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The alpha7 (α7) nicotinic acetylcholine receptor is a therapeutic target for cognitive disorders. Here we describe 3-(3,4-difluorophenyl)-N-(1-(6-(4-(pyridin-2-yl)piperazin-1-yl)pyrazin-2-yl)ethyl)propanamide (B-973), a novel piperazine-containing molecule that acts as a positive allosteric modulator of the α7 receptor. We characterize the action of B-973 on the α7 receptor using electrophysiology and radioligand binding. At 0.1 mM acetylcholine, 1 μM B-973 potentiated peak acetylcholine-induced currents 6-fold relative to maximal acetylcholine (3 mM) and slowed channel desensitization, resulting in a 6900-fold increase in charge transfer. The EC 50 of B-973 was approximately 0.3 μM at acetylcholine concentrations ranging from 0.03 to 3 mM. At a concentration of 1 μM, B-973 shifted the acetylcholine EC 50 of peak currents from 0.30 mM in control to 0.007 mM. B-973 slowed channel deactivation upon acetylcholine removal (τ=50 s) and increased the affinity of the α7 agonist [ 3 H]A-585539. In the absence of exogenously added acetylcholine, application of B-973 at concentrations >1 μM induced large methyllycaconitine-sensitive currents, suggesting B-973 can function as an Ago-PAM at high concentrations. B-973 will be a useful probe for investigating the biological consequences of increasing α7 receptor activity through allosteric modulation. [ABSTRACT FROM AUTHOR]

Positive allosteric modulators (PAMs) of the GABA B receptor have emerged as a novel approach to the pharmacological manipulation of the GABA B receptor, enhancing the effects of receptor agonists with few side effects. Here, we identified N-cyclohexyl-4-methoxy-6-(4-(trifluoromethyl)phenyl)pyrimidin-2-amine (SSD114) as a new compound with activity as a GABA B PAM in in vitro and in vivo assays. SSD114 potentiated GABA-stimulated [ 35 S]GTPγS binding to native GABA B receptors, whereas it had no effect when used alone. Its effect on GTPγS stimulation was suppressed when GABA-induced activation was blocked with CGP54626, a competitive antagonist of the GABA B receptor. SSD114 failed to potentiate WIN55,212,2-, morphine- and quinpirole-induced [ 35 S]GTPγS binding to cortical and striatal membranes, respectively, indicating that it is a selective GABA B PAM. Increasing SSD114 fixed concentrations induced a leftward shift of the GABA concentration-response curve, enhancing the potency of GABA rather than its efficacy. SSD114 concentration-response curves in the presence of fixed concentrations of GABA (1, 10, and 20 μM) revealed a potentiating effect on GABA-stimulated binding of [ 35 S]GTPγS to rat cortical membranes, with EC 50 values in the low micromolar range. Bioluminescence resonance energy transfer (BRET) experiments in Chinese Hamster Ovary (CHO)-cells expressing GABA B receptors showed that SSD114 potentiates the GABA inhibition of adenylyl-cyclase mediated by GABA B receptors. Our compound is also effective in vivo potentiating baclofen-induced sedation/hypnosis in mice, with no effect when tested alone. These findings indicate that SSD114, a molecule with a different chemical structure compared to known GABA B PAMs, is a novel GABA B PAM with potential usefulness in the GABA B -receptor research field. [ABSTRACT FROM AUTHOR]

Some drugs that are positive allosteric nAChR modulators in vitro, desformylflustrabromine (dFBr), PNU-120596 and LY 2087101, have not been fully characterized in vivo. These drugs were examined for their capacity to share or modify the hypothermic and discriminative stimulus effects of nicotine (1 mg/kg s.c.) in male C57Bl/6J mice. Nicotine, dFBr, and PNU-120596 produced significant hypothermia, whereas LY 2087101 (up to 100 mg/kg) did not. Nicotine dose-dependently increased nicotine-appropriate responding and decreased response rate; the respective ED 50 values were 0.56 mg/kg and 0.91 mg/kg. The modulators produced no more than 38% nicotine-appropriate responding up to doses that disrupted operant responding. Rank order potency was the same for hypothermia and rate-decreasing effects: nicotine>dFBr>PNU-120596=LY 2087101. Mecamylamine and the α4β2 nAChR antagonist dihydro-β-erythroidine, but not the α7 antagonist methyllycaconitine, antagonized the hypothermic effects of nicotine. In contrast, mecamylamine did not antagonize the hypothermic effects of the modulators. The combined discriminative stimulus effects of DFBr and nicotine were synergistic, whereas the combined hypothermic effects of nicotine with either dFBr or PNU-120596 were infra-additive. PNU-120596 did not modify the nicotine discriminative stimulus, and LY 2087101 did not significantly modify either effect of nicotine. Positive modulation of nicotine at nAChRs by PNU-120596 and LY 2087101 in vitro does not appear to confer enhancement of the nAChR-mediated hypothermic or discriminative stimulus effects of nicotine. However, dFBr appears to be a positive allosteric modulator of some behavioral effects of nicotine at doses of dFBr smaller than the doses producing unwanted effects (e.g. hypothermia) through non-nAChR mechanisms. [ABSTRACT FROM AUTHOR]

In previous experiments, we have discovered that positive allosteric modulation of metabotropic glutamate 2 (mGlu 2) receptors enhances the anti-parkinsonian action of an optimal dose of L-3,4-dihydroxyphenylalanine (L-DOPA). Whether selective mGlu 2 positive allosteric modulation would also alleviate parkinsonian disability as monotherapy or as adjunct to a sub-optimal dose of L-DOPA has not been determined. Here, we assessed the anti-parkinsonian effect of mGlu 2 positive allosteric modulation as monotherapy and adjunct to a sub-optimal dose of L-DOPA in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned marmosets. The highly selective positive allosteric modulator (PAM) LY-487,379 was utilised to activate mGlu 2 receptors. When administered as monotherapy, LY-487,379 10 mg/kg diminished global parkinsonism by 48% (P < 0.001) and increased duration of on-time by 7-fold, when compared to vehicle treatment (P < 0.05). When added to a sub-optimal dose of L-DOPA, LY-487,379 10 mg/kg decreased global parkinsonism by 44% (P < 0.001) and extended duration of on-time by 2.5-fold (P < 0.01). Our results indicate that selective mGlu 2 positive allosteric modulation elicits anti-parkinsonian benefits as monotherapy and as adjunct to sub-optimal dose of L-DOPA paradigms, potentially suggesting that mGlu 2 PAMs may have a therapeutic niche early in the treatment of PD as DOPA-sparing agents. [ABSTRACT FROM AUTHOR]

Abstract: In the central nervous system, deficits in cholinergic neurotransmission correlate with decreased attention and cognitive impairment, while stimulation of neuronal nicotinic acetylcholine receptors improves attention, cognitive performance and neuronal resistance to injury as well as produces robust analgesic and anti-inflammatory effects. The rational basis for the therapeutic use of orthosteric agonists and positive allosteric modulators (PAMs) of nicotinic receptors arises from the finding that functional nicotinic receptors are ubiquitously expressed in neuronal and non-neuronal tissues including brain regions highly vulnerable to traumatic and ischemic types of injury (e.g., cortex and hippocampus). Moreover, functional nicotinic receptors do not vanish in age-, disease- and trauma-related neuropathologies, but their expression and/or activation levels decline in a subunit- and brain region-specific manner. Therefore, augmenting the endogenous cholinergic tone by nicotinic agents is possible and may offset neurological impairments associated with cholinergic hypofunction. Importantly, because neuronal damage elevates extracellular levels of choline (a selective agonist of ?7 nicotinic acetylcholine receptors) near the site of injury, ?7-PAM-based treatments may augment pathology-activated ?7-dependent auto-therapies where and when they are most needed (i.e., in the penumbra, post-injury). Thus, nicotinic-PAM-based treatments are expected to augment the endogenous cholinergic tone in a spatially and temporally restricted manner creating the potential for differential efficacy and improved safety as compared to exogenous orthosteric nicotinic agonists that activate nicotinic receptors indiscriminately. In this review, I will summarize the existing trends in therapeutic applications of nicotinic PAMs. [Copyright &y& Elsevier]

Abstract: γ-Aminobutyric acid-B (GABAB) receptor positive allosteric modulators (PAMs) act on an allosteric site on the GABAB receptor to potentiate the effects of GABA and GABAB receptor agonists. It has previously been demonstrated that the GABAB receptor agonist baclofen increases food intake in non-deprived rats. The aim of this study was to investigate whether the GABAB receptor PAM 2,6-di tert-butyl-4-(2-hydroxy-2,2-dimethyl-propyl)-phenol (CGP7930) would (i) increase food intake, and (ii) potentiate the hyperphagic effects of baclofen in rats. In Experiment 1, the effects of intraperitoneal (i.p.) administration of CGP7930 (1, 6 and 12mg/kg) was investigated on food intake in non-deprived male Wistar rats. The 12mg/kg dose of CGP7930 significantly increased cumulative food intake 30, 60 and 120min (P<0.05, in each case) after administration. The 1 and 6mg/kg doses were without effect. In Experiment 2, the effects of pretreatment with CGP7930 (6mg/kg; i.p.) 5min prior to administration of baclofen (2mg/kg, i.p.) was investigated on 30min cumulative food intake in non-deprived male Wistar rats. Baclofen (2mg/kg) significantly increased food intake compared with vehicle treatment (P<0.01). CGP7930 (6mg/kg) had no effect on feeding. However, pretreatment with CGP7930 (6mg/kg) significantly potentiated the hyperphagic effects of baclofen (2mg/kg) (P<0.01). These findings show that CGP7930 increases food intake and enhances the hyperphagic effects of baclofen, and are consistent with in vitro studies that suggest that it potentiates the effects of endogenous GABA and GABAB receptor agonists by allosteric modulation of the GABAB receptor. [Copyright &y& Elsevier]

Abstract: Nicotinic acetylcholine receptors mediate fast cholinergic modulation of glutamatergic transmission and synaptic plasticity. Here we investigated the effects of subtype selective activation of the α7 nicotinic acetylcholine receptors on hippocampal transmission and the inhibition of synaptic long-term potentiation by the Alzheimer''s disease associated amyloid ß-protein (Aß). The α7 nicotinic acetylcholine receptor agonist “compound A” ((R)-N-(1-azabicyclo[2.2.2]oct-3-yl)(5-(2-pyridyl))thiophene-2-carboxamide) induced a rapid-onset persistent enhancement of synaptic transmission in the dentate gyrus in vitro. Consistent with a requirement for activation of α7 nicotinic acetylcholine receptors, the type II α7-selective positive allosteric modulator PheTQS ((3aR, 4S, 9bS)-4-(4-methylphenyl)-3a,4,5,9b-tetrahydro-3H-cyclopenta[c]quinoline-8-sulfonamide) potentiated, and the antagonist methyllycaconitine (MLA) prevented the persistent enhancement. Systemic injection of the agonist also induced a similar MLA-sensitive persistent enhancement of synaptic transmission in the CA1 area in vivo. Remarkably, although compound A did not affect control long-term potentiation (LTP) in vitro, it prevented the inhibition of LTP by Aß1–42 and this effect was inhibited by MLA. These findings strongly indicate that activation of α7 nicotinic acetylcholine receptors is sufficient to persistently enhance hippocampal synaptic transmission and to overcome the inhibition of LTP by Aß. [Copyright &y& Elsevier]

Abstract: Positive allosteric modulators of centrally expressed nicotinic acetylcholine receptors have therapeutic potentials in areas of cognition, motor function and reward. Several chemical classes of allosteric modulators that are selective for α7 nicotinic receptors have been characterised, but potentiators for the most widely expressed α4β2 nicotinic receptor subtype are few and less defined, owing probably to the difficulty to achieve selectivity over other heteromeric receptor subtypes. 2087101 (2-amino-5-keto)thiazole) is a potent potentiator of both α7 and α4β2 receptors and it has selectivity against the α3β4 subtype, which may be responsible for the undesirable peripheral side effects. To further characterise its ability to differentiate between native nicotinic receptors, we examined the effects of 2087101 on α7, α4β2* and α3β4* receptor-mediated responses in the rat brain in electrophysiological and neurochemical experiments. 2087101 significantly potentiated agonist-induced, α7 and non-α7 receptor-mediated, GABAergic postsynaptic currents in cultured hippocampal neurones, but not the nicotine-stimulated [3H]noradrenaline release from hippocampal slices, which was primarily mediated by α3β4* receptors, confirming its selectivity for α7 and α4β2* receptors in native systems. 2087101 also significantly enhanced nicotine-stimulated firing increase in dopamine neurones of the ventral tegmental area, an effect that was dihydro-β-erythroidine-sensitive and thereby mediated by α4β2* nicotinic receptors. 2087101 can therefore enhance native nicotinic activities mediated by α7 and α4β2*, but not α3β4* receptors, showing its unique ability to discriminate between native heteromeric nicotinic receptor subtypes and its therapeutic potential for treating brain disorders by concurrent modulation of both α7 and α4β2* nicotinic receptors. [Copyright &y& Elsevier]

Abstract: The NMDA (N-methyl-D-aspartate)-receptor is fundamentally involved in cognitive functions. Recent studies demonstrated a functional interaction between the metabotropic glutamate receptor 5 (mGlu5 receptor) and the NMDA-receptor in neurons. In rat hippocampal slices, it was shown that activation of mGlu5 receptor by a positive modulator in the presence of a subthreshold agonist concentration potentiated NMDA-receptor mediated currents and phosphorylation of intracellular signalling proteins. In the present study, we investigated the functional interaction of mGlu5 receptor and NMDA-receptor by the selective mGlu5 receptor positive modulator ADX-47273 in-vitro and in-vivo. In rat primary neurons, this compound potentiated Ca2+ mobilization in the presence of a subthreshold concentration of the mGluR1/5 agonist DHPG (0.3µM) with an EC50 of 0.28±0.05µM. NMDA-induced Ca2+-mobilization in primary neurons could be potentiated when neurons were pre-stimulated with 1µM ADX-47273 in the presence of 0.3µM DHPG. The specific mGlu5 receptor antagonist MPEP and the Src-family kinase inhibitor PP2 blocked this potentiation demonstrating the functional interaction of the NMDA-receptor and mGlu5 receptor in neurons. Furthermore, ADX-47273 elicited an enhancement of NMDA-receptor dependent long-term potentiation in rat hippocampal slices that could be reversed by MPEP. After intraperitoneal administration to rats, ADX-47273 showed a dose-dependent reduction of NMDA-receptor antagonist (ketamine) induced hyperlocomotion, supporting the mechanistic interaction of the NMDA-receptor and mGlu5 receptor in-vivo. In conclusion, these findings further support the idea of a functional interaction between the mGlu5 receptor and NMDA-receptor, which may provide a pharmacological strategy for addressing CNS diseases with cognitive impairments linked to NMDA-receptor hypofunction. [Copyright &y& Elsevier]

Abstract: Metabotropic glutamate mGlu1 receptors play a modulatory role in the nervous system. They enhance cell excitability, modulate synaptic neurotransmission and are involved in synaptic plasticity. During the last 10years, several selective metabotropic glutamate mGlu1 receptor competitive antagonists and potentiators have been discovered. These pharmacological tools, together with early and later work in metabotropic glutamate mGlu1 receptor mutant mice have allowed studying the role of the receptor in various aspects of psychiatric illnesses such as anxiety, depression and schizophrenia. We here review the data on selective metabotropic glutamate mGlu1 receptor antagonists in support of their potential as anxiolytic and antidepressant treatments. We propose a rationale for the development of metabotropic glutamate mGlu1 receptor positive allosteric modulators for the treatment of schizophrenia. Potential side effects of blockade and activation of metabotropic glutamate mGlu1 receptors are addressed, with special focus on the differential effects of metabotropic glutamate mGlu1 receptor antagonists in cognition models with positive reinforcement versus those that use aversive learning procedures. Further development of negative allosteric modulators and more drug-like positive allosteric modulators will be required in order to decipher the therapeutic efficacy and safety margin of these compounds in the clinic. [Copyright &y& Elsevier]

Abstract: Compiling pharmacological evidence implicates metabotropic glutamate mGlu2 receptors in the regulation of emotional states and suggests positive modulators as a novel therapeutic approach of Anxiety/Depression and Schizophrenia. Here, we investigated subcutaneous effects of the metabotropic glutamate mGlu2/3 agonist (LY354740) on sleep–wake architecture in rat. To confirm the specific effects on rapid eye movement (REM) sleep were mediated via metabotropic glutamate mGlu2 receptors, we characterized the sleep–wake cycles in metabotropic glutamate mGlu2 receptor deficient mice (mGlu2R−/−) and their arousal response to LY354740. We furthermore examined effects on sleep behavior in rats of the positive allosteric modulator, biphenyl-indanone A (BINA) alone and in combination with LY354740 at sub-effective doses. LY354740 (1, 3 and 10 mg/kg) dose-dependently suppressed REM sleep and prolonged its onset latency. Metabotropic glutamate mGlu2R−/− and their wild type (WT) littermates exhibited similar spontaneous sleep–wake phenotype, while LY354740 (10 mg/kg) significantly affected REM sleep variables in WT but not in the mutant. In rats, BINA (1, 3, 10, 20, 40 mg/kg) dose-dependently suppressed REM sleep, lengthened its onset latency and slightly enhanced passive waking. Additionally, combined treatment elicited a synergistic action on REM sleep variables. Our findings show common changes of REM sleep variables following modulation of metabotropic glutamate mGlu2 receptor and support an active role of this receptor in the regulation of REM sleep. The synergistic action of BINA on LY354740''s effects on sleep pattern implies that positive modulators would tune the endogenous glutamate tone suggesting potential benefit in the treatment of psychiatric disorders, in which REM sleep overdrive is manifested. [Copyright &y& Elsevier]

α7 nicotinic acetylcholine receptor (α7 nAChR) is an extensively validated target for several neurological and psychiatric conditions namely, dementia and schizophrenia, owing to its vital roles in cognition and sensorimotor gating. Positive allosteric modulation (PAM) of α7 nAChR represents an innovative approach to amplify endogenous cholinergic signaling in a temporally restricted manner in learning and memory centers of brain. α7 nAChR PAMs are anticipated to side-step burgeoning issues observed with several clinical-stage orthosteric α7 nAChR agonists, related to selectivity, tolerance/tachyphylaxis, thus providing a novel dimension in therapeutic strategy and pharmacology of α7 nAChR ion-channel. Here we describe a novel α7 nAChR PAM, LL-00066471, which potently amplified agonist-induced Ca2+ fluxes in neuronal IMR-32 neuroblastoma cells in a α-bungarotoxin (α-BTX) sensitive manner. LL-00066471 showed excellent oral bioavailability across species (mouse, rat and dog), low clearance and good brain penetration (B/P ratio > 1). In vivo , LL-00066471 robustly attenuated cognitive deficits in both procognitive and antiamnesic paradigms of short-term episodic and recognition memory in novel object recognition task (NORT) and social recognition task (SRT), respectively. Additionally, LL-00066471 mitigated apomorphine-induced sensorimotor gating deficits in acoustic startle reflex (ASR) and enhanced antipsychotic efficacy of olanzapine in conditioned avoidance response (CAR) task. Further, LL-00066471 corrected redox-imbalances and reduced cortico-striatal infarcts in stroke model. These finding together suggest that LL-00066471 has potential to symptomatically alleviate cognitive deficits associated with dementias, attenuate sensorimotor gating deficits in schizophrenia and correct redox-imbalances in cerebrovascular disorders. Therefore, LL-00066471 presents potential for management of cognitive impairments associated with neurological and psychiatric conditions. Image 1 • α7 nAChR signaling is crucial for human sensorimotor-gating, cognition and regulation of neuroinflammation. • α7 nAChR activation attenuates cognitive deficits. α7 nAChR PAMs may overcome limitations of orthosteric agonists. • LL-00066471, a novel orally bioavailable, brain-permeable α7 nAChR PAM shows procognitive and antidementia potential. • LL-00066471 complements neuroleptic drugs, reduces neuronal oxidative stress and infarct formation in stroke models. • Results support utility of LL-00066471 in management of cognitive impairments in several neuropsychiatric indications. [ABSTRACT FROM AUTHOR]

The gamma-aminobutyric acid type B (GABA B) receptor agonist, the sodium salt of gamma-hydroxybutyrate (GHB), significantly improved pain, sleep disturbance and fatigue in fibromyalgia (FM) patients. However, the use of GABA B receptor agonists is limited by their undesirable side-effects. To clarify whether GABA B receptor positive allosteric modulator (PAM) approach would achieve analgesia with less side-effects than GABA B receptor agonist in FM, we investigated the potential of a novel GABA B receptor PAM, ASP8062, for FM treatment. We examined the in vitro profiles of ASP8062, the effects of a GABA B receptor PAM and an agonist on pain in a rat model of FM, and the sleep/wake cycle, EEG during sleep stages and motor coordination in rats. ASP8062 showed PAM activity on human and rat GABA B receptors. Oral administration of ASP8062 significantly reversed the decrease in muscle pressure threshold in reserpine-induced myalgia rats. The analgesic effects of ASP8062 were significantly blocked by a GABA B receptor antagonist. ASP8062 had a significant effect on motor coordination at a 1000-fold higher dose than the analgesic dose in rats. ASP8062 significantly decreased total REM sleep time and frequency of sleep interruptions, and increased the power in delta waves frequency during non-REM sleep in rats. ASP8062, a novel GABA B receptor PAM, has therapeutic potential to exert analgesic effects with less side-effects compared to GABA B receptor agonists in patients with FM. [ABSTRACT FROM AUTHOR]