Marble Burying in NMRI Male Mice Is Preferentially Sensitive to Pre- Versus Postsynaptic 5-HT1A Receptor Biased Agonists.

Obsessive compulsive disorder (OCD) is a psychiatric disorder characterized by excessive and repetitive thoughts and gestures, mainly treated pharmacologically with selective serotonin reuptake inhibitors (SSRIs). The marble burying test in mice is commonly used to model OCD and has been shown to be sensitive to SSRIs, which decrease burying behavior. The activity of SSRIs in this model is mediated through activation of 5-hydroxytryptamine (5-HT) 1A receptors, but the respective implication of pre- versus postsynaptic 5-HT1A receptors has not been elucidated. Here, we investigated marble burying behavior by male NMRI mice following acute administration of 3 biased agonists, which preferentially activate presynaptic 5-HT1A receptors (F13714) or postsynaptic receptors (NLX-101) or which exhibit balanced activation of both pre- and postsynaptic 5-HT1A receptors (NLX-112). When administered at the dose of 2.5 mg/kg i.p., all 3 biased agonists completely or nearly completely abolished marble burying behavior. However, they varied in their potency with minimal effective doses of 0.16, 0.63, and 2.5 mg/kg i.p., for F13714, NLX-112, and NLX-101, respectively. The selective 5-HT1A receptor antagonist, WAY100,635 was inactive up to 2.5 mg/kg. These results suggest that marble burying behavior in male NMRI mice is preferentially sensitive to activation of pre- versus postsynaptic 5-HT1A receptors. Moreover, they suggest that targeting 5-HT1A receptors with biased agonists could provide an innovative therapeutic approach to combat OCD.

Pre- and post-synaptic modulation by GABAB receptors of rat neuroendocrine dopamine neurones.

The secretion of prolactin from the pituitary is negatively controlled by tuberoinfundibular dopamine (TIDA) neurones. The electrical properties of TIDA cells have recently been identified as a modulatory target of neurotransmitters and hormones in the lactotrophic axis. The role of the GABAB receptor in this control has received little attention, yet is of particular interest because it may act as a TIDA neurone autoreceptor. Here, this issue was explored in a spontaneously active rat TIDA in vitro slice preparation using whole-cell recordings. Application of the GABAB receptor agonist, baclofen, dose-dependently slowed down or abolished the network oscillations typical of this preparation. Pharmacological manipulations identify the underlying mechanism as an outward current mediated by G-protein-coupled inwardly rectifying K+ -like channels. In addition to this postsynaptic modulation, we describe a presynaptic modulation where GABAB receptors restrain the release of glutamate and GABA onto TIDA neurones. Our data identify both pre- and postsynaptic modulation of TIDA neurones by GABAB receptors that may play a role in the neuronal network control of pituitary prolactin secretion and lactation.

Functional characterization of the antiepileptic drug candidate, padsevonil, on GABAA receptors.

OBJECTIVE: The antiepileptic drug candidate, padsevonil, is the first in a novel class of drugs designed to interact with both presynaptic and postsynaptic therapeutic targets: synaptic vesicle 2 proteins and γ-aminobutyric acid type A receptors (GABAA Rs), respectively. Functional aspects of padsevonil at the postsynaptic target, GABAA Rs, were characterized in experiments reported here. METHODS: The effect of padsevonil on GABA-mediated Cl- currents was determined by patch clamp on recombinant human GABAA Rs (α1ß2γ2) stably expressed in a CHO-K1 cell line and on native GABAA Rs in cultured rat primary cortical neurons. Padsevonil selectivity for GABAA R subtypes was evaluated using a two-electrode voltage clamp on recombinant human GABAA Rs (α1-5/ß2/γ2) in Xenopus oocytes. RESULTS: In recombinant GABAA Rs, padsevonil did not evoke Cl- currents in the absence of the agonist GABA. However, when co-administered with GABA at effective concentration (EC)20 , padsevonil potentiated GABA responses by 167% (EC50 138 nmol/L) and demonstrated a relative efficacy of 41% compared with zolpidem, a reference benzodiazepine site agonist. Similarly, padsevonil demonstrated GABA-potentiating activity at native GABAA Rs (EC50 208 nmol/L) in cultured rat cortical neurons. Padsevonil also potentiated GABA (EC20 ) responses in GABAA Rs expressed in oocytes, with higher potency at α1- and α5-containing receptors (EC50 295 and 281 nmol/L) than at α2- and α3-containing receptors (EC50 1737 and 2089 nmol/L). Compared with chlordiazepoxide-a nonselective, full GABAA R agonist-the relative efficacy of padsevonil was 60% for α1ß2γ2, 26% for α2ß2γ2, 56% for α3ß2γ2, and 41% for α5ß2γ2; no activity was observed at benzodiazepine-insensitive α4ß2γ2 receptors. SIGNIFICANCE: Results of functional investigations on recombinant and native neuronal GABAA Rs show that padsevonil acts as a positive allosteric modulator of these receptors, with a partial agonist profile at the benzodiazepine site. These properties may confer better tolerability and lower potential for tolerance development compared with classic benzodiazepines currently used in the clinic.

Pharmacological MRI to investigate the functional selectivity of 5-HT1A receptor biased agonists.

The emerging concept of "biased agonism" denotes the phenomenon whereby agonists can preferentially direct receptor signalling to specific intracellular responses among the different transduction pathways, thus potentially avoiding side effects and improving therapeutic effects. The aim of this study was to investigate biased agonism by using pharmacological magnetic resonance imaging (phMRI). The cerebral blood oxygen level dependent (BOLD) signal changes induced by increasing doses of two serotonin 5-HT1A receptor biased agonists, NLX-112 and NLX-101, were mapped in anaesthetized rats. Although both compounds display high affinity, selectivity and agonist efficacy for 5-HT1A receptors, NLX-101 is known to preferentially activate post-synaptic receptors, whereas NLX-112 targets both pre- and post-synaptic receptors. We used several doses of agonists in order to determine if the regional selectivity of NLX-101 was dose-dependent. NLX-112 and NLX-101 induced different positive and negative hemodynamic changes patterns at equal doses. Importantly, NLX-101 had no significant effect in regions expressing pre-synaptic receptors contrary to NLX-112. NLX-112 also produced higher BOLD changes than NLX-101 in the orbital cortex, the somatosensory cortex, and the magnocellular preoptic nuclei. In other regions such as the retrosplenial cortex and the dorsal thalamus, the drugs had similar effects. In terms of functional connectivity, NLX-112 induced more widespread changes than NLX-101. The present phMRI study demonstrates that two closely-related agonists display notable differences in their hemodynamic "fingerprints". These data support the concept of biased agonism at 5-HT1A receptors and raise the prospect of identifying novel therapeutics which exhibit improved targeting of brain regions implicated in neuropsychiatric disorders. This article is part of the special issue entitled 'Serotonin Research: Crossing Scales and Boundaries'.

The therapeutic effect of quetiapine on cognitive impairment associated with 5-HT1A presynaptic receptor involved schizophrenia.

The cognitive impairment associated with schizophrenia is highly prevalent and affects the overall functioning of subjects. The stimulation of the serotonin 1A receptor is a primary characteristic of some atypical antipsychotic drugs. We measured the levels of cognitive impairment using the Morris water maze test and protein kinase A activity in hippocampal neurons on presynaptic and postsynaptic serotonin 1A receptors to investigate the effect of dizocilpine-induced cognitive impairment associated with atypical antipsychotic drugs in rats treated by quetiapine alone or combined with WAY100635/tandospirone. The results of the Morris water maze test presented evidence that quetiapine alone alleviated the cognitive impairment associated with atypical antipsychotic drugs induced by dizocilpine. However, quetiapine plus WAY100635 induced no improvement of cognitive impairment associated with atypical antipsychotic drugs. The results of protein kinase A assay suggested that neither quetiapine alone nor in combination with tandospirone, but not quetiapine plus WAY100635, raised protein kinase A activity in hippocampus neurons. The present study demonstrated the key role of presynaptic serotonin 1A receptors on the therapeutic effect of quetiapine on cognitive impairment associated with atypical antipsychotic drugs. Moreover, that protein kinase A activity in hippocampal cells is involved in the mechanism of quetiapine's effect on cognitive impairment associated with atypical antipsychotic drugs.

Mitogen-activated protein kinase signaling mediates opioid-induced presynaptic NMDA receptor activation and analgesic tolerance.

Opioid-induced hyperalgesia and analgesic tolerance can lead to dose escalation and inadequate pain treatment with µ-opioid receptor agonists. Opioids cause tonic activation of glutamate NMDA receptors (NMDARs) at primary afferent terminals, increasing nociceptive input. However, the signaling mechanisms responsible for opioid-induced activation of pre-synaptic NMDARs in the spinal dorsal horn remain unclear. In this study, we determined the role of MAPK signaling in opioid-induced pre-synaptic NMDAR activation caused by chronic morphine administration. Whole-cell recordings of excitatory post-synaptic currents (EPSCs) were performed on dorsal horn neurons in rat spinal cord slices. Chronic morphine administration markedly increased the frequency of miniature EPSCs, increased the amplitude of monosynaptic EPSCs evoked from the dorsal root, and reduced the paired-pulse ratio of evoked EPSCs. These changes were fully reversed by an NMDAR antagonist and normalized by inhibiting extracellular signal-regulated kinase 1/2 (ERK1/2), p38, or c-Jun N-terminal kinase (JNK). Furthermore, intrathecal injection of a selective ERK1/2, p38, or JNK inhibitor blocked pain hypersensitivity induced by chronic morphine treatment. These inhibitors also similarly attenuated a reduction in morphine's analgesic effect in rats. In addition, co-immunoprecipitation assays revealed that NMDARs formed a protein complex with ERK1/2, p38, and JNK in the spinal cord and that chronic morphine treatment increased physical interactions of NMDARs with these three MAPKs. Our findings suggest that opioid-induced hyperalgesia and analgesic tolerance are mediated by tonic activation of pre-synaptic NMDARs via three functionally interrelated MAPKs at the spinal cord level. OPEN SCIENCE BADGES: This article has received a badge for *Open Materials* because it provided all relevant information to reproduce the study in the manuscript. The complete Open Science Disclosure form for this article can be found at the end of the article. More information about the Open Practices badges can be found at https://cos.io/our-services/open-science-badges/.

Opposing actions of CRF-R1 and CB1 receptors on VTA-GABAergic plasticity following chronic exposure to ethanol.

Dopamine neurons in the ventral tegmental area (VTA) influence learned behaviors and neuropsychiatric diseases including addiction. The stress peptide corticotrophin-releasing factor (CRF) contributes to relapse to drug and alcohol seeking following withdrawal, although the cellular actions are poorly understood. In this study, we show that presynaptic CRF type 1 receptors (CRF-R1) potentiate GABA release onto mouse VTA dopamine neurons via a PKC-Ca2+ signaling mechanism. In naive animals, activation of CRF-R1 by bath application of CRF or ethanol enhanced GABAA inhibitory postsynaptic currents (IPSCs). Following 3 days of withdrawal from four weekly cycles of chronic intermittent ethanol (CIE) vapor exposure, spontaneous IPSC frequency was enhanced while CRF and ethanol potentiation of IPSCs was intact. However, withdrawal for 3 weeks or more was associated with reduced spontaneous IPSC frequency and diminished CRF and ethanol responses. Long-term withdrawal was also accompanied by decreased sensitivity to the CB1 receptor agonist WIN55212 as well as greatly enhanced sensitivity to the CB1 antagonist AM251. Inclusion of BAPTA in the internal recording solution restored the responsiveness to CRF or ethanol and reduced the potentiating actions of AM251. Together, these data suggest that GABAA inhibition of VTA dopamine neurons is regulated by presynaptic actions of CRF and endocannabinoids and that long-term withdrawal from CIE treatment enhances endocannabinoid-mediated inhibition, thereby suppressing CRF facilitation of GABA release. Such findings have implications for understanding the impact of chronic alcohol on stress-related, dopamine-mediated alcohol-seeking behaviors.

Ambient Glutamate Promotes Paroxysmal Hyperactivity in Cortical Pyramidal Neurons at Amyloid Plaques via Presynaptic mGluR1 Receptors.

Synaptic dysfunctions and altered neuronal activity play major role in the pathophysiology of Alzheimer's disease (AD), with underlying mechanisms largely unknown. We report that in the prefrontal cortex of amyloid precursor protein-presenilin 1 and APP23 AD mice, baseline activity of pyramidal cells is disrupted by episodes of paroxysmal hyperactivity. Induced by spontaneous EPSC bursts, these incidents are prevalent in neurons proximal to amyloid plaques and involve enhanced activity of glutamate with metabotropic effects. Abolition of EPSC bursts by tetrodotoxin and SERCA ATPase blockers thapsigargin or cyclopiasonic acid suggests their presynaptic origin and sensitized store-released calcium. Accordingly, the rate of EPSC bursts activated by single axon stimulation is enhanced. Aggravation of the hyperactivity by blockers of excitatory amino acid transporter (±)-HIP-A and DL-TBOA together with histochemical and ultrastructural evidence for enrichment of plaque-related dystrophies with synaptic vesicles and SNARE protein SNAP-25 infer the later as hot-spots for ectopic release of glutamate. Inhibition of EPSC bursts by I/II mGluR1 blocker MCPG or selective mGluR1 antagonist LY367385 implicate metabotropic glutamatergic effects in generation of paroxysmal bursts. These findings demonstrate for the first time that at amyloid plaques, enhanced activity of nonsynaptic glutamate can promote irregular EPSC bursts with hyperactivity of pyramidal cells via mGluR1 receptors.

Rescue of Synaptic Phenotypes and Spatial Memory in Young Fragile X Mice.

Fragile X syndrome (FXS) is characterized by synaptic immaturity, cognitive impairment, and behavioral changes. The disorder is caused by transcriptional shutdown in neurons of thefragile X mental retardation 1gene product, fragile X mental retardation protein. Fragile X mental retardation protein is a repressor of dendritic mRNA translation and its silencing leads to dysregulation of synaptically driven protein synthesis and impairments of intellect, cognition, and behavior, and FXS is a disorder that currently has no effective therapeutics. Here, young fragile X mice were treated with chronic bryostatin-1, a relatively selective protein kinase Cεactivator, which induces synaptogenesis and synaptic maturation/repair. Chronic treatment with bryostatin-1 rescues young fragile X mice from the disorder phenotypes, including normalization of most FXS abnormalities in 1) hippocampal brain-derived neurotrophic factor expression, 2) postsynaptic density-95 levels, 3) transformation of immature dendritic spines to mature synapses, 4) densities of the presynaptic and postsynaptic membranes, and 5) spatial learning and memory. The therapeutic effects were achieved without downregulation of metabotropic glutamate receptor (mGluR) 5 in the hippocampus and are more dramatic than those of a late-onset treatment in adult fragile X mice. mGluR5 expression was in fact lower in fragile X mice and its expression was restored with the bryostatin-1 treatment. Our results show that synaptic and cognitive function of young FXS mice can be normalized through pharmacological treatment without downregulation of mGluR5 and that bryostatin-1-like agents may represent a novel class of drugs to treat fragile X mental retardation at a young age and in adults.

Region-specific effects of repeated ketamine administration on the presynaptic GABAergic neurochemistry in rat brain.

A growing body of evidence indicates that clinical use of ketamine as a promising antidepressant can be accompanied by psychotic-like side effects. Although, the generation of such effects is thought to be attributed to dysfunction of prefrontal GABAergic interneurons, the mechanism underlying ketamine's propsychotic-like action is not fully understood. Due to wide spectrum of behavioral abnormalities, it is hypothesized that ketamine action is not limited to only cortical GABA metabolism but may also involve alterations in other functional brain areas. To test it, we treated rats with ketamine (30 mg/kg, i.p.) for 5 days, and next we analyzed GABA metabolizing enzymes in cortex, cerebellum, hippocampus and striatum. Our results demonstrated that diminished GAD67 expression in cortex, cerebellum (by ∼60%) and in hippocampus (by ∼40%) correlated with lowered protein level in these areas. The expression of GAD65 isoform decreased by ∼45% in striatum, but pronounced increase by ∼90% was observed in hippocampus. Consecutively, reduction in glutamate decarboxylase activity and GABA concentration were detected in cortex, cerebellum and striatum, but not in hippocampus. Ketamine administration decreased GABA transaminase protein in cortex and striatum (by ∼50% and 30%, respectively), which was reflected in diminished activity of the enzyme. Also, a significant drop in succinic semialdehyde dehydrogenase activity in cortex, cerebellum and striatum was present. These data suggest a reduced utilization of GABA for energetic purposes. In addition, we observed synaptic GABA release to be reduced by ∼30% from striatal terminals. It correlated with lowered KCl-induced Ca(2+) influx and decreased amount of L-type voltage-dependent calcium channel. Our results indicate that unique changes in GABA metabolism triggered by chronic ketamine treatment in functionally distinct brain regions may be involved in propsychotic-like effects of this drug.

Nicotinic receptors modulate the function of presynaptic AMPA receptors on glutamatergic nerve terminals in the trigeminal caudal nucleus.

In this study, we demonstrate the existence on trigeminal caudal nucleus (TCN) glutamatergic terminals of α4ß2 nicotinic receptors (nAChRs) capable of enhancing the terminals' spontaneous release of [(3)H]d-aspartate ([(3)H]D-Asp). In rat TCN synaptosomes, spontaneous [(3)H]D-Asp release was increased by nicotine and the nicotinic receptor agonists (±)epibatidine and RJR2403. The increase was potentiated by the positive allosteric modulator of nAChRs LY2087101, inhibited by the nicotinic antagonists mecamylamine (MEC) and dihydro-ß-erythroidine hydrobromide (DHßE), and unaffected by α-bungarotoxin (α-BgTx) and methyllycaconitine (MLA). Evidence of functional interaction was observed between the α4ß2 nAChRs and cyclothiazide-sensitive, alfa-amino-3-hydroxy-5-methyl-4-isoxazolone propionate (AMPA) receptors co-localized on the TCN synaptosomes. Brief pre-exposure of synaptosomes to 30 µM nicotine or 10 µM RJR2403 abolished the AMPA (100 µM) -induced potentiation of [K(+)]e-evoked [(3)H]D-Asp release, an effect that seems to be caused by nicotine-induced increases in the internalization of AMPA receptors. Indeed, the effects of nicotine-pretreatment were not seen in synaptosomes containing pre-entrapped pep2-SVKI, a peptide known to compete for the binding of GluA2 subunit to scaffolding proteins involved in AMPA endocytosis, while entrapment of pep2-SVKE, an inactive peptide used as negative control, was inefficacious. These findings show that nicotine can negatively modulate the function of AMPA receptors present on glutamatergic nerve terminals in the rat TCN. Dynamic control of AMPA receptors by the nicotinic cholinergic system has been observed under other experimental conditions, and it can contribute to the control of synaptic plasticity such as long-term depression and potentiation. Nicotine's ability to reduce the functionality of presynaptic AMPA receptors could contribute to its analgesic effects by diminishing glutamatergic transmission from the primary afferent terminals that convey nociceptive input to TCN.

Enhanced function of inhibitory presynaptic cannabinoid CB1 receptors on sympathetic nerves of DOCA-salt hypertensive rats.

AIMS: This study was performed to examine whether hypertension affects the sympathetic transmission to resistance vessels of pithed rats via inhibitory presynaptic cannabinoid CB1 receptors and whether endocannabinoids are involved in this response. MATERIALS AND METHODS: We compared uninephrectomised rats rendered hypertensive by high salt diet and deoxycorticosterone acetate (DOCA) injections with normotensive animals (uninephrectomy only). Experiments were performed on vagotomised and pithed animals. Increases in diastolic blood pressure (DBP) were induced four times (S1-S4) by electrical stimulation or phenylephrine injection. KEY FINDINGS: Electrical stimulation (0.75Hz, 1ms, 50V, 5 impulses) of the preganglionic sympathetic nerve fibres innervating the blood vessels more strongly increased DBP in normotensive than in DOCA-salt rats. Phenylephrine (0.01µmol/kg) induced similar increases in DBP in both groups. The cannabinoid receptor agonist CP55940 (0.01-1µmol/kg) did not modify the rises in DBP induced by phenylephrine. However, it inhibited the electrically stimulated increases in DBP, more strongly in DOCA-salt than in normotensive animals (maximally by 50 and 30%, respectively). The effect of CP55940 was attenuated by the CB1 antagonist AM251 (3µmol/kg). AM251 enhanced the neurogenic vasopressor response during S4 by itself in hypertensive rats only. URB597 (3µmol/kg), which inhibits degradation of the endocannabinoid anandamide, did not modify the electrically stimulated increases in DBP. SIGNIFICANCE: The function of inhibitory presynaptic CB1 receptors on sympathetic nerves is enhanced in DOCA-salt hypertensive rats. Thus, the CB1 receptor-mediated inhibition of noradrenaline release from the sympathetic nerve fibres innervating the resistance vessels might play a protective role in hypertension.

Antinociceptive effects of endomorphin-2: suppression of substance P release in the inflammatory pain model rat.

Endomorphin-2 (EM2) and Substance P (SP) exert suppressive and facilitative influences upon nociception, respectively. Although EM2 and SP were often co-expressed in single neurons in dorsal root ganglion (DRG), it is still unknown if and how the nociception-suppressive influences of EM2 might be exerted upon nociception-facilitative effects of SP in the DRG neurons. We examined these issues in the inflammatory pain model rats produced by subcutaneous injection of the complete Freund's adjuvant into the hind paw. The paw withdrawal threshold for mechanical allodynia was measured. Changes of EM2 and SP release were estimated by measuring intrathecal levels of EM2 and SP through in vivo microdialysis analysis of cerebrospinal fluid. The mechanical allodynia was dose-dependently attenuated by intrathecal injection of EM2 or a neurokinin-1 receptor antagonist, and facilitated by intrathecal injection of SP or a mu-opioid receptor (MOR) antagonist. Importantly, intrathecal level of SP was found to be lowered by intrathecal injection of EM2. Morphologically, colocalization of EM2-, MOR- and SP-immunoreactivity in single DRG neurons was observed by immunofluorescent histochemistry, and co-expression of EM2 and SP in large, dense-cored presynaptic vesicles in primary afferents, as well as localization of MOR on pre- and postsynaptic membrane in spinal dorsal horn, was also confirmed electron miscroscopically. Thus, the results indicated that analgesic influences of EM2 upon inflammatory pain might be exerted through suppression of SP release, supporting the assumptions that binding of EM2 to presynaptic MOR might induce such effects.

Presynaptic modulation of spinal nociceptive transmission by glial cell line-derived neurotrophic factor (GDNF).

The role of glial cell line-derived neurotrophic factor (GDNF) in nociceptive pathways is still controversial, as both pronociceptive and antinociceptive actions have been reported. To elucidate this role in the mouse, we performed combined structural and functional studies in vivo and in acute spinal cord slices where C-fiber activation was mimicked by capsaicin challenge. Nociceptors and their terminals in superficial dorsal horn (SDH; laminae I-II) constitute two separate subpopulations: the peptidergic CGRP/somatostatin+ cells expressing GDNF and the nonpeptidergic IB4+ neurons expressing the GFRα1-RET GDNF receptor complex. Ultrastructurally the dorsal part of inner lamina II (LIIid) harbors a mix of glomeruli that either display GDNF/somatostatin (GIb)-IR or GFRα1/IB4 labeling (GIa). LIIid thus represents the preferential site for ligand-receptor interactions. Functionally, endogenous GDNF released from peptidergic CGRP/somatostatin+ nociceptors upon capsaicin stimulation exert a tonic inhibitory control on the glutamate excitatory drive of SDH neurons as measured after ERK1/2 phosphorylation assay. Real-time Ca(2+) imaging and patch-clamp experiments with bath-applied GDNF (100 nM) confirm the presynaptic inhibition of SDH neurons after stimulation of capsaicin-sensitive, nociceptive primary afferent fibers. Accordingly, the reduction of the capsaicin-evoked [Ca(2+)]i rise and of the frequency of mEPSCs in SDH neurons is specifically abolished after enzymatic ablation of GFRα1. Therefore, GDNF released from peptidergic CGRP/somatostatin+ nociceptors acutely depresses neuronal transmission in SDH signaling to nonpeptidergic IB4+ nociceptors at glomeruli in LIIid. These observations are of potential pharmacological interest as they highlight a novel modality of cross talk between nociceptors that may be relevant for discrimination of pain modalities.

Metabotropic glutamate receptors inhibit GABA release in rat histamine neurons.

The modulation of GABAergic transmission by metabotropic glutamate (mGlu) receptors was examined in histaminergic neurons using a conventional whole-cell patch clamp technique. DHPG, a selective group I mGlu receptor agonist, had no effect on GABAergic inhibitory postsynaptic currents (IPSCs). However, DCG-IV (1µÐœ) and L-AP4 (1µÐœ), selective group II or III mGlu receptor agonists, respectively, decreased the amplitude of GABAergic IPSCs and simultaneously increased the paired-pulse ratio. The inhibitory effect of DCG-IV was completely blocked by 200nM LY341495, a group II and III mGlu receptor antagonist, and the inhibitory effect of L-AP4 was completely blocked by 10µÐœ LY341495. These results suggest that multiple mGlu receptors are involved in regulating the excitability of histaminergic neurons.

Differential effects of presynaptic versus postsynaptic adenosine A2A receptor blockade on Δ9-tetrahydrocannabinol (THC) self-administration in squirrel monkeys.

Different doses of an adenosine A2A receptor antagonist MSX-3 [3,7-dihydro-8-[(1E)-2-(3-ethoxyphenyl)ethenyl]-7 methyl-3-[3-(phosphooxy)propyl-1-(2 propynil)-1H-purine-2,6-dione] were found previously to either decrease or increase self-administration of cannabinoids delta-9-tetrahydrocannabinol (THC) or anandamide in squirrel monkeys. It was hypothesized that the decrease observed with a relatively low dose of MSX-3 was related to blockade of striatal presynaptic A2A receptors that modulate glutamatergic neurotransmission, whereas the increase observed with a higher dose was related to blockade of postsynaptic A2A receptors localized in striatopallidal neurons. This hypothesis was confirmed in the present study by testing the effects of the preferential presynaptic and postsynaptic A2A receptor antagonists SCH-442416 [2-(2-furanyl)-7-[3-(4-methoxyphenyl)propyl]-7H-pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidin-5-amine] and KW-6002 [(E)-1, 3-diethyl-8-(3,4-dimethoxystyryl)-7-methyl-3,7-dihydro-1H-purine-2,6-dione], respectively, in squirrel monkeys trained to intravenously self-administer THC. SCH-442416 produced a significant shift to the right of the THC self-administration dose-response curves, consistent with antagonism of the reinforcing effects of THC. Conversely, KW-6002 produced a significant shift to the left, consistent with potentiation of the reinforcing effects of THC. These results show that selectively blocking presynaptic A2A receptors could provide a new pharmacological approach to the treatment of marijuana dependence and underscore corticostriatal glutamatergic neurotransmission as a possible main mechanism involved in the rewarding effects of THC.

dAcsl, the Drosophila ortholog of acyl-CoA synthetase long-chain family member 3 and 4, inhibits synapse growth by attenuating bone morphogenetic protein signaling via endocytic recycling.

Fatty acid metabolism plays an important role in brain development and function. Mutations in acyl-CoA synthetase long-chain family member 4 (ACSL4), which converts long-chain fatty acids to acyl-CoAs, result in nonsyndromic X-linked mental retardation. ACSL4 is highly expressed in the hippocampus, a structure critical for learning and memory. However, the underlying mechanism by which mutations of ACSL4 lead to mental retardation remains poorly understood. We report here that dAcsl, the Drosophila ortholog of ACSL4 and ACSL3, inhibits synaptic growth by attenuating BMP signaling, a major growth-promoting pathway at neuromuscular junction (NMJ) synapses. Specifically, dAcsl mutants exhibited NMJ overgrowth that was suppressed by reducing the doses of the BMP pathway components, accompanied by increased levels of activated BMP receptor Thickveins (Tkv) and phosphorylated mothers against decapentaplegic (Mad), the effector of the BMP signaling at NMJ terminals. In addition, Rab11, a small GTPase involved in endosomal recycling, was mislocalized in dAcsl mutant NMJs, and the membrane association of Rab11 was reduced in dAcsl mutant brains. Consistently, the BMP receptor Tkv accumulated in early endosomes but reduced in recycling endosomes in dAcsl mutant NMJs. dAcsl was also required for the recycling of photoreceptor rhodopsin in the eyes, implying a general role for dAcsl in regulating endocytic recycling of membrane receptors. Importantly, expression of human ACSL4 rescued the endocytic trafficking and NMJ phenotypes of dAcsl mutants. Together, our results reveal a novel mechanism whereby dAcsl facilitates Rab11-dependent receptor recycling and provide insights into the pathogenesis of ACSL4-related mental retardation.

[How do antiepileptic drugs work?]. / Hvordan virker antiepileptika?

BACKGROUND: There are currently around 25 antiepileptic drugs in use in Norway, of which 15 have entered the market in the last 20 years. All have somewhat different effect- and adverse effect profiles and mechanisms of action. Here we present a brief overview of current knowledge regarding the basic mechanisms of action of these drugs. METHOD: The review is based on a discretionary selection of relevant articles found through a literature search in PubMed and our own clinical and research experience. RESULTS: There are, roughly speaking, four main mechanisms; 1) modulation of ion channels (sodium and calcium channel blockers, potassium channel openers), 2) potentiation of GABAergic inhibition, 3) reduction of glutamatergic excitation and 4) modulation of presynaptic neurotransmitter release. Some of the drugs have several mechanisms of action, and for some of them it is unclear which mechanism is clinically most important. To some extent, the drugs' mechanisms of action predict their effect against different types of epilepsy and seizures. For instance, sodium channel blockers work best against focal seizures, while calcium channel blockers work best against absences, a type of generalised seizure. INTERPRETATION: Optimal treatment of patients with epilepsy requires not only thorough knowledge of seizure- and epilepsy classification, but also insight into the mechanisms of action of antiepileptic drugs.

Acetylcholine encodes long-lasting presynaptic plasticity at glutamatergic synapses in the dorsal striatum after repeated amphetamine exposure.

Locomotion and cue-dependent behaviors are modified through corticostriatal signaling whereby short-term increases in dopamine availability can provoke persistent changes in glutamate release that contribute to neuropsychiatric disorders, including Parkinson's disease and drug dependence. We found that withdrawal of mice from repeated amphetamine treatment caused a chronic presynaptic depression (CPD) in glutamate release that was most pronounced in corticostriatal terminals with a low probability of release and lasted >50 d in treated mice. An amphetamine challenge reversed CPD via a dopamine D1-receptor-dependent paradoxical presynaptic potentiation (PPP) that increased corticostriatal activity in direct pathway medium spiny neurons. This PPP was correlated with locomotor responses after a drug challenge, suggesting that it may underlie the sensitization process. Experiments in brain slices and in vivo indicated that dopamine regulation of acetylcholine release from tonically active interneurons contributes to CPD, PPP, locomotor sensitization, and cognitive ability. Therefore, a chronic decrease in corticostriatal activity during withdrawal is regulated around a new physiological range by tonically active interneurons and returns to normal upon reexposure to amphetamine, suggesting that this paradoxical return of striatal activity to a more stable, normalized state may represent an additional source of drug motivation during abstinence.

5-Hydroxytryptamine 1A receptors inhibit glutamate release in rat medullary dorsal horn neurons.

We examined 5-hydroxytryptamine 1A (5-HT1A) receptor-mediated modulation of glutamatergic transmission in rat medullary dorsal horn neurons using a conventional whole-cell patch clamp technique. 5-HT reversibly and concentration dependently decreased the amplitude of glutamatergic excitatory postsynaptic currents and increased the paired-pulse ratio, indicating that 5-HT acts presynaptically to reduce glutamate release from primary afferents. The 5-HT-induced inhibition of excitatory postsynaptic currents was partially occluded by NAN-190, a 5-HT1A receptor antagonist, and mimicked by 8-OH-DPAT, a 5-HT1A receptor agonist. Our results suggest that presynaptic 5-HT1A receptors inhibit glutamate release from trigeminal primary afferents onto medullary dorsal horn neurons, and thus in addition to other 5-HT1 receptor subtypes, 5-HT1A receptors could be a potential target for treatment of pain from orofacial tissues.