GABAmimetic agents display anxiolytic-like effects in the social interaction and elevated plus maze procedures

Anxiolytic and sedative effects of sodium valproate with different experimental paradigms in male and female rats

Valproic acid or sodium valproate is a widely used drug in the treatment of epilepsy, although it also appears to have anxiolytic and sedative properties derived from its agonistic action on the GABAergic system. To analyze these potential effects of the drug, we conducted three experiments with rats using procedures designed to assess anxiety in rodents. In the first experiment, with a fear conditioning procedure, three groups of male rats were included that received either 100 mg/kg or 300 mg/kg of valproate or an equivalent volume of saline solution. In Experiment 2, recording spontaneous activity in an open field, we compared the effects of valproic acid (300 mg/kg) on male and female rats. In the third experiment, we analyzed the effect of valproic acid using a novelty-induced hypophagia test and tested again for potential differences as a function of the sex of the animals. The results showed an anxiolytic effect restricted to the 300 mg/kg dose of the drug in Experiment 1. Such an effect was restricted to the female sample in Experiment 2, but in the third experiment affected both sexes. As for the sedative effect, it was observed in all experiments irrespective of the sex of the rats. These findings hold significant implications for the treatment of anxiety disorders since valproate may offer a novel therapeutic approach for anxiety-related conditions with distinct benefits and fewer side effects. However, clinical studies are needed to validate the translation of these findings from animal models to human patients.

Unconditioned and conditioned anxiolytic effects of Sodium Valproate on flavor neophobia and fear conditioning

In three experiments with rats, we analyzed the potential anxiolytic effects of sodium valproate, an anticonvulsant drug that has shown additional pharmacodynamic effects in animal models, including anxiolytic action. Since previous results have revealed that injecting valproate before allowing animals to consume a novel flavor solution resulted in an attenuation of neophobia, we predicted a similar effect when the novel flavor is presented on a drug-free trial in the presence of a context previously associated with the drug. In line with this hypothesis, in our first experiment we observed a reduction in neophobia to a novel flavor for those animals tested in the presence of the context associated with Sodium Valproate. However, a control group that received the drug before being allowed access to the novel flavor showed a significant reduction in consumption. Experiment 2 revealed that the unconditioned effects of the drug include a deleterious effect on the animals' locomotor activity that probably interferes with drinking behavior. Finally, in a third experiment, we directly tested the potential anxiolytic properties of sodium valproate by injecting the drug before implementing a fear conditioning procedure. These findings are explained in terms of the unconditioned anxiolytic action of the drug and the formation of an association between the context and the effects of the drug that evokes a conditioned response reminiscent of such anxiolytic effect.

Mycotherapy: Potential of Fungal Bioactives for the Treatment of Mental Health Disorders and Morbidities of Chronic Pain

Mushrooms have been used as traditional medicine for millennia, fungi are the main natural source of psychedelic compounds. There is now increasing interest in using fungal active compounds such as psychedelics for alleviating symptoms of mental health disorders including major depressive disorder, anxiety, and addiction. The anxiolytic, antidepressant and anti-addictive effect of these compounds has raised awareness stimulating neuropharmacological investigations. Micro-dosing or acute dosing with psychedelics including Lysergic acid diethylamide (LSD) and psilocybin may offer patients treatment options which are unmet by current therapeutic options. Studies suggest that either dosing regimen produces a rapid and long-lasting effect on the patient post administration with a good safety profile. Psychedelics can also modulate immune systems including pro-inflammatory cytokines suggesting a potential in the treatment of auto-immune and other chronic pain conditions. This literature review aims to explore recent evidence relating to the application of fungal bioactives in treating chronic mental health and chronic pain morbidities.

GABAergic and glutamatergic effects on nigrostriatal and mesolimbic dopamine release in the rat

In this review, a series of experiments is presented, in which γ-amino butyric acid (GABA)ergic and glutamatergic effects on dopamine function in the rat nigrostriatal and mesolimbic system was systematically assessed after pharmacological challenge with GABAA receptor (R) and and N-methyl d-aspartate (NMDA)R agonists and antagonists. In these studies, [123I]iodobenzamide binding to the D2/3R was mesured in nucleus accumbens (NAC), caudateputamen (CP), substantia nigra/ventral tegmental area (SN/VTA), frontal (FC), motor (MC) and parietal cortex (PC) as well as anterior (aHIPP) and posterior hippocampus (pHIPP) with small animal SPECT in baseline and after injection of either the GABAAR agonist muscimol (1 mg/kg), the GABAAR antagonist bicuculline (1 mg/kg), the NMDAR agonist d-cycloserine (20 mg/kg) or the NMDAR antagonist amantadine (40 mg/kg). Muscimol reduced D2/3R binding in NAC, CP, SN/VTA, THAL and pHIPP, while, after amantadine, decreases were confined to NAC, CP and THAL. In contrast, d-cycloserine elevated D2/3R binding in NAC, SN/VTA, THAL, frontal cortex, motor cortex, PC, aHIPP and pHIPP, while, after bicuculline, increases were confined to CP and THAL. Taken together, similar actions on regional dopamine levels were exterted by the GABAAR agonist and the NMDAR antagonist on the one side and by the GABAAR antagonist and the NMDAR agonist on the other, with agonistic action, however, affecting more brain regions. Thereby, network analysis suggests different roles of GABAARs and NMDARs in the mediation of nigrostriatal, nigrothalamocortical and mesolimbocortical dopamine function.

Valproate (depakine-chrono) in the acute treatment of outpatients with generalized anxiety disorder without psychiatric comorbidity: Randomized, double-blind placebo-controlled study

Objective

Anxiety disorders are highly prevalent in population of European countries. However, the effect of Valproate (depakine-chrono) on generalized anxiety disorder (GAD) has not been studied in a double-blind placebo-controlled design.

Method

Eighty patients (all men) were washout from the all medications. Each patient was randomized to receive either depakine-chrono (40 patients) for 6 weeks or matched placebo (40 patients) in a double-blind manner. Eligible participants, in addition to meeting the DSM-IV criteria for GAD and having a minimum score of 25 and more on the Hamilton Anxiety Scale, were required to be between 18 and 65 years. Response was defined as a 50% reduction in the Hamilton anxiety scale score. Response and side effects with depakine-chrono and placebo were compared by using analysis of variance (ANOVA) and chi-square tests. Six patients did not return for at least one subsequent assessment, leaving 74 patients (36 taking depakine-chrono and 38 taking placebo) in the valuables study group.

Results

Twenty six of the 36 depakine-chrono-treated participants responded by 6 weeks, versus six of the 38 placebo-treated participants (p< 0.001). The most common and problematic side effect in the depakine-chrono group was dizziness and nausea.

Conclusions

The authors believe this to be the first double-blind placebo-controlled randomization study to test the efficacy of a depakine-chrono in the management of anxiety disorders. They need to be replicated in a larger study group.

Acute alcohol exposure dose-dependently alleviates social avoidance in adolescent mice and inhibits social investigation in adult mice

BACKGROUND

Motivations for alcohol consumption often focus on ethanol's purported prosocial effects: social enhancement and reduction of socially focused anxiety. Despite substantial research supporting prosocial effects, contrary research exists demonstrating alcohol-elicited antisocial and asocial behaviours. Additionally, evidence typically fails to delineate whether alcohol-induced prosocial effects are due to alcohol expectancies or pharmacological actions of ethanol. Studies exploring ethanol's pharmacological effects on social behaviour and factors that modulate apparent contradictory prosocial versus asocial effects are lacking.

OBJECTIVES

This study investigated whether factors of age, ethanol dose and social fear modulate ethanol-induced pharmacological effects on sociability and social anxiety-like avoidance.

METHODS

Experiments examined the acute effects of ethanol doses (0, 0.25, 0.8, 1.6 g/kg; i.p.) in adult (10-week-old) and adolescent (PND 31-33) C57BL/6J male mice on social interaction using a social fear conditioning paradigm. Control experiments assessed whether ethanol-induced effects were social-specific.

RESULTS

In adult mice, no specific effects of ethanol on social avoidance were observed at any dose. However, high-dose ethanol (1.6 g/kg) suppressed social approach in all adult mice. In contrast, low-dose ethanol (0.25 g/kg) alleviated social avoidance in adolescent mice and no social suppression was observed at higher ethanol doses. Thus, higher doses of ethanol impair social behaviour in adult mice, whereas lower doses specifically alleviate social anxiety-like avoidance in adolescent mice.

CONCLUSIONS

Age, dose and social fear are critical modulators of acute ethanol-induced pharmacological effects on social behaviour. Inconsistencies in ethanol-induced social consequences appear at least partly mediated by pharmacological interactions-not solely alcohol expectancies.

Hypothesis-driven investigations of diverse pharmacological targets in two mouse models of autism

Autism spectrum disorder is a neurodevelopmental syndrome diagnosed primarily by persistent deficits in social interactions and communication, unusual sensory reactivity, motor stereotypies, repetitive behaviors, and restricted interests. No FDA‐approved medical treatments exist for the diagnostic symptoms of autism. Here we interrogate multiple pharmacological targets in two distinct mouse models that incorporate well‐replicated autism‐relevant behavioral phenotypes. Compounds that modify inhibitory or excitatory neurotransmission were selected to address hypotheses based on previously published biological abnormalities in each model. Shank3B is a genetic model of a mutation found in autism and Phelan‐McDermid syndrome, in which deficits in excitatory neurotransmission and synaptic plasticity have been reported. BTBR is an inbred strain model of forms of idiopathic autism in which reduced inhibitory neurotransmission and excessive mTOR signaling have been reported. The GABA‐A receptor agonist gaboxadol significantly reduced repetitive self‐grooming in three independent cohorts of BTBR. The TrkB receptor agonist 7,8‐DHF improved spatial learning in Shank3B mice, and reversed aspects of social deficits in BTBR. CX546, a positive allosteric modulator of the glutamatergic AMPA receptor, and d‐cycloserine, a partial agonist of the glycine site on the glutamatergic NMDA receptor, did not rescue aberrant behaviors in Shank3B mice. The mTOR inhibitor rapamycin did not ameliorate social deficits or repetitive behavior in BTBR mice. Comparison of positive and negative pharmacological outcomes, on multiple phenotypes, evaluated for replicability across independent cohorts, enhances the translational value of mouse models of autism for therapeutic discovery. GABA agonists present opportunities for personalized interventions to treat components of autism spectrum disorder. Autism Res 2019, 12: 401–421 © 2019 The Authors. Autism Research published by International Society for Autism Research published by Wiley Periodicals, Inc.

Lay Summary

Many of the risk genes for autism impair synapses, the connections between nerve cells in the brain. A drug that reverses the synaptic effects of a mutation could offer a precision therapy. Combining pharmacological and behavioral therapies could reduce symptoms and improve the quality of life for people with autism. Here we report reductions in repetitive behavior by a GABA‐A receptor agonist, gaboxadol, and improvements in social and cognitive behaviors by a TrkB receptor agonist, in mouse models of autism.

Embryonic stem cell transplants as a therapeutic strategy in a rodent model of autism

Autism is a neurodevelopmental disorder characterized by disruptions in three core behavioral domains: deficits in social interaction, impairments in communication, and repetitive and stereotyped patterns of behavior or thought. There are currently no drugs available for the treatment of the core symptoms of ASD and drugs that target comorbid symptoms often have serious adverse side effects, suggesting an urgent need for new therapeutic strategies. The neurobiology of autism is complex, but converging evidence suggests that ASD involves disruptions in the inhibitory GABAergic neurotransmitter system. Specifically, people with autism have a reduction in parvalbumin (PV)-containing interneurons in the PFC, leading to the suggestion that restoring interneuron function in this region may be a novel therapeutic approach for ASD. Here we used a dual-reporter embryonic stem cell line to generate enriched populations of PV-positive interneurons, which were transplanted into the medial prefrontal cortex (mPFC) of the Poly I:C rodent model of autism. PV interneuron transplants were able to decrease pyramidal cell firing in the mPFC and alleviated deficits in social interaction and cognitive flexibility. Our results suggest that restoring PV interneuron function in the mPFC may be a novel and effective treatment strategy to reduce the core symptoms of autism.

Effects of AMPA receptor antagonist, NBQX, and extrasynaptic GABAA agonist, THIP, on social behavior of adolescent and adult rats

Adolescence is characterized by high significance of social interactions, along with a propensity to exhibit social facilitating effects of ethanol while being less sensitive than adults to the inhibition of social behavior that emerges at higher doses of ethanol. Among the neural characteristics of adolescence are generally enhanced levels of glutamatergic (especially NMDA receptor) activity relative to adults, whereas the GABA system is still developmentally immature. Activation of NMDA receptors likely plays a role in modulation of social behavior in adolescent animals as well as in socially facilitating and suppressing effects of ethanol. For instance, adolescent and adult rats differ in their sensitivities to the effects of NMDA antagonists and ethanol on social behavior, with adolescents but not adults demonstrating social facilitation at lower doses of both drugs and adults being more sensitive to the socially suppressing effects evident at higher doses of each. The roles of AMPA and extrasynaptic GABA_A receptors in modulation of social behavior during adolescence and in adulthood are still unknown. The present study was designed to assess whether pharmacological blockade of AMPA receptors and/or activation of extrasynaptic GABA_A receptors results in age-dependent alterations of social behavior. Adolescent and adult male and female Sprague-Dawley rats were injected with an assigned dose of either a selective AMPA antagonist, NBQX (Experiment 1) or extrasynaptic GABA_A agonist, THIP (Experiment 2) and placed into a modified social interaction chamber for a 30-min habituation period prior to a 10-min social interaction test with a novel age- and sex-matched partner. Behaviors such as social investigation, contact behavior and play behavior were scored from video recordings of the interaction tests. In Experiment 1, NBQX produced similar social inhibition at higher doses in both age groups. In Experiment 2, THIP induced inhibition in adolescents, but not adults. No social facilitation was evident following low doses of either drug. Therefore, AMPA and extrasynaptic GABA_A receptors appear to play little role if any in modulation of peer-directed social behavior in adolescence and adulthood and not likely to contribute to previously observed age differences in the social effects of acute ethanol.

Comparative effects of sertraline, haloperidol or olanzapine treatments on ketamine-induced changes in mouse behaviours

Effects of sertraline, haloperidol or olanzapine administration on ketamine-induced behaviours in mice were examined. The aim was to ascertain the degree of reversal of such behaviours by sertraline, and compare its effectiveness to haloperidol and olanzapine. Ten-week old mice (N = 120) were equally divided into main groups; 1 (open-field, radial-arm maze and elevated plus maze {EPM} tests), and 2 (social interaction test). Mice in each main group were assigned into six groups of ten (n = 10) each. Group 1 received intraperitoneal (i.p) injection of vehicle, while groups 2-6 received i.p ketamine at 15 mg/kg daily for 10 days. From day 11 to 24, mice in group 1 (vehicle) were given distilled water (i.p at 2 ml/kg and oral at 10 ml/kg), group 2 (ketamine control) received daily i.p ketamine and oral distilled water; while animals in groups 3-6 received daily i.p. ketamine and oral haloperidol (4 mg/kg), olanzapine (2 mg/kg), or one of two doses of sertraline (SERT) (2.5 or 5 mg/kg), respectively. Treatments were administered daily, and behaviours assessed on days 11 and 24. Results showed that repeated ketamine administration caused hyperlocomotion, increased self-grooming, memory loss and social withdrawal. Administration of sertraline (both doses), haloperidol, and olanzapine reversed ketamine-induced behavioural changes. However, in the EPM, sertraline and olanzapine were anxiolytic, while haloperidol was anxiogenic. Sertraline's effect on behaviours tested was comparable to olanzapine and better than haloperidol. In conclusion, this study shows that sertraline's ability to counteract ketamine-induced behavioural changes in mice is comparable to known antipsychotics.

GABAergic control of neostriatal dopamine D2 receptor binding and behaviors in the rat

PURPOSE

The present study assessed the influence of the GABA_A receptor agonist muscimol and the GABA_A receptor antagonist bicuculline on neostriatal dopamine D₂ receptor binding in relation to motor and exploratory behaviors in the rat.

METHODS

D₂ receptor binding was measured in baseline and after challenge with either 1mg/kg muscimol or 1mg/kg bicuculline. In additional rats, D₂ receptor binding was measured after injection of saline. After treatment with muscimol, bicuculline and saline, motor and exploratory behaviors were assessed for 30min in an open field prior to administration of [¹²³I]S-3-iodo-N-(1-ethyl-2-pyrrolidinyl)methyl-2-hydroxy-6-methoxybenzamide ([¹²³I]IBZM). For baseline and challenges, striatal equilibrium ratios (V₃″) were computed as estimation of the binding potential.

RESULTS

Muscimol but not bicuculline reduced D₂ receptor binding relative to baseline and to saline. Travelled distance, duration of rearing and frequency of rearing and of head-shoulder motility were lower after muscimol compared to saline. In contrast, duration of rearing and grooming and frequency of rearing, head-shoulder motility and grooming were elevated after bicuculline relative to saline. Moreover, bicuculline decreased duration of sitting and head-shoulder motility.

CONCLUSIONS

The muscimol-induced decrease of motor/exploratory behaviors can be related to an elevation of striatal dopamine levels. In contrast, bicuculline is likely to elicit a decline of synaptic dopamine, which, however, is compensated by the time of D₂ receptor imaging studies. The results indicate direct GABAergic control over D₂ receptor binding in the neostriatum in relation to behavioral action, and, thus, complement earlier pharmacological studies.

The role of CA3 GABAA receptors on anxiolytic-like behaviors and avoidance memory deficit induced by NMDA receptor antagonists

Cognitive functions are influenced by memory and anxiety states. However, a non-linear relation has been shown between these two domains. The important role of the hippocampus in memory and emotional responses may link the pathogenesis of anxiety to memory-related GABAergic and glutamatergic processes in the hippocampus. To investigate the role of GABAA receptors in relation to blocking N-methyl-D-aspartate (NMDA) receptors in the CA3 region, and balancing the glutamatergic and GABAergic system activities as an approach for the management of related disorders, the elevated plus-maze test-retest paradigm was used to investigate the anxiolytic-like state on the test day and avoidance memory state on the retest day. The data showed that injection of D-AP5, the NMDA receptor antagonist, induced anxiolytic-like behavior and impaired avoidance memory. Injection of GABAA agonist (muscimol), but not the antagonist (bicuculline), induced avoidance memory impairment. Neither muscimol nor bicuculline altered anxiety-like behaviors. Muscimol pretreatment did not change D-AP5-induced anxiolytic-like behaviors but potentiated avoidance memory impairment. Bicuculline pretreatment blocked D-AP5-induced anxiolytic-like behaviors and contradicted its effect on avoidance memory. Our findings indicate that alteration of the CA3 GABAA receptor activity can effectively affect the anxiolytic-like behaviors and avoidance memory deficit induced by D-AP5.

Anxiolytic and nootropic activity of Vetiveria zizanioides roots in mice

Background:

Vetiveria zizanioides (VZ) (family: Poaceae), an aromatic plant commonly known as “Vetiver” has been used for various ailments. Concerning the various ailments being listed as the traditional uses of VZ, no mention about anxiety and memory was found.

Objective:

The present study examined the anxiolytic and memory enhancing activity of ethanolic extract of V. zizanioides (EEVZ) dried roots in mice.

Materials and Methods:

Activity of EEVZ was assessed using models of anxiety (elevated plus-maze [EPM], light/dark test, hole board test, marble-burying test) and learning and memory (EPM, passive shock avoidance paradigm).

Results:

EEVZ at doses of 100, 200, and 300 mg/kg b.w. illustrated significant anxiolytic activity indicated by increase in time spent and number of entries in open arm, time spent in lightened area, number of head poking and number marble buried when compared to that of diazepam (1 mg/kg b.w.), a reference standard. The same treatment showed a significant decrease in transfer latency to reach open arm, shock-free zone, and number of mistakes when compared to that of scopolamine (0.3 mg/kg b.w.). EEVZ in all the doses (100, 200, and 300 mg/kg b.w.) significantly decreased mortality in sodium nitrite (250 mg/kg b.w.) induced hypoxia and also significantly increases contraction induced by acetylcholine on rat ileum preparation.

Conclusion:

The result emanated in the present investigation revealed EEVZ possesses significant anxiolytic and nootropic activity by possibly interplaying with neurotransmitters implicated in anxiety and learning and memory.

Altered expression of δGABAA receptors in health and disease

γ-Aminobutyric acid type A receptors that contain the δ subunit (δGABAA receptors) are expressed in multiple types of neurons throughout the central nervous system, where they generate a tonic conductance that shapes neuronal excitability and synaptic plasticity. These receptors regulate a variety of important behavioral functions, including memory, nociception and anxiety, and may also modulate neurogenesis. Given their functional significance, δGABAA receptors are considered to be novel therapeutic targets for the treatment of memory dysfunction, pain, insomnia and mood disorders. These receptors are highly responsive to sedative-hypnotic drugs, general anesthetics and neuroactive steroids. A further remarkable feature of δGABAA receptors is that their expression levels are highly dynamic and fluctuate substantially during development and in response to physiological changes including stress and the reproductive cycle. Furthermore, the expression of these receptors varies in pathological conditions such as alcoholism, fragile X syndrome, epilepsy, depression, schizophrenia, mood disorders and traumatic brain injury. Such fluctuations in receptor expression have significant consequences for behavior and may alter responsiveness to therapeutic drugs. This review considers the alterations in the expression of δGABAA receptors associated with various states of health and disease and the implications of these changes.

Social interaction and social withdrawal in rodents as readouts for investigating the negative symptoms of schizophrenia

Negative symptoms (e.g., asociality and anhedonia) are a distinct symptomatic domain that has been found to significantly affect the quality of life in patients diagnosed with schizophrenia. Additionally, the primary negative symptom of asociality (i.e., withdrawal from social contact that derives from indifference or lack of desire to have social contact) is a major contributor to poor psychosocial functioning and has been found to play an important role in the course of the disorder. Nonetheless, the pathophysiology underlying these symptoms is unknown and currently available treatment options (e.g., antipsychotics and cognitive-behavioral therapy) fail to reliably produce efficacious benefits. Utilizing rodent paradigms that measure social behaviors (e.g., social withdrawal) to elucidate the neurobiological substrates that underlie social dysfunction and to identify novel therapeutic targets may be highly informative and useful to understand more about the negative symptoms of schizophrenia. Accordingly, the purpose of this review is to provide an overview of the behavioral tasks for assessing social functioning that may be translationally relevant for investigating negative symptoms associated with schizophrenia.

The effect of a clinically effective and non-effective dose of lorazepam on 7.5% CO₂-induced anxiety

Symptoms of anxiety induced by 7.5% CO₂ inhalation can be attenuated by acute administration of GABA(A) receptor anxiolytics such as lorazepam and alprazolam. This study investigated if these effects are dose-related, by comparing a 0.5 mg dose (considered non-clinically effective) and a 2 mg dose of lorazepam (clinically effective) on 7.5% CO₂ inhalation. Eighteen healthy males (mean age 20.6 years, SD 1.29), judged physically and mentally fit, attended three visits, each one week apart, to take each treatment in a randomised double-blind crossover design. Drugs were given 60 min prior to 20 min air inhalation, followed by 20 min 7.5% CO₂ inhalation. The order of gas presentation was single blind. Subjective ratings using visual analogue scales (VAS) and questionnaires were recorded before and after each inhalation. Blood pressure (BP), heart rate (HR), respiration rate (RR) and expired CO₂ were recorded during each inhalation. Inhalation of 7.5% CO₂ significantly raised BP, HR, RR and expired CO₂. Ratings of feeling like leaving the room were significantly lower on 2 mg compared with 0.5 mg and placebo, and dose-dependent trends were seen in scores for VAS fearful, anxious, stressed, tense, and worried. Results may be indicative of dose-dependent effects of lorazepam in a CO₂ model of anxiety.

Hippocampus-specific deletion of tissue plasminogen activator "tPA" in adult mice impairs depression- and anxiety-like behaviors

Anxiety and depression are multifactorial disorders that have become prominent health problems all over the world. Neurotrophic factors have emerged underlying pathogenesis of these diseases. Although a number of studies indicate that the hippocampus-brain-derived neurotrophic factor (BDNF) may be involved in these psychiatric illnesses, little is known about the molecular mediators of these disorders. In this study we further investigate the role of tissue plasminogen activator (tPA), a serine protease involved in pro-BDNF cleavage to BDNF, in depression and anxiety-like behaviors in adult mice. To address this issue, we investigated the effect of hippocampus tPA manipulation, using viral vectors, on anxiety- and depression-like behaviors, including the marble burying test (MBT), elevated plus maze (EPM), tail suspension test (TST), novelty suppressed feeding (NSF) and forced swim test (FST). Our results showed that tPA knock-down - using lentiviral vectors expressing specific short hairpin RNAs (LV-shRNA) - increased the number of buried marbles together with the digging time in the MBT and decreased the time spent in open the arms of an EPM. In addition, tPA-knock down in the hippocampus increased immobility in the FST and TST, and increased time to feed in the NSF test. These effects were reversed when tPA-over-expressing vectors (LV-tPA) were injected in the hippocampus. We also found that BDNF protein levels were elevated in the hippocampus of mice receiving tPA-expressing vectors. Together, our results imply that tPA manipulation may provide an effective therapeutic intervention for depression and anxiety disorders.

Distinct neurobehavioural effects of cannabidiol in transmembrane domain neuregulin 1 mutant mice

The cannabis constituent cannabidiol (CBD) possesses anxiolytic and antipsychotic properties. We have previously shown that transmembrane domain neuregulin 1 mutant (Nrg1 TM HET) mice display altered neurobehavioural responses to the main psychoactive constituent of cannabis, Δ⁹-tetrahydrocannabinol. Here we investigated whether Nrg1 TM HET mice respond differently to CBD and whether CBD reverses schizophrenia-related phenotypes expressed by these mice. Adult male Nrg1 TM HET and wild type-like littermates (WT) received vehicle or CBD (1, 50 or 100 mg/kg i.p.) for 21 days. During treatment and 48 h after withdrawal we measured behaviour, whole blood CBD concentrations and autoradiographic receptor binding. Nrg1 HET mice displayed locomotor hyperactivity, PPI deficits and reduced 5-HT_2A receptor binding density in the substantia nigra, but these phenotypes were not reversed by CBD. However, long-term CBD (50 and 100 mg/kg) selectively enhanced social interaction in Nrg1 TM HET mice. Furthermore, acute CBD (100 mg/kg) selectively increased PPI in Nrg1 TM HET mice, although tolerance to this effect was manifest upon repeated CBD administration. Long-term CBD (50 mg/kg) also selectively increased GABA_A receptor binding in the granular retrosplenial cortex in Nrg1 TM HET mice and reduced 5-HT_2A binding in the substantia nigra in WT mice. Nrg1 appears necessary for CBD-induced anxiolysis since only WT mice developed decreased anxiety-related behaviour with repeated CBD treatment. Altered pharmacokinetics in mutant mice could not explain our findings since no genotype differences existed in CBD blood concentrations. Here we demonstrate that Nrg1 modulates acute and long-term neurobehavioural effects of CBD, which does not reverse the schizophrenia-relevant phenotypes.

Stress during development alters anxiety-like behavior and hippocampal neurotransmission in male and female rats

Epidemiological data indicate that early stress increases vulnerability to psychiatric disorders, including anxiety and depression. In the present study we sought to investigate the long-term behavioral and neurochemical consequences of increased and sustained corticosterone levels induced by a 24 h bout of maternal deprivation (DEP) imposed on postnatal day 11 (DEP11). As adults, animals were exposed to the elevated plus maze for assessment of anxiety-like behavior and corticosterone response to this challenge, or decapitated for determination of monoamines and amino acid neurotransmitters content in the hippocampus by HPLC method. The results showed that DEP11 male and female rats displayed increased time in the central hub of the maze and more risk assessment behavior, reflecting increased anxiety-like behavior; in addition, these animals continuously secreted corticosterone in response to the behavioral test until the latest time-point, e.g., 60 min post-stress. In males, maternal deprivation increased aspartate and glutamate levels and reduced taurine levels compared to non-deprived (NDEP) rats. DEP11 females displayed reduced noradrenaline, aspartate and GABA levels compared to NDEP counterparts. These results indicate that maternal deprivation at 11 days of age produced changes in hippocampal neurotransmission that may mediate the increased anxiety-like behavior observed in male and female deprived rats. This article is part of a Special Issue entitled 'Anxiety and Depression'.

Repeated restraint stress alters sensitivity to the social consequences of ethanol in adolescent and adult rats

Human adolescents consume alcohol largely to enhance social interactions. Adolescent, but not adult rats likewise exhibit ethanol-induced social facilitation under low-stress circumstances. Since the relationship between stress and ethanol sensitivity across ontogeny still has yet to be well explored, the present study sought to characterize possible age-associated differences in the influence of stressor exposure on ethanol-induced changes in social behavior in adolescent [postnatal days (P) 30-36] and adult (P65-71) male and female Sprague-Dawley rats. Animals were repeatedly restrained (90min/day) for 5days, followed by examination of ethanol-induced (0, 0.25, 0.5, 0.75, or 1.0g/kg) alterations in social behaviors on the last day. Results revealed typical age-related differences in sensitivity to ethanol among controls, with adolescents being uniquely sensitive to low-dose ethanol stimulation of social investigation and play fighting, but less sensitive than adults to the social suppression emerging at higher doses. At both ages, stressor exposure decreased sensitivity to social inhibitory effects of ethanol, while augmenting expression of ethanol's social facilitatory effects. Ethanol also attenuated the stress-related suppression of social motivation at both ages. These results suggest that repeated stressor exposure diminishes age-related differences in the social consequences of ethanol, with stress enhancing ethanol-induced social facilitation across age.

Mice lacking adenylyl cyclase-5 cope badly with repeated restraint stress

Physiological responses to acute stress proceed with the activation of the hypothalamus-pituitary-adrenal gland (HPA) system. Many brain regions are known to modulate the HPA axis activation in stress responses, but the detailed neural circuits and signaling system in the upstream of the HPA axis have to be explored further. Type 5 adenylyl cyclase (AC5) is highly concentrated in the dorsal striatum and nucleus accumbens, which are implicated in reward and stress-related behavior. AC5(-/-) mice exposed to daily 2-hr restraint stress for only 3-5 days showed poor stress-coping responses, including severe body weight loss, poor coat condition, respiratory difficulties, and freezing behavior. Plasma corticosterone levels during 2-hr stress sessions increased in AC5(-/-) mice compared with those of AC5(+/+) mice. However, neither the corticosterone receptor antagonist RU486 nor the CRH receptor antagonist NBI27914 blocked their poor stress coping, whereas the administration of the GABA(A) receptor allosteric modulator diazepam or the D1 dopamine receptor antagonist SCH23390 prior to restraint stress sessions changed their stress-coping response to the stressed AC5(+/+) mouse level. Stress-triggered c-Fos expression was completely blunted in the dorsal striatum of AC5(-/-). These results suggest that the AC5-associated signal system and neural network are involved in the regulation of anxiety and stress-coping response.

The anti-epileptic drug lacosamide (Vimpat) has anxiolytic property in rodents

Lacosamide ((R)-2-acetamido-N-benzyl-3-methoxypropionamide; formerly harkoseride, SPM 927; Vimpat), has been recently approved by US and European regulatory authorities for use as add-on therapy for partial-onset seizures in adults. Because a number of anti-epileptic drugs are used to treat conditions beyond epilepsy, including anxiety, in the present study we investigated the anxiolytic potential of lacosamide in a conditioned emotional response (CER) model in rat, and the mouse marble burying assay. In each test lacosamide produced a significant effect consistent with anxiolysis, i.e. lacosamide increased suppression ratio in the CER test, and reduced the number of marbles buried in the marble burying assay. The doses necessary for an anxiolytic effect were higher than those necessary for efficacy in seizure tests conducted in the same species. For example in the mouse, the lacosamide oral ED(50) in the maximal electroshock seizure (MES) and 6 Hz tests was 5.3 and 9.6 mg/kg respectively, and the minimal effective dose in the marble burying assay was 30 mg/kg. In both seizure and anxiety tests, the (S)-enantiomer of lacosamide was inactive suggesting a similar mechanism of action, possibly use-dependent inhibition of sodium channel function (Errington et al., 2008). Efficacy in the CER model was equivalent to diazepam and pregabalin (Lyrica). In tests of side-effects, lacosamide had no effect on choice accuracy in the delayed match to position task of working memory, although at the 30 mg/kg dose, response rates and response latencies were significantly affected. In sum, the present results identify for the first time, an anxiolytic potential of lacosamide.

Involvement of the GABA/benzodiazepine receptor in the axiolytic-like effect of nociceptin/orphanin FQ

We investigated the mechanism underlying the anxiolytic actions of the neuropeptide nociceptin/orphanin FQ (N/OFQ) with an elevated plus-maze test. In mice, intracerebroventricular (i.c.v.) infusions of N/OFQ (0.1 and 0.32 nmol) led to an increase in time spent in the open arms (anxiolytic-like effects). A non-peptidyl N/OFQ receptor (NOP) antagonist, J-113397(1-{(3R,4R)-1-cyclooctylmethyl-3-hydroxymethyl-4-piperidyl}-3-ethyl-1,3-dihydro-2H-benzimidazol-2-one), (1.0 and 3.2 mg/kg, s.c.) blocked the increase induced by N/OFQ. On the other hand, a benzodiazepine receptor antagonist, flumazenil, (10 mg/kg, i.p.) and a GABAA receptor antagonist, (+)-bicuculline, (5.6 mg/kg, i.p.) also inhibited the increase induced by N/OFQ. In rats, microinfusions of N/OFQ (10 and 32 pmol) into the amygdala led to an increase in time spent in the open arms. However, intracranial infusions of N/OFQ (10-100 pmol) into the dorsal hippocampus did not affect the time spent in the open arms. These findings suggest that the anxiolytic-like effects of N/OFQ may be related to the GABA/benzodiazepine system in the amygdala.

Adenylyl cyclase-5 activity in the nucleus accumbens regulates anxiety-related behavior

Type 5 adenylyl cyclase (AC5) is highly concentrated in the dorsal striatum and nucleus accumbens (NAc), two brain areas which have been implicated in motor function, reward, and emotion. Here we demonstrate that mice lacking AC5 (AC5-/-) display strong reductions in anxiety-like behavior in several paradigms. This anxiolytic behavior in AC5-/- mice was reduced by the D(1) receptor antagonist SCH23390 and enhanced by the D(1) dopamine receptor agonist, dihydrexidine (DHX). DHX-stimulated c-fos induction in AC5-/- mice was blunted in the dorso-lateral striatum, but it was overactivated in the dorso-medial striatum and NAc. The siRNA-mediated inhibition of AC5 levels within the NAc was sufficient to produce an anxiolytic-like response. Microarray and RT-PCR analyses revealed an up-regulation of prodynorphin and down-regulation of cholecystokinin (CCK) in the NAc of AC5-/- mice. Administration of nor-binaltorphimine (a kappa opioid receptor antagonist) or CCK-8s (a CCK receptor agonist) reversed the anxiolytic-like behavior exhibited by AC5-/- mutants. Taken together, these results suggest an essential role of AC5 in the NAc for maintaining normal levels of anxiety.

Enhanced behavioral sensitivity to the competitive GABA agonist, gaboxadol, in transgenic mice over-expressing hippocampal extrasynaptic alpha6beta GABA(A) receptors

The behavioral and functional significance of the extrasynaptic inhibitory GABA(A) receptors in the brain is still poorly known. We used a transgenic mouse line expressing the GABA(A) receptor alpha6 subunit gene in the forebrain under the Thy-1.2 promoter (Thy1alpha6) mice ectopically expressing alpha6 subunits especially in the hippocampus to study how extrasynaptically enriched alphabeta(gamma2)-type receptors alter animal behavior and receptor responses. In these mice extrasynaptic alpha6beta receptors make up about 10% of the hippocampal GABA(A) receptors resulting in imbalance between synaptic and extrasynaptic inhibition. The synthetic GABA-site competitive agonist gaboxadol (4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol; 3 mg/kg) induced remarkable anxiolytic-like response in the light : dark exploration and elevated plus-maze tests in Thy1alpha6 mice, while being almost inactive in wild-type mice. The transgenic mice also lost quicker and for longer time their righting reflex after 25 mg/kg gaboxadol than wild-type mice. In hippocampal sections of Thy1alpha6 mice, the alpha6beta receptors could be visualized autoradiographically by interactions between gaboxadol and GABA via [(35)S]TBPS binding to the GABA(A) receptor ionophore. Gaboxadol inhibition of the binding could be partially prevented by GABA. Electrophysiology of recombinant GABA(A) receptors revealed that GABA was a partial agonist at alpha6beta3 and alpha6beta3delta receptors, but a full agonist at alpha6beta3gamma2 receptors when compared with gaboxadol. The results suggest strong behavioral effects via selective pharmacological activation of enriched extrasynaptic alphabeta GABA(A) receptors, and the mouse model represents an example of the functional consequences of altered balance between extrasynaptic and synaptic inhibition.

Effects of acute and chronic valproate treatments on p-CREB levels in the rat amygdala and nucleus accumbens

Valproate may exert its effects by modulating signalling pathways controlling gene expression as they are known to alter both CREB and ERK pathways in the rat hippocampus and frontal cortex. The action of valproate on these signalling pathways has not been studied yet in limbic areas such as the nucleus accumbens and the amygdala which are central for the regulation of emotional behaviors. To this aim, the effect of valproate on phosphorylated CREB (p-CREB) and ERK (p-ERK) in the amygdala and nucleus accumbens, by using immunohistochemical and Western blot analysis, was investigated. The immunohistochemistry was followed by a stereological quantification of the number of immunoreactive cells. Acute valproate (80 mg/kg, i.p.) increased the density of p-CREB-positive cells and enhanced p-CREB, but not p-ERK, protein levels in the amygdala and the accumbens. In contrast, following chronic valproate (80 mg/kg/day for 4 weeks) p-CREB and p-ERK protein levels were markedly attenuated in the amygdala, while the number of p-CREB immunoreactive cells was increased in the accumbens. These data suggest that valproate exert differential effects depending on the brain region examined, the duration and the dose of treatment. The increasing effect of chronic valproate on p-CREB levels in the accumbens is consistent with previous studies in the cortex and the hippocampus, while the decrease of amygdalar p-CREB levels might be specific to mood stabilizers compared to antidepressant drugs, and might be linked to the anti-manic action of valproate.

Gaboxadol, a selective extrasynaptic GABA(A) agonist, does not generalise to other sleep-enhancing drugs: a rat drug discrimination study

Gaboxadol is a selective extrasynaptic GABA(A) receptor agonist (SEGA) which enhances slow-wave sleep, and may act principally at extrasynaptic GABA(A)alpha4betadelta receptors. Drug discrimination is a very useful approach for exploring in vivo pharmacological similarities and differences between compounds and was therefore used to compare gaboxadol and zolpidem, an established hypnotic drug, against zopiclone, S-zopiclone, indiplon and tiagabine, all of which have been reported to enhance sleep. Gaboxadol generalised to itself, but not to zolpidem, zopiclone, S-zopiclone, R-zopiclone, indiplon or tiagabine. By contrast, zolpidem generalised to itself, zopiclone, S-zopiclone and indiplon, but not to R-zopiclone (the inactive enantiomer of zopiclone), gaboxadol or tiagabine. This suggests that zolpidem, zopiclone, S-zopiclone and indiplon share a discriminative stimulus, which may be mediated by their efficacy at GABA(A)alpha1betagamma receptors. Gaboxadol and tiagabine each have a different discriminative stimulus from all the other drugs tested.

Picrotoxin blocks the anxiolytic- and panicolytic-like effects of sodium valproate in the rat elevated T-maze

The effect of acute sodium valproate administration, an anxiolytic and putative panicolytic drug, was evaluated in rats tested in the elevated T-maze, an animal model that measures two defensive reactions: avoidance (inhibitory avoidance), related to generalized anxiety, and escape (escape from open arms), related to panic. Additionally, the involvement of gamma-aminobutyric acid (GABA) neurotransmission in sodium valproate effects was studied by picrotoxin co-administration. Sodium valproate (300 mg/kg, intraperitoneally, 30 min before the test) impaired both avoidance latency (time to leave the closed arm) and one-way escape (latency to enter the closed arm) indicating anxiolytic and panicolytic effects, respectively. Pre-treatment with picrotoxin (0.5 mg/kg, intraperitoneally, 5 min before sodium valproate administration) blocked the effects of sodium valproate on inhibitory avoidance and one-way escape. No locomotor effect was seen in the open-field. These data suggest that sodium valproate exerts anxiolytic-like and panicolytic-like effects in the elevated T-maze and that these effects were mediated by picrotoxin-sensitive GABA type A receptors.

Lamotrigine has an anxiolytic-like profile in the rat conditioned emotional response test of anxiety: a potential role for sodium channels?

RATIONALE

Many anticonvulsants are used in disorders other than epilepsy. For example, lamotrigine is reported to be effective in post-traumatic stress disorder and mania.

OBJECTIVE

We assessed the effects of the anticonvulsants lamotrigine, valproate and carbamazepine in an animal model of anxiety. We assessed a wide range of pharmacological tools to delineate the mechanism of lamotrigine's anxiolytic effect.

METHODS

We assessed these compounds in the rat conditioned emotional response (CER) test of anxiety.

RESULTS

Lamotrigine (30-80 mg/kg) dose-dependently and reproducibly engendered an anxiolytic response in this test, with similar efficacy to benzodiazepines. Carbamazepine (20-40 mg/kg) and riluzole (10 mg/kg), which block Na+ channels by a similar mechanism as lamotrigine, were also anxiolytic. By contrast, valproate (100-600 mg/kg) was inactive and appears to differ in its interaction with Na+ channels. The SSRI paroxetine, the GABA(A) receptor positive modulator propofol, the NMDA antagonists memantine and (+)MK-801, and the Ca2+ channel antagonist nifedipine were all inactive in the CER test, suggesting these mechanisms may not mediate the anxiolytic effect of lamotrigine. More directly, we showed that the anxiolytic effect of lamotrigine could be blocked by co-administering rats with the Na+ channel activator veratrine (0.1 mg/kg). By contrast, neither the Ca2+ channel agonist BAYK8644 (0.5 mg/kg) nor the 5-HT1A or 5-HT(1/2) antagonists WAY100635 (0.3 mg/kg) and metergoline (3 mg/kg), respectively, were able to block the effect.

CONCLUSION

Lamotrigine's anxiolytic effect in the CER test may be mediated via block of Na+ channels, and this may represent a target for the development of novel anxiolytics.

Effects of methyl-eugenol administration on behavioral models related to depression and anxiety, in rats

Croton zehntneri (Cz) is a popular plant in Brazilian folk medicine. Recently, the use of its essential oil showed depressive activity response in the central nervous system (CNS). Chemical studies show that the main compound of this oil is the methyl-eugenol (ME). This work seeks to evaluate the ME activity in behavioral models of depression and anxiety, in the rat. Male rats (60 days old) were divided into four groups (n = 10) and treated with doses of 1.0, 3.0 and 10.0 ml/100 g body wt., v.o., of ME (experimental) and saline (control). One hour after treatment, they were observed in the forced swimming test and 15 min later in the open-field test. A decrease was observed in the immobility time during the forced swimming test for all experimental groups, in comparison with control group (C = 168.8 +/- 27.3; 1.0 microl = 139.1 +/- 23.5; 3.0 microl = 137.2 +/- 18.7 and 10.0 microl = 139.8 +/- 23.6). The open-field results showed no differences in comparison to the control group. The same was observed for social interaction, plus-maze and holeboard tests, suggesting no alterations in anxiety behavior. These data suggest that ME administration induced antidepressive CNS alterations, expressed by the smallest immobility in the swimming model, and not of a level able to alter motor and exploratory activity in the open-field. The absence of effects observed in the open-field can be a result of the experimental contingency, taking low anxiety levels. These data are in contradiction to observations with Cz essential oil in these models.

Antagonism by NOS inhibition of the behavioral effects of benzodiazepine and GABAA receptor agonists in the mouse elevated plus-maze

Earlier we implicated nitric oxide (NO) in mediation of the behavioral effects of benzodiazepines. Since benzodiazepines work through facilitation of GABAergic inhibitory neurotransmission, this study was designed to determine whether the direct-acting gamma-aminobutyric acidA (GABAA) receptor agonist THIP (4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol) evokes behavioral effects similar to those of benzodiazepines and whether behavioral effects of THIP are also NO dependent. When challenged with either chlordiazepoxide or THIP in an elevated plus-maze paradigm, male NIH Swiss mice exhibited a dose-related increase in open-arm activity. The chlordiazepoxide-induced effects were sensitive to antagonism by a benzodiazepine antagonist, and the effects of THIP were blocked by a GABAA receptor antagonist. Pretreatment with the NO synthase (NOS) inhibitor L-NG-nitro arginine antagonized the effects of both chlordiazepoxide and THIP; similar pretreatment with the D-isomer, D-NG-nitro arginine, which is inactive as an NOS inhibitor, was without effect on chlordiazepoxide and THIP. These findings indicate that chlordiazepoxide and THIP evoke similar behavioral effects in mice in the elevated plus-maze through actions on different parts of the GABAA receptor, and that NO appears to play a key role in mediation of the behavioral effects of both chlordiazepoxide and THIP.

Altered taste function in mice deficient in the 65-kDa isoform of glutamate decarboxylase

The 65-kDa isoform of glutamate decarboxylase (GAD65) is considered to play an important role for GABA synthesis in the central nervous system. Using mice with targeted ablation of the GAD65 gene (GAD65(-/-) mice) we investigated a possible involvement of GABAergic neurotransmission in several taste functions. Preference/aversion responses to four basic tastes were not different between GAD65(-/-) and wild-type mice during a 48-h two-bottle choice test. GAD65(-/-) mice consumed less sucrose-quinine mixtures than did wild-type mice. The injection of midazolam (5 mg/kg), a benzodiazepine agonist, significantly increased the consumption of 100 mM sucrose in the wild-type mice. The same injection, however, failed to increase intake of the 100 mM sucrose in GAD65(-/-) mice. These results suggest that GAD65-generated GABA is not implicated in basic taste functions such as simple detection and discrimination. Rather, more complex processing of taste information including taste mixtures and palatability may be finely tuned by GAD65-mediated GABA synthesis.

Estragole-induced behavioural changes in rats

Croton zehntneri is a popular plant used in the Brazilian folk medicine. Recently, the use of its essential oil showed depressive activity on the central nervous system (CNS). Chemical studies show that estragole (ES) is one of the main compounds of this oil. This work seeks to evaluate the activity of ES on behaviour models of depression and anxiety, in rats. Male rats (60 days) were distributed to four groups (n = 10) and treated with 1.0, 3.0 and 10.0 microL/100 g body weight, v.o. of ES (experimental) and saline (control). Forced swimming and open-field parameters were unaffected by the ES treatment suggesting no alterations on depression behaviour. A decrease was observed in the total time of social interaction in the 10.0 microL/100 g group in relation to other groups. This group showed a reduction in the total entries frequency on the elevated plus-maze without differences to the other parameters of this test. No differences in holeboard parameters were observed suggesting no alterations in exploratory activity. These data suggest that administration of ES induced alterations in the CNS related to anxiety behaviour, expressed by the shortest total time in the social interaction model. Exposure to ES was capable of altering the motor activity in the plus-maze test. These data are antagonistic to those observed with the Croton zehntneri essential oil in these models.

Behavioral effects of type II pyrethroid cyhalothrin in rats

Synthetic pyrethroids such as cyhalothrin are extensively used in agriculture for the control of a broad range of ectoparasites in farm animals. It has been suggested that type II pyrethroids might induce anxiogenic-like effects in laboratory animals. The present study was undertaken to investigate a possible anxiogenic-like outcome of cyhalothrin in rats. Adult male rats were orally dosed for 7 days with 1.0, 3.0, or 7.0 mg/kg/day of cyhalothrin, present in a commercial formulation (Grenade Coopers do Brazil S.A.). The neurobehavioral changes induced by cyhalothrin as well as those produced on corticosterone serum levels were measured 24 h after the last treatment. Picrotoxin (1.0 mg/kg) was also acutely used as a positive control for anxiety. Results showed that cyhalothrin: (1) induced some signs and symptoms of intoxication that included salivation, tremors, and liquid feces; (2) reduced total locomotor activity in the open-field; (3) reduced the percentage of time spent in open-field central zones; (4) increased immobility time in the open-field; (5) reduced the percentage of time spent in plus-maze open arms exploration; (6) reduced the time spent in social interactions, and (7) increased the levels of serum corticosterone. The behavioral changes reported for cyhalothrin (3.0 mg/kg/day) were similar of those induced by picrotoxin. The no effect level dose obtained for cyhalothrin in this study was 1.0 mg/kg/day. These results provide experimental evidence that cyhalothrin induces anxiety-like symptoms, with this effect being dose-related. Thus, anxiety must be included among the several signs and symptoms of pesticide intoxication.

A preliminary study of baclofen-induced growth hormone release in generalised social phobia

OBJECTIVE

The authors sought to examine central GABA(B) receptor responses in patients with generalised social phobia using the growth hormone (GH) response to baclofen.

METHOD

Baclofen 20 mg was administered to 15 patients and 15 healthy matched controls and plasma growth hormone was monitored over a 3 h period.

RESULTS

The GH response in patients was significantly reduced in comparison to that of controls when calculated as both area under the curve (AUC) and delta (Delta) response.

CONCLUSIONS

The results suggest an abnormality of central GABA(B) receptor function in this disorder.

Progesterone withdrawal increases the anxiolytic actions of gaboxadol: role of alpha4betadelta GABA(A) receptors

Hippocampal alpha4betadelta GABA(A) receptors (GABA(A)-R) are increased following progesterone withdrawal (PWD) in a rodent model of premenstrual anxiety. This alpha4betadelta receptor isoform uniquely responds to the GABA agonist gaboxadol (THIP) with a maximum current greater than that gated by GABA, and is potentiated more by pentobarbital than are other GABA(A)-R. We therefore investigated the anxiolytic effects of these drugs using the elevated plus maze. Gaboxadol (1.25 mg/kg) was markedly more anxiolytic in animals undergoing PWD than in controls. Pentobarbital (10 mg/kg) also produced a greater anxiolytic effect during PWD. These results suggest that the pharmacological properties of alpha4betadelta GABA(A)-R following PWD are evident behaviorally. Alterations in the alpha4betadelta GABA(A)-R population may have implications for the etiology and treatment of premenstrual syndrome.

Medial prefrontal transection enhances social interaction. II: neurochemical studies

Medial prefrontal cortex (MPFC) transection enhances social interaction in an open arena test. Social interaction enhances dopaminergic activity in the nucleus accumbens (NAC). In the present set of experiments, microdialysis probes were implanted in the NAC, and glutamate, gamma-aminobutyric acid (GABA) and dopamine (DA) were measured during electrical stimulation of the MPFC, after coronal transection caudal to the MPFC and after a systemic injection of amphetamine in transected rats. Electrical stimulation of the MPFC caused a transient enhancement of glutamate release in the NAC, no change in GABA levels and a long lasting increase in DA levels. Medial prefrontal transection did not change basal glutamate or GABA levels in the NAC, but increased basal DA levels. Amphetamine administration decreased GABA levels in medial prefrontal transected rats, had no effect on glutamate and increased DA levels more than in controls. The experiments suggest that glutamatergic activity in the accumbens decreases dopamine release. Medial prefrontal transection reduces glutamatergic tone and enhances dopamine release, which probably decreases GABAergic activity in the NAC. Presumably, GABA inhibition in the NAC enhances social interaction.

Croton zehntneri essential oil: effects on behavioral models related to depression and anxiety

Croton zehntneri (Cz), a popular plant used to treat "nervous disturbance", contains a complex mixture of compounds, including substances exhibiting central nervous system activity. The effects of Cz essential oil administration (p.o.) on the rat's central nervous system were studied in behavioral models used to evaluate anxiety and antidepressive drugs. The results showed that administration of Cz essential oil: 1) increased the immobility duration measured in the forced swimming test as compared to control group (control = 89.8 +/- 45.8; 1 microl = 153.0 +/- 48.7; 3 microl = 157.4 +/- 45.3; 10 microl = 145.3 +/- 51.0); 2) reduced the locomotion frequency observed in the open field (control = 62.5 +/- 22.7; 3 microl = 38.0 +/- 13.5; 10 microl = 39.2 +/- 22.2); 3) had no effect on the experimental group (1 microl) observed in open field; 4) had no effect on animals tested in social interactions, plus-maze and holeboard tests. These data suggest that Cz oil produced central depressor effects in rats without any anxiety alterations. These results may explain the popular use of this plant in Brazilian folk medicine for treating "nervous disturbances".

Open field locomotion and neurotransmission in mice evaluated by principal component factor analysis-effects of housing condition, individual activity disposition and psychotropic drugs

Effects of housing condition and individual disposition on dopaminergically and GABAergically influenced open field locomotion and neurochemistry were studied in mice. Mice characterized as high active (HAM) and low active (LAM) by a running-wheel test were housed in groups or isolated for 1 day, 1 week, 3, 6, 12 or 18 weeks before an open field test was performed with saline, apomorphine (0.75 mg/kg) or diazepam (1.00 mg/kg) administration. Immediately afterwards animals were decapitated and brain sections were frozen for subsequent HPLC-analysis of dopaminergic and serotonergic transmitter metabolism. Principal component factor analysis (PCA) of locomotion variables provided three factors explaining 78.5% of total variance. Variables related to the amount of locomotion loaded highly on Factor 1 (F1-Activity), variables related to place utilization loaded highly on Factor 2 (F2-Exploration) and variables related to immobility and place preference loaded highly on Factor 3 (F3-Irritation). Apomorphine decreased F1-Activity with smaller effects in HAM and without changes in F2-Exploration and F3-Irritation independent on housing conditions. Diazepam exerted a decrease in F2-Exploration with a small increase in FI-Activity and no effects in F3-Irritation. Diazepam induced changes depended on housing conditions and were especially pronounced in isolated HAM. PCA of considerable locomotion and neurochemical data revealed interrelationships between striatal dopamine metabolism and F1-Activity, between cortical dopamine and serotonin metabolism and F2-Exploration as well as between cerebellar, hippocampal and striatal serotonin metabolism and F3-Irritation. The authors concluded that the application of PCA is a useful method to provide functionally relevant characteristics of behaviors and functionally relevant descriptions of interrrelationships between behavior and appropriate central nervous mechanisms. Furthermore the received behavioral characteristics (F1, F2, F3) of open field locomotion were sensitive to reveal housing and drug effects.

Possible anxiogenic effects of fenvalerate, a type II pyrethroid pesticide, in rats

Pyrethroids are insecticides extensively used to control pests around houses as well as in agriculture. It has been suggested that type II pyrethroids may act on GABA receptors as benzodiazepine antagonists. Because benzodiazepines are used in anxiety, the present study was undertaken to investigate the possible anxiogenic effects of fenvalerate, a type II pyrethroid, in rats. Behavior in the open-field, social interaction, plus-maze behavior, and one-way passive avoidance were studied in rats orally treated with 1, 10, or 30 mg/kg fenvalerate. This pyrethroid reduced locomotion and rearing frequencies and increased immobility duration. Ten and 30 mg/kg of fenvalerate reduced social interaction, whereas the 1 mg/kg dose had no effect on this behavior. Fenvalerate administration did not change the plus-maze behavior of rats. Pretraining administration (1, 10, and 30 mg/kg) did not modify the behavior of rats during the training session of a passive avoidance task, while in the test session 10 mg/kg fenvalerate caused an increase in the crossing latency, and the 30 mg/kg dose reduced this parameter and increased the percent of animals crossing to the shock compartment. The behavioral alterations observed in this study suggest that fenvalerate has an anxiolytic effect on rats.

Behavioral effects of diazepam in the murine plus-maze: flumazenil antagonism of enhanced head dipping but not the disinhibition of open-arm avoidance

Although it is widely believed that benzodiazepines reduce anxiety through positive allosteric modulation of the GABA(A)-chloride channel complex, this is not the only mechanism through which agents of this class can modify CNS function. Furthermore, a significant number of reports of apparent flumazenil blockade of diazepam anxiolysis in animal models have paid limited attention to possible intrinsic behavioral actions of the antagonist per se. In the present study, ethological methods were employed to assess in detail the effects of diazepam, flumazenil, and their combination on the behavior of male DBA/2 mice in the elevated plus-maze paradigm. In two experiments, diazepam (1.5 mg/kg) alone reduced open-arm avoidance and increased head dipping, whereas flumazenil (10-40 mg/kg) alone was without significant behavioral effect. However, with the sole exception of head dipping, prior administration of flumazenil (10 and 40 mg/kg) failed to block the behavioral effects of diazepam under present test conditions. These findings imply that the anxiolytic effects of diazepam in the mouse plus-maze are not mediated through flumazenil-sensitive benzodiazepine receptors and that alternate mechanisms must be considered.

Increased anxiety and altered responses to anxiolytics in mice deficient in the 65-kDa isoform of glutamic acid decarboxylase

The larger isoform of the enzyme glutamate decarboxylase, GAD67, synthesizes >90% of basal levels of gamma-aminobutyric acid (GABA) in the brain. In contrast, the smaller isoform, GAD65, has been implicated in the fine-tuning of inhibitory neurotransmission. Mice deficient in GAD65 exhibit increased anxiety-like responses in both the open field and elevated zero maze assays. Additionally, GAD65-deficient mice have a diminished response to the anxiolytics diazepam and pentobarbital, both of which interact with GABA-A receptors in a GABA-dependent fashion to facilitate GABAergic neurotransmission. Loss of GAD65-generated GABA does not appear to result in compensatory postsynaptic GABA-A receptor changes based on radioligand receptor binding studies, which revealed no change in the postsynaptic GABA-A receptor density. Furthermore, mutant and wild-type animals do not differ in their behavioral response to muscimol, which acts independently of the presence of GABA. We propose that stress-induced GABA release is impaired in GAD65-deficient mice, resulting in increased anxiety-like responses and a diminished response to the acute effects of drugs that facilitate the actions of released GABA.

Anxiety, defence and the elevated plus-maze

The elevated plus-maze test has been in use as a rodent model of anxiety for a decade, and is representative of those tests that are based upon the study of spontaneous behaviour patterns and which have high ecological validity. The origins of the test in studies of the relationship between exploration and fear are reviewed, and attention is drawn to the distinct possibility that variation in the pharmacosensitivity of the procedure may be attributable to often extreme methodological variation between laboratories. In considering further this issue, attention is also drawn to the need to collect data under constant test conditions and to provide the minimum database necessary to reach conclusions regarding the behavioural specificity of drug action. Recent research, which has extended the conventional plus-maze scoring technique to include specific behavioural acts and postures (in particular, those relating to defensive behaviour), is described. The value of such an ethological approach to the plus-maze is then exemplified with original data that demonstrate behaviourally selective, anti-anxiety effects of the GABAA receptor agonist, muscimol (0.125-1.0 mg/kg). It is concluded that, when used appropriately, the elevated plus-maze test can be a very valuable tool in drug screening and in the study of the neurobiology of anxiety and defence. More attention to behaviour and somewhat less emphasis on test simplicity and convenience would seem to be warranted.

Comparative analysis of anxiety-like behavior in partition and plus-maze tests after agonistic interactions in mice

The behavior of C57BL/6J male mice with experience of repeated victories (winners) or defeats (losers) in daily agonistic interactions, was examined in the plus-maze and partition tests. The latter procedure assesses the reactivity of mice to another conspecific in the neighboring compartment of a common cage, communicative behavior or level of sociability. The behavior of mice after 10 days (T10) and 20 days (T20) of agonistic confrontations, as well as in controls (5 days of individual housing) was analyzed. Significant differences were found between T10 and T20 losers and controls in both tests. In the partition test, a decrease in the number of approaches and total and average time spent near the partition was found in T10 and, more pronounced, in T20 losers. In the plus-maze, losers showed fewer open and total entries than controls. Moreover, rarely did they pass from one enclosed arm to another, and also showed a decreased number of 'peepings' from enclosed arms. Percentage of open time did not differ significantly in losers compared to controls. It is suggested that the level of losers' sociability, estimated as low by the partition test, can include anxiety as a component, which is confirmed, at least partly, by some parameters of the plus-maze test. There were no differences in the partition or plus-maze tests between T10 winners and controls. However, all parameters of partition behavior were significantly different between T20 winners and controls. In the plus-maze, similar to losers, T20 winners displayed fewer open arm entries, number of "peepings,' and passages than controls. It was concluded that parameters of the partition and plus-maze tests correlate in mice with the alternative experience of agonistic confrontations, positive or negative. A combination of these two tests may be used for estimation of developing anxiety in mice.

The antidepressant drug phenelzine produces antianxiety effects in the plus-maze and increases in rat brain GABA

Research on the effects of antidepressant/ antipanic drugs in animal models of anxiety has yielded equivocal results, even after chronic drug regimens. In contrast, we found that the antidepressant/antipanic drug phenelzine, given acutely, produced a clear anxiolytic effect in the elevated plus-maze, a widely-used animal model of "anxiety" that is primarily sensitive to benzodiazepine-type anxiolytics (e.g., diazepam). Furthermore, the effective dose of phenelzine (15 mg/kg) administered to rats was associated with more than a 2- fold increase in whole brain levels of gamma-aminobutyric acid (GABA), whereas an ineffective dose of phenelzine (5.1 mg/kg) did not significantly change GABA levels. The N-acetylated metabolite of phenelzine, N2-acetylphenelzine, produced neither an anxiolytic effect in the elevated plus-maze nor a significant change in whole-brain levels of GABA. However, both phenelzine and N2-acetylphenelzine potently inhibited monoamine oxidase, a mechanism commonly thought to be involved in the therapeutic effects of monoamine oxidase inhibitors such as phenelzine in the treatment of depression in humans. These results suggest that the mechanism whereby phenelzine produces anxiolytic effects in the plus-maze model is unique to a facilitatory action on brain levels of GABA, in contrast to classical benzodiazepines, which produce anxiolytic effects by enhancing the affinity of the GABAA-receptor for GABA.

Social isolation increases aggressive behaviour and alters the effects of diazepam in the rat social interaction test

Isolation rearing in the early stages of life has been shown to modify a variety of behaviours in many animals and the responsitivity to psychotropic drugs. The aims of the present study were to investigate the effects of isolation rearing on anxiety using the social interaction paradigm and to compare the effects of diazepam on social interaction behaviours in isolation and socially reared rats. Male Lister hooded rats were reared from weaning either alone (isolation reared) or in groups of four (socially reared) for 6 weeks and then were tested for social interaction. Both isolation and socially reared rats were exposed to the social interaction test either without drug treatment or following saline or diazepam (1 and 2.5 mg/kg, i.p., 30 min before testing). The results demonstrate that under high light in an unfamiliar arena, the isolation compared to the socially reared rats showed a significantly (P < 0.01) higher level of social interaction, manifested as increases in aggressive and avoidance behaviours, and that this interaction occur for a greater length of time during the test period (10 min). However, when the light level was decreased or when the arena was familiar, active social interaction of isolation reared rats decreased but increased in the socially reared rats. In both conditions the isolation reared rats displayed more aggressive behaviours, in particular biting and boxing the partners which did not occur with the socially reared rats. Pretreatment of diazepam (1 and 2.5 mg/kg., i.p.) caused a dose-related reduction in aggressive behaviours in rats reared under both conditions but increased passive interactions in the socially reared rats. In contrast diazepam (2.5 mg/kg) reduced active interaction in the isolation reared rats but had no effect on passive interaction. These results indicate that isolation rearing increases aggressive behaviours and alters the effects of diazepam.

Effects of valproate and lorazepam on experimental anxiety: tolerance, withdrawal, and role of clonidine

The anxiolytic-like effects tolerance and withdrawal from chronic treatment with sodium valproate [200, 300, and 400 mg/kg, intraperitoneally (i.p.)] were compared with those of a known anxiolytic drug, lorazepam (0.025, 0.05, and 0.10 mg/kg, i.p.), in the light-dark aversion test in mice. Furthermore, we investigated whether acute treatment with clonidine, 0.03 mg/kg i.p., an alpha 2-adrenoceptor agonist, could reduce the increased anxiety on withdrawal from chronic treatment. Mice were given 14 daily i.p. injections of valproate, lorazepam, or vehicle and were tested in the light-dark aversion test 30 min or 24 or 48 h after the last drug or vehicle administration. Results showed that both acute and chronic valproate treatment reduced the aversion of mice for the light area, as well as increased the number of transitions, thus indicating an anxiolytic-like potential. Furthermore, in contrast to lorazepam, tolerance to the anxiolytic-like effects of valproate did not occur, and withdrawal from chronic treatment (300 mg/kg, i.p.) in our behavioral paradigm was not associated with any behavioral disturbances referring to an increased anxiety state. Finally, low doses of clonidine (0.03 mg/kg, i.p.) were shown to have anxiolytic properties and to reverse the anxiogenic effects of lorazepam on withdrawal.