GABA and behavior: the role of receptor subtypes

Molecular signature of excessive female aggression: study of stressed mice with genetic inactivation of neuronal serotonin synthesis

Aggression is a complex social behavior, critically involving brain serotonin (5-HT) function. The neurobiology of female aggression remains elusive, while the incidence of its manifestations has been increasing. Yet, animal models of female aggression are scarce. We previously proposed a paradigm of female aggression in the context of gene x environment interaction where mice with partial genetic inactivation of tryptophan hydroxylase-2 (Tph2+/- mice), a key enzyme of neuronal 5-HT synthesis, are subjected to predation stress resulting in pathological aggression. Using deep sequencing and the EBSeq method, we studied the transcriptomic signature of excessive aggression in the prefrontal cortex of female Tph2+/- mice subjected to rat exposure stress and food deprivation. Challenged mutants, but not other groups, displayed marked aggressive behaviors. We found 26 genes with altered expression in the opposite direction between stressed groups of both Tph2 genotypes. We identified several molecular markers, including Dgkh, Arfgef3, Kcnh7, Grin2a, Tenm1 and Epha6, implicated in neurodevelopmental deficits and psychiatric conditions featuring impaired cognition and emotional dysregulation. Moreover, while 17 regulons, including several relevant to neural plasticity and function, were significantly altered in stressed mutants, no alteration in regulons was detected in stressed wildtype mice. An interplay of the uncovered pathways likely mediates partial Tph2 inactivation in interaction with severe stress experience, thus resulting in excessive female aggression.

Functional MRS studies of GABA and glutamate/Glx - A systematic review and meta-analysis

Functional magnetic resonance spectroscopy (fMRS) can be used to investigate neurometabolic responses to external stimuli in-vivo, but findings are inconsistent. We performed a systematic review and meta-analysis on fMRS studies of the primary neurotransmitters Glutamate (Glu), Glx (Glutamate + Glutamine), and GABA. Data were extracted, grouped by metabolite, stimulus domain, and brain region, and analysed by determining standardized effect sizes. The quality of individual studies was rated. When results were analysed by metabolite type small to moderate effect sizes of 0.29-0.47 (p < 0.05) were observed for changes in Glu and Glx regardless of stimulus domain and brain region, but no significant effects were observed for GABA. Further analysis suggests that Glu, Glx and GABA responses differ by stimulus domain or task and vary depending on the time course of stimulation and data acquisition. Here, we establish effect sizes and directionality of GABA, Glu and Glx response in fMRS. This work highlights the importance of standardised reporting and minimal best practice for fMRS research.

Median raphe region GABAergic neurons contribute to social interest in mouse

Gamma-aminobutyric acid (GABA) is a well-known inhibitory neurotransmitter implicated in numerous physiological and pathological behaviors including social interest. Dysregulation of the median raphe region (MRR), a main serotoninergic nucleus, is also characterized by increased social problems. As the majority of MRR cells are GABAergic, we aimed to reveal the social role of these cells. Chemogenetic techniques were used in vesicular GABA transporter Cre mice and with the help of adeno-associated virus vectors artificial receptors (DREADDs, stimulatory, inhibitory or control, containing only a fluorophore) were expressed in MRR GABAergic cells confirmed by immunohistochemistry. Four weeks after viral injection a behavioral test battery (sociability; social interaction; resident-intruder) was conducted. The artificial ligand (clozapine-N-oxide, 1 mg/10 ml/kg) was administrated 30 min before the tests. As possible confounding factors, locomotion (open field/OF), anxiety-like behavior (elevated plus maze/EPM), and short-term memory (Y-maze) were also evaluated. Stimulation of the GABAergic cells in MRR had no effect on locomotion or working and social memory; however, it increased social interest during sociability and social interaction but not in resident-intruder tests. Accordingly, c-Fos elevation in MRR-GABAergic cells was detected after sociability, but not resident-intruder tests. In the EPM test, the inhibitory group entered into the open arms later, suggesting an anxiogenic-like tendency. We confirmed the role of MRR-GABAergic cells in promoting social interest. However, different subpopulations (e.g. long vs short projecting, various neuropeptide containing) might have divergent roles, which might remain hidden and requires further studies.

Deficient neurotransmitter systems and synaptic function in frontotemporal lobar degeneration-Insights into disease mechanisms and current therapeutic approaches

Frontotemporal lobar degeneration (FTLD) comprises a heterogenous group of fatal neurodegenerative diseases and, to date, no validated diagnostic or prognostic biomarkers or effective disease-modifying therapies exist for the different clinical or genetic subtypes of FTLD. Current treatment strategies rely on the off-label use of medications for symptomatic treatment. Changes in several neurotransmitter systems including the glutamatergic, GABAergic, dopaminergic, and serotonergic systems have been reported in FTLD spectrum disease patients. Many FTLD-related clinical and neuropsychiatric symptoms such as aggressive and compulsive behaviour, agitation, as well as altered eating habits and hyperorality can be explained by disturbances in these neurotransmitter systems, suggesting that their targeting might possibly offer new therapeutic options for treating patients with FTLD. This review summarizes the present knowledge on neurotransmitter system deficits and synaptic dysfunction in model systems and patients harbouring the most common genetic causes of FTLD, the hexanucleotide repeat expansion in C9orf72 and mutations in the granulin (GRN) and microtubule-associated protein tau (MAPT) genes. We also describe the current pharmacological treatment options for FLTD that target different neurotransmitter systems.

Advances in Nutritional Epigenetics-A Fresh Perspective for an Old Idea. Lessons Learned, Limitations, and Future Directions

Nutritional epigenetics is a rapidly expanding field of research, and the natural modulation of the genome is a non-invasive, sustainable, and personalized alternative to gene-editing for chronic disease management. Genetic differences and epigenetic inflexibility resulting in abnormal gene expression, differential or aberrant methylation patterns account for the vast majority of diseases. The expanding understanding of biological evolution and the environmental influence on epigenetics and natural selection requires relearning of once thought to be well-understood concepts. This research explores the potential for natural modulation by the less understood epigenetic modifications such as ubiquitination, nitrosylation, glycosylation, phosphorylation, and serotonylation concluding that the under-appreciated acetylation and mitochondrial dependant downstream epigenetic post-translational modifications may be the pinnacle of the epigenomic hierarchy, essential for optimal health, including sustainable cellular energy production. With an emphasis on lessons learned, this conceptional exploration provides a fresh perspective on methylation, demonstrating how increases in environmental methane drive an evolutionary down regulation of endogenous methyl groups synthesis and demonstrates how epigenetic mechanisms are cell-specific, making supplementation with methyl cofactors throughout differentiation unpredictable. Interference with the epigenomic hierarchy may result in epigenetic inflexibility, symptom relief and disease concomitantly and may be responsible for the increased incidence of neurological disease such as autism spectrum disorder.

Age-related GABAergic differences in the primary sensorimotor cortex: A multimodal approach combining PET, MRS and TMS

Healthy aging is associated with mechanistic changes in gamma-aminobutyric acid (GABA), the most abundant inhibitory neurotransmitter in the human brain. While previous work mainly focused on magnetic resonance spectroscopy (MRS)-based GABA+ levels and transcranial magnetic stimulation (TMS)-based GABA_A receptor (GABA_AR) activity in the primary sensorimotor (SM1) cortex, the aim of the current study was to identify age-related differences in positron emission tomography (PET)-based GABA_AR availability and its relationship with GABA+ levels (i.e. GABA with the contribution of macromolecules) and GABA_AR activity. For this purpose, fifteen young (aged 20–28 years) and fifteen older (aged 65–80 years) participants were recruited. PET and MRS images were acquired using simultaneous time-of-flight PET/MR to evaluate age-related differences in GABA_AR availability (distribution volume ratio with pons as reference region) and GABA+ levels. TMS was applied to identify age-related differences in GABA_AR activity by measuring short-interval intracortical inhibition (SICI). Whereas GABA_AR availability was significantly higher in the SM cortex of older as compared to young adults (18.5%), there were neither age-related differences in GABA+ levels nor SICI. A correlation analysis revealed no significant associations between GABA_AR availability, GABA_AR activity and GABA+ levels. Although the exact mechanisms need to be further elucidated, it is possible that a higher GABA_AR availability in older adults is a compensatory mechanism to ensure optimal inhibitory functionality during the aging process.

Influence of prenatal transportation stress-induced differential DNA methylation on the physiological control of behavior and stress response in suckling Brahman bull calves

The objective of this experiment was to examine potential differential methylation of DNA as a mechanism for altered behavioral and stress responses in prenatally stressed (PNS) compared with nonprenatally stressed (Control) young bull calves. Mature Brahman cows (n = 48) were transported for 2-h periods at 60 ± 5, 80 ± 5, 100 ± 5, 120 ± 5, and 140 ± 5 d of gestation (Transported group) or maintained as nontransported Controls (n = 48). From the offspring born to Transported and Control cows, a subset of 28-d-old intact bulls (n = 7 PNS; n = 7 Control) were evaluated for methylation of DNA of behavior and stress response-associated genes. Methylation of DNA from white blood cells was assessed via reduced representation bisulfite sequencing methods. Because increased methylation of DNA within gene promoter regions has been associated with decreased transcriptional activity of the corresponding gene, differentially methylated (P ≤ 0.05) CG sites (cytosine followed by a guanine nucleotide) located within promoter regions (n = 1,205) were used to predict (using Ingenuity Pathway Analysis software) alterations to canonical pathways in PNS compared with Control bull calves. Among differentially methylated genes (P ≤ 0.05) related to behavior and the stress response were OPRK1, OPRM1, PENK, POMC, NR3C2, TH, DRD1, DRD5, COMT, HTR6, HTR5A, GABRA4, GABRQ, and GAD2. Among altered (P < 0.05) signaling pathways related to behavior and the stress response were Opioid Signaling, Corticotropin-Releasing Hormone Signaling, Dopamine Receptor Signaling, Dopamine-DARPP32 Feedback in cAMP Signaling, Serotonin Receptor Signaling, and GABA Receptor Signaling. Alterations to behavior and stress response-related genes and canonical pathways supported previously observed elevations in temperament score and serum cortisol through weaning in the larger population of PNS calves from which bulls in this study were derived. Differential methylation of DNA and predicted alterations to behavior and stress response-related pathways in PNS compared with Control bull calves suggest epigenetic programming of behavior and the stress response in utero.

Fish exposed to water contaminated with eprinomectin show inhibition of the activities of AChE and Na+/K+-ATPase in the brain, and changes in natural behavior

The objective of this study was to evaluate whether antiparasitic eprinomectin may be an environmental contaminant in water compartment in low concentrations, negatively affecting neurotransmission and, consequently, the natural behavior of the jundiá (Rhamdia quelen). Fish were randomly allocated in tanks and exposed for 24 and 48 h to eprinomectin concentrations in water [0.0 (Control), 1.124 (T1), 1.809 (T2) and 3.976 (T3) μg L^-1], followed by 48 h of recovery in eprinomectin-free water, in order to evaluate the behavioral parameters, levels of reactive oxygen species (ROS) in the brain, as well as cerebral enzymatic activities of acetylcholinesterase (AChE) and of the sodium-potassium ATPase pump (Na⁺/K⁺-ATPase). Especially at the two highest concentrations of eprinomectin (T2 and T3), the fish showed alterations in natural behavior, particularly hyperlocomotion and longer time on the surface. Furthermore, at these same concentrations, cerebral ROS levels increased and cerebral AChE activity decreased. At the highest concentration (T3) cerebral Na⁺/K⁺-ATPase activity was reduced. Increased ROS and impairment of AChE and Na⁺/K⁺-ATPase enzymes in the brain may have contributed directly to behavioral changes, due to neuronal damage and synapse impairment. Even after 48 h in water without eprinomectin, behavioral changes and neurotoxic effects were observed in fish, suggesting residual effects of the antiparasitic. In conclusion, eprinomectin even in low concentrations may be a hazardous environmental contaminant for aquatic organisms, as it causes brain damage and affects the natural behavior of fish.

The role of GABAA in the expression of updated information through the reconsolidation process in humans

Consolidated memory can be again destabilized by the presentation of a memory cue (reminder) of the previously acquired information. During this process of labilization/restabilization memory traces can be either impaired, strengthened or updated in content. Here, we study if a consolidated memory can be updated by linking one original cue to two different outcomes and whether this process was modulated by the GABAergic system. To aim that, we designed two experiments carried out in three consecutive days. All participants learned a list of non-sense syllable pairs on day 1. On day 2 the new information was introduced after the reminder or no-reminder presentation. Participants were tested on day 3 for the updated or original list (Exp. 1). In Exp. 2 we tested whether this new information was incorporated by an inhibitory process mediated by the GABAergic system. For that, participants retrieved the original information before being taken Clonazepam 0.25mg (GABA_A agonist) or Placebo pill. We found that the groups that received the reminder correctly recalled the old and new information. However, the no reminder groups only correctly recalled the original information. Furthermore, when testing occurred in the presence of Clonazepam, the group that received the reminder plus the new information showed an impaired original memory performance compared to the group that received only Clonazepam (without reminder) or the reminder plus Placebo pill. These results show that new information can be added to a reactivated declarative memory in humans by linking one cue to two different outcomes. Furthermore, we shed light on the mechanisms of memory updating being the GABAergic system involved in the modulation of the old and new information expression.

Effects in dogs with behavioural disorders of a commercial nutraceutical diet on stress and neuroendocrine parameters

The well-being of dogs can be affected by changes in human lifestyle, eating habits and increased stressors that lead to behavioural disorders including fear, hyperactivity and anxiety, followed by negative affective moods and poor welfare. This randomised, controlled clinical evaluation involved 69 dogs, 38 males and 31 females, of different breeds, with behavioural disorders related to anxiety and chronic stress. They were fed a control diet or a nutraceutical diet (ND group) for 45 days. Neuroendocrine (serotonin, dopamine, β-endorphins, noradrenaline and cortisol) and stress (derivatives of reactive oxygen metabolites (dROMs) and biological antioxidant potential (BAP)) parameters related to behavioural disorders were evaluated at the beginning and end of the study period. Results showed a significant increase in serotonin, dopamine and β-endorphins plasma concentrations (*P<0.05, *P<0.05 and **P<0.01, respectively) and a significant decrease in noradrenaline and cortisol plasma concentrations in the ND group (*P<0.05). dROMs significantly decreased in the ND group (*P<0.05) while BAP was not affected. This study demonstrated for the first time that a specific diet significantly and positively affected neuroendocrine parameters and dROMs. These results open significant perspectives concerning the use of diet and nutraceuticals in the treatment of behavioural disorders.

Biochemical Constituents and in Vitro Antioxidant and Anticholinesterase Potential of Seeds from Native Korean Persimmon Genotypes

In the current study, the functional and biochemical potential of the seeds of four persimmon cultivars (PC1, PC2, PC3 and PC4) and their role against oxidative stress and acetylcholinesterase (AChE) inhibition were evaluated. In terms of biochemical compositions, free amino acids, fatty acids and organic acids analysis was performed. The free amino acids ranged from 2617.31 (PC2) to 3773.01 μg∙g(-1) dry weight (PC4). Oleic acid and linoleic acid were the principal fatty acids, which were significantly higher in PC4 and PC1, respectively. PC4 presented the highest amount of organic acid content (4212 mg∙kg(-1)), whereas PC2 presented the lowest (2498 mg∙kg(-1)). PC2 contained higher total phenolic content and flavonoid content, whereas PC3 had the lowest amount as compared to other cultivars. The in vitro DPPH, ABTS and superoxide anion radicals scavenging activity increased in a dose-dependent manner, whereas PC2 showed significantly higher scavenging activities as compared to PC1, PC2 and PC4 types. In the case of AChE inhibition, PC4 showed a moderate activity (67.34% ± 1.8%). In conclusion, the current findings reveal that the studied persimmon seeds cultivars are a source of bioactive natural antioxidants and AChE inhibitors. Such natural products could be employed in pharmaceutical and food industries, whilst can also be considered for the treatment of neurodegenerative diseases such as Alzheimer's.

GABA-BZD Receptor Modulating Mechanism of Panax quinquefolius against 72-h Sleep Deprivation Induced Anxiety like Behavior: Possible Roles of Oxidative Stress, Mitochondrial Dysfunction and Neuroinflammation

Rationale:Panax quinquefolius (American Ginseng) is known for its therapeutic potential against various neurological disorders, but its plausible mechanism of action still remains undeciphered. GABA (Gamma Amino Butyric Acid) plays an important role in sleep wake cycle homeostasis. Thus, there exists rationale in exploring the GABA-ergic potential of Panax quinquefolius as neuroprotective strategy in sleep deprivation induced secondary neurological problems.

Objective: The present study was designed to explore the possible GABA-ergic mechanism in the neuro-protective effect of Panax quinquefolius against 72-h sleep deprivation induced anxiety like behavior, oxidative stress, mitochondrial dysfunction, HPA-axis activation and neuroinflammation.

Materials and Methods: Male laca mice were sleep deprived for 72-h by using Grid suspended over water method. Panax quinquefolius (American Ginseng 50, 100, and 200 mg/kg) was administered alone and in combination with GABA modulators (GABA Cl⁻ channel inhibitor, GABA-benzodiazepine receptor inhibitor and GABAA agonist) for 8 days, starting 5 days prior to 72-h sleep deprivation period. Various behavioral (locomotor activity, mirror chamber test), biochemical (lipid peroxidation, reduced glutathione, catalase, nitrite levels), mitochondrial complexes, neuroinflammation marker (Tumor Necrosis Factor, TNF-alpha), serum corticosterone, and histopathological sections of brains were assessed.

Results: Seventy two hours sleep deprivation significantly impaired locomotor activity, caused anxiety-like behavior, conditions of oxidative stress, alterations in mitochondrial enzyme complex activities, raised serum corticosterone levels, brain TNFα levels and led to neuroinflammation like signs in discrete brain areas as compared to naive group. Panax quinquefolius (100 and 200 mg/kg) treatment restored the behavioral, biochemical, mitochondrial, molecular and histopathological alterations. Pre-treatment of GABA Cl⁻ channel inhibitor as well as GABA-benzodiazepine receptor inhibitor, significantly reversed the protective effect of P. quinquefolius (100 mg/kg) in 72-h sleep deprived animals (P < 0.05). However, pretreatment with GABAA agonist, potentiated Panax quinquefolius's protective effect which was significant as compared to their effect per se (p < 0.05).

Conclusion: GABA-ergic mechanism could be involved in the neuroprotective effect of P.quinquefolius against sleep deprivation induced anxiety-like behavior, oxidative stress, mitochondrial dysfunction, HPA axis activation and neuroinflammation.

Control of brain development, function, and behavior by the microbiome

Animals share an intimate and life-long partnership with a myriad of resident microbial species, collectively referred to as the microbiota. Symbiotic microbes have been shown to regulate nutrition and metabolism and are critical for the development and function of the immune system. More recently, studies have suggested that gut bacteria can impact neurological outcomes--altering behavior and potentially affecting the onset and/or severity of nervous system disorders. In this review, we highlight emerging evidence that the microbiome extends its influence to the brain via various pathways connecting the gut to the central nervous system. While understanding and appreciation of a gut microbial impact on neurological function is nascent, unraveling gut-microbiome-brain connections holds the promise of transforming the neurosciences and revealing potentially novel etiologies for psychiatric and neurodegenerative disorders.

Proton Magnetic Resonance Spectroscopy: Relevance of Glutamate and GABA to Neuropsychology

Proton Magnetic Resonance Spectroscopy (MRS) has been widely used to study the healthy and diseased brain in vivo. The availability of whole body MR scanners with a field strength of 3 Tesla and above permit the quantification of many metabolites including the neurotransmitters glutamate (Glu) and γ-aminobutyric acid (GABA). The potential link between neurometabolites identified by MRS and cognition and behavior has been explored in numerous studies both in healthy subjects and in patient populations. Preliminary findings suggest direct or opposite associations between GABA or Glu with impulsivity, anxiety, and dexterity. This chapter is intended to provide an overview of basic principles of MRS and the literature reporting correlations between GABA or Glu and results of neuropsychological assessments.

GABA transporter-1 inhibitor NO-711 alters the EEG power spectra and enhances non-rapid eye movement sleep during the active phase in mice

GABA transporter subtype 1 (GAT1) constructs high affinity reuptake sites for GABA in the CNS and regulates GABAergic transmission. Compounds that inhibit GAT1 are targets often used for the treatment of epilepsy; however sedation has been reported as a side effect of these agents, indicating potential sedative and/or hypnotic uses for these compounds. In the current study, we observed the sleep behaviors of mice treated with NO-711, a selective GAT1 inhibitor, in order to elucidate the role of GAT1 in sleep-wake regulation during the active phase. The data revealed that NO-711 at a high dose of 10 mg/kg caused a marked enhancement of EEG activity in the frequency ranges of 3-25 Hz during wakefulness as well as rapid eye movement (REM) sleep. During the non-REM (NREM) sleep, NO-711 (10 mg/kg) elevated EEG activity in the frequency ranges of 1.5-6.75 Hz. Similar changes were found in mice treated with a low dose of 3 mg/kg. NO-711 administered i.p. at a dose of 1, 3 or 10 mg/kg significantly shortened the sleep latency of NREM sleep, increased the amount of NREM sleep and the number of NREM sleep episodes. NO-711 did not affect the sleep latency and the amount of REM sleep. NO-711 dose-dependently increased c-Fos expression in sleep-promoting nucleus of the ventrolateral preoptic area and median preoptic area. However, c-Fos expression was decreased in the wake-promoting nuclei, tuberomammillary nucleus and lateral hypothalamus. These results indicate that NO-711 can increase NREM sleep in mice.

Modulation of the arcuate nucleus-medial preoptic nucleus lordosis regulating circuit: a role for GABAB receptors

Estradiol rapidly activates a microcircuit in the arcuate nucleus of the hypothalamus (ARH) that is needed for maximal female sexual receptivity. Membrane estrogen receptor-α complexes with and signals through the metabotropic glutamate receptor-1a stimulating NPY release within the ARH activating proopiomelanocortin (POMC) neurons. These POMC neurons project to the medial preoptic nucleus (MPN) and release β-endorphin. Estradiol treatment induces activation/internalization of MPN μ-opioid receptors (MOR) to inhibit lordosis. Estradiol membrane action modulates ARH gamma-aminobutyric acid receptor-B (GABAB) activity. We tested the hypothesis that ARH GABAB receptors mediate estradiol-induced MOR activation and facilitation of sexual receptivity. Double-label immunohistochemistry revealed expression of GABAB receptors in NPY, ERα and POMC expressing ARH neurons. Approximately 70% of POMC neurons expressed GABAB receptors. Because estradiol initially activates an inhibitory circuit and maintains activation of this circuit, the effects of blocking GABAB receptors were evaluated before estradiol benzoate (EB) treatment and after at the time of lordosis testing. Bilateral infusions of the GABAB receptor antagonist, CGP52432, into the ARH prior to EB treatment of ovariectomized rats prevented estradiol-induced activation/internalization of MPN MOR, and the rats remained unreceptive. However, in EB-treated rats, bilateral CGP52432 infusions 30 min before behavior testing attenuated MOR internalization and facilitated lordosis. These results indicated that GABAB receptors were located within the lordosis-regulating ARH microcircuit and are necessary for activation and maintenance of the estradiol inhibition of lordosis behavior. Although GABAB receptors positively influence estradiol signaling, they negatively regulate lordosis behavior since GABAB activity maintains the estradiol-induced inhibition.

Possible interaction of cholinergic and GABAergic systems between MS and CA1 upon memory acquisition in rats

The present study explored the possibility that cholinergic and GABAergic systems of medial septum (MS) might influence acquisition of memory by regulation of acetylcholine (Ach) and γ-aminobutyric acid (GABA) receptors function in hippocampus and vice versa. The step-through passive avoidance (PA) task was used. The results showed that pre-training intra-MS/CA1 administration of nonselective muscarinic Ach antagonist, scopolamine (0.5, 1 and 2 μg/rat) and GABA(A) receptor agonist, muscimol (0.01 and 0.02 μg/rat) impaired, while acetylcholinesterase inhibitor, physostigmine (0.5 and 1 μg/rat) and GABA(A) receptor antagonist, bicuculline (0.25 μg/rat) improved memory acquisition. Moreover, intra-CA1/MS administration of a subthreshold dose of muscimol or bicuculline increased and reversed the impairment induced by scopolamine in MS/CA1 respectively (cross injection). Also, the result revealed that, intra-CA1/MS administration subthreshold dose of muscimol reduced improvement of memory induced by physostigmine in the MS/CA1, respectively (cross injection). On the other hand, subthreshold dose of bicuculline in CA1/MS did not alter memory improvement induced by physostigmine in the other site (MS/CA1). In conclusion, both cholinergic and GABAergic systems not only seem to play a role in the modulation of memory in the MS and CA1 but also to have a complex interaction.

Enhancing a declarative memory in humans: the effect of clonazepam on reconsolidation

A consolidated memory recalled by a specific reminder can become unstable (labile) and susceptible to facilitation or impairment for a discrete period of time. This labilization phase is followed by a process of stabilization called reconsolidation. The phenomenon has been shown in diverse types of memory, and different pharmacological agents have been used to disclose its presence. Several studies have revealed the relevance of the GABAergic system to this process. Consequently, our hypothesis is that the system is involved in the reconsolidation of declarative memory in humans. Thus, using our verbal learning task, we analyzed the effect of benzodiazepines on the re-stabilization of the declarative memory. On Day 1, volunteers learned an association between five cue- response-syllables. On Day 2, the verbal memory was labilized by a reminder presentation, and then a placebo capsule or 0.25 mg or 0.03 mg of clonazepam was administered to the subjects. The verbal memory was evaluated on Day 3. The volunteers who had received the 0.25 mg clonazepam along with the specific reminder on Day 2, exhibited memory improvement. In contrast, there was no effect when the drug was given without retrieval, when the memory was simply retrieved instead of being reactivated or when short-term memory testing was performed 4 h after reactivation. We discuss the GABAergic role in reconsolidation, which shows a collateral effect on other memories when the treatment is aimed at treating anxiety disorders. Further studies might elucidate the role of GABA in the reconsolidation process associated with dissimilar scenarios. This article is part of a Special Issue entitled 'Cognitive Enhancers'.

Regulation of neurosteroid biosynthesis by neurotransmitters and neuropeptides

The enzymatic pathways leading to the synthesis of bioactive steroids in the brain are now almost completely elucidated in various groups of vertebrates and, during the last decade, the neuronal mechanisms involved in the regulation of neurosteroid production have received increasing attention. This report reviews the current knowledge concerning the effects of neurotransmitters, peptide hormones, and neuropeptides on the biosynthesis of neurosteroids. Anatomical studies have been carried out to visualize the neurotransmitter- or neuropeptide-containing fibers contacting steroid-synthesizing neurons as well as the neurotransmitter, peptide hormones, or neuropeptide receptors expressed in these neurons. Biochemical experiments have been conducted to investigate the effects of neurotransmitters, peptide hormones, or neuropeptides on neurosteroid biosynthesis, and to characterize the type of receptors involved. Thus, it has been found that glutamate, acting through kainate and/or AMPA receptors, rapidly inactivates P450arom, and that melatonin produced by the pineal gland and eye inhibits the biosynthesis of 7α-hydroxypregnenolone (7α-OH-Δ(5)P), while prolactin produced by the adenohypophysis enhances the formation of 7α-OH-Δ(5)P. It has also been demonstrated that the biosynthesis of neurosteroids is inhibited by GABA, acting through GABA(A) receptors, and neuropeptide Y, acting through Y1 receptors. In contrast, it has been shown that the octadecaneuropetide ODN, acting through central-type benzodiazepine receptors, the triakontatetraneuropeptide TTN, acting though peripheral-type benzodiazepine receptors, and vasotocin, acting through V1a-like receptors, stimulate the production of neurosteroids. Since neurosteroids are implicated in the control of various neurophysiological and behavioral processes, these data suggest that some of the neurophysiological effects exerted by neurotransmitters and neuropeptides may be mediated via the regulation of neurosteroid production.

Persistent hypothermia after intrathecal morphine: case report and literature review

PURPOSE

To describe a case of persistent hypothermia following spinal anesthesia with intrathecal morphine.

CLINICAL FEATURES

Following elective right total knee arthroplasty under spinal anesthesia with isobaric 0.5% bupivacaine 11 mg, fentanyl 15 μg, and preservative-free morphine 150 μg, a 57-yr-old female (93.5 kg, 151 cm) developed postoperative hypothermia with a nadir rectal temperature of 33.6°C four hours after surgery. At times, her temperature could not be measured by tympanic, temporal arterial, oral, axillary, or rectal routes. In spite of the low temperature, the patient complained of feeling hot and was diaphoretic without shivering. With the exception of her temperature, her vital signs were normal postoperatively, and aside from hyperglycemia, complete blood count, electrolytes, thyroid-stimulating hormone, serum cortisol, troponin, and twelve-lead electrocardiogram were normal. Her temperature did not respond to warming efforts with a forced-air warming blanket, infusion of warmed intravenous crystalloid, and hourly bladder irrigation with warm saline through an indwelling urinary catheter. Normothermia returned after she received a small dose of sublingual lorazepam eight hours after surgery. The remainder of her postoperative stay was uneventful.

CONCLUSION

Patients undergoing spinal anesthesia with intrathecal morphine may develop postoperative hypothermia that is resistant to warming measures. This complication may be treated successfully with lorazepam.

Fragile X: leading the way for targeted treatments in autism

Two different mutations in the FMR1 gene may lead to autism. The full mutation, with >200 CGG repeats in the 5' end of FMR1, leads to hypermethylation and transcriptional silencing of FMR1, resulting in absence or deficiency of the protein product, FMRP. Deficiency of FMRP in the brain causes fragile X syndrome (FXS). Autism occurs in approximately 30% of those with FXS, and pervasive developmental disorders-not otherwise specified occur in an additional 30%. FMRP is an RNA binding protein that modulates receptor-mediated dendritic translation; deficiency leads to dysregulation of many proteins important for synaptic plasticity. Group I metabotropic glutamate receptor (mGluR1/5) activated translation is upregulated in FXS, and new targeted treatments that act on this system include mGluR5 antagonists and GABA agonists, which may reverse the cognitive and behavioral deficits in FXS. Matrix metalloproteinase 9 (MMP-9) is one of the proteins elevated in FXS, and minocycline reduces excess MMP-9 activity in the Fmr1 knockout mouse model of FXS. Both minocycline and mGluR5 antagonists are currently being evaluated in patients with FXS through controlled treatment trials. The premutation (55-200 CGG repeats) may also contribute to the mechanism of autism in approximately 10% of males and 2-3% of females. Premutations with <150 repeats exert cellular effects through a different molecular mechanism, one that involves elevated levels of FMR1 mRNA, CGG-mediated toxicity to neurons, early cell death, and fragile X-associated tremor/ataxia syndrome. In those with large premutations (150-200), lowered levels of FMRP also occur.

Corticotropin-Releasing Hormone, Glutamate, and γ-Aminobutyric Acid in Depression

Stress response and depression have a significant impact on modern society. Although the symptoms are well characterized, the molecular mechanisms underlying depression are largely unknown. The monoamine hypothesis, which postulates dysfunctional noradrenergic and serotonergic systems as the underlying primary cause of depression, has been valuable for the development of conventional antidepressants, which can reverse these dysfunctional states to some degree. However, recent data from various neuroscience disciplines have questioned the major role of amines in the pathogenesis of depression. A considerable amount of evidence has accumulated that suggests that normalization of the hypothalamo—pituitary—adrenal (HPA) system might be the final step necessary for a remission of depression. In addition, an increasing body of clinical and postmortem evidence is pointing to a role played by γ-aminobutyric acid (GABA) and glutamate in the etiology of depression. This review examines the evidence, mainly obtained from clinical studies or from postmortem brain material, for a major role of the HPA axis, glutamatergic, and GABAergic systems in the pathogenesis of major and bipolar depression. The authors hope that these insights will stimulate further studies with the final aim of developing new types of antidepressants that combine increased efficacy with a shorter delay of the onset of action and reduced side-effect profiles.

Depression and antidepressants: molecular and cellular aspects

Clinical depression is viewed as a physical and psychic disease process having a neuropathological basis, although a clear understanding of its ethiopathology is still missing. The observation that depressive symptoms are influenced by pharmacological manipulation of monoamines led to the hypothesis that depression results from reduced availability or functional deficiency of monoaminergic transmitters in some cerebral regions. However, there are limitations to current monoamine theories related to mood disorders. Recently, a growing body of experimental data has showed that other classes of endogenous compounds, such as neuropeptides and amino acids, may play a significant role in the pathophysiology of affective disorders. With the development of neuroscience, neuronal networks and intracellular pathways have been identified and characterized, describing the existence of the interaction between monoamines and receptors in turn able to modulate the expression of intracellular proteins and neurotrophic factors, suggesting that depression/antidepressants may be intermingled with neurogenesis/neurodegenerative processes.

Effects of acute tiagabine administration on aggressive responses of adult male parolees

Experimental and clinical studies have supported a relationship between gamma-aminobutyric acid (GABA) and aggressive behavior in non-humans and humans. Tiagabine is a GABA uptake inhibitor that has been shown to produce acute behavioral effects in animals. In addition, tiagabine has been shown to decrease aggression in agitated patients when administered chronically. The present study was designed to investigate the effects of acute administration of tiagabine on aggressive responding on a laboratory task in adult humans. Ten adult males participated in experimental sessions on the Point Subtraction Aggression Paradigm (PSAP), which provided subjects with aggressive, escape, and monetary-reinforced response options. All subjects received four acute oral doses of Tiagabine (4, 8, 12 and 16 mg) separated by placebo sessions. Tiagabine decreased aggression at doses that either did not affect, or affected to a lesser extent, monetary-reinforced responding. The results are consistent with some prior research using the PSAP showing a possible unique role for GABA in the regulation of human aggression. A possible behavioral mechanism for the rate-decreasing effects on aggressive responding produced in the present study is that tiagabine may modify aggressive responding by suppressing reactions to aversive stimuli.

Decreased expression of the GABAA receptor in fragile X syndrome

After our initial discovery of under expression of the GABA(A) receptor delta subunit in a genome wide screening for differentially expressed mRNAs in brain of fragile X mice, a validated model for fragile X mental retardation syndrome, we analyzed expression of the 17 remaining subunits of the GABA(A) receptor using real-time PCR. We confirmed nearly 50% under expression of the delta subunit and found a significant 35%-50% reduction in expression of 7 additional subunit mRNAs, namely alpha(1), alpha(3), and alpha(4), beta(1) and beta(2) and gamma(1) and gamma(2), in fragile X mice compared to wild-type littermates. In concordance with previous results, under expression was found in cortex, but not in cerebellum. Moreover, decreased expression of specific GABA(A) receptor subunits in fragile X syndrome seems to be an evolutionary conserved hallmark since in the fragile X fly (Drosophila melanogaster) model we also found almost 50% under expression of all 3 subunits which make up the invertebrate GABA receptor, namely Grd, Rdl and Lcch3. In addition, we demonstrated a direct correlation between the amount of dFmrp and the expression of the GABA receptor subunits Rdl and Grd. Our results add evidence to previous observations of an altered GABAergic system in fragile X syndrome. Because GABA(A) receptors are the major inhibitory receptors in brain, involved in anxiety, depression, insomnia, learning and memory and epilepsy, processes also disturbed in fragile X patients, the well described GABA(A) receptor pharmacology might open new powerful opportunities for treatment of the behavioral and epileptic phenotype associated with fragile X syndrome.

Antidepressant-like activity of CGP 36742 and CGP 51176, selective GABAB receptor antagonists, in rodents

BACKGROUND AND PURPOSE

A crucial role for the GABAB receptor in depression was proposed several years ago, but there are limited data to support this proposition. Therefore we decided to investigate the antidepressant-like activity of the selective GABAB receptor antagonists CGP 36742 and CGP 51176, and a selective agonist CGP 44532 in models of depression in rats and mice.

EXPERIMENTAL APPROACH

Effects of CGP 36742 and CGP 51176 as well as the agonist CGP 44532 were assessed in the forced swim test in mice. Both antagonists were also investigated in an olfactory bulbectomy (OB) model of depression in rats, while CGP 51176 was also investigated in the chronic mild stress (CMS) rat model of depression. The density of GABAB receptors in the mouse hippocampus after chronic administration of CGP 51176 was also investigated.

KEY RESULTS

The GABAB receptor antagonists CGP 36742 and CGP 51176 exhibited antidepressant-like activity in the forced swim test in mice. The GABAB receptor agonist CGP 44532 was not effective in this test, however, it counteracted the antidepressant-like effects of CGP 51176. The antagonists CGP 36742 and CGP 51176 were effective in an OB model of depression in rats. CGP 51176 was also effective in the CMS rat model of depression. Administration of CGP 51176 increased the density of GABAB receptors in the mouse hippocampus.

CONCLUSIONS AND IMPLICATIONS

These data suggest that selective GABAB receptor antagonists may be useful in treatment of depression, and support an important role for GABA-ergic transmission in this disorder.

Immobilization and characterization of γ-aminobutyric acid on gold surface

gamma-Aminobutyric acid (GABA) is one of two main inhibitory neurotransmitters in the central nervous system that plays an important role in neuronal function and dysfunction. Immobilization of GABA molecules on a rigid surface in an ordered fashion will provide an opportunity to understand some of the fundamental properties related to its structure and function. In this study, we report a novel strategy for immobilization of bioactive GABA on gold substrate. GABA was immobilized in three consecutive steps, namely gold substrate amination, dextran covalent attachment, and GABA immobilization. Surface chemistry was verified at each step using XPS and FTIR. Bioactivity of GABA immobilized on the gold surface was studied using atomic force microscopy to reveal antigen-antibody binding. Nonspecific protein adsorption on the bioactive surface was analyzed quantitatively using anti-GABA antibody and an enzyme linked nonspecific anti-immunoglobulin-G antibody in an ELISA assay. GABA functionalized surface has high affinity for anti-GABA, while showing significantly low affinity for nonspecific anti-IgG antibody. All these data support the presence of a bio-functional immobilized GABA on the gold surface. In conclusion, we report a novel technique for immobilizing bioactive GABA molecules in an orderly fashion on gold substrates.

Behavioral differences between subgroups of rats with high and low threshold to clonic convulsions induced by DMCM, a benzodiazepine inverse agonist

In epileptic patients, there is a high incidence of psychiatric comorbidities, such as anxiety. Gamma-aminobutyric acid (GABA) ionotropic receptor GABA(A)/benzodiazepine allosteric site is involved in both epilepsy and anxiety. This involvement is based on the fact that benzodiazepine allosteric site agonists are anticonvulsant and anxiolytic drugs; on the other hand, benzodiazepine inverse agonists are potent convulsant and anxiogenic drugs. The aim of this work was to determine if subgroups of rats selected according to their susceptibility to clonic convulsions induced by a convulsant dose 50% (CD50) of DMCM, a benzodiazepine inverse agonist, would differ in behavioral tests commonly used to measure anxiety (elevated plus-maze, open field) and depression (forced swimming test). In the first experiment, subgroups of adult male Wistar rats were selected after a single dose of DMCM and in the second experiment they were selected after two injections of DMCM given after an interval of 1 week. Those rats presenting full clonic convulsions were termed Low Threshold rats to DMCM-induced clonic convulsions (LTR) and those not having clonic convulsions High Threshold rats to DMCM-induced clonic convulsions (HTR). In both experiments, only those rats presenting full clonic convulsions induced by DMCM and those not showing any signs of motor disturbances were used in the behavioral tests. The results showed that the LTR subgroup selected after two injections of a CD50 of DMCM spent a significantly lower time in the open arms of the elevated plus-maze and in the off the walls area of the open field; moreover, this group also presented a higher number of rearings in the open field. There were no significant differences between HTR and LTR subgroups in the forced swimming test. LTR and HTR subgroups selected after only one injection of DMCM did not differ in the three behavioral tests. To verify if the behavioral differences between HTR and LTR subgroups of rats selected after two injections of DMCM were due to the clonic convulsion, another experiment was carried out in which subgroups of rats susceptible and nonsusceptible to clonic convulsions induced by a CD50 of picrotoxin, a GABA(A) receptor channel blocker, were selected and submitted to the elevated plus-maze and open field tests. The results obtained did not show any significant differences between these two subgroups in the elevated plus-maze and open field tests. In another approach to determine the relation between fear/anxiety and susceptibility to clonic convulsions, subgroups of rats were selected in the elevated plus-maze as more or less fearful/anxious. The CD50 for clonic convulsions induced by DMCM was determined for each of these two subgroups. The results showed a significantly lower CD50 for the more fearful/anxious subgroup, which means a higher susceptibility to clonic convulsions induced by DMCM. The present findings show a relation between susceptibility to clonic convulsions and fear/anxiety and vice versa which may be due to differences in the assembly of GABA(A)/allosteric benzodiazepine site receptors in regions of the brain.

Interactions between GABAergic and cholinergic processes in the nucleus pontis oralis: neuronal mechanisms controlling active (rapid eye movement) sleep and wakefulness

The cholinergic system within the nucleus pontis oralis (NPO) of the pontine tegmentum is critically involved in the generation of active (rapid eye movement) sleep. Previously, we demonstrated that a GABAergic system in the NPO also plays an important role in the control of the behavioral states of wakefulness as well as active sleep. The present study examined interactions between these two neuronal systems vis-a-vis the occurrence of these behavioral states. Accordingly, cholinergic and GABAergic agonists and antagonists were injected into the NPO, and their combined effects on sleep and waking states of chronic, unanesthetized cats were examined. Microinjections of carbachol into the NPO elicited active sleep with a short latency. However, a preinjection of muscimol (a GABA(A) agonist) completely blocked the active sleep-inducing effects of carbachol. The induction of active sleep by carbachol was also suppressed by a subsequent injection of muscimol. On the other hand, the microinjection of scopolamine (a muscarinic receptor antagonist) did not block the induction of active sleep by bicuculline (a GABA(A) antagonist). We conclude that the excitatory cholinergic control of NPO neurons that are involved in the generation of active sleep is gated by a pontine GABAergic system that exerts its effects postsynaptically by inhibiting NPO neurons, resulting in the suppression of active sleep and the generation of wakefulness. In the absence of the activation of this GABAergic gating mechanism, active sleep occurs. These results reveal that specific interactions between cholinergic and GABAergic processes in the NPO play a critical role in the generation of active sleep and wakefulness.

Tetrodotoxin inactivation of pontine regions: Influence on sleep–wake states

Studies using various methodologies have implicated n. reticularis pontis oralis (RPO) and n. subcoeruleus (SubC) in the generation of rapid eye movement sleep (REM). In rats, electrolytic lesions in these regions may give rise to the phenomenon of REM without atonia (REM-A), in which the electrophysiological features of REM are normal except that atonia is absent and elaborate behaviors may be exhibited. However, electrolytic lesions damage both cell bodies and fibers of passage, and the neural reorganization and adaptation that can occur post-lesion can complicate interpretation. Tetrodotoxin (TTX) is a sodium channel blocker that temporarily inactivates both neurons and fibers of passage and thus may be functionally equivalent to an electrolytic lesion, but without allowing time for neural adaptation. In this study, we examined the influence of microinjections of TTX into RPO and SubC on sleep in freely behaving rats. Rats (90 day old male Sprague-Dawley) were implanted with electrodes for recording EEG and EMG. Guide cannulae were implanted aimed into RPO or SubC. Each animal received one unilateral microinjection (TTXUH: 5.0 ng/0.2 microl) and two bilateral microinjections (TTXBL: 2.5 ng/0.1 microl; TTXBH: 5.0 ng/0.2 microl) of TTX, and control microinjections of saline alone (SAL). The injections were made 2 h following lights on, and sleep was recorded for the subsequent 22 h. Sleep was scored from computerized records in 10 s epochs. Recordings from the 10-h light period and the 12-h dark period were examined separately. TTX inactivation of RPO could decrease REM and non-REM (NREM), whereas inactivation of SubC produced relatively more specific decreases in REM with smaller effects on NREM. The results complement studies that have implicated RPO and SubC in REM generation. REM-A was not observed, suggesting that REM-A is a complex phenomenon that requires time for reorganization of the nervous system after insult.

GABA and glutamate systems as therapeutic targets in depression and mood disorders

Advances made in diverse areas of neuroscience suggest that neurotransmitter systems, additional to the monoaminergic, contribute to the pathophysiology of mood disorders. This ever accruing body of preclinical and clinical research is providing increased recognition of the contribution made by amino acid neurotransmitters to the neurobiology of mood disorders. This review examines evidence supporting the role of GABA and glutamate in these processes and explores the potential to target these systems in the development of novel compounds; the viability of these agents for treatment-related co-morbidities will also be considered.

Sexual experience and conditioned place preference in male rats

We have previously shown that sexual behavior induces a reward state, as evaluated by conditioned place preference (CPP), only when males or females are able to control the rate of sexual interaction. In the present experiment, we evaluated if male rats that are repeatedly tested in a situation in which they are not able to control the sexual interaction eventually develop CPP. Three groups of sexually naïve male rats were used. One group never mated. A second group was tested once a week for 10 consecutive weeks in a chamber in which they controlled the rate of the sexual interaction. The third group was mated for the same number of weeks in a chamber in which the female, but not the male, controlled mating. The three groups were then tested for CPP. Only the group able to control the sexual interaction developed CPP. The group that had no control over the rate of the sexual interaction did not develop CPP even after 10 tests in which they consistently displayed sexual behavior. These results suggest that an estrous female and/or sexual behavior are powerful incentives that maintain mating even if the rewarding properties of the incentive are reduced.

GABAergic regulation of REM sleep in reticularis pontis oralis and caudalis in rats

The nucleus reticularis pontis oralis (RPO) and nucleus reticularis pontis caudalis (RPC) are implicated in the generation of rapid eye movement sleep (REM). Work in cats has indicated that GABA in RPO plays a role in the regulation of REM. We assessed REM after local microinjections into RPO and RPC of the gamma-aminobutyric acid-A (GABA(A)) agonist, muscimol (MUS), and the GABA(A) antagonist, bicuculline (BIC). Rats (90-day-old male Sprague-Dawley) were implanted with electrodes for recording electroencephalographs (EEG) and electromyographs (EMG). Guide cannulae were aimed into RPO (n = 9) and RPC (n = 8) for microinjecting MUS (200, 1,000.0 microM) and BIC (0.056, 0.333, 1.0, 1,000.0, and 10,000.0 microM). Animals received bilateral microinjections of saline, MUS, and BIC (0.2 microl microinjected at 0.1 microl/min) into each region followed by 6-h sleep recordings. In RPO, MUS (1,000.0 microM) suppressed REM and BIC (1,000.0 microM) enhanced REM. In RPC, MUS (200, 1,000.0 microM) suppressed REM, but BIC (1,000.0 microM and less) did not significantly affect REM. Higher concentrations of BIC (10,000.0 microM) injected into RPO (n = 9) and RPC (n = 4) produced wakefulness and escape behavior. The results indicate that GABA in RPO/RPC is involved in the regulation of REM and suggest site-specific differences in this regulation.

Medial preoptic area/anterior hypothalamus and sexual motivation

The medial preoptic area/anterior hypothalamus (MPOA/AH) is a brain site derived from proliferative zones from the diencephalon and telencephalon. It is probably this characteristic that makes this brain region participate in different physiological and behavioral functions. The present review addresses the role of the MPOA/AH in the control of male sexual behavior. It is clear that the MPOA/AH is a crucial site in the control of sexual behavior in males of all species studied to date. But although many different publications have followed the contribution of Heimer and Larsson there is no agreement as to what is specifically the role of the MPOA/AH in sexual behavior. At least three hypotheses have been presented. The first one suggests that this brain region is involved in the consummatory aspects (execution) of sexual behavior. The second indicates that the MPOA/AH is involved in the appetitive components (motivation) of masculine sexual behavior. The third hypothesis considers that MPOA/AH neurons are involved in the regulation of consummatory and appetitive aspects of sexual behavior. From the literature reviewed, it will become evident that the evidence supporting a role of the MPOA/AH in the execution of sexual behavior is based on a number of limited studies not easy to interpret. On the other hand, several lines of evidence using a variety of methodologies support the notion that the MPOA/AH is involved in the motivational aspects of male sexual behavior.

The GABA(A) receptor mediates the hypnotic activity of melatonin in rats

The present investigation assessed whether hypnotic activity of melatonin was mediated by the GABA(A) receptor in rats. Electroencephalography (EEG) was measured in this experiment. Melatonin, at a dose of 10 mg/kg ip, showed a significant sleep-promoting effect in rats. Flumazenil (3.5 and 7 mg/kg), a specific antagonist of the benzodiazepine (BZP) recognition site on the GABA(A) receptor, and picrotoxin (2 and 4 mg/kg), the ligand of the picrotoxin site on the GABA(A) receptor, seemed to be devoid of intrinsic influence on each sleep parameter when used alone, but they significantly antagonized the melatonin-induced increase in total sleep time (TS), slow-wave sleep time (SWS) and paradoxical sleep time (PS), and the decrease in time to sleep onset (TSO) and wakefulness time (W). A significant interaction was shown between melatonin and flumazenil or picrotoxin. When bicuculline methiodide (2 and 4 mg/kg), a specific antagonist of the GABA binding site on the GABA(A) receptor, was used together with melatonin, the melatonin-induced increase in TS, SWS and PS, and the decrease in W were abolished. However, there was no interaction between melatonin and bicuculline methiodide on sleep parameters except PS. These results indicate that the hypnotic activity of melatonin may be linked to the GABA(A) receptor and mediated through the BZP recognition site, the picrotoxin site on the GABA(A) receptor and partially through the GABA binding site on the GABA(A) receptor.

Possible mechanism involved in the anticonvulsant action of butorphanol in mice

The study was designed to examine the effect of butorphanol, a classical opioid on convulsive behaviour using maximal electroshock (MES) test. An attempt was also made to investigate the role of possible receptor mechanisms involved. MES seizures were induced in mice via transauricular electrodes (60 mA, 0.2 s). Seizure severity was assessed by the duration of tonic hindlimb extensor phase and mortality due to convulsions. Intraperitoneal administration of butorphanol produced a dose-dependent (0.25-2 mg/kg) protection against hindlimb extensor phase. The anticonvulsant effect of butorphanol was antagonized by all the three opioid receptor antagonists (i.e., naloxone [mu], MR2266 [kappa], and naltrindole [delta], respectively). Coadministration of gamma-aminobutyric acid (GABA)-ergic drugs (diazepam, GABA, muscimol, and baclofen) and N-methyl-D-aspartate (NMDA) receptor antagonist, dizocilpine (MK801), with butorphanol augmented the anticonvulsant action of the latter drug. In contrast, flumazenil, a central benzodiazepine (BZD) receptor antagonist, reversed the facilitatory effect of diazepam on the anti-MES effect of butorphanol. Similarly, delta-aminovaleric acid (DAVA), a GABA(B) receptor antagonist, antagonized the facilitatory effect of baclofen, a GABA(B) agonist on anti-MES action of butorphanol. These BZD-GABAergic antagonists, flumazenil or DAVA, per se also counteracted the anti-MES effect of butorphanol given alone. These data exemplify the benefits of using the MES test, which is sensitive to opioidergic compounds and distinguished convulsive behavioural changes associated with GABAergic and NMDAergic effects. Taken together, the results implicate a role for multitude of neurotransmitter systems, i.e., opioid (mu, kappa, delta), NMDA channel, BZD-GABA(A) chloride channel complex, and GABA(B) receptors in the anti-MES action of butorphanol.

Localisation of GABA(A) receptor epsilon-subunit in cholinergic and aminergic neurones and evidence for co-distribution with the theta-subunit in rat brain

In situ hybridisation and immunohistochemical methodologies suggest the existence of a large diversity of GABA(A) receptor subtypes in the brain. These are hetero-oligomeric proteins modulated by a number of clinically important drugs, depending on their subunit composition. We recently cloned and localised the rat GABA(A) receptor epsilon-subunit by in situ hybridisation and immunohistochemical procedures. Here, in a dual-labelling immunohistochemical study in the rat brain, we used our affinity-purified antiserum to epsilon with antisera to markers of cholinergic, catecholaminergic, and serotonergic neurones. As far as cholinergic systems were concerned, epsilon-immunoreactivity was expressed in all forebrain cell-groups, as well as in the caudal lateral pontine tegmentum and dorsal motor nucleus of the vagus nerve. As far as dopaminergic systems were concerned, epsilon-immunoreactivity was found to be expressed in a great number of hypothalamic cell-groups (A15, A14 and A12) and in the substantia nigra pars compacta. The noradrenergic, and to a lesser extent, adrenergic cell-groups were all epsilon-immunoreactive. Also, epsilon-immunoreactivity was detected in all serotonergic cell-groups. We also revealed by in situ hybridisation in a monkey brain that epsilon mRNA was expressed in the locus coeruleus, as previously observed in rats. Finally, by using in situ hybridisation in rat brains, we compared the distribution of the mRNA of epsilon with that of the recently cloned theta-subunit of the GABA(A) receptor. Both subunits showed strikingly overlapping expression patterns throughout the brain, especially in the septum, preoptic areas, various hypothalamic nuclei, amygdala, and thalamus, as well as the aforementioned monoaminergic cell-groups. No theta-mRNA signals were detected in cholinergic cell-groups. Taken together with previously published evidence of the presence of the alpha3-subunit in monoamine- or acetylcholine-containing systems, our data suggest the existence of novel GABA(A) receptors comprising alpha3/epsilon in cholinergic and alpha3/theta/epsilon in monoaminergic cell-groups.

GABA mechanisms and sleep

GABA is the main inhibitory neurotransmitter of the CNS. It is well established that activation of GABA(A) receptors favors sleep. Three generations of hypnotics are based on these GABA(A) receptor-mediated inhibitory processes. The first and second generation of hypnotics (barbiturates and benzodiazepines respectively) decrease waking, increase slow-wave sleep and enhance the intermediate stage situated between slow-wave sleep and paradoxical sleep, at the expense of this last sleep stage. The third generation of hypnotics (imidazopyridines and cyclopyrrolones) act similarly on waking and slow-wave sleep but the slight decrease of paradoxical sleep during the first hours does not result from an increase of the intermediate stage. It has been shown that GABA(B) receptor antagonists increase brain-activated behavioral states (waking and paradoxical sleep: dreaming stage). Recently, a specific GABA(C) receptor antagonist was synthesized and found by i.c.v. infusion to increase waking at the expense of slow-wave sleep and paradoxical sleep. Since the sensitivity of GABA(C) receptors for GABA is higher than that of GABA(A) and GABA(B) receptors, GABA(C) receptor agonists and antagonists, when available for clinical practice, could open up a new era for therapy of troubles such as insomnia, epilepsy and narcolepsy. They could possibly act at lower doses, with fewer side effects than currently used drugs. This paper reviews the influence of different kinds of molecules that affect sleep and waking by acting on GABA receptors.

Pharmacological evidence for GABAergic regulation of specific behaviors in Drosophila melanogaster

We have identified several GABAergic-modulated behaviors in Drosophila melanogaster by employing a pharmacological approach to disrupt GABA transporter function in vivo. Systemic treatment of adult female flies with the GABA transport inhibitors DL-2,4-diaminobutyric acid (DABA) or R,S-nipecotic acid (NipA), resulted in diminished locomotor activity, deficits in geotaxis, and the induction of convulsive behaviors with a secondary loss of the righting reflex. Pharmacological evidence suggested that the observed behavioral phenotypes were specific to disruption of GABA transporter function and GABAergic activity. The effects of GABA reuptake inhibitors on locomotor activity were dose dependent, pharmacologically distinct, and paralleled their known effects in mammalian systems. Recovery of normal locomotor activity and the righting reflex in DABA- and NipA-treated flies was achieved by coadministration of bicuculline (BIC), a GABA receptor antagonist that supresses GABAergic activity in mammals. Recovery of these behaviors was also achieved by coadministration of gabapentin, an anticonvulsant agent that interacts with mammalian GABAergic systems. Finally, behavioral effects were selective because other specific behaviors such as feeding activity and female sexual receptivity were not affected. Related pharmacological analyses performed in vitro on isolated Drosophila synaptic plasma membrane vesicles demonstrated high affinity, saturable uptake mechanisms for [3H]-GABA; further competitive inhibition studies with DABA and NipA demonstrated their ability to inhibit [3H]-GABA transport. The existence of experimentally accessible GABA transporters in Drosophila that share conserved pharmacological properties with their mammalian counterparts has resulted in the identification of specific behaviors that are modulated by GABA.

Genetic basis of anxiety-like behaviour: a critical review

The way genetic and/or environmental factors influence psychiatric disorders is an enduring question in the field of human psychiatric diseases. Anxiety-related disorders provide a relevant example of how such an interaction is involved in the aetiology of a psychiatric disease. In this paper we review the literature on that subject, reporting data derived from human and rodent studies. We present in a critical way the animal models used in the studies aimed at investigating the genetic basis of anxiety, including inbred mice, selected lines, multiple marker strains, or knockout mice and review data reporting environmental components influencing anxiety-related behaviours. We conclude that anxiety is a complex behaviour, underlined not only by genetic or environmental factors but also by multiple interactions between these two factors.