Experimental anxiety and antidepressant drugs: the effects of moclobemide, a selective reversible MAO-A inhibitor, fluoxetine and imipramine in mice

The hole-board apparatus in the study of anxiety

Anxiety disorders pose a significant challenge in contemporary society, and their impact in terms of social and economic burden is overwhelming. Behavioral research conducted on animal subjects is crucial for comprehending these disorders and, from a translational standpoint, for introducing innovative therapeutic approaches. In this context, the Hole-Board apparatus has emerged as a widely utilized test for studying anxiety-related behaviors in rodents. Although a substantial body of literature underscores the utility and reliability of the Hole-Board in anxiety research, recent decades have witnessed a range of studies that have led to uncertainties and misinterpretations regarding the validity of this behavioral assay. The objective of this review is twofold: firstly, to underscore the utility and reliability of the Hole-Board assay, and concurrently, to examine the underlying factors contributing to potential misconceptions surrounding its utilization in the study of anxiety and anxiety-related behaviors. We will present results from both conventional quantitative analyses and multivariate approaches, while referencing a comprehensive collection of studies conducted using the Hole-Board.

Sex-specific behavioral, neurobiological, and cardiovascular responses to chronic social stress in mice

Psychosocial stress promotes and links mood and cardiovascular disorders in a sex-specific manner. However, findings in animal models are equivocal, in some cases opposing human dimorphisms. We examined central nervous system (CNS), behavioral, endocrine, cardiac, and hepatic outcomes in male or female C57Bl/6 mice subjected to chronic social stress (56 days of social isolation, with intermittent social confrontation encounters twice daily throughout the final 20 days). Females exhibited distinct physiological and behavioral changes, including relative weight loss, and increases in coronary resistance, hepatic inflammation, and thigmotaxic behavior in the open field. Males evidence reductions in coronary resistance and cardiac ischemic tolerance, with increased circulating and hippocampal monoamine levels and emerging anhedonia. Shared CNS gene responses include reduced hippocampal Maoa and increased Htr1b expression, while unique responses include repression of hypothalamic Ntrk1 and upregulation of cortical Nrf2 and Htr1b in females; and repression of hippocampal Drd1 and hypothalamic Gabra1 and Oprm in males. Declining cardiac stress resistance in males was associated with repression of cardiac leptin levels and metabolic, mitochondrial biogenesis, and anti-inflammatory gene expression. These integrated data reveal distinct biological responses to social stress in males and females, and collectively evidence greater biological disruption or allostatic load in females (consistent with propensities to stress-related mood and cardiovascular disorders in humans). Distinct stress biology, and molecular to organ responses, emphasize the importance of sex-specific mechanisms and potential approaches to stress-dependent disease.

Lithium potentiated, pyridoxine abolished and fluoxetine attenuated the anxiolytic effect of diazepam in mice

In the present study, the anxiolytic effect of diazepam (1 and 2 mg/kg, i.p.) was determined alone and in combination with lithium (50 mg/kg, i.p.), pyridoxine (90 mg/kg, i.p.) and fluoxetine (10 mg/kg, i.p.) using elevated plus maze (EPM) and light/dark box (LDB) tests in experimental mice. The effect of various treatments on the brain GABA levels and glutamic acid decarboxylase (GAD) expression were also determined. The results obtained suggested that the diazepam (2 mg/kg, i.p.) exerted anxiolytic effect and significantly increased the brain GABA levels and GAD expression as compared to control group. Fluoxetine (10 mg/kg, i.p.) exerted anxiogenic effects, but did not affect the brain GABA levels and GAD activity significantly as compared to control. Pretreatments of pyridoxine (90 mg/kg, i.p.) abolished; lithium (50 mg/kg, i.p.) potentiated while fluoxetine (10 mg/kg, i.p.) attenuated the anxiolytic and neurochemical effects of diazepam (1 and 2 mg/kg, i.p.) treatment in mice. Therefore, the combined treatment of lithium and diazepam might be a promising treatment for anxiety.

Effects of acute or repeated paroxetine and fluoxetine treatment on affective behavior in male and female adolescent rats

RATIONALE

The SSRI antidepressant fluoxetine is one of the few drugs that is effective at treating depression in adolescent humans. In contrast, the SSRI paroxetine has limited efficacy and is more at risk for inducing suicidal behavior.

OBJECTIVE

The purpose of the present study was to more fully characterize the differential actions of paroxetine and fluoxetine.

METHODS

In experiment 1, male and female rats were injected with paroxetine (2.5 or 10 mg/kg), fluoxetine (10 mg/kg), or vehicle for 10 days starting on postnatal day (PD) 35, and affective behaviors were assessed using sucrose preference and elevated plus maze tasks. A separate set of rats were used to examine monoamine levels. In experiment 2, rats were injected with paroxetine (2.5, 5, or 10 mg/kg), fluoxetine (5, 10, or 20 mg/kg), or vehicle during the same time frame as experiment 1, and anxiety-like behaviors were measured using elevated plus maze, light/dark box, and acoustic startle.

RESULTS

Repeated SSRI treatment failed to alter sucrose preference, although both paroxetine and fluoxetine reduced time spent in the open arms of the elevated plus maze and light compartment of the light/dark box. Paroxetine, but not fluoxetine, enhanced acoustic startle and interfered with habituation. Serotonin turnover was decreased by both acute and repeated fluoxetine treatment but unaltered by paroxetine administration.

DISCUSSION

These results show that repeated treatment with paroxetine and fluoxetine has dissociable actions in adolescent rats. In particular, paroxetine, but not fluoxetine, increases acoustic startle at low doses and may increase sensitivity to environmental stressors.

A new furofuran lignan diglycoside and other secondary metabolites from the antidepressant extract of Castilleja tenuiflora Benth

Castilleja tenuiflora has been used for the treatment of several Central Nervous System (CNS) diseases. Herein we report the antidepressant activity of the methanol extract from the leaves of this medicinal plant. The oral administration of MeOH extract (500 mg/kg) induced a significant (p < 0.05) decrement of the immobility parameter on Forced Swimming Test (FST) and an increment in the latency and duration of the hypnosis, induced by administration of sodium pentobarbital (Pbi, 40 mg/kg, i.p.). Chemical analysis of this antidepressant extract allowed the isolation of (+)-piperitol-4-O-xylopyranosyl-(1→6)-O-glucopyranoside. This new furofuran lignan diglycoside was named tenuifloroside (1) and its complete chemical structure elucidation on the basis of 1D and 2D NMR spectra analysis of the natural compound 1 and its peracetylated derivative 1a is described. This compound was found together with two flavones—apigenin and luteolin 5-methyl ether—a phenylethanoid—verbascoside—and three iridoids—geniposide, caryoptoside and aucubin. All these compounds were purified by successive normal and reverse phase column chromatography. Tenuifloroside, caryoptoside and luteolin 5-methyl ether were isolated from Castilleja genus for the first time. These findings demonstrate that C. tenuiflora methanol extract has beneficial effect on depressive behaviors, and the knowledge of its chemical constitution allows us to propose a new standardized treatment for future investigations of this species in depressive illness.

Monoamine Oxidase A is Required for Rapid Dendritic Remodeling in Response to Stress

BACKGROUND

Acute stress triggers transient alterations in the synaptic release and metabolism of brain monoamine neurotransmitters. These rapid changes are essential to activate neuroplastic processes aimed at the appraisal of the stressor and enactment of commensurate defensive behaviors. Threat evaluation has been recently associated with the dendritic morphology of pyramidal cells in the orbitofrontal cortex (OFC) and basolateral amygdala (BLA); thus, we examined the rapid effects of restraint stress on anxiety-like behavior and dendritic morphology in the BLA and OFC of mice. Furthermore, we tested whether these processes may be affected by deficiency of monoamine oxidase A (MAO-A), the primary enzyme catalyzing monoamine metabolism.

METHODS

Following a short-term (1-4h) restraint schedule, MAO-A knockout (KO) and wild-type (WT) mice were sacrificed, and histological analyses of dendrites in pyramidal neurons of the BLA and OFC of the animals were performed. Anxiety-like behaviors were examined in a separate cohort of animals subjected to the same experimental conditions.

RESULTS

In WT mice, short-term restraint stress significantly enhanced anxiety-like responses, as well as a time-dependent proliferation of apical (but not basilar) dendrites of the OFC neurons; conversely, a retraction in BLA dendrites was observed. None of these behavioral and morphological changes were observed in MAO-A KO mice.

CONCLUSIONS

These findings suggest that acute stress induces anxiety-like responses by affecting rapid dendritic remodeling in the pyramidal cells of OFC and BLA; furthermore, our data show that MAO-A and monoamine metabolism are required for these phenomena.

Antidepressant-like effect of Ilex paraguariensis in rats

In this study, we investigated the possible antidepressant-like effect of I. paraguariensis in rats. Rats were treated for four weeks with an aqueous extract of I. paraguariensis in drinking water, following the traditional preparation of this beverage. After the period of treatment, behavioral (elevated plus-maze, open field test, and forced swimming test) and biochemical parameters (lipid peroxidation assay, thiol content, vitamin C levels, and monoamine oxidase activity) were evaluated. Animals were also analyzed on forced swimming test after 24 hours of I. paraguariensis intake. An additional group was injected with selegiline 24 hours and 30 minutes before forced swimming test as positive control. HPLC analysis revealed the profile of I. paraguariensis extract. I. paraguariensis reduced the immobility time on forced swimming test without significant changes in locomotor activity in the open field test. Any anxiolytic/anxiogenic effect of I. paraguariensis was observed in rats through the elevated plus-maze test. The antidepressant-like effect of I. paraguariensis was not accompanied by inhibitory effect on monoamine oxidase activity. There were no significant alterations on lipid peroxidation, thiol content, and vitamin C levels among the groups. In conclusion, aqueous extract of I. paraguariensis decreases the time of immobility in rats suggesting an antidepressant-like effect.

Inactivation of glucocorticoid receptor in noradrenergic system influences anxiety- and depressive-like behavior in mice

The aim of this study was to investigate whether conditional inactivation of the glucocorticoid receptors (GRs) in noradrenergic neurons affects animal behavior in mice. Selective ablation of GRs in the noradrenergic system was achieved using the Cre/loxP approach. We crossed transgenic mice expressing the Cre recombinase under the dopamine beta-hydroxylase (DBH) promoter with animals harboring the floxed GR gene. The resulting GR(DBHCre) mutant mice exhibited no alterations in terms of normal cage behavior, weight gain, spatial memory or spontaneous locomotor activity, regardless of gender. To assess depressive- and anxiety-like behaviors we performed the Tail Suspension Test and the Light-Dark Box Test. While male mutant animals did not show any alternations in both tests, female GR(DBHCre) mutants displayed depressive- and anxiety-like behavior. Additionally, male GR(DBHCre) mice were exposed to chronic restraint stress but still exhibited immobility times and anxiety statuses similar to those of non-stressed animals while stressed control mice clearly revealed depressive- and anxiety-like phenotype. Thus, in males the effects of the mutation were precipitated only after chronic restraint stress procedure. Our data reveal a possible gender-dependent role of GRs in the noradrenergic system in anxiety- and depressive-like behavior in mice.

The potential antidepressant-like effect of imidazoline I2 ligand 2-BFI in mice

The compound 2-(2-benzofuranyl)-2-imidazoline (2-BFI) is a 2-imidazoline derivative that selectively inhibits the in vitro activity of monoamine oxidase-A and it is also an imidazoline I(2) agonist. However, the antidepressant potential of this compound and its mechanism of action have not been well defined. Therefore, in this study we investigated the antidepressant-like effect of 2-BFI in mice. 2-BFI (100 and 300μmol/kg, s.c.) significantly reduced the immobility time on the tail suspension test (TST) without changing locomotion in the open field test. The reduced the immobility time of 2-BFI (100μmol/kg, s.c.) was confirmed with the forced swimming test (FST). The antidepressant-like effect of 2-BFI (100μmol/kg, s.c.) in the TST was prevented by pretreatment with idazoxan (0.4μmol/kg, i.p., a I(2) site antagonist), methysergide (4μmol/kg, i.p., a non-selective serotonergic receptor antagonist) and haloperidol (0.1μmol/kg, i.p., a non-selective dopaminergic receptor antagonist). The anxiolytic effect of 2-BFI was also evaluated, using the elevated plus-maze test. 2-BFI (300μmol/kg, s.c.) was able to significantly increase the % of number of entries and the % of time spent in the open arms, indicating that it possesses an anxiolytic effect at high doses. In conclusion, these results suggest that the antidepressant-like effect of 2-BFI might involve serotonergic, dopaminergic and imidazoline systems, and then the imidazoline site could represent a new pharmacological target for the treatment of depression.

Modeling anxiety using adult zebrafish: a conceptual review

Zebrafish (Danio rerio) are rapidly emerging as a useful animal model in neurobehavioral research. Mounting evidence shows the suitability of zebrafish to model various aspects of anxiety-related states. Here, we evaluate established and novel approaches to uncover the molecular substrates, genetic pathways and neural circuits of anxiety using adult zebrafish. Experimental approaches to modeling anxiety in zebrafish include novelty-based paradigms, pharmacological and genetic manipulations, as well as innovative video-tracking, 3D-reconstructions, bioinformatics-based searchable databases and omics-based tools. Complementing traditional rodent models of anxiety, we provide a conceptual framework for the wider application of zebrafish and other aquatic models in anxiety research. This article is part of a Special Issue entitled 'Anxiety and Depression'.

The age of anxiety: role of animal models of anxiolytic action in drug discovery

Anxiety disorders are common, serious and a growing health problem worldwide. However, the causative factors, aetiology and underlying mechanisms of anxiety disorders, as for most psychiatric disorders, remain relatively poorly understood. Animal models are an important aid in giving insight into the aetiology, neurobiology and, ultimately, the therapy of human anxiety disorders. The approach, however, is challenged with a number of complexities. In particular, the heterogeneous nature of anxiety disorders in humans coupled with the associated multifaceted and descriptive diagnostic criteria, creates challenges in both animal modelling and in clinical research. In this paper, we describe some of the more widely used approaches for assessing the anxiolytic activity of known and potential therapeutic agents. These include ethological, conflict-based, hyponeophagia, vocalization-based, physiological and cognitive-based paradigms. Developments in the characterization of translational models are also summarized, as are the challenges facing researchers in their drug discovery efforts in developing new anxiolytic drugs, not least the ever-shifting clinical conceptualization of anxiety disorders. In conclusion, to date, although animal models of anxiety have relatively good validity, anxiolytic drugs with novel mechanisms have been slow to emerge. It is clear that a better alignment of the interactions between basic and clinical scientists is needed if this is to change.

Pharmacological modulation of anxiety-like phenotypes in adult zebrafish behavioral models

Zebrafish (Danio rerio) are becoming increasingly popular in neurobehavioral research. Here, we summarize recent data on behavioral responses of adult zebrafish to a wide spectrum of putative anxiolytic and anxiogenic agents. Using the novel tank test as a sensitive and efficient behavioral assay, zebrafish anxiety-like behavior can be bi-directionally modulated by drugs affecting the gamma-aminobutyric acid, monoaminergic, cholinergic, glutamatergic and opioidergic systems. Complementing human and rodent data, zebrafish drug-evoked phenotypes obtained in this test support this species as a useful model for neurobehavioral and psychopharmacological research.

Strain-specific battery of tests for domains of mania: effects of valproate, lithium and imipramine

The lack of efficient animal models for bipolar disorder (BPD), especially for the manic pole, is a major factor hindering the research of its pathophysiology and the development of improved drug treatments. The present study was designed to identify an appropriate mouse strain for modeling some behavioral domains of mania and to evaluate the effects of drugs using this strain. The study compared the behavior of four strains: Black Swiss, C57Bl/6, CBA/J and A/J mice in a battery of tests that included spontaneous activity; sweet solution preference; light/dark box; resident-intruder; forced-swim and amphetamine-induced hyperactivity. Based on the 'manic-like' behavior demonstrated by the Black Swiss strain, the study evaluated the effects of the mood stabilizers valproate and lithium and of the antidepressant imipramine in the same tests using this strain. Results indicated that lithium and valproate attenuate the 'manic-like' behavior of Black Swiss mice whereas imipramine had no effects. These findings suggest that Black Swiss mice might be a good choice for modeling several domains of mania and distinguishing the effects of drugs on these specific domains. However, the relevance of the behavioral phenotype of Black Swiss mice to the biology of BPD is unknown at this time and future studies will investigate molecular differences between Black Swiss mice and other strains and asess the interaction between strain and mood stabilizing treatment.

Direct and indirect 5-HT receptor agonists produce gender-specific effects on locomotor and vertical activities in C57 BL/6J mice

It is well established that the dopamine (DA) and serotonin (5-HT) systems have extensive and complex interactions. However, the effects of specific 5-HT receptor agonists on traditionally DA-related behaviors remain unclear. Our goal in these studies was to characterize the effects of 5-HT receptor agonists on measures of locomotor activity and vertical rearing. The SSRIs fluoxetine and citalopram produced significant decreases in locomotor activity and vertical rearing at the highest doses used with females significantly more sensitive to citalopram. The 5-HT(1A) agonist 8-OH-DPAT and the 5-HT(2C) agonist MK 212 significantly decreased activity in both male and female mice, with females more sensitive to 8-OH-DPAT. In contrast, the 5-HT(1B) agonist RU 24969 and the 5-HT(2A) agonist DOI both increased activity, with DOI exhibiting differential effects with regard to sex. Finally, the 5-HT(3) agonist SR 57227 produced significant locomotor increases only in female mice at the lowest dose. The results of these experiments define locomotor profiles of several 5-HT agonists in male and female C57BL/6J mice, providing a foundation for further explorations of 5-HT receptor effects on activity.

Phosphodiesterase 10A inhibition is associated with locomotor and cognitive deficits and increased anxiety in mice

Phosphodiesterase 10A (PDE10A) mRNA and protein levels decline in the striatum of R6/1 and R6/2 Huntington's disease (HD) mice prior to motor symptom development. In human HD, PDE10A protein levels are significantly decreased in the caudate-putamen of patients with grade 3 HD compared to age-matched controls. To test whether the loss of PDE10A activity in the striatum was detrimental to normal brain function, we treated wild-type (WT) mice with chronic administration of papaverine, which is a specific inhibitor of PDE10A. At 7 weeks of age, mice were introduced to a weekly battery of motor tests, including assessment of weight, locomotion, gait, and coordination. Beginning at 8 weeks of age, mice received 0, 5, 10 or 20 mg/kg papaverine once daily until the completion of behavioral testing. Following 14 days of papaverine injections, mice were assessed for deficits in cognitive performance as measured in the Morris water maze (MWM). All behavioral tests occurred either immediately prior to or 30 min following a subcutaneous papaverine challenge dose. Twenty-four hours following completion of the 2-3 week MWM protocol, mice were given a dose of papaverine and 30 min later psychological function assessed in the Light-Dark (LD) Test. Chronic administration of papaverine for 42 days was associated with distinct motor perturbations, mild cognitive disturbance and anxiety-like behaviors. Subsequently, we assessed the effect of 14 days papaverine (i.e. sub-chronic) treatment on psychological function of WT and R6/1 HD mice. While sub-chronic papaverine induced anxiety-like behavior in WT mice, it appeared to have little effect on the behavior of R6/1 HD mice. Finally, a separate group of 6-week old WT and R6/2 HD mice were treated for 21 days with saline or 10 mg/kg fluoxetine, an agent with anxiolytic and anti-depressant effects, in order to compare the effects of papaverine and fluoxetine on anxiety-like behavior in the LD test. CREB and PDE10A protein levels in striatum and hippocampus were determined by western blot. While papaverine treatment reduced CREB protein levels in the hippocampus and striatum, fluoxetine increased CREB in the hippocampus. These data suggest that papaverine and fluoxetine may produce quite different effects on behavior; these behaviors may be linked to CREB expression in brain regions associated with motor and cognitive functions. PDE10A protein levels were decreased by both papaverine and fluoxetine. Chronic PDE10A inhibition produced a variety of behavioral and central neurochemical deficits and these effects were exacerbated by stress. The unique localization of PDE10A and its apparent role in basal ganglia function may underlie its role in psychiatric and neurological disorders involving the basal ganglia.

Addictive and non-addictive drugs induce distinct and specific patterns of ERK activation in mouse brain

A major goal of research on addiction is to identify the molecular mechanisms of long-lasting behavioural alterations induced by drugs of abuse. Cocaine and delta-9-tetrahydrocannabinol (THC) activate extracellular signal-regulated kinase (ERK) in the striatum and blockade of the ERK pathway prevents establishment of conditioned place preference to these drugs. However, it is not known whether activation of ERK in the striatum is specific for these two drugs and/or this brain region. We studied the appearance of phospho-ERK immunoreactive neurons in CD-1 mouse brain following acute administration of drugs commonly abused by humans, cocaine, morphine, nicotine and THC, or of other psychoactive compounds including caffeine, scopolamine, antidepressants and antipsychotics. Each drug generated a distinct regional pattern of ERK activation. All drugs of abuse increased ERK phosphorylation in nucleus accumbens, lateral bed nucleus of the stria terminalis, central amygdala and deep layers of prefrontal cortex, through a dopamine D1 receptor-dependent mechanism. Although some non-addictive drugs moderately activated ERK in a few of these areas, they never induced this combined pattern of strong activation. Antidepressants and caffeine activated ERK in hippocampus and cerebral cortex. Typical antipsychotics mildly activated ERK in dorsal striatum and superficial prefrontal cortex, whereas clozapine had no effect in the striatum, but more widespread effects in cortex and amygdala. Our results outline a subset of structures in which ERK activation might specifically contribute to the long-term effects of drugs of abuse, and suggest mapping ERK activation in brain as a way to identify potential sites of action of psychoactive drugs.

The open field as a paradigm to measure the effects of drugs on anxiety-like behaviors: a review

The open field is a very popular animal model of anxiety-like behavior. An overview of the literature on the action elicited by effective or putative anxiolytics in animal subjected to this procedure indicates that classical treatments such as benzodiazepine receptor full agonists or 5-HT(1A) receptor full or partial agonists elicit an anxiolytic-like effect in this procedure in most cases (approximately 2/3). However, compounds (triazolobenzodiazepines such as adinazolam and alprazolam, selective serotonin reuptake inhibitors) that have a different spectrum of therapeutic efficacy in anxiety disorders such as panic attacks, generalized anxiety disorder or obsessive-compulsive disorder were poorly effective as anxiolytics in the open field test, suggesting that this paradigm may not model features of anxiety disorders. The procedure is also relevant for the study of compounds endowed with anxiogenic effects, as such effects were detected after treatments with benzodiazepine receptor inverse agonists or with corticotropin releasing factor (CRF) receptor agonists.

Induction of hyperlocomotion in mice exposed to a novel environment by inhibition of serotonin reuptake. A pharmacological characterization of diverse classes of antidepressant agents

This study characterized the influence of acute administration of diverse classes of antidepressant agent upon the spontaneous locomotor activity (LA) of mice in a novel, open-field environment. The selective serotonin (5-HT) reuptake inhibitors (SSRIs), citalopram, fluoxetine, paroxetine, fluvoxamine, litoxetine and zimelidine, dose-dependently enhanced LA. Their actions were mimicked by the mixed 5-HT/noradrenaline (NA) reuptake inhibitors (SNRIs), venlafaxine, duloxetine and S33005. In contrast, clomipramine only slightly elevated LA and two further tricyclics, imipramine and amitriptyline, were inactive. Further, the selective NA vs. 5-HT reuptake inhibitors (NARIs), reboxetine, desipramine, maprotiline, nisoxetine and nortriptyline all failed to increase LA. The "atypical antidepressants," mianserin and mirtazapine, neither of which modify 5-HT reuptake, as well as the mixed SSRI/5-HT(2) antagonists, nefazodone and trazodone, also failed to increase LA. Doses of SSRI and SNRI which increased LA did not modify motor performance in the rotarod test. Further, they did not enhance LA in rats, suggesting that this response is characteristic of mice. Finally, upon prehabituation of mice to the activity chamber, the SSRI, citalopram, and the SNRI, venlafaxine, failed to increase LA. In conclusion, in mice exposed to a novel environment, inhibition of 5-HT reuptake by SSRIs and SNRIs enhances spontaneous LA in the absence of a generalized influence upon motor function. This response provides a simple parameter for characterization of SSRIs and SNRIs, and differentiates them from other classes of antidepressant agent. Although an influence upon arousal and/or anxiety is likely related to the increase in LA, the functional significance of this response requires additional elucidation.

The alpha(2a)-adrenergic receptor plays a protective role in mouse behavioral models of depression and anxiety

The noradrenergic system is involved in the regulation of many physiological and psychological processes, including the modulation of mood. The alpha(2)-adrenergic receptors (alpha(2)-ARs) modulate norepinephrine release, as well as the release of serotonin and other neurotransmitters, and are therefore potential targets for antidepressant and anxiolytic drug development. The current studies were undertaken to examine the role of the alpha(2A) subtype of alpha(2)-AR in mouse behavioral models of depression and anxiety. We have observed that the genetic knock-out of the alpha(2A)-AR makes mice less active in a modified version of Porsolt's forced swim test and insensitive to the antidepressant effects of the tricyclic drug imipramine in this paradigm. Furthermore, alpha(2A)-AR knock-out mice appear more anxious than wild-type C57 Bl/6 mice in the rearing and light-dark models of anxiety after injection stress. These findings suggest that the alpha(2A)-AR may play a protective role in some forms of depression and anxiety and that the antidepressant effects of imipramine may be mediated by the alpha(2A)-AR.

Acute trazodone and quipazine treatment attenuates apomorphine-induced aggressive behaviour in male rats without major impact on emotional behaviour or monoamine content post mortem

We have studied the effect of acute trazodone (3--20 mg kg(-1)) and quipazine (1--3 mg kg(-1)) treatment on the apomorphine-induced (1 mg kg(-1), once daily over 2 weeks) aggressive behaviour in male Wistar rats. All doses of trazodone and quipazine tested attenuated the aggressiveness as evidenced by the abolished intensity of aggressive behaviour and increased time of latency before the first attack. The acute trazodone (3--10 mg kg(-1)) or quipazine (1--3 mg kg(-1)) treatment had no or only a minor effect on rat behaviour in the elevated plus-maze, open field, and forced swimming test. Concomitant apomorphine (1 mg kg(-1)) plus trazodone (3 mg kg(-1)), but not apomorphine (1 mg kg(-1)) plus quipazine (1 mg kg(-1)), treatment slowed the development of aggressive behaviour. Repeated apomorphine treatment moderately reduced the dopamine post mortem and increased the DOPAC and HVA contents in striatum. Other monoamines or their metabolites were unchanged. Neither trazodone and quipazine treatment nor forced swimming stress induced any changes in the monoamine contents. In conclusion, our results indicate that acute trazodone and quipazine treatment attenuates the apomorphine-induced aggressive behaviour in male rats, but this phenomenon cannot be implicated in the changes in emotional and motivational behaviour, or in changes of monoamine content post mortem.

Flibanserin has anxiolytic effects without locomotor side effects in the infant rat ultrasonic vocalization model of anxiety

This study compared the effects of flibanserin, a novel 5-HT(1A) agonist/5-HT(2A) antagonist; diazepam, a traditional anxiolytic; and imipramine, a traditional antidepressant, on separation-induced ultrasonic vocalizations (USVs), locomotor behaviour, negative geotaxis and body temperature of 7 - 8-day-old rat pups. Flibanserin (5, 10, 25 and 50 mg kg(-1) s.c.) reduced USVs but had no effects on locomotor behaviour or negative geotaxis. Lower doses of flibanserin (0.5, 1, 2 and 4 mg kg(-1) s.c.) had no effect on any behaviour. Diazepam (0.25, 0.5, 1 and 2 mg kg(-1) s.c.) not only reduced the USVs but also increased rolling and increased the latency of the negative geotaxic response. Imipramine (10, 15, 20 and 30 mg kg(-1) s.c.) reduced USVs, increased total locomotor activity and rolling but had no effect on negative geotaxis. None of the drugs altered body temperature. Our data showed that flibanserin is as effective in reducing the USVs as diazepam and imipramine but has a lower incidence of motor side effects. This suggests that flibanserin might be effective for the treatment of mood disturbances such as anxiety.

The anxiolytic-like properties of two selective MAOIs, moclobemide and selegiline, in a standard and an enhanced light/dark aversion test

The present study was designed to investigate the putative anxiolytic effects of moclobemide (MOC), a reversible inhibitor of type A monoamine oxidase enzyme (RIMA) antidepressant, in an experimental model of anxiety in mice. The test selected was the light/dark aversion test. In the present investigation, an anxiogenic-like behavior was induced by light, alone as the stimulus (standard version of the test) or by pretreatment with a subconvulsant dose of pentylenetetrazole (PTZ) (15 mg/kg IP) 45 min before testing ("enhanced" version of the test). In mice, the effect of repeated administration for 2 weeks of MOC (0.5, 1, and 5 mg/kg IP) was compared with those of selegiline (SEL) (5, 10, and 20 mg/kg IP), an irreversible and selective MAO-B inhibitor. For comparative purpose, the chronic effect of an established reference anxiolytic, such as lorazepam (LOR) (0.025, 0.05, and 0.10 mg/kg IP), was also evaluated. Results demonstrated that PTZ-treated mice showed a decrease in the number of transitions as well as in the time spent in the lit area, when compared with vehicle controls, an effect characteristic of an anxiogenic response. This anxiogenic-like behavior was reduced by chronic administration of LOR as well as MOC, suggesting an anxiolytic-like effect (as shown in the "standard" version of the test). In addition, the increased aversion of mice for the light compartment of the light/dark box was significantly reduced compared to PTZ-treated mice or vehicle controls. SEL failed to significantly alter the anxiogenic-like behavior induced by subconvulsant doses of PTZ. These data provide additional evidence for the anxiolytic-like effects of MOC administered chronically in the mouse.