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KCC2 is CNS neuron-specific chloride extruder, essential for the establishment and maintenance of the transmembrane chloride gradient, thereby enabling synaptic inhibition within the CNS. Herein, we highlight KCC2 hypofunction as a fundamental and conserved pathology contributing to neuronal circuit excitation/inhibition (E/I) imbalances that underly epilepsies, chronic pain, neuro-developmental/-traumatic/-degenerative/-psychiatric disorders. Indeed, downstream of both acquired and genetic factors, multiple pathologies (e.g., hyperexcitability and inflammation) converge to impair KCC2-dependent inhibition in CNS. When KCC2 hypofunction occurs, affected neurons are disinhibited due to impaired inhibitory responses to GABA/glycine. This causes neuronal hyperexcitability, disinhibition within neuron circuits, and disrupted neurological functions. More recently, KCC2 was identified as a genetically-validated target for epilepsy, intellectual disability, and autism spectrum disorder, and pathogenic mutations in human SLC12A5 gene were linked to psychiatric/mood disorders. The broad therapeutic utility of KCC2-upmodulating drugs relates to its critical role in determining inhibitory activity of GABAergic neurotransmission, a mechanism widely targeted by several drugs. However, in cases of KCC2 hypofunction GABAergic neurotransmission can be depolarizing/excitatory, thereby impairing endogenous neuronal inhibition while also limiting the effectiveness of existing therapeutics targeting/requiring GABAergic pathway inhibition. Several preclinical reports have shown that KCC2 upmodulating treatments rescue and increase the efficacy of anti-seizure and analgesic medications. Thus, a first-in-class KCC2-potentiating therapy would provide a novel mechanism for restoring physiological CNS inhibition and addressing drug resistance in patients with E/I imbalance pathologies. Herein, we discuss progress toward and further work needed to develop the first-in-class KCC2 therapeutics to treat neurological disorder patients. [ABSTRACT FROM AUTHOR]

KCC2 is CNS neuron-specific chloride extruder, essential for the establishment and maintenance of the transmembrane chloride gradient, thereby enabling synaptic inhibition within the CNS. Herein, we highlight KCC2 hypofunction as a fundamental and conserved pathology contributing to neuronal circuit excitation/inhibition (E/I) imbalances that underly epilepsies, chronic pain, neuro-developmental/-traumatic/-degenerative/-psychiatric disorders. Indeed, downstream of both acquired and genetic factors, multiple pathologies (e.g., hyperexcitability and inflammation) converge to impair KCC2-dependent inhibition in CNS. When KCC2 hypofunction occurs, affected neurons are disinhibited due to impaired inhibitory responses to GABA/glycine. This causes neuronal hyperexcitability, disinhibition within neuron circuits, and disrupted neurological functions. More recently, KCC2 was identified as a genetically-validated target for epilepsy, intellectual disability, and autism spectrum disorder, and pathogenic mutations in human SLC12A5 gene were linked to psychiatric/mood disorders. The broad therapeutic utility of KCC2-upmodulating drugs relates to its critical role in determining inhibitory activity of GABAergic neurotransmission, a mechanism widely targeted by several drugs. However, in cases of KCC2 hypofunction GABAergic neurotransmission can be depolarizing/excitatory, thereby impairing endogenous neuronal inhibition while also limiting the effectiveness of existing therapeutics targeting/requiring GABAergic pathway inhibition. Several preclinical reports have shown that KCC2 upmodulating treatments rescue and increase the efficacy of anti-seizure and analgesic medications. Thus, a first-in-class KCC2-potentiating therapy would provide a novel mechanism for restoring physiological CNS inhibition and addressing drug resistance in patients with E/I imbalance pathologies. Herein, we discuss progress toward and further work needed to develop the first-in-class KCC2 therapeutics to treat neurological disorder patients.

Objective: Epilepsy is a common neurological disorder characterized by recurrent epilepsy episodes. As a non-pharmacological treatment, the ketogenic diet has been widely applied in treating epilepsy. However, the exact therapeutic mechanism of the ketogenic diet for epilepsy remains unclear. This study investigates the molecular mechanisms of the ketogenic diet in regulating fatty acid metabolism and activating the ADCY3-initiated cAMP signaling pathway to enhance neuronal inhibition and thereby treat epilepsy. Methods and results: Meta-analysis reveals that the ketogenic diet is superior to the conventional diet in treating epilepsy. Animal experiments demonstrate that the ketogenic diet is more effective than the conventional diet in treating epilepsy, with the best results achieved using the classic ketogenic diet. Transcriptome sequencing analysis identifies six essential genes, among which ADCY3 shows increased expression in the ketogenic diet. In vivo experiments confirm that the activation of the cAMP-PKA signaling pathway by ADCY3 enhances neuronal inhibition and improves epilepsy control. Conclusion: Clinical observations indicate that the ketogenic diet improves patient epilepsy episodes by regulating the ADCY3-initiated cAMP signaling pathway. [ABSTRACT FROM AUTHOR]

Optical manipulations of genetically defined cell types have generated significant insights into the dynamics of neural circuits. While optogenetic activation has been relatively straightforward, rapid and reversible synaptic inhibition has proven more elusive. Here, we leveraged the natural ability of inhibitory presynaptic GPCRs to suppress synaptic transmission and characterize parapinopsin (PPO) as a GPCR-based opsin for terminal inhibition. PPO is a photoswitchable opsin that couples to Gi/o signaling cascades and is rapidly activated by pulsed blue light, switched off with amber light, and effective for repeated, prolonged, and reversible inhibition. PPO rapidly and reversibly inhibits glutamate, GABA, and dopamine release at presynaptic terminals. Furthermore, PPO alters reward behaviors in a time-locked and reversible manner in vivo. These results demonstrate that PPO fills a significant gap in the neuroscience toolkit for rapid and reversible synaptic inhibition and has broad utility for spatiotemporal control of inhibitory GPCR signaling cascades.

To further advance functional MRI (fMRI)-based brain science, it is critical to dissect fMRI activity at the circuit level. To achieve this goal, we combined brain-wide fMRI with neuronal silencing in well-defined regions. Since focal inactivation suppresses excitatory output to downstream pathways, intact input and suppressed output circuits can be separated. Highly specific cerebral blood volume-weighted fMRI was performed with optogenetic stimulation of local GABAergic neurons in mouse somatosensory regions. Brain-wide spontaneous somatosensory networks were found mostly in ipsilateral cortical and subcortical areas, which differed from the bilateral homotopic connections commonly observed in resting-state fMRI data. The evoked fMRI responses to somatosensory stimulation in regions of the somatosensory network were successfully dissected, allowing the relative contributions of spinothalamic (ST), thalamocortical (TC), corticothalamic (CT), corticocortical (CC) inputs, and local intracortical circuits to be determined. The ventral posterior thalamic nucleus receives ST inputs, while the posterior medial thalamic nucleus receives CT inputs from the primary somatosensory cortex (S1) with TC inputs. The secondary somatosensory cortex (S2) receives mostly direct CC inputs from S1 and a few TC inputs from the ventral posterolateral nucleus. The TC and CC input layers in cortical regions were identified by laminar-specific fMRI responses with a full width at half maximum of <150 µm. Long-range synaptic inputs in cortical areas were amplified approximately twofold by local intracortical circuits, which is consistent with electrophysiological recordings. Overall, whole-brain fMRI with optogenetic inactivation revealed brain-wide, population-based, long-range circuits, which could complement data typically collected in conventional microscopic functional circuit studies. [ABSTRACT FROM AUTHOR]

Reduced anticonvulsant efficacy of benzodiazepines is a problem in the treatment of status epilepticus, with up to 50% of patients failing to respond to their first dose. KCC2 is a neuronal K+‐Cl− co‐transporter that helps set and maintain intracellular Cl− concentrations. KCC2 functional downregulation is a potential contributor to benzodiazepine resistance. We tested this idea using male and female doxycycline‐inducible, conditional transgenic mice to increase the functional expression of KCC2 in pyramidal neurons. We administered mice with two doses of the chemoconvulsant kainic acid (5 mg/kg, i.p.) 60 min apart and quantified the resultant seizures with electroencephalography (EEG) recordings. Overexpression of KCC2 prior to the chemoconvulsant challenge did not affect seizure latency or other measures of seizure severity, but it did increase diazepam's efficacy in stopping EEG seizures. Spike rate, time in seizure, and EEG spectral power following diazepam (5 mg/kg, i.p) were all significantly lower in KCC2 overexpression mice as compared to control mice. Our results indicate that, in the context of benzodiazepine resistance during sustained seizures, addressing impaired Cl− homeostasis alone appreciably improves the efficacy of γ‐aminobutyric acid (GABA)ergic inhibition. We therefore suggest the simultaneous targeting of KCC2 and GABAA receptors as a pathway for improving current anticonvulsant therapeutic strategies. [ABSTRACT FROM AUTHOR]

GABAA receptors are ligand-gated chloride channels and ionotropic receptors of GABA, the main inhibitory neurotransmitter in vertebrates. In this review, we discuss the major and diverse roles GABAA receptors play in the regulation of neuronal communication and the functioning of the brain. GABAA receptors have complex electrophysiological properties that enable them to mediate different types of currents such as phasic and tonic inhibitory currents. Their activity is finely regulated by membrane voltage, phosphorylation and several ions. GABAA receptors are pentameric and are assembled from a diverse set of subunits. They are subdivided into numerous subtypes, which differ widely in expression patterns, distribution and electrical activity. Substantial variations in macroscopic neural behavior can emerge from minor differences in structure and molecular activity between subtypes. Therefore, the diversity of GABAA receptors widens the neuronal repertoire of responses to external signals and contributes to shaping the electrical activity of neurons and other cell types. [ABSTRACT FROM AUTHOR]

In the central nervous system, regional neuronal inhibition plays important roles in functional segregation. Here, we showed how brain deactivation, which is a putative index of neuronal inhibition, develops and ages using a unimanual motor task. Healthy right-handed children (8–11 years), adolescents (12–15 years), young adults (20–24 years), and older adults (69–75 years; 21 participants in each group) underwent functional magnetic resonance imaging with their eyes closed while they performed 1-Hz alternating extension–flexion of the right wrist. In young adults, we found deactivations in the hand/arm section of the ipsilateral primary sensorimotor cortices (SM1) including the dorsal premotor cortex (interhemispheric inhibition), foot and face SM1 sections (cross-somatotopic inhibition), visual and auditory cortices (cross-modal inhibition), and precuneus and medial prefrontal cortex of the default mode network (DMN; DMN inhibition). Interhemispheric, cross-modal, and DMN inhibitions developed from childhood to adulthood, but cross-somatotopic inhibition showed no developmental changes. Conversely, interhemispheric, cross-somatotopic, and cross-modal inhibitions, but not DMN inhibition, decreased with aging. Thus, neuronal inhibition generally progresses with development and deteriorates with aging, with some noted regional differences. This was the first study to systematically describe the development and aging of brain deactivation, which may reflect regional neuronal inhibition. [ABSTRACT FROM AUTHOR]

There is no consensus on the best inhibitory optogenetic tool. Since Gi/o signalling is a native mechanism of neuronal inhibition, we asked whether Lamprey Parapinopsin ("Lamplight"), a Gi/o‐coupled bistable animal opsin, could be used for optogenetic silencing. We show that short (405 nm) and long (525 nm) wavelength pulses repeatedly switch Lamplight between stable signalling active and inactive states, respectively, and that combining these wavelengths can be used to achieve intermediate levels of activity. These properties can be applied to produce switchable neuronal hyperpolarisation and suppression of spontaneous spike firing in the mouse hypothalamic suprachiasmatic nucleus. Expressing Lamplight in (predominantly) ON bipolar cells can photosensitise retinas following advanced photoreceptor degeneration, with 405 and 525 nm stimuli producing responses of opposite sign in the output neurons of the retina. We conclude that bistable animal opsins can co‐opt endogenous signalling mechanisms to allow optogenetic inhibition that is scalable, sustained and reversible. SYNOPSIS: Lamprey parapinopsin is a Gi/o‐coupled bistable animal opsin activated and deactivated by short and long wavelength light, respectively. This study shows that Lamplight can be used as a reversible inhibitory optogenetic tool in mice. Lamplight can produce reversible hyperpolarisation in brain neurons and photoswitchable changes in the retina.Single light pulses can produce sustained inhibition.Lamplight‐driven Go activity can be controlled by modulating either the intensity or the spectral composition of the light stimulus. [ABSTRACT FROM AUTHOR]

Understanding the role of the noradrenergic nucleus locus coeruleus (LC) in cognition and behavior is critical: It is involved in several key behavioral functions such as stress and vigilance, as well as in cognitive processes such as attention and decision making. In recent years, the development of viral tools has provided a clear insight into numerous aspects of brain functions in rodents. However, given the specificity of primate brains and the key benefit of monkey research for translational applications, developing viral tools to study the LC in monkeys is essential for understanding its function and exploring potential clinical strategies. Here, we describe a pharmacogenetics approach that allows to selectively and reversibly inactivate LC neurons using Designer Receptors Exclusively Activated by Designer Drugs (DREADD). We show that the expression of the hM4Di DREADD can be restricted to noradrenergic LC neurons and that the amount of LC inhibition can be adjusted by adapting the dose of the specific DREADD activator deschloroclozapine (DCZ). Indeed, even if high doses (>0.3 mg/kg) induce a massive inhibition of LC neurons and a clear decrease in vigilance, smaller doses (

Type-A and -B GABA receptors (GABA A Rs/GABA B Rs) control brain function and behaviour by fine tuning neurotransmission. Over-time these receptors have become important therapeutic targets for treating neurodevelopmental and neuropsychiatric disorders. Several positive allosteric modulators (PAMs) of GABARs have reached the clinic and selective targeting of receptor subtypes is crucial. For GABA B Rs, CGP7930 is a widely used PAM for in vivo studies, but its full pharmacological profile has not yet been established. Here, we reveal that CGP7930 has multiple effects not only on GABA B Rs but also GABA A Rs, which for the latter involves potentiation of GABA currents, direct receptor activation, and also inhibition. Furthermore, at higher concentrations, CGP7930 also blocks G protein-coupled inwardly-rectifying K+ (GIRK) channels diminishing GABA B R signalling in HEK 293 cells. In male and female rat hippocampal neuron cultures, CGP7930 allosteric effects on GABA A Rs caused prolonged rise and decay times and reduced the frequency of inhibitory postsynaptic currents and potentiated GABA A R-mediated tonic inhibition. Additional comparison between predominant synaptic- and extrasynaptic-isoforms of GABA A R indicated no evident subtype selectivity for CGP7930. In conclusion, our study of CGP7930 modulation of GABA A Rs, GABA B Rs and GIRK channels, indicates this compound is unsuitable for use as a specific GABA B R PAM. • CGP7930, an established GABA B R PAM, inhibits GABA B R signalling at >3 μM concentration. • CGP7930 apparent inhibitory activity at GABA B Rs results from inhibition of GIRK channels. • CGP7930 is also an efficacious and potent GABA A R ligand. • CGP7930 is approximately equipotent at GABA A Rs and GABA B Rs. • Physiological actions of CGP7930 will involve an array of targets including type-A and -B GABARs and K+ channels. [ABSTRACT FROM AUTHOR]

Genetic epilepsies are caused by mutations in a range of different genes, many of them encoding ion channels, receptors or transporters. While the number of detected variants and genes increased dramatically in the recent years, pleiotropic effects have also been recognized, revealing that clinical syndromes with various degrees of severity arise from a single gene, a single mutation, or from different mutations showing similar functional defects. Accordingly, several genes coding for GABAA receptor subunits have been linked to a spectrum of benign to severe epileptic disorders and it was shown that a loss of function presents the major correlated pathomechanism. Here, we identified six variants in GABRA3 encoding the α3-subunit of the GABAA receptor. This gene is located on chromosome Xq28 and has not been previously associated with human disease. Five missense variants and one microduplication were detected in four families and two sporadic cases presenting with a range of epileptic seizure types, a varying degree of intellectual disability and developmental delay, sometimes with dysmorphic features or nystagmus. The variants co-segregated mostly but not completely with the phenotype in the families, indicating in some cases incomplete penetrance, involvement of other genes, or presence of phenocopies. Overall, males were more severely affected and there were three asymptomatic female mutation carriers compared to only one male without a clinical phenotype. X-chromosome inactivation studies could not explain the phenotypic variability in females. Three detected missense variants are localized in the extracellular GABA-binding NH2-terminus, one in the M2-M3 linker and one in the M4 transmembrane segment of the α3-subunit. Functional studies in Xenopus laevis oocytes revealed a variable but significant reduction of GABA-evoked anion currents for all mutants compared to wild-type receptors. The degree of current reduction correlated partially with the phenotype. The microduplication disrupted GABRA3 expression in fibroblasts of the affected patient. In summary, our results reveal that rare loss-of-function variants in GABRA3 increase the risk for a varying combination of epilepsy, intellectual disability/developmental delay and dysmorphic features, presenting in some pedigrees with an X-linked inheritance pattern. [ABSTRACT FROM AUTHOR]

Intracellular chloride ([Cl-]i) andpH(pHi) are fundamental regulators of neuronal excitability. They exert wide-ranging effects on synaptic signaling and plasticity and on development and disorders of the brain. The ideal technique to elucidate the underlying ionic mechanisms is quantitative and combined two-photon imaging of [Cl-]i and pHi, but this has never been performed at the cellular level in vivo. Here, by using a genetically encoded fluorescent sensor that includes a spectroscopic reference (an element insensitive to Cl- and pH), we show that ratiometric imaging is strongly affected by the optical properties of the brain. We have designed a method that fully corrects for this source of error. Parallel measurements of [Cl-]i and pHi at the single-cell level in the mouse cortex showed the in vivo presence of the widely discussed developmental fall in [Cl-]i and the role of the K-Cl cotransporter KCC2 in this process. Then, we introduce a dynamic twophoton excitation protocol to simultaneously determine the changes of pHi and [Cl-]i in response to hypercapnia and seizure activity. [ABSTRACT FROM AUTHOR]

Optogenetic manipulation is uniquely useful in unraveling the functional organization of neuronal circuits in the central nervous system by enabling reversible gain- or loss-of-function of discrete populations of neurons within restricted brain regions. This state-of-the-art technology can produce circuit-specific neuromodulation by overexpressing light-sensitive proteins (opsins) in particular cell types of interest. Here, we discuss the principle of optogenetic manipulation and its application in pain research using animal models, and we also discuss how to potentially use optogenetic stimulation in the treatment of migraine headache in the future.

Alzheimer’s disease (AD) is characterized pathologically by the deposition of -amyloid peptides (A) and the accumulation of neurofibrillary tangles (NFTs) composed of hyper-phosphorylated tau. Regardless of the pathological hallmarks, synaptic dysfunction is widely accepted as a causal event in AD. Of the two major types of synapses in the CNS: glutamatergic and GABAergic, which provide excitatory and inhibitory outputs respectively, abundant data implicate an impaired glutamatergic system during disease progression. However, emerging evidence supports the notion that disrupted default neuronal network underlies impaired memory, and that alterations of GABAergic circuits, either plays a primary role or as a compensatory response to excitotoxicity, may also contribute to AD by disrupting the overall network function. The goal of this review is to provide an overview of the involvement of A, tau and apoE4, the major genetic risk factor in late-onset AD, in GABAergic neurotransmission and the potential of modulating the GABAergic function as AD therapy.

The structure-guided design of chloride-conducting channelrhodopsins has illuminated mechanisms underlying ion selectivity of this remarkable family of light-activated ion channels. The first generation of chloride-conducting channelrhodopsins, guided in part by development of a structure-informed electrostatic model for pore selectivity, included both the introduction of amino acids with positively charged side chains into the ion conduction pathway and the removal of residues hypothesized to support negatively charged binding sites for cations. Engineered channels indeed became chloride selective, reversing near -65 mV and enabling a new kind of optogenetic inhibition; however, these first-generation chloride-conducting channels displayed small photocurrents and were not tested for optogenetic inhibition of behavior. Here we report the validation and further development of the channelrhodopsin pore model via crystal structure-guided engineering of next-generation light-activated chloride channels (iC++) and a bistable variant (SwiChR++) with net photocurrents increased more than 15-fold under physiological conditions, reversal potential further decreased by another ~15 mV, inhibition of spiking faithfully tracking chloride gradients and intrinsic cell properties, strong expression in vivo, and the initial microbial opsin channel-inhibitor-based control of freely moving behavior. We further show that inhibition by light-gated chloride channels is mediated mainly by shunting effects, which exert optogenetic control much more efficiently than the hyperpolarization induced by light-activated chloride pumps. The design and functional features of these next-generation chloride-conducting channelrhodopsins provide both chronic and acute timescale tools for reversible optogenetic inhibition, confirm fundamental predictions of the ion selectivity model, and further elucidate electrostatic and steric structure- function relationships of the light-gated pore. [ABSTRACT FROM AUTHOR]

Sensory stimuli not only activate specific populations of cortical neurons but can also silence other populations. However, it remains unclear whether neuronal silencing per se leads to memory formation and behavioral expression. Here we show that mice can report optogenetic inactivation of auditory neuron ensembles by exhibiting fear responses or seeking a reward. Mice receiving pairings of footshock and silencing of a neuronal ensemble exhibited a fear response selectively to the subsequent silencing of the same ensemble. The valence of the neuronal silencing was preserved for at least 30 d and was susceptible to extinction training. When we silenced an ensemble in one side of auditory cortex for conditioning, silencing of an ensemble in another side induced no fear response. We also found that mice can find a reward based on the presence or absence of the silencing. Neuronal silencing was stored as working memory. Taken together, we propose that neuronal silencing without explicit activation in the cerebral cortex is enough to elicit a cognitive behavior. [ABSTRACT FROM AUTHOR]

A reduction in GABAergic neurotransmission has been put forward as a pathophysiological mechanism for human epilepsy. However, in slices of human epileptogenic neocortex, GABAergic inhibition can be clearly demonstrated. In this article we present data showing an increase in the functional lability of GABAergic inhibition in epileptogenic tissue compared with nonepileptogenic human tissue. We have previously shown that the glycolytic enzyme GAPDH is the kinase involved in the glycolysis-dependent endogenous phosphorylation of the α1-subunit of GABAA receptor, a mechanism necessary for maintaining GABAA function. In human epileptogenic cortex obtained during curative surgery of patients with partial seizures, we demonstrate an intrinsic deficiency of GABAA receptor endogenous phosphorylation resulting in an increased lability of GABAergic currents in neurons isolated from this tissue when compared with neurons from nonepileptogenic human tissue. This feature was not related to a reduction in the number of GABAA receptor α1-subunits in the epileptogenic tissue as measured by [³H]flunitrazepam photoaffinity labeling. Maintaining the receptor in a phosphorylated state either by favoring the endogenous phosphorylation or by inhibiting a membrane-associated phosphatase is needed to sustain GABAA receptor responses in epileptogenic cortex. The increased functional lability induced by the deficiency in phosphorylation can account for transient GABAergic disinhibition favoring seizure initiation and propagation. These findings imply new therapeutic approaches and suggest a functional link to the regional cerebral glucose hypometabolism observed in patients with partial epilepsy, because the dysfunctional GABAergic mechanism depends on the locally produced glycolytic ATP. [ABSTRACT FROM AUTHOR]

The medial nucleus of the trapezoid body (MNTB) plays an important role in the processing of interaural intensity differences, a feature that is critical for the localization of sound sources. It is generally believed that the MNTB functions primarily as a passive relay in converting excitatory input originating from the contralateral cochlear nucleus (CN) into an inhibitory input to the ipsilateral lateral superior olive. However, studies showing that the MNTB itself is also the target of inhibitory input suggest that the MNTB may serve more than a sign-converting function. To examine the fidelity of signal transmission at the CN-MNTB synapse, presynaptic calyceal potentials (‘prepotentials’), reflecting the excitatory input to the MNTB neuron, and postsynaptic action potentials were simultaneously monitored with the same electrode during in vivo extracellular recordings from the gerbil's MNTB. Presynaptic activity differed from postsynaptic activity in several respects: (1) Spontaneous and sound-evoked discharge rates were greater presynaptically than postsynaptically. (2) Frequency tuning was sharper postsynaptically than presynaptically. (3) Calyceal terminals and MNTB neurons both showed phasic-tonic response patterns to tonal stimulation, but the duration of the onset response and the level of the tonic component were reduced postsynaptically. (4) Phase-locking to sound frequencies up to 1 kHz was greater postsynaptically than presynaptically. (5) The rate-intensity characteristics of pre- and postsynaptic activities differed significantly from each other in half of the MNTB neurons. To test the hypothesis that acoustically evoked inhibition of MNTB neurons contributed to the relatively lower levels of postsynaptic discharge, two-tone stimulation was applied, wherein the response to one tone-burst, set at the neuron's characteristic frequency, can be reduced by addition of a second ‘inhibitory’ tone. The inhibitory tone caused a much larger reduction in post- than in presynaptic activity, indicating an acoustically evoked inhibitory influence directly on MNTB units. These findings show that transmission at the CN-MNTB synapse does not occur in a fixed one-to-one manner and that the response of MNTB neurons reflects the integration of their excitatory and inhibitory inputs. [ABSTRACT FROM AUTHOR]

The microenvironment of the CNS has been considered to tonically inhibit glial activities. It has been shown that glia become activated where neuronal death occurs in the aging brain. We have previously demonstrated that neurons tonically inhibit glial activities including their responses to the bacterial endotoxin lipopolysaccharide (LPS). It is not clear whether activation of glia, especially microglia in the aging brain, is the consequence of disinhibition due to neuronal death. This study was designed to determine if glia regain their responsiveness to LPS once the neurons have died in aged cultures. When cultured alone, glia from postnatal day one rat mesencephalons stimulated with LPS (0.1–1000 ng/mL) produced both nitric oxide (NO) and tumor necrosis factor α (TNFα), yielding a sigmoid and a bell-shaped curve, respectively. When neuron-containing cultures were prepared from embryonic day 14/15 mesencephalons, the shape of the dose–response curve for NO was monotonic and the bell-shaped curve for TNFα production was shifted to the right. After 1 month of culture under conditions where neurons die, the production curves for NO and TNFα in LPS-stimulated glia shifted back to the left compared to mixed neuron–glia cultures. Immunostaining of rat microglia for the marker CR3 (the receptor for complement component C3) demonstrated that high concentrations of LPS (1 µg/mL) reduced the number of microglia in mixed-glial cultures. In contrast, reduction of CR3 immunostaining was not observed in LPS-stimulated mixed neuron–glia cultures. Taken together, the results demonstrate that disinhibition of the glial response to LPS occurs after neurons die in aged cultures. Once neurons have died, the responsiveness of glia to LPS is restored. Neurons prevented injury to microglia by reducing their responsiveness to LPS. This study broadens our understanding of the ways in which the CNS microenvironment affects cerebral inflammation. [ABSTRACT FROM AUTHOR]

Understanding the role of the noradrenergic nucleus locus coeruleus (LC) in cognition and behavior is critical: It is involved in several key behavioral functions such as stress and vigilance, as well as in cognitive processes such as attention and decision making. In recent years, the development of viral tools has provided a clear insight into numerous aspects of brain functions in rodents. However, given the specificity of primate brains and the key benefit of monkey research for translational applications, developing viral tools to study the LC in monkeys is essential for understanding its function and exploring potential clinical strategies. Here, we describe a pharmacogenetics approach that allows to selectively and reversibly inactivate LC neurons using Designer Receptors Exclusively Activated by Designer Drugs (DREADD). We show that the expression of the hM4Di DREADD can be restricted to noradrenergic LC neurons and that the amount of LC inhibition can be adjusted by adapting the dose of the specific DREADD activator deschloroclozapine (DCZ). Indeed, even if high doses (>0.3 mg/kg) induce a massive inhibition of LC neurons and a clear decrease in vigilance, smaller doses (<0.3 mg/kg) induce a more moderate decrease in LC activity, but it does not affect vigilance, which is more compatible with an assessment of subtle cognitive functions such as decision making and attention. [ABSTRACT FROM AUTHOR]

Changes in respiration and heart rate during sleep states have been recorded by a polygraphic device in healthy preterm infants. Cardiac slowing/bradycardia often coincide with respiratory arrest/apnea. Bradycardia starts early during apneic spells. The incidence of respiratory arrest and cardiac slowing and their simultaneous occurrence is significantly increased by the active or REM sleep state. The physiologic, inhibitory mechanisms of active sleep suggest a neurogenic etiology of episodes of cardiac slowing/bradycardia and/or respiratory arrest/apnea in prematures. [ABSTRACT FROM AUTHOR]

Neurons have the capacity to adapt to environmental stimuli, a phenomenon termed cellular plasticity. The underlying processes are controlled by a network of RNA-binding proteins (RBPs). Their precise impact, however, is largely unknown. To address this important question, we chose Pumilio2 (Pum2) and Staufen2 (Stau2), which both regulate synaptic transmission. Surprisingly, even though both RBPs dynamically interact with each other in neurons, their respective impact on the transcriptome and proteome is highly selective. Although Pum2 deficiency leads to reduced translation and protein expression, Stau2 depletion preferentially impacts RNA levels and increases protein abundance. Furthermore, we show that Pum2 activates expression of key GABAergic synaptic components, e.g., the GABA A receptor scaffold protein Gephyrin. Consequently, Pum2 depletion selectively reduced the amplitude of miniature inhibitory postsynaptic currents. Together, our data argue for an important role of RBPs to maintain proteostasis in order to control distinct aspects of synaptic transmission. [Display omitted] • Pum2 and Stau2 selectively regulate the neuronal proteome • Stau2 preferentially regulates mRNA levels, while Pum2 activates translation • Pum2 regulates efficient GABAergic transmission Neurons maintain proteome homeostasis (proteostasis) through a network of RNA-binding proteins (RBPs). Schieweck et al. report that the RBPs Pumilio2 (Pum2) and Staufen2 regulate distinct steps in posttranscriptional gene regulations and are both needed for synaptic proteostasis. Thereby, Pum2 activates translation in order to enhance transmission preferentially at inhibitory synapses. [ABSTRACT FROM AUTHOR]

In modern life sciences, the issue of a specific, exogenously directed manipulation of a cell's biochemistry is a highly topical one. In the case of electrically excitable cells, the aim of the manipulation is to control the cells' electrical activity, with the result being either excitation with subsequent generation of an action potential or inhibition and suppression of the excitatory currents. The techniques of electrical activity stimulation are of particular significance in tackling the most challenging basic problem: figuring out how the nervous system of higher multicellular organisms functions. At this juncture, when neuroscience is gradually abandoning the reductionist approach in favor of the direct investigation of complex neuronal systems, minimally invasive methods for brain tissue stimulation are becoming the basic element in the toolbox of those involved in the field. In this review, we describe three approaches that are based on the delivery of exogenous, genetically encoded molecules sensitive to external stimuli into the nervous tissue. These approaches include optogenetics (Part I) as well as chemogenetics and thermogenetics (Part II), which are significantly different not only in the nature of the stimuli and structure of the appropriate effector proteins, but also in the details of experimental applications. The latter circumstance is an indication that these are rather complementary than competing techniques., (Copyright ® 2021 National Research University Higher School of Economics.)