35 S]GTP-γ-S autoradiography suggested that altered 5-HT 1A R G-protein coupling only partially contributes to the functional presynaptic 5-HT 1A R desensitization, and not at all to the blunted postsynaptic 5-HT 1A R-mediated responses, seen in GABA B1a -/- mice., Conclusion: These data demonstrate distinct functional links between 5-HT 1A Rs and the GABA B1a subunit isoform and suggest that the GABA B1a isoform may be implicated in the antidepressant-like effects of GABA B receptor antagonists and in neurobiological mechanisms underlying depression.

Febrile seizure (FS) is the most common seizure type in infants and young children. FS may induce functional changes in the hippocampal circuitries. Abnormality of excitatory and inhibitory neurotransmissions was previously related to wide-spread seizure attack in the hippocampus following recurrent seizure onset. To clarify the involvement of expressional changes and functional alterations of hippocampal interneurons with epileptogenesis following FS, we investigated long-term effects following recurrent seizure in a hyperthermia-induced seizure animal model. At 12 weeks following FS, the recurrent seizure time period, local field potentials (LFP) revealed high amplitude potential and a sharp wave characteristic of epilepsy. Mossy fiber reorganization in the hippocampus was also detected as abnormal synaptic connection at 8 weeks. Calretinin (CR) -positive interneurons were transiently enhanced during epileptogenic period at 7-9 weeks after FS in the CA1 and DG region and it is double labeled with VGLUT-1. However, although GABA A -α1 immunoreactivities were un-changed as similar to control hippocampus at 7-9 weeks after seizure onset, its expression was significantly enhanced at 4 weeks and 12 weeks and it is colocalized with GABA. Furthermore, the field excitatory postsynaptic potential (fEPSP) and the paired-pulse responses including population spike (PS) latency, excitability ratio and PS2/PS1 ratio were markedly altered in the CA1 and DG region at 12 weeks after FS. Therefore, our findings in present study indicate that these time-dependent changes may be based on the persistent alterations of hippocampal neuronal circuits in balance between excitatory and inhibitory responses, and may lead to the epileptogenesis and spread of seizure activity following FS., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Topography in the avian cochlear nucleus magnocellularis (NM) is represented as gradually increasing characteristic frequency (CF) along the caudolateral-to-rostromedial axis. In this study, we characterized the organization and cell biophysics of the caudolateral NM (NMc) in chickens ( Gallus gallus ). Examination of cellular and dendritic architecture first revealed that NMc contains small neurons and extensive dendritic processes, in contrast to adendritic, large neurons located more rostromedially. Individual dye-filling study further demonstrated that NMc is divided into two subregions, with NMc2 neurons having larger and more complex dendritic fields than NMc1. Axonal tract tracing studies confirmed that NMc1 and NMc2 neurons receive afferent inputs from the auditory nerve and the superior olivary nucleus, similar to the adendritic NM. However, the auditory axons synapse with NMc neurons via small bouton-like terminals, unlike the large end bulb synapses on adendritic NM neurons. Immunocytochemistry demonstrated that most NMc2 neurons express cholecystokinin but not calretinin, distinct from NMc1 and adendritic NM neurons that are cholecystokinin negative and mostly calretinin positive. Finally, whole-cell current clamp recordings revealed that NMc neurons require significantly lower threshold current for action potential generation than adendritic NM neurons. Moreover, in contrast to adendritic NM neurons that generate a single-onset action potential, NMc neurons generate multiple action potentials to suprathreshold sustained depolarization. Taken together, our data indicate that NMc contains multiple neuron types that are structurally, connectively, molecularly, and physiologically different from traditionally defined NM neurons, emphasizing specialized neural properties for processing low-frequency sounds.

The lateral habenula (LHb) plays an important role in the regulation of depression. At present, it is not clear whether GABA A receptor-mediated inhibitory transmission in the LHb is involved in Parkinson's disease (PD)-associated depression. In this study, unilateral 6-hydroxydopamine lesions of the substantia nigra in rats induced depressive-like behaviors and led to hyperactivity of LHb neurons compared to sham-operated rats, which attribute to depletion of dopamine, and decreased synthesis and release of GABA and increased release of glutamate in the LHb. Intra-LHb injection of GABA A receptor agonist muscimol produced antidepressant-like effects, while the injection of GABA A receptor antagonist picrotoxin induced or increased the expression of depressive-like behaviors in sham-operated and the lesioned rats. However, the doses producing these behavioral effects in the lesioned rats were lower than those in sham-operated rats. Intra-LHb injection of muscimol decreased the firing rate of LHb neurons and increased the medial prefrontal cortex serotonin (5-HT) release; conversely, picrotoxin increased the firing rate of the neurons and decreased 5-HT release in two groups of rats. Compared to sham-operated rats, the duration of muscimol and picrotoxin action on the firing rate of the neurons and 5-HT release was prolonged in the lesioned rats. These changes in the lesioned rats were associated with up-regulation of the expression of α1 subunit-containing GABA A receptors and reduction of GABA release in the LHb. Collectively, our findings suggest that degeneration of the nigrostriatal pathway impairs GABA A receptor-mediated inhibitory transmission in the LHb, and the transmission is important for regulating PD-associated depression., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

In birds and mammals, the neuroendocrine regulation of energy balance is conserved in many aspects. Despite significant similarities between the two groups, differences in the regulatory mechanisms were detected. The present study was performed to carry out investigations of the influence of human leptin and GABA B -receptor agonist and antagonist on the firing rate of neurons of the Nucleus infundibuli hypothalami in brain slices from juvenile chickens. For the first time, we demonstrated a clear, dose-related change in the firing rate of hypothalamic neurons in juvenile chickens after the acute application of recombinant human leptin (1, 10, and 100 nM). All investigated neurons increased their subsequent firing rate. Application of GABA B -receptor agonist baclofen (1 µM) blocked, while antagonist CGP 35348 (10 µM) increased the spontaneous neuronal activity. Simultaneous application of baclofen and leptin reduced the effect observed from single leptin application. This was not found after simultaneously application of leptin and CGP. Altogether, our results indicate that in bird brain slices, and exemplarily in those of the chicken, hypothalamic neurons show mammalian-like responsiveness after acute leptin and GABA application. GABA B -mechanisms involved in GABA release play a likely important role in the leptin-mediated effects on NI neurons via functional leptin receptors.

Hyperbaric oxygen induced in rats a decrease in striatal dopamine levels. Such decrease could be a result of changes in glutamatergic and GABAergic controls of the dopaminergic neurons into the Substantia Nigra Pars Compacta. The aim of this study was to determine the role of gluatamatergic and Gama-Amino-Butyric-Acid neurotransmissions in this alteration. Dopamine-sensitive electrodes were implanted into the striatum under general anesthesia. After one week rest, awaked rats were exposed to oxygen-nitrogen mixture at a partial pressure of oxygen of 3 absolute atmospheres. Dopamine level was monitored continuously (every 3 min) by in vivo voltammetry with multifiber carbon electrodes before and during hyperbaric oxygen exposure. Hyperbaric oxygen induced a decrease in dopamine level in relationship with the increase in partial pressure of oxygen (-40% at 3 ATA). The used of N-Methyl-D-Aspartate, agonist of glutamatergic N-Methyl-D-Aspartate receptors did not improve considerably this change and gabazine antagonist of Gama-Amino-Butyric-Acid-a receptors induced some little alteration of this change. These results suggest the involvement of other mechanisms.

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). This article has been retracted at the request of the authors. The authors have requested to retract this paper as the corresponding author had not sought the prior agreement of his co-authors to submit the paper for publication., (Copyright © 2016 Elsevier Inc. All rights reserved.)

The gene transfer-mediated expression of inhibitory ion channels in nociceptive neurons holds promise for treating intractable pain. Chemogenetics, which involves expressing constructs activated by biologically inert molecules, is of particular interest as it permits tunable neuromodulation. However, current chloride-permeable chemogenetic constructs are problematic as they mediate a tonic chloride influx which over time would deplete the chloride electrochemical gradient and reduce inhibitory efficacy. Inflammatory pain sensitization can be caused by prostaglandin E2-mediated inhibition of glycinergic inhibitory postsynaptic currents in spinal nociceptive neurons. We developed a highly conducting (100 pS) inhibitory chemogenetic construct based on a human glycine receptor (α1 Y279F,A288G ) with high ivermectin sensitivity. When virally infected into spinal neurons, 10 nM ivermectin increased the magnitude and frequency of glycinergic postsynaptic currents without activating a tonic chloride flux. The construct should thus produce analgesia. Its human origin and the well-established biocompatibility of its ligand suggest it may be suited to human use.

In chronic pain, the medial prefrontal cortex (mPFC) is deactivated and mPFC-dependent tasks such as attention and working memory are impaired. We investigated the mechanisms of mPFC deactivation in the rat spared nerve injury (SNI) model of neuropathic pain. Patch-clamp recordings in acute slices showed that, 1 week after the nerve injury, cholinergic modulation of layer 5 (L5) pyramidal neurons was severely impaired. In cells from sham-operated animals, focal application of acetylcholine induced a left shift of the input/output curve and persistent firing. Both of these effects were almost completely abolished in cells from SNI-operated rats. The cause of this impairment was an ∼60% reduction of an M1-coupled, pirenzepine-sensitive depolarizing current, which appeared to be, at least in part, the consequence of M1 receptor internalization. Although no changes were detected in total M1 protein or transcript, both the fraction of the M1 receptor in the synaptic plasma membrane and the biotinylated M1 protein associated with the total plasma membrane were decreased in L5 mPFC of SNI rats. The loss of excitatory cholinergic modulation may play a critical role in mPFC deactivation in neuropathic pain and underlie the mPFC-specific cognitive deficits that are comorbid with neuropathic pain. SIGNIFICANCE STATEMENT The medial prefrontal cortex (mPFC) undergoes major reorganization in chronic pain. Deactivation of mPFC output is causally correlated with both the cognitive and the sensory component of neuropathic pain. Here, we show that cholinergic excitation of commissural layer 5 mPFC pyramidal neurons is abolished in neuropathic pain rats due to a severe reduction of a muscarinic depolarizing current and M1 receptor internalization. Therefore, in neuropathic pain rats, the acetylcholine (ACh)-dependent increase in neuronal excitability is reduced dramatically and the ACh-induced persisting firing, which is critical for working memory, is abolished. We propose that the blunted cholinergic excitability contributes to the functional mPFC deactivation that is causal for the pain phenotype and represents a cellular mechanism for the attention and memory impairments comorbid with chronic pain., (Copyright © 2017 the authors 0270-6474/17/372292-13$15.00/0.)

The N-methyl-d-aspartate (NMDA) receptor antagonist, phencyclidine, induces behavioral changes in rodents mimicking symptoms of schizophrenia, possibly mediated through dysregulation of glutamatergic control of mesolimbic dopamine release. We tested the hypothesis that NMDA receptor activation modulates accumbens dopamine release, and that phencyclidine pretreatment altered this modulation. NMDA caused a receptor-specific, dose-dependent decrease in electrically stimulated dopamine release in nucleus accumbens brain slices. This decrease was unaffected by picrotoxin, making it unlikely to be mediated through GABAergic neurones, but was decreased by the metabotropic glutamate receptor antagonist, (RS)-α-methyl-4-sulfonophenylglycine, indicating that NMDA activates mechanisms controlled by these receptors to decrease stimulated dopamine release. The effect of NMDA was unchanged by in vivo pretreatment with phencyclidine (twice daily for 5 days), with a washout period of at least 7 days before experimentation, which supports the hypothesis that there is no enduring direct effect of PCP at NMDA receptors after this pretreatment procedure. We propose that NMDA depression of accumbal dopamine release is mediated by metabotropic glutamate receptors located pre- or perisynaptically, and suggest that NMDA evoked increased extrasynaptic spillover of glutamate is sufficient to activate these receptors that, in turn, inhibit dopamine release. Furthermore, we suggest that enduring functional changes brought about by subchronic phencyclidine pretreatment, modeling deficits in schizophrenia, are downstream effects consequent on chronic blockade of NMDA receptors, rather than direct effects on NMDA receptors themselves.

The serotonin (5-HT) system and the amygdala are key regulators of emotional behavior. Several lines of evidence suggest that 5-HT transmission in the amygdala is implicated in the susceptibility and drug treatment of mood disorders. Therefore, elucidating the physiological mechanisms through which midbrain 5-HT neurons modulate amygdala circuits could be pivotal in understanding emotional regulation in health and disease. To shed light on these mechanisms, we performed patch-clamp recordings from basal amygdala (BA) neurons in brain slices from mice with channelrhodopsin genetically targeted to 5-HT neurons. Optical stimulation of 5-HT terminals at low frequencies (≤1 Hz) evoked a short-latency excitation of BA interneurons (INs) that was depressed at higher frequencies. Pharmacological analysis revealed that this effect was mediated by glutamate and not 5-HT because it was abolished by ionotropic glutamate receptor antagonists. Optical stimulation of 5-HT terminals at higher frequencies (10-20 Hz) evoked both slow excitation and slow inhibition of INs. These effects were mediated by 5-HT because they were blocked by antagonists of 5-HT 2A and 5-HT 1A receptors, respectively. These fast glutamate- and slow 5-HT-mediated responses often coexisted in the same neuron. Interestingly, fast-spiking and non-fast-spiking INs displayed differential modulation by glutamate and 5-HT. Furthermore, optical stimulation of 5-HT terminals did not evoke glutamate release onto BA principal neurons, but inhibited these cells directly via activation of 5-HT 1A receptors and indirectly via enhanced GABA release. Collectively, these findings suggest that 5-HT neurons exert a frequency-dependent, cell-type-specific control over BA circuitry via 5-HT and glutamate co-release to inhibit the BA output. SIGNIFICANCE STATEMENT The modulation of the amygdala by serotonin (5-HT) is important for emotional regulation and is implicated in the pathogenesis and treatment of affective disorders. Therefore, it is essential to determine the physiological mechanisms through which 5-HT neurons in the dorsal raphe nuclei modulate amygdala circuits. Here, we combined optogenetic, electrophysiological, and pharmacological approaches to study the effects of activation of 5-HT axons in the basal nucleus of the amygdala (BA). We found that 5-HT neurons co-release 5-HT and glutamate onto BA neurons in a cell-type-specific and frequency-dependent manner. Therefore, we suggest that theories on the contribution of 5-HT neurons to amygdala function should be revised to incorporate the concept of 5-HT/glutamate cotransmission., (Copyright © 2017 Sengupta et al.)

GABA mediated neuronal system regulates hippocampus-dependent memory and stress responses by controlling plasticity and neuronal excitability. Here, we demonstrate that betaine ameliorates water-immersion restraint stress (WIRS)-induced memory impairments. This improvement was inhibited by a betaine/GABA transporter-1 (GABA transporter-2: GAT2) inhibitor, NNC 05-2090. In this study, we investigated whether memory amelioration by betaine was mediated by the GABAergic neuronal system. Adult male mice were co-administered betaine and GABA receptor antagonists after WIRS. We also examined whether memory impairment after WIRS was attenuated by GABA receptor agonists. The memory functions were evaluated using a novel object recognition test 3-6 days after WIRS and/or the step-down type passive avoidance test at 7-8 days. The co-administration of the GABA A receptor antagonist bicuculline (1mg/kg) or the GABA B receptor antagonist phaclofen (10mg/kg) 1h after WIRS suppressed the memory-improving effects induced by betaine. Additionally, the administration of the GABA A receptor agonist muscimol (1mg/kg) or the GABA B receptor agonist baclofen (10mg/kg) 1h after WIRS attenuated memory impairments. These results were similar to the data observed with betaine. The treatment with betaine after WIRS significantly decreased the expression of GABA transaminase, and this effect was partially blocked by NNC 05-2090 in the hippocampus. WIRS caused a transient increase in hippocampal GABA levels and the changes after WIRS were not affected by betaine treatment in an in vivo microdialysis study. These results suggest that the beneficial effects of betaine may be mediated in part by changing the GABAergic neuronal system., (Copyright © 2016 Elsevier B.V. All rights reserved.)

The neostriatum plays a central role in motor coordination where nerve cells operate neuronal inhibition through GABAergic transmission. The neostriatum expresses a wide range of GABA-A subunits, including GABAρ1 and ρ2 which are restricted to a fraction of GABAergic interneurons and astrocytes. Spontaneous postsynaptic currents (sPSCs) evoked by 4-aminopyridine (4-AP) were recorded from neurones of the dorsal neostriatum, and their frequency was reduced > 50% by the selective GABAρ antagonist (1,2,5,6-Tetrahydropyridine-4-yl) methylphosphinic acid (TPMPA). Additionally, we recorded GABA evoked currents from astrocytes in vitro and in situ. Astrocytes in vitro showed modulation by pentobarbital and desensitization upon consecutive applications of GABA. However, modulation by pentobarbital was absent and no significant desensitization was detected from astrocytes in situ. Moreover, TPMPA-sensitive GABA-currents that were insensitive to bicuculline were also recorded from astrocytes in situ, consistent with our previous study where GABAρ expression was demonstrated. Finally, we assessed the mRNA expression of GABAρ3, through different stages of postnatal development; double immunofluorescence disclosed GABAρ3 expression in calretinin-positive interneurons as well as in astrocytes (>70%). These results add new information about the participation of GABAρ subunits in neostriatal interneurons and astrocytes., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Three neuronal pentraxins are expressed in brain, the membrane-bound "neuronal pentraxin receptor" (NPR) and the secreted proteins NP1 and NARP (i.e., NP2). Neuronal pentraxins bind to AMPARs at excitatory synapses and play important, well-documented roles in the activity-dependent regulation of neural circuits via this binding activity. However, it is unknown whether neuronal pentraxins perform roles in synapses beyond modulating postsynaptic AMPAR-dependent plasticity, and whether they may even act in inhibitory synapses. Here, we show that NPR expressed in non-neuronal cells potently induces formation of both excitatory and inhibitory postsynaptic specializations in cocultured hippocampal neurons. Knockdown of NPR in hippocampal neurons, conversely, dramatically decreased assembly and function of both excitatory and inhibitory postsynaptic specializations. Overexpression of NPR rescued the NPR knockdown phenotype but did not in itself change synapse numbers or properties. However, the NPR knockdown decreased the levels of NARP, whereas NPR overexpression produced a dramatic increase in the levels of NP1 and NARP, suggesting that NPR recruits and stabilizes NP1 and NARP on the presynaptic plasma membrane. Mechanistically, NPR acted in excitatory synapse assembly by binding to the N-terminal domain of AMPARs; antagonists of AMPA and GABA receptors selectively inhibited NPR-induced heterologous excitatory and inhibitory synapse assembly, respectively, but did not affect neurexin-1β-induced synapse assembly as a control. Our data suggest that neuronal pentraxins act as signaling complexes that function as general trans-synaptic organizers of both excitatory and inhibitory synapses by a mechanism that depends, at least in part, on the activity of the neurotransmitter receptors at these synapses., Significance Statement: Neuronal pentraxins comprise three neuronal proteins, neuronal pentraxin receptor (NPR) which is a type-II transmembrane protein on the neuronal surface, and secreted neuronal pentraxin-1 and NARP. The general functions of neuronal pentraxins at synapses have not been explored, except for their basic AMPAR binding properties. Here, we examined the functional role of NPR at synapses because it is the only neuronal pentraxin that is anchored to the neuronal cell-surface membrane. We find that NPR is a potent inducer of both excitatory and inhibitory heterologous synapses, and that knockdown of NPR in cultured neurons decreases the density of both excitatory and inhibitory synapses. Our data suggest that NPR performs a general, previously unrecognized function as a universal organizer of synapses., (Copyright © 2017 the authors 0270-6474/17/371062-19$15.00/0.)

Rationale: Little is known about the structural characteristics of the behavior of rats with enhanced anxiety level. To fill this gap, a study was undertaken where effects of an anxiogenic drug were examined on behavioral structure of rats tested in hole board., Objectives: This study investigates effects of increased anxiety level on the structure of the behavior of rats tested in hole board METHODS: Different doses of FG7142 (1, 4, 8 mg/kg IP), a potent anxiety-inducing drug, were administered to three groups of male Wistar rats. A further group was administered saline. Experiments were recorded through a digital camera. Quantitative and multivariate approaches were applied., Results: Percent distributions and durations showed increases of immobile sniffing, rearing, head dip, and edge sniff and a significant reduction of grooming activities and of walking. In addition, a decrease of head dip/edge sniff ratio was detected. Transition matrices evidenced that FG7142 provoked evident modifications of behavioral structure mainly of general exploration of environment and focused exploration of the hole. Finally, adjusted residuals showed a reduced effectiveness of FG7142 on transitions from head dip to edge sniff; on the contrary, transitions from edge sniff to head dip underwent evident dose-dependent changes., Conclusions: Present study provides a useful tool to analyze behavioral responses to different anxiety conditions. Accordingly, it is demonstrated that a condition of increased anxiety deeply modifies the structure of male Wistar rat's behavior in hole board. In addition, our results suggest that evaluation of head dip/edge sniff ratio can be considered a reliable index to appraise effects of pharmacological manipulation of anxiety and related behavioral elements.

Despite extensive studies in hippocampal slices and incentive from computational theories, the synaptic mechanisms underlying information transfer at mossy fiber (mf) connections between the dentate gyrus (DG) and CA3 neurons in vivo are still elusive. Here we used an optogenetic approach in mice to selectively target and control the activity of DG granule cells (GCs) while performing whole-cell and juxtacellular recordings of CA3 neurons in vivo In CA3 pyramidal cells (PCs), mf-CA3 synaptic responses consisted predominantly of an IPSP at low stimulation frequency (0.05 Hz). Upon increasing the frequency of stimulation, a biphasic response was observed consisting of a brief mf EPSP followed by an inhibitory response lasting on the order of 100 ms. Spike transfer at DG-CA3 interneurons recorded in the juxtacellular mode was efficient at low presynaptic stimulation frequency and appeared insensitive to an increased frequency of GC activity. Overall, this resulted in a robust and slow feedforward inhibition of spike transfer at mf-CA3 pyramidal cell synapses. Short-term plasticity of EPSPs with increasing frequency of presynaptic activity allowed inhibition to be overcome to reach spike discharge in CA3 PCs. Whereas the activation of GABA A receptors was responsible for the direct inhibition of light-evoked spike responses, the slow inhibition of spiking activity required the activation of GABA B receptors in CA3 PCs. The slow inhibitory response defined an optimum frequency of presynaptic activity for spike transfer at ∼10 Hz. Altogether these properties define the temporal rules for efficient information transfer at DG-CA3 synaptic connections in the intact circuit., Significance Statement: Activity-dependent changes in synaptic strength constitute a basic mechanism for memory. Synapses from the dentate gyrus (DG) to the CA3 area of the hippocampus are distinctive for their prominent short-term plasticity, as studied in slices. Plasticity of DG-CA3 connections may assist in the encoding of precise memory in the CA3 network. Here we characterize DG-CA3 synaptic transmission in vivo using targeted optogenetic activation of DG granule cells while recording in whole-cell patch-clamp and juxtacellular configuration from CA3 pyramidal cells and interneurons. We show that, in vivo, short-term plasticity of excitatory inputs to CA3 pyramidal cells combines with robust feedforward inhibition mediated by both GABA A and GABA B receptors to control the efficacy and temporal rules for information transfer at DG-CA3 connections., (Copyright © 2017 the authors 0270-6474/17/370587-12$15.00/0.)

The presence of α-synuclein (α-syn) in Lewy bodies and Lewy neurites is an important characteristic of the neurodegenerative processes of substantia nigra pars compacta (SNpc) dopaminergic (DAergic) neurons in Parkinson's disease (PD) and other synucleinopathies. Here we report that Berlin-Druckrey rats carrying a spontaneous mutation in the 3' untranslated region of α-syn mRNA (m/m rats) display a marked accumulation of α-syn in the mesencephalic area, striatum and frontal cortex, accompanied to severe dysfunctions in the dorsolateral striatum. Despite a small reduction in the number of SNpc and ventral tegmental area DAergic cells, the surviving dopaminergic neurons of the m/m rats do not show clear-cut alterations of the spontaneous and evoked firing activity, DA responses and somatic amphetamine-induced firing inhibition. Interestingly, mutant DAergic neurons display diminished whole-cell Ih conductance and a reduced frequency of spontaneous excitatory synaptic currents. By contrast, m/m rats show a severe impairment of DA and glutamate release in the dorsolateral striatum, as revealed by amperometric measure of DA currents and by electrophysiological recordings of glutamatergic synaptic events in striatal medium spiny neurons. These functional impairments are paralleled by a decreased expression of the DA transporter and VGluT1 proteins in the same area. Thus, together with α-syn overload in the mesencephalic region, striatum and frontal cortex, the main functional alterations occur in the DAergic and glutamatergic terminals in the dorsal striatum of the m/m rats., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Ghrelin, a peptide hormone produced in the stomach, has been known to be involved in the regulation of gastric contraction in humans and rodents. To elucidate the detailed mechanisms of ghrelin on gastric contractions, we used Suncus murinus, a recently established small animal model for gastrointestinal motility. S. murinus produces motilin, a family peptide of ghrelin, and its stomach anatomy and physiological patterns of gastric contractions, in fed and fasted states, are closely similar to humans. Ghrelin administration in phase II, and latter half of phase I, of the migrating motor contractions (MMC) enhanced gastric motility in S. murinus. In addition, we showed that ghrelin and motilin coordinately stimulated strong gastric contractions in vitro and in vivo. We also demonstrated that a pretreatment with a ghrelin antagonist, D-Lys3-GHRP6, inhibited the effects of motilin-induced gastric contractions, and a γ-aminobutyric acid (GABA) antagonist reversed this inhibition. Our results suggest that ghrelin is essential for motilin-induced gastric contractions and that ghrelin-mediated GABAergic neurons are involved in this neural pathway.

GSG1L is an AMPA receptor (AMPAR) auxiliary subunit that regulates AMPAR trafficking and function in hippocampal CA1 pyramidal neurons. However, its physiological roles in other types of neurons remain to be characterized. Here, we investigated the role of GSG1L in hippocampal dentate granule cells and found that GSG1L is important for the regulation of synaptic strength but is not critical for the modulation of AMPAR deactivation and desensitization kinetics. These data demonstrate a neuronal type-specific role of GSG1L and suggest that physiological function of AMPAR auxiliary subunits may vary in different types of neurons., New & Noteworthy: GSG1L is a newly identified AMPA receptor (AMPAR) auxiliary subunit and plays a unique role in the regulation of AMPAR trafficking and function in hippocampal CA1 pyramidal neurons. However, its role in the regulation of AMPARs in hippocampal dentate granule cells remains to be characterized. The current work reveals that GSG1L regulates strength of AMPAR-mediated synaptic transmission but not the receptor kinetic properties in hippocampal dentate granule neurons.

Testosterone exerts profound effects on reproduction and energy homeostasis. Like other orexigenic hormones, it increases endocannabinoid tone within the hypothalamic feeding circuitry. Therefore, we tested the hypothesis that testosterone upregulates the expression of diacylglycerol lipase (DAGL)α in the hypothalamic arcuate nucleus (ARC) to increase energy intake via enhanced endocannabinoid-mediated retrograde inhibition of anorexigenic proopiomelanocortin (POMC) neurons. Energy intake, meal patterns, and energy expenditure were evaluated in orchidectomized, male guinea pigs treated subcutaneously with testosterone propionate (TP; 400 μg) or its sesame oil vehicle (0.1 mL). TP rapidly increased energy intake, meal size, O2 consumption, CO2 production, and metabolic heat production, all of which were antagonized by prior administration of the DAGL inhibitor orlistat (3 μg) into the third ventricle. These orlistat-sensitive, TP-induced increases in energy intake and expenditure were temporally associated with a significant elevation in ARC DAGLα expression. Electrophysiological recordings in hypothalamic slices revealed that TP potentiated depolarization-induced suppression of excitatory glutamatergic input onto identified ARC POMC neurons, which was also abolished by orlistat (3 μM), the CB1 receptor antagonist AM251 (1 μM), and the AMP-activated protein kinase inhibitor compound C (30 μM) and simulated by transient bath application of the dihydrotestosterone mimetic Cl-4AS-1 (100 nM) and testosterone-conjugated bovine serum albumin (100 nM). Thus, testosterone boosts DAGLα expression to augment retrograde, presynaptic inhibition of glutamate release onto ARC POMC neurons that, in turn, increases energy intake and expenditure. These studies advance our understanding of how androgens work within the hypothalamic feeding circuitry to affect changes in energy balance., (© 2016 S. Karger AG, Basel.)

Evidence from preclinical and clinical studies shows that ketamine, a noncompetitive NMDA receptor antagonist, exerts rapid and sustained antidepressant responses. However, ketamine's psychotomimetic side effects and abuse liability limit the clinical use of the compound. Interestingly, memantine, another NMDA receptor channel blocker, processes no defined antidepressant property but is much safer and clinical tolerated. Understanding why ketamine but not memantine exhibits rapid antidepressant responses is important to elucidate the cellular signaling underlying the fast antidepressant actions of ketamine and to design a new safer generation of fast-acting antidepressants. Here we show that ketamine but memantine caused a rapid and sustained antidepressant-like responses in forced swim test (FST). Both drugs enhanced GluA1 S845 phosphorylation and potentiated Schaffer collateral-CA1 synaptic transmission. However, ketamine but not memantine elevated the expression of GluA1. Incubating acutely prepared hippocampal slices with ketamine but not memantine enhanced mTOR phosphorylation in a time course parallel to the time course of GluA1 elevation. Our results suggest that distinct properties in regulation of mTOR phosphorylation and synaptic protein expression may underlie the differential effectiveness of ketamine and memantine in their antidepressant responses., (Copyright © 2016 Elsevier B.V. All rights reserved.)

The spatial and temporal patterns of spontaneous synchronous Ca 2+ oscillations (SCOs) regulate physiological pathways that influence neuronal development, excitability, and health. Hippocampal neuronal cultures (HN) and neuron/glia co-cultures (HNG) produced from neonatal mice were loaded with Fluo-4/AM and SCOs recorded in real-time using a Fluorescence Imaging Plate Reader at different developmental stages in vitro. HNG showed an earlier onset of SCOs, with low amplitude and low frequency SCOs at 4days in vitro (DIV), whereas HN were quiescent at this point. SCO amplitude peaked at 9 DIV for both cultures. SCO network frequency peaked at 12 DIV in HN, whereas in HNG the frequency peaked at 6 DIV. SCO patterns were associated with the temporal development of neuronal networks and their ratio of glutamatergic to GABAergic markers of excitatory/inhibitory balance. HN and HNG exhibited differential responses to the convulsant tetramethylenedisulfotetramine (TETS) and were highly dependent on DIV. In HN, TETS triggered an acute rise of intracellular Ca 2+ (Phase I response) only in 14 DIV and a sustained decrease of SCO frequency with increased amplitude (Phase II response) at all developmental stages. In HNG, TETS decreased the SCO frequency and increased the amplitude at 6 and 14 but not 9 DIV. There was no acute Ca 2+ rise (Phase I response) in any age of HNG tested with TETS. These data demonstrated the importance of glia and developmental stage in modulating neuronal responses to TETS. Our results illustrate the applicability of the model for investigating how caged convulsants elicit abnormal network activity during the development of HN and HNG cultures in vitro., Competing Interests: The authors declare no conflicts of interest., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Objective: The maturation of adult-born granule cells and their functional integration into the network is thought to play a key role in the proper functioning of the dentate gyrus. In temporal lobe epilepsy, adult-born granule cells in the dentate gyrus develop abnormally and possess a hilar basal dendrite (HBD). Although morphological studies have shown that these HBDs have synapses, little is known about the functional properties of these HBDs or the intrinsic and network properties of the granule cells that possess these aberrant dendrites., Methods: We performed patch-clamp recordings of granule cells within the granule cell layer "normotopic" from sham-control and status epilepticus (SE) animals. Normotopic granule cells from SE animals possessed an HBD (SE + HBD + cells) or not (SE + HBD - cells). Apical and basal dendrites were stimulated using multiphoton uncaging of glutamate. Two-photon Ca 2+ imaging was used to measure Ca 2+ transients associated with back-propagating action potentials (bAPs)., Results: Near-synchronous synaptic input integrated linearly in apical dendrites from sham-control animals and was not significantly different in apical dendrites of SE + HBD - cells. The majority of HBDs integrated input linearly, similar to apical dendrites. However, 2 of 11 HBDs were capable of supralinear integration mediated by a dendritic spike. Furthermore, the bAP-evoked Ca 2+ transients were relatively well maintained along HBDs, compared with apical dendrites. This further suggests an enhanced electrogenesis in HBDs. In addition, the output of granule cells from epileptic tissue was enhanced, with both SE + HBD - and SE + HBD + cells displaying increased high-frequency (>100 Hz) burst-firing. Finally, both SE + HBD - and SE + HBD + cells received recurrent excitatory input that was capable of generating APs, especially in the absence of feedback inhibition., Significance: Taken together, these data suggest that the enhanced excitability of HBDs combined with the altered intrinsic and network properties of granule cells collude to promote excitability and synchrony in the epileptic dentate gyrus., (Wiley Periodicals, Inc. © 2016 International League Against Epilepsy.)

Key Points: The midbrain periaqueductal grey (PAG) forms part of an endogenous analgesic system which is tightly regulated by the neurotransmitter GABA. The role of endocannabinoids in regulating GABAergic control of this system was examined in rat PAG slices. Under basal conditions GABAergic neurotransmission onto PAG output neurons was multivesicular. Activation of the endocannabinoid system reduced GABAergic inhibition by reducing the probability of release and by shifting release to a univesicular mode. Blockade of endocannabinoid system unmasked a tonic control over the probability and mode of GABA release. These findings provides a mechanistic foundation for the control of the PAG analgesic system by disinhibition., Abstract: The midbrain periaqueductal grey (PAG) has a crucial role in coordinating endogenous analgesic responses to physiological and psychological stressors. Endocannabinoids are thought to mediate a form of stress-induced analgesia within the PAG by relieving GABAergic inhibition of output neurons, a process known as disinhibition. This disinhibition is thought to be achieved by a presynaptic reduction in GABA release probability. We examined whether other mechanisms have a role in endocannabinoid modulation of GABAergic synaptic transmission within the rat PAG. The group I mGluR agonist DHPG ((R,S)-3,5-dihydroxyphenylglycine) inhibited evoked IPSCs and increased their paired pulse ratio in normal external Ca 2+ , and when release probability was reduced by lowering Ca 2+ . However, the effect of DHPG on the coefficient of variation and kinetics of evoked IPSCs differed between normal and low Ca 2+ . Lowering external Ca 2+ had a similar effect on evoked IPSCs to that observed for DHPG in normal external Ca 2+ . The low affinity GABA A receptor antagonist TPMPA ((1,2,5,6-tetrahydropyridin-4-yl)methylphosphinic acid) inhibited evoked IPSCs to a greater extent in low than in normal Ca 2+ . Together these findings indicate that the normal mode of GABA release is multivesicular within the PAG, and that DHPG and lowering external Ca 2+ switch this to a univesicular mode. The effects of DHPG were mediated by mGlu5 receptor engagement of the retrograde endocannabinoid system. Blockade of endocannabinoid breakdown produced a similar shift in the mode of release. We conclude that endocannabinoids control both the mode and the probability of GABA release within the PAG., (© 2016 The Authors. The Journal of Physiology © 2016 The Physiological Society.)

In mouse models of Huntington's disease (HD), striatal neuron properties are significantly altered. These alterations predict changes in striatal output regions. However, little is known about alterations in those regions. The present study examines changes in passive and active membrane properties of neurons in the external globus pallidus (GPe), the first relay station of the indirect pathway, in the R6/2 mouse model of juvenile HD at presymptomatic (1 month) and symptomatic (2 month) stages. In GPe, two principal types of neurons can be distinguished based on firing properties and the presence (type A) or absence (type B) of I h currents. In symptomatic animals (2 month), cell membrane capacitance and input resistance of type A neurons were increased compared with controls. In addition, action potential afterhyperpolarization amplitude was reduced. Although the spontaneous firing rate of GPe neurons was not different between control and R6/2 mice, the number of spikes evoked by depolarizing current pulses was significantly reduced in symptomatic R6/2 animals. In addition, these changes were accompanied by altered firing patterns evidenced by increased interspike interval variation and increased number of bursts. Blockade of GABA A receptors facilitated bursting activity in R6/2 mice but not in control littermates. Thus, alterations in firing patterns could be caused by changes in intrinsic membrane conductances and modulated by synaptic inputs. © 2016 Wiley Periodicals, Inc., (© 2016 Wiley Periodicals, Inc.)

Memantine is one of the few drugs currently approved for treatment of Alzheimer's disease (AD). The clinical effects of memantine are thought to be associated with inhibition of NMDA receptors (NMDARs). Surprisingly, other open-channel NMDAR blockers have unacceptable side effects that prevent their consideration for AD treatment. One of the mechanisms proposed to explain the therapeutic benefits of memantine involves preferential decrease of excitatory drive to inhibitory neurons in the cortical circuitry and consequent changes in balance between excitation and inhibition (E/I). In this study we addressed effects of memantine on E/I balance in the prefrontal cortex (PFC). We found that a moderate concentration of memantine shifted E/I balance away from inhibition in the PFC circuitry. Indeed, memantine decreased the frequency and amplitude of spontaneous inhibitory postsynaptic currents in pyramidal neurons while leaving spontaneous excitatory postsynaptic currents unaffected. These circuitry effects of memantine were occluded by the competitive NMDAR inhibitor AP-5, and thus are associated with NMDAR inhibition. We also found that memantine decreased feed-forward disynaptic inhibitory input to pyramidal neurons, which is thought to be mediated by parvalbumin (PV)-positive interneurons. Accordingly, memantine caused a greater decrease of the amplitude of NMDAR-mediated synaptic responses in PV-positive interneurons than in pyramidal neurons. Finally, memantine reduced firing activity in PV-positive interneurons while increasing firing in pyramidal neurons. This study elucidates a novel mechanism of action of memantine associated with shifting of the E/I balance away from inhibition in neocortical circuitry, and provides important insights for AD drug development., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Key Points: Retinal ganglion cells (RGCs) in dark-adapted retinas show a range of threshold sensitivities spanning ∼3 log units of illuminance. Here, we show that the different threshold sensitivities of RGCs reflect an inhibitory mechanism that masks inputs from certain rod pathways. The masking inhibition is subserved by GABA C receptors, probably on bipolar cell axon terminals. The GABAergic masking inhibition appears independent of dopaminergic circuitry that has been shown also to affect RGC sensitivity. The results indicate a novel mechanism whereby inhibition controls the sensitivity of different cohorts of RGCs. This can limit and thereby ensure that appropriate signals are carried centrally in scotopic conditions when sensitivity rather than acuity is crucial., Abstract: The responses of rod photoreceptors, which subserve dim light vision, are carried through the retina by three independent pathways. These pathways carry signals with largely different sensitivities. Retinal ganglion cells (RGCs), the output neurons of the retina, show a wide range of sensitivities in the same dark-adapted conditions, suggesting a divergence of the rod pathways. However, this organization is not supported by the known synaptic morphology of the retina. Here, we tested an alternative idea that the rod pathways converge onto single RGCs, but inhibitory circuits selectively mask signals so that one pathway predominates. Indeed, we found that application of GABA receptor blockers increased the sensitivity of most RGCs by unmasking rod signals, which were suppressed. Our results indicate that inhibition controls the threshold responses of RGCs under dim ambient light. This mechanism can ensure that appropriate signals cross the bottleneck of the optic nerve in changing stimulus conditions., (© 2016 The Authors. The Journal of Physiology © 2016 The Physiological Society.)

Stress is a response of the organism to homeostasis-threatening stimuli and is coordinated by two main neural systems: the hypothalamic-pituitary-adrenal and the autonomic nervous system. Acute restraint stress (RS) is a model of unavoidable stress, which is characterized by autonomic responses including an increase in mean arterial pressure (MAP) and heart rate (HR), as well as a drop in tail temperature. The prelimbic cortex (PL) has been implicated in the modulation of functional responses caused by RS. The present study aimed to evaluate the role of PL GABAergic neurotransmission in the modulation of autonomic changes induced by RS. Bilateral microinjection of the GABA A receptor antagonist bicuculline methiodide into the PL reduced pressor and tachycardic responses evoked by RS, in a dose-dependent manner, without affecting the tail temperature drop evoked by RS. In order to investigate which peripheral autonomic effector modulated the reduction in RS-cardiovascular responses caused by the blockade of PL GABA A receptors, rats were intravenously pretreated with either atenolol or homatropine methylbromide. The blockade of the cardiac sympathetic nervous system with atenolol blunted the reducing effect of PL treatment with bicuculline methiodide on RS-evoked pressor and tachycardic responses. The blockade of the parasympathetic nervous system with homatropine methylbromide, regardless of affecting the beginning of the tachycardic response, did not impact on the reduction of RS-evoked tachycardic and pressor responses caused by the PL treatment with bicuculline methiodide. The present results indicate that both cardiac sympathetic and parasympathetic activities are involved in the reduction of RS-evoked cardiovascular responses evidenced after the blockade of PL GABA A receptors by bicuculline methiodide.

Trafficking of anesthetic-sensitive receptors within the plasma membrane, or from one cellular component to another, occurs continuously. Changes in receptor trafficking have implications in altering anesthetic sensitivity. γ-Aminobutyric acid type A receptors (GABAARs) are anion-permeable ion channels and are the major class of receptor in the adult mammalian central nervous system that mediates inhibition. GABAergic signaling allows for precise synchronized firing of action potentials within brain circuits that is critical for cognition, behavior, and consciousness. This precision depends upon tightly controlled trafficking of GABAARs into the membrane. General anesthetics bind to and allosterically enhance GABAARs by prolonging the open state of the receptor and thereby altering neuronal and brain circuit activity. Subunit composition and GABAAR localization strongly influence anesthetic end points; therefore, changes in GABAAR trafficking could have significant consequences to anesthetic sensitivity. GABAARs are not static membrane structures but are in a constant state of flux between extrasynaptic and synaptic locations and are continually endocytosed and recycled from and to the membrane. Neuronal activity, posttranslational modifications, and some naturally occurring and synthetic compounds can influence the expression and trafficking of GABAARs. In this article, we review GABAARs, their trafficking, and how phosphorylation of GABAAR subunits can influence the surface expression and function of the receptor. Ultimately, alterations of GABAAR trafficking could modify anesthetic end points, both unintentionally through pathologic processes but potentially as a therapeutic target to adjust anesthetic-sensitive GABAARs., Competing Interests: The authors declare no conflicts of interest.

Background: Extrasynaptic γ-aminobutyric acid type A (GABAA) receptors that contain the δ subunit (δGABAA receptors) contribute to memory performance. Dysregulation of δGABAA receptor expression, which occurs in some neurological disorders, is associated with memory impairment. Mice lacking δGABAA receptors (Gabrd) exhibit deficits in their ability to distinguish between similar memories, a process which is referred to as pattern separation. The CA3 and dentate gyrus subfields of the hippocampus regulate pattern separation, raising the possibility that synaptic plasticity is impaired in these regions in Gabrd mice. Although long-term potentiation (LTP), the most widely studied form of synaptic plasticity, is normal in the dentate gyrus of Gabrd mice, LTP in the CA3 subfield has not been studied. Here, we tested the hypothesis that LTP is reduced in the CA3 subfield of Gabrd mice., Methods: LTP of extracellular field postsynaptic potentials was studied in the mossy fiber (MF)-CA3 pathway using hippocampal slices from Gabrd and wild-type (WT) mice. We also examined paired pulse responses and input-output relationships at MF-CA3 synapses., Results: MF-CA3 LTP was reduced in Gabrd mice, as evidenced by decreased potentiation of field postsynaptic potentials (WT: 178.3% ± 16.1% versus Gabrd: 126.3% ± 6.9%; P = 0.0091). Thus, the deletion of δGABAA receptors is associated with impaired plasticity. Bicuculline (BIC), a GABAA receptor antagonist, reduced plasticity in WT but not in Gabrd mice (WT + BIC: 123.9% ± 7.6% versus Gabrd + BIC: 136.5% ± 7.0%). Paired pulse responses and input-output relationships did not differ between the genotypes (all Ps > 0.05)., Conclusions: Both genetic deletion and pharmacological blockade of δGABAA receptors impair MF-CA3 LTP, suggesting that δGABAA receptors are necessary for synaptic plasticity in the CA3 subfield. Drugs that enhance δGABAA receptor function may reverse deficits in synaptic plasticity in the CA3 subfield and improve pattern separation in neurological disorders.

Fipronil (F) a pesticide considered of second generation cause various toxic effects in target and non-target organisms including humans in which provoke neurotoxicity, having the antagonism of gamma-amino butyric acid (GABA) as their main mechanism for toxic action. GABAergic system has been involved in processes related to the memory formation and consolidation. The present work studied the importance of GABA to the mechanisms involved in the very early development of fipronil-induced memory impairment in rats. Memory behavior was assessed using new object recognition task (ORT) and eight radial arm maze task (8-RAM) to study effects on cognitive and spatial memory. Locomotor behavior was assessed using open field task (OF). The dose of fipronil utilized was studied through a pilot experiment. The GABA antagonist picrotoxin (P) was used to enhance fipronil effects on GABAergic system. Fipronil or picrotoxin decrease memory studied in ORT and 8-RAM tasks. Additionally, F and P co-exposure enhanced effects on memory compared to controls, F, and P, suggesting strongly a GABAergic effect. Weight gain modulation and fipronil in blood were utilized as animal's intoxication indicators. In conclusion, here we report that second-generation pesticides, such as fipronil, can have toxic interactions with the CNS of mammals and lead to memory impairment by modulating the GABAergic system., (Copyright © 2016 Elsevier Inc. All rights reserved.)

The cannabinoid receptor type 1 (CB1) is highly expressed in the dorsal portion of hippocampus - a brain region that has been involved in the control of conditioned emotional response (CER) in the contextual fear conditioning (CFC) model. These responses are characterized by increased freezing behavior and autonomic parameters. Moreover, CB1 receptors activation negatively modulate the release of several neurotransmitters, including glutamate and GABA, which also have been related to modulation of CER. Therefore, our aim was to investigate the involvement of CB1 receptors in the dorsal hippocampus on CER expression. Independent groups of male Wistar rats submitted to the contextual fear conditioning received bilateral intra-hippocampal injections (500 nL/side) of the following drugs or vehicle before re-exposure to the aversive context: AM251 (CB1 antagonist; 0.1, 0.3 and 1nmol); AP7 (NMDA antagonist; 1nmol)+AM251 (0.3nmol); NPLA (0.01nmol; nNOS inhibitor)+AM251 (0.3nmol); Bicuculline (1.3pmol; GABAA antagonist)+AM251 (0.1 and 1nmol). In the present paper, AM251 (0.3nmol) increased CER, while this response was prevented by both AP7 and NPLA pretreatment. After pretreatment with Bicuculline, the lower and higher ineffective doses of AM251 were able to increase the CER, supporting the balance between GABAergic and glutamatergic mechanisms controlling this response. Our results suggest that increased CER evoked by CB1 blockade in the dorsal hippocampus depends on NMDA receptor activation and NO formation. Moreover, a fine-tune control promoted by GABAergic and glutamatergic mechanisms in this brain area modulate the CER after CB1 blockade., (Copyright © 2016 Elsevier B.V. and ECNP. All rights reserved.)

Ethanol is widely known for its ability to cause dramatic changes in emotion, social cognition, and behavior following systemic administration in humans. Human neuroimaging studies suggest that alcohol dependence and chronic pain may share common mechanisms through amygdala-medial prefrontal cortex (mPFC) interactions. However, whether acute administration of ethanol in the mPFC can modulate pain perception is unknown. Here we showed that bilateral microinjections of ethanol into the prelimbic and infralimbic areas of the mPFC lowered the bilateral mechanical pain threshold for 48 h without influencing thermal pain sensitivity in adult rats. However, bilateral microinjections of artificial cerebrospinal fluid into the mPFC or bilateral microinjections of ethanol into the dorsolateral PFC (also termed as motor cortex area 1 in Paxinos and Watson's atlas of The Rat Brain. Elsevier Academic Press, Amsterdam, 2005) failed to do so, suggesting regional selectivity of the effects of ethanol. Moreover, bilateral microinjections of ethanol did not change the expression of either pro-apoptotic (caspase-3 and Bax) or anti-apoptotic (Bcl-2) proteins, suggesting that the dose was safe and validating the method used in the current study. To determine whether γ-aminobutyric acid A (GABAA) receptors are involved in mediating the ethanol effects, muscimol, a selective GABAA receptor agonist, or bicuculline, a selective GABAA receptor antagonist, was administered alone or co-administered with ethanol through the same route into the bilateral mPFC. The results showed that muscimol mimicked the effects of ethanol while bicuculline completely reversed the effects of ethanol and muscimol. In conclusion, ethanol increases mechanical pain sensitivity through activation of GABAA receptors in the mPFC of rats.

Unlabelled: The suprachiasmatic nucleus (SCN) is the master circadian oscillator encoding time-of-day information. SCN timekeeping is sustained by a cell-autonomous transcriptional-translational feedback loop, whereby expression of the Period and Cryptochrome genes is negatively regulated by their protein products. This loop in turn drives circadian oscillations in gene expression that direct SCN electrical activity and thence behavior. The robustness of SCN timekeeping is further enhanced by interneuronal, circuit-level coupling. The aim of this study was to combine pharmacological and genetic manipulations to push the SCN clockwork toward its limits and, by doing so, probe cell-autonomous and emergent, circuit-level properties. Circadian oscillation of mouse SCN organotypic slice cultures was monitored as PER2::LUC bioluminescence. SCN of three genetic backgrounds-wild-type, short-period CK1ε(Tau/Tau) mutant, and long-period Fbxl3(Afh/Afh) mutant-all responded reversibly to pharmacological manipulation with period-altering compounds: picrotoxin, PF-670462 (4-[1-Cyclohexyl-4-(4-fluorophenyl)-1H-imidazol-5-yl]-2-pyrimidinamine dihydrochloride), and KNK437 (N-Formyl-3,4-methylenedioxy-benzylidine-gamma-butyrolactam). This revealed a remarkably wide operating range of sustained periods extending across 25 h, from ≤17 h to >42 h. Moreover, this range was maintained at network and single-cell levels. Development of a new technique for formal analysis of circadian waveform, first derivative analysis (FDA), revealed internal phase patterning to the circadian oscillation at these extreme periods and differential phase sensitivity of the SCN to genetic and pharmacological manipulations. For example, FDA of the CK1ε(Tau/Tau) mutant SCN treated with the CK1ε-specific inhibitor PF-4800567 (3-[(3-Chlorophenoxy)methyl]-1-(tetrahydro-2H-pyran-4-yl)-1H-pyrazolo[3,4-d]pyrimidin-4-amine hydrochloride) revealed that period acceleration in the mutant is due to inappropriately phased activity of the CK1ε isoform. In conclusion, extreme period manipulation reveals unprecedented elasticity and temporal structure of the SCN circadian oscillation., Significance Statement: The master circadian clock of the suprachiasmatic nucleus (SCN) encodes time-of-day information that allows mammals to predict and thereby adapt to daily environmental cycles. Using combined genetic and pharmacological interventions, we assessed the temporal elasticity of the SCN network. Despite having evolved to generate a 24 h circadian period, we show that the molecular clock is surprisingly elastic, able to reversibly sustain coherent periods between ≤17 and >42 h at the levels of individual cells and the overall circuit. Using quantitative techniques to analyze these extreme periodicities, we reveal that the oscillator progresses as a sequence of distinct stages. These findings reveal new properties of how the SCN functions as a network and should inform biological and mathematical analyses of circadian timekeeping., (Copyright © 2016 Patton et al.)

Rationale: We previously reported that the fluvoxamine-induced increase in prefrontal dopamine levels is enhanced by adrenalectomy/castration (which results in circulating neurosteroid deficiency), via combined activation of serotonin1A (5-HT1A) and σ1 receptors. However, the mechanistic details of the interaction between 5-HT1A and σ1 receptors are unknown., Objectives: Because most neurosteroids have affinity for γ-aminobutyric acid (GABA)A receptors, in the present study, we examined the involvement of GABAA receptors in this process., Results: Adrenalectomy/castration decreased pentobarbital-induced sleeping time in mice, suggesting that it reduced GABAA receptor function. The GABAA receptor antagonist picrotoxin (1 mg/kg) enhanced the fluvoxamine-induced increase in prefrontal dopamine, but not noradrenaline or serotonin, levels in mice, suggesting that picrotoxin mimicked the effect of adrenalectomy/castration. Picrotoxin also potentiated the increase in prefrontal dopamine levels mediated by co-administration of the 5-HT1A receptor agonist osemozotan and the σ1 receptor agonist (+)-SKF-10,047, while it did not affect the co-administration-induced changes in noradrenaline and serotonin levels. Conversely, the GABAA receptor agonist diazepam (1 mg/kg) blocked the effect of adrenalectomy/castration on the fluvoxamine-induced increase in prefrontal dopamine levels. Co-administration of osemozotan and (+)-SKF-10,047 did not affect the expression of the neuronal activity marker c-Fos in the prefrontal cortex, ventral tegmental area, and nucleus accumbens in control mice, while it increased the c-Fos expression only in the prefrontal cortex and ventral tegmental area in picrotoxin-treated mice., Conclusions: These results suggest that the GABAA receptor plays a key role in mediating the synergistic effects of 5-HT1A and σ1 receptor activation on prefrontal dopamine neurotransmission.

Unlabelled: Neuroligins are postsynaptic cell-adhesion molecules that contribute to synapse specification. However, many other postsynaptic cell-adhesion molecules are known and the relative contributions of neuroligins versus other such molecules in different types of synapses and neurons remains largely unknown. Here, we have studied the role of neuroligins in cerebellar stellate interneurons that participate in a well defined circuit that converges on Purkinje cells as the major output neurons of cerebellar cortex. By crossing triple conditional knock-out (cKO) mice targeting all three major neuroligins [neuroligin-1 to neuroligin-3 (NL123)] with parvalbumin-Cre (PV-Cre) transgenic mice, we deleted neuroligins from inhibitory cerebellar interneurons and Purkinje cells, allowing us to study the effects of neuroligin deletions on cerebellar stellate cell synapses by electrophysiology in acute slices. PV-Cre/NL123 cKO mice did not exhibit gross alterations of cerebellar structure or cerebellar interneuron morphology. Strikingly, electrophysiological recordings in stellate cells from these PV-Cre/NL123 cKO mice revealed a large decrease in NMDAR-mediated excitatory synaptic responses, which, in stellate cells, are largely extrasynaptic, without a change in AMPA-receptor-mediated responses. Parallel analyses in PV-Cre/NL1 mice that are single NL1 cKO mice uncovered the same phenotype, demonstrating that NL1 is responsible for recruiting extrasynaptic NMDARs. Moreover, we observed only a modest impairment in inhibitory synaptic responses in stellate cells lacking NL123 despite a nearly complete suppression of inhibitory synaptic transmission in Purkinje cells by the same genetic manipulation. Our results suggest that, unlike other types of neurons investigated, neuroligins are selectively essential in cerebellar stellate interneurons for enabling the function of extrasynaptic NMDARs., Significance Statement: Neuroligins are postsynaptic cell-adhesion molecules genetically linked to autism. However, the contributions of neuroligins to interneuron functions remain largely unknown. Here, we analyzed the role of neuroligins in cerebellar stellate interneurons. We deleted neuroligin-1, neuroligin-2, and neuroligin-3, the major cerebellar neuroligin isoforms, from stellate cells in triple NL123 conditional knock-out mice and analyzed synaptic responses by acute slice electrophysiology. We find that neuroligins are selectively essential for extrasynaptic NMDAR-mediated signaling, but dispensable for both AMPAR-mediated and inhibitory synaptic transmission. Our results reveal a critical and selective role for neuroligins in the regulation of NMDAR responses in cerebellar stellate interneurons., (Copyright © 2016 the authors 0270-6474/16/369070-14$15.00/0.)

Unlabelled: Cerebellar granule cell GABAA receptor responses to alcohol vary as a function of alcohol consumption phenotype, representing a potential neural mechanism for genetic predilection for alcohol abuse (Kaplan et al., 2013; Mohr et al., 2013). However, there are numerous molecular targets of alcohol in the cerebellum, and it is not known how they interact to affect cerebellar processing during consumption of socially relevant amounts of alcohol. Importantly, direct evidence for a causative role of the cerebellum in alcohol consumption phenotype is lacking. Here we determined that concentrations of alcohol that would be achieved in the blood after consumption of 1-2 standard units (9 mm) suppresses transmission through the cerebellar cortex in low, but not high, alcohol consuming rodent genotypes (DBA/2J and C57BL/6J mice, respectively). This genotype-selective suppression is mediated exclusively by enhancement of granule cell GABAA receptor currents, which only occurs in DBA/2J mice. Simulating the DBA/2J cellular phenotype in C57BL/6J mice by infusing the GABAA receptor agonist, 4,5,6,7-tetrahydroisoxazolo-[5,4-c]pyridine-3-ol hydrochloride, into cerebellar lobules IV-VI, in vivo, significantly reduced their alcohol consumption and blood alcohol concentrations achieved. 4,5,6,7-Tetrahydroisoxazolo-[5,4-c]pyridine-3-ol hydrochloride infusions also significantly decreased sucrose consumption, but they did not affect consumption of water or general locomotion. Thus, genetic differences in cerebellar response to alcohol contributes to alcohol consumption phenotype, and targeting the cerebellar GABAA receptor system may be a clinically viable therapeutic strategy for reducing excessive alcohol consumption., Significance Statement: Alcohol abuse is a leading cause of preventable death and illness; and although alcohol use disorders are 50%-60% genetically determined, the cellular and molecular mechanisms of such genetic influences are largely unknown. Here we demonstrate that genetic differences in cerebellar granule cell GABAA receptor responses to recreational concentrations of alcohol are the primary determinant of alcohol's impact on cerebellar processing and that pharmacologically modifying such responses alters alcohol consumption. These data highlight the cerebellum as an important neuroanatomical region in alcohol consumption phenotype and as a target for pharmacological treatment of alcohol use disorders. The results also add to the growing list of cognitive/emotional roles of the cerebellum in psychiatric disease and drug abuse., (Copyright © 2016 the authors 0270-6474/16/369020-07$15.00/0.)

Accumulating evidence indicates that the synaptic activation of N-methyl-D-aspartate receptors (NMDARs) has a neuroprotective effect on neurons. Our previous study demonstrated that APPL1 (adaptor protein containing pleckstrin homology domain, phosphotyrosine-binding domain, and leucine zipper motif) mediates the synaptic activity-dependent activation of PI3K-Akt signaling via coupling this pathway with NMDAR-PSD95 (postsynaptic density protein 95) complexes. However, the molecular mechanism underlying this process is still unknown. In the present study, we investigated the interaction of APPL1 with PSD95 using co-immunocytochemical staining and western blotting. We found that the PDZ2 domain of PSD95 is a binding partner of APPL1. Furthermore, we identified serine 707 of APPL1, a predicted phosphorylation site within the PDZ-binding motif at the C-terminus, as critical for the binding of APPL1 to PSD95, as well as for activation of the Akt signaling pathway during synaptic activity. This suggests that serine 707 of APPL1 is a potential phosphorylation site and may be involved in regulating the neuroprotective Akt signaling pathway that depends on synaptic NMDAR activity.

Neurosteroids are synthesized in the nervous system from cholesterol or steroidal precursors imported from peripheral sources. These compounds are important allosteric modulators of γ-aminobutyric acid A receptors (GABAARs), which play a vital role in pain modulation in the lateral thalamus, a main gate where somatosensory information enters the cerebral cortex. Using high-performance liquid chromatography/tandem mass spectrometry, we found increased levels of neurosteroids (pregnenolone, progesterone, deoxycorticosterone, allopregnanolone, and tetrahydrodeoxycorticosterone) in the chronic stage of neuropathic pain (28 days after spared nerve injury) in rats. The expression of the translocator protein TSPO, the upstream steroidogenesis rate-limiting enzyme, increased at the same time. In vivo stereotaxic microinjection of neurosteroids or the TSPO activator AC-5216 into the lateral thalamus (AP -3.0 mm, ML ±3.0 mm, DV 6.0 mm) alleviated the mechanical allodynia in neuropathic pain, while the TSPO inhibitor PK 11195 exacerbated it. The analgesic effects of AC-5216 and neurosteroids were significantly attenuated by the GABAAR antagonist bicuculline. These results suggested that elevated neurosteroids in the lateral thalamus play a protective role in the chronic stage of neuropathic pain.

Unlabelled: Select adhesion proteins control the development of synapses and modulate their structural and functional properties. Despite these important roles, the extent to which different synapse-organizing mechanisms act across brain regions to establish connectivity and regulate network properties is incompletely understood. Further, their functional roles in different neuronal populations remain to be defined. Here, we applied diffusion tensor imaging (DTI), a modality of magnetic resonance imaging (MRI), to map connectivity changes in knock-out (KO) mice lacking the synaptogenic cell adhesion protein SynCAM 1. This identified reduced fractional anisotropy in the hippocampal CA3 area in absence of SynCAM 1. In agreement, mossy fiber refinement in CA3 was impaired in SynCAM 1 KO mice. Mossy fibers make excitatory inputs onto postsynaptic specializations of CA3 pyramidal neurons termed thorny excrescences and these structures were smaller in the absence of SynCAM 1. However, the most prevalent targets of mossy fibers are GABAergic interneurons and SynCAM 1 loss unexpectedly reduced the number of excitatory terminals onto parvalbumin (PV)-positive interneurons in CA3. SynCAM 1 KO mice additionally exhibited lower postsynaptic GluA1 expression in these PV-positive interneurons. These synaptic imbalances in SynCAM 1 KO mice resulted in CA3 disinhibition, in agreement with reduced feedforward inhibition in this network in the absence of SynCAM 1-dependent excitatory drive onto interneurons. In turn, mice lacking SynCAM 1 were impaired in memory tasks involving CA3. Our results support that SynCAM 1 modulates excitatory mossy fiber inputs onto both interneurons and principal neurons in the hippocampal CA3 area to balance network excitability., Significance Statement: This study advances our understanding of synapse-organizing mechanisms on two levels. First, the data support that synaptogenic proteins guide connectivity and can function in distinct brain regions even if they are expressed broadly. Second, the results demonstrate that a synaptogenic process that controls excitatory inputs to both pyramidal neurons and interneurons can balance excitation and inhibition. Specifically, the study reveals that hippocampal CA3 connectivity is modulated by the synapse-organizing adhesion protein SynCAM 1 and identifies a novel, SynCAM 1-dependent mechanism that controls excitatory inputs onto parvalbumin-positive interneurons. This enables SynCAM 1 to regulate feedforward inhibition and set network excitability. Further, we show that diffusion tensor imaging is sensitive to these cellular refinements affecting neuronal connectivity., (Copyright © 2016 the authors 0270-6474/16/367465-12$15.00/0.)

Opioids induce rewarding and locomotor effects by inhibiting rostromedial tegmental GABA neurons that express μ-opioid and nociceptin receptors. These GABA neurons then strongly inhibit dopamine neurons. Opioid-induced reward, locomotion and dopamine release also depend on pedunculopontine and laterodorsal tegmental cholinergic and glutamate neurons, many of which project to and activate ventral tegmental area dopamine neurons. Here we show that laterodorsal tegmental and pedunculopontine cholinergic neurons project to both rostromedial tegmental nucleus and ventral tegmental area, and that M4 muscarinic receptors are co-localized with μ-opioid receptors associated with rostromedial tegmental GABA neurons. To inhibit or excite rostromedial tegmental GABA neurons, we utilized adeno-associated viral vectors and DREADDs to express designed muscarinic receptors (M4D or M3D respectively) in GAD2::Cre mice. In M4D-expressing mice, clozapine-N-oxide increased morphine-induced, but not vehicle-induced, locomotion. In M3D-expressing mice, clozapine-N-oxide blocked morphine-induced, but not vehicle-induced, locomotion. We propose that cholinergic inhibition of rostromedial tegmental GABA neurons via M4 muscarinic receptors facilitates opioid inhibition of the same neurons. This model explains how mesopontine cholinergic systems and muscarinic receptors in the rostromedial tegmental nucleus and ventral tegmental area are important for dopamine-dependent and dopamine-independent opioid-induced rewards and locomotion., (© 2016 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

Investigation of the unexpected photo-instability of 2,6-sulfonamide-substituted derivatives of the boron dipyrromethene (BODIPY) fluorophore led to the discovery of a photoreaction accompanied by multiple bond scissions. We characterized the photoproducts and utilized the photoreaction to design a caged γ-aminobutyric acid (GABA) derivative that can release GABA upon irradiation in the visible range (>450 nm). This allowed us to stimulate neural cells in mouse brain slices., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)