Ethopharmacological analysis of the effects of putative 'anxiogenic' agents in the mouse elevated plus-maze

Pharmacology of the beta-carboline FG-7,142, a partial inverse agonist at the benzodiazepine allosteric site of the GABA A receptor: neurochemical, neurophysiological, and behavioral effects

Given the well-established role of benzodiazepines in treating anxiety disorders, beta-carbolines, spanning a spectrum from full agonists to full inverse agonists at the benzodiazepine allosteric site for the GABA(A) receptor, can provide valuable insight into the neural mechanisms underlying anxiety-related physiology and behavior. FG-7,142 is a partial inverse agonist at the benzodiazepine allosteric site with its highest affinity for the alpha1 subunit-containing GABA(A) receptor, although it is not selective. FG-7,142 also has its highest efficacy for modulation of GABA-induced chloride flux mediated at the alpha1 subunit-containing GABA(A) receptor. FG-7,142 activates a recognized anxiety-related neural network and interacts with serotonergic, dopaminergic, cholinergic, and noradrenergic modulatory systems within that network. FG-7,142 has been shown to induce anxiety-related behavioral and physiological responses in a variety of experimental paradigms across numerous mammalian and non-mammalian species, including humans. FG-7,142 has proconflict actions across anxiety-related behavioral paradigms, modulates attentional processes, and increases cardioacceleratory sympathetic reactivity and neuroendocrine reactivity. Both acute and chronic FG-7,142 treatment are proconvulsive, upregulate cortical adrenoreceptors, decrease subsequent actions of GABA and beta-carboline agonists, and increase the effectiveness of subsequent GABA(A) receptor antagonists and beta-carboline inverse agonists. FG-7,142, as a partial inverse agonist, can help to elucidate individual components of full agonism of benzodiazepine binding sites and may serve to identify the specific GABA(A) receptor subtypes involved in specific behavioral and physiological responses.

Voluntary oral nicotine intake in mice down-regulates GluR2 but does not modulate depression-like behaviors

Repeated exposure to nicotine induces adaptive changes in the central nervous system including the mesolimbic dopamine (DA) projections from the ventral tegmental area (VTA) to the nucleus accumbens (NAc). These modifications can modulate nicotine reward and reinforcement, but also anxiety and depression-related behaviors. The development of addiction-related phenotypes is known to be modulated by regulation of glutamate receptors, as well as activation of transcription factors including cAMP response element-binding protein (CREB), in the NAc. We investigated the effects of nicotine pre-exposure on nicotine preference and levels of GluR1/2 and CREB in the mesolimbic system in male mice C57BL/6J and BALB/c inbred mice. We also evaluated locomotor activity, anxiety-like and depression-like behaviors known to be affected by nicotine. There were few behavioral changes in mice subjected to chronic nicotine exposure, but there was a marked regulation of GluR2 in the mesolimbic system. Both treated and non-treated animals showed a significant preference for nicotine when facing a choice with a control solution. These results suggest that voluntary nicotine drinking induces nicotine preference in mice, but does not alter a number of affective behaviors. In addition, alterations in CREB and GluR1 levels are not sufficient to explain preference for nicotine in a 2-bottle choice paradigm.

Behavioral effects of 6-bromoflavanone and 5-methoxy-6,8-dibromoflavanone as anxiolytic compounds

Benzodiazepines (BDZs) are the most used psychoactive drugs in the pharmacotherapy of anxiety. A large number of structurally different classes of ligands are also active in the modulation of anxiety, showing high affinity for the benzodiazepine binding site (BDZ-bs) of the GABA (A) receptor complex. Various synthetic derivatives of natural flavonoids have been found to have very potent anxiolytic properties. This study was undertaken to provide a behavioral characterization of two novels halogenated flavonoids, 5-methoxy-6, 8-dibromoflavanone (FV1), and 6-bromoflavanone (FV2). These compounds were tested and compared to diazepam (0.5 mg/kg) and to the natural flavonoid chrysin (1 mg/kg) as a standard of activity. When injected in mice (0.5, 1 mg/kg i.p) both synthetic flavonoids increased the locomotor activity and the exploratory skills of the animals, as measured in the open-field and in the hole-board tests. Both compounds, indeed, had a clear anxiolytic activity in the elevated plus-maze, as measured by an increased number of entries and the percentage of time spent in the open arms. At the tested doses, both compounds did not induce sedative action or compulsive behaviour. These results encourage making deeper investigations on this field.

Anxiety and otovestibular disorders: linking behavioral phenotypes in men and mice

Human anxiety and vestibular disorders have long been known to co-occur. Paralleling human clinical and non-clinical data, mounting genetic, pharmacological and behavioral evidence confirms that animal anxiety interplays and co-exists with vestibular/balance deficits. However, relatively few animal models have addressed the nature of this relationship. This paper examines side-by-side human psychiatric and otovestibular phenotypes with animal experimentation data, and outlines future directions of translational research in this field. Discussed here are recently developed specific animal models targeting this interplay, other traditional animal tests sensitive to altered anxiety and vestibular domains, and the existing problems with translation of animal data into human phenotypes. The role of hearing deficits and their contribution to anxiety and vestibular phenotypes are also outlined. Overall, the overlap between anxiety and balance disorders emerges as an important phenomenon in both animal and clinical studies, and may contribute markedly to the complexity of behavioral and physiological phenotypes. Animal experimental models that focus on the interplay between anxiety and vestibular disorders are needed to improve our understanding of this important biomedical problem.

Pharmacological modulation of anxiety-related behaviors in the murine Suok test

We have recently introduced a new model of anxiety--the Suok test and its light-dark modification--for behavioral characterization in mice and rats, including simultaneous assessment of their anxiety, activity, and neurological phenotypes. In the present study, testing different inbred (129S1, BALB/c) and hybrid (C57-129S1) mouse strains in both Suok test modifications, we examined the effects on anxiety-related behaviours produced by traditional anxiogenic and anxiolytic drugs. Here we show dose-dependent increases in anxiety-related behaviors produced by anxiogenic drug pentylenetetrazole (10 and 20 mg/kg). In contrast, anxiolytic drugs ethanol (0.75 and 1.5 g/kg) and diazepam (0.5 mg/kg) reduced anxiety and increased mouse exploration in this test. Hyperemotional anxious BALB/c mice were particularly sensitive to pharmacogenic anxiety in Suok test, also showing robust light-dark shifts in the light-dark version of this test. Overall, the results of this study confirm the potential utility of both murine Suok tests, especially when used in selected "sensitive" mouse strains, for high-throughput screening of potential anxiotropic drugs.

What's wrong with my mouse model?

Stress plays a key role in pathogenesis of anxiety and depression. Animal models of these disorders are widely used in behavioral neuroscience to explore stress-evoked brain abnormalities, screen anxiolytic/antidepressant drugs and establish behavioral phenotypes of gene-targeted or transgenic animals. Here we discuss the current situation with these experimental models, and critically evaluate the state of the art in this field. Noting a deficit of fresh ideas and especially new paradigms for animal anxiety and depression models, we review existing challenges and outline important directions for further research in this field.

Anxiety in mice: a principal component analysis study

Two principal component analyses of anxiety were undertaken investigating two strains of mice (ABP/Le and C57BL/6ByJ) in two different experiments, both classical tests for assessing anxiety in rodents. The elevated plus-maze and staircase were used for the first experiment, and a free exploratory paradigm and light-dark discrimination were used for the second. The components in the analyses produced definitions of four fundamental behavior patterns: novelty-induced anxiety, general activity, exploratory behavior, and decision making. We also noted that the anxious phenotype was determined by both strain and experimental procedure. The relationship between behavior patterns and the use of specific tests plus links with the genetic background are discussed.

Behavioral neuroscience, exploration, and K.C. Montgomery's legacy

Exploration is a key animal and human behavior. Kay C. Montgomery (1921-1956) has made an important contribution to behavioral neuroscience of exploration, as well as motivation and learning. His works have many important applications to current experimental models of stress, fear and memory, continuing to influence research in this field. This paper, dedicated to the 85th anniversary of Montgomery's birth, and 50 years since his tragic death, summarizes Montgomery's contribution to behavioral neuroscience, and discusses its current importance for further progress in this field. It is aimed at neuroscientists with strong interests in both theory of animal exploration and motivation, and the history of behavioral neuroscience.

L-655,708 enhances cognition in rats but is not proconvulsant at a dose selective for α5-containing GABAA receptors

The in vitro and in vivo properties of L-655,708, a compound with higher affinity for GABA(A) receptors containing an alpha5 compared to an alpha1, alpha2 or alpha3 subunit have been examined further. This compound has weak partial inverse agonist efficacy at each of the four subtypes but, and consistent with the binding data, has higher functional affinity for the alpha5 subtype. In a mouse hippocampal slice model, L-655,708 was able to enhance the long-term potentiation produced by a theta burst stimulation, consistent with a potential role for the alpha5 subtype in processes involving synaptic plasticity, such as learning and memory. When administered in a formulation specifically designed to achieve relatively constant plasma drug concentrations, and therefore maintain selective occupancy of alpha5- compared to alpha1-, alpha2- and alpha3-containing receptors (75+/-4% versus 22+/-10%, respectively), L-655,708 did not alter the dose of pentylenetetrazole required to induce seizures, indicating that the inverse agonist effects of L-655,708 at the alpha5 subtype are not associated with a proconvulsant liability. In the Morris water maze, L-655,708 enhanced performance not only during acquisition but also in a probe trial, demonstrating that this compound has cognition enhancing effects. These data further support the potential of alpha5-containing GABA(A) receptors as a target for novel cognition enhancing drugs.

Effects of unpredictable chronic mild stress on anxiety and depression-like behavior in mice

The widely accepted stress-diathesis hypothesis of depression postulates that genetic factors contribute to biological vulnerability. Based on this concept, the unpredictable chronic mild stress (UCMS) animal model was developed. Most effects of UCMS can be reversed by antidepressant agents, illustrating a strong predictive validity. In rodents, UCMS also has good face validity as it can elicit depression-like symptoms. While abundant for rats, the UCMS literature on mice is relatively limited. Reports sometimes are contradictory, making it difficult to establish a clear profile of stress-induced depression-like behaviors in mice. As different groups often use different strains for their experiments, differential strain susceptibility to UCMS may provide at least a partial explanation of these discrepancies. Moreover, differences in testing methodology add another level of complexity. Very little is known about the role of genetic factors and their interactions with the environment in the development of stress-induced behavioral changes relevant to depression, though recent studies unequivocally demonstrated the effects of specific gene polymorphisms on stress-induced depressive symptoms, as well as the effects of stress on gene expression. In the present study, we investigated the effects of UCMS on a battery of different tests measuring anxiety and depression-like behaviors in three behaviorally and genetically distinct inbred strains. The goals of these experiments are to obtain a clearer behavioral profile of genetically/phenotypically distant mouse strains after UCMS treatment and to evaluate the limitations and strengths of the UCMS model in mice.

Reduced attention and increased impulsivity in mice lacking NPY Y2 receptors: Relation to anxiolytic-like phenotype

Neuropeptide (NPY) Y2 receptors play an important role in some anxiety-related and stress-related behaviours in mice. Changes in the level of anxiety can affect some cognitive functions such as memory, attention and inhibitory response control. We investigated the effects of NPY Y2 receptor deletion (Y2(-/-)) in mice on visual attention and response control using the five-choice serial reaction time (5-CSRT) task in which accuracy of detection of a brief visual stimulus across five spatial locations may serve as a valid behavioural index of attentional functioning. Anticipatory and perseverative responses provide a measure of inhibitory response control. During training, the Y2(-/-) mice had lower accuracy (% correct), and made more anticipatory responses. At stimulus durations of 2 and 4s the Y2(-/-) were as accurate as the Y2(+/+) mice but still more impulsive than Y(+/+). At stimulus durations of 0.25 and 0.5s both groups performed worse but the Y2(-/-) mice made significantly fewer correct responses than the Y2(+/+) controls. The anxiolytic drug diazepam at 2mg/kg IP greatly increased the anticipatory responding of Y2(-/-) mice compared to Y2(+/+). The anxiogenic inverse benzodiazepine agonist, FG 7142, at 10mg/kg IP reduced the anticipatory responding of Y2(-/-) but not Y2(+/+) mice. These data suggest that NPY Y2 receptors make an important contribution to mechanisms controlling attentional functioning and "impulsivity". They also show that "impulsivity" of NPY Y2(-/-) mice may depend on their level of anxiety. These findings may help in understanding the pathophysiology of stress disorders and depression.

Persistent anxiogenic effects of a single or repeated doses of cocaine and methamphetamine: interactions with endogenous cannabinoid receptor ligands

As persistent behavioural changes, such as increased anxiety-related behaviours, can be predicted based on the phenomenon of psychostimulant-induced neuronal plasticity, the time course (3-, 5- and 10-day time points) of the effects of both a single and repeated (daily for 7 days) i.p. administrations of cocaine (COC) and methamphetamine (MA) on anxiety-related behavioural symptoms in the elevated plus-maze test were examined in mice. Furthermore, based on the reported interactions between brain dopamine versus cannabinoid (CB) receptors and the contribution of CB receptors to the occurrence of persistent anxiety-related behavioural symptoms, the interactions of the agonist CP 55940 (CP) and the endogenous ligands anandamide (arachidonylethanolamide: AEA), 2-arachidonylglycerol (ARA), N-arachidonyldopamine (NADA), noladin ether (NL), and virodhamine (VA) with the COC- or MA-induced anxiety-related behaviours were also studied. In both an acute experiment using a single COC (30 mg/kg) or MA (4 mg/kg) dose and a chronic experiment using repeated COC (15 mg/kg) or MA (2 mg/kg) doses, anxiety-related behavioural symptoms were observed similarly at 3- and 5-day time points, but disappeared at the 10-day time point. Among the CB ligands, the agonists CP, AEA, ARA, NADA, and NL provided strong protective effects against each parameter at 3- and 5-day time points. Therefore, it was concluded that both COC and MA caused persistent anxiety-related behavioural symptoms following both a single and repeated treatments. Since these anxiogenic effects were attenuated by the endogenous CB agonists, the involvement of brain CB receptors was suspected.

Anxiogenic profile of AM-251, a selective cannabinoid CB1 receptor antagonist, in plus-maze-na??ve and plus-maze-experienced mice

The notoriously inconsistent effects of cannabinoids on anxiety-like behaviour may be explained by recent research on CB1 receptor knockout (CB1-KO) mice suggesting that cannabinoids exert bidirectional effects via the CB1 receptor (anxiolysis) and a novel rimonabant-sensitive neuronal cannabinoid receptor (anxiogenesis). This hypothesis is supported by the anxiogenic-like profile of AM-251, an analogue of rimonabant that is a potent and selective CB1 receptor antagonist but which, unlike rimonabant, has no activity at the novel receptor. As we have previously shown that rimonabant reduces anxiety-like behaviour in test-experienced animals only, the current study assessed the effects of AM-251 (1.5-3.0 mg/kg) in male Swiss-Webster mice that were either plus-maze-naïve or had been exposed undrugged to the apparatus 24 h prior to testing. Results confirmed that prior maze experience per se significantly increases behavioural indices of anxiety without altering measures of general activity. In maze-naïve mice, the lower dose of AM-251 (1.5 mg/kg) significantly reduced % open-arm time and increased grooming while the higher dose (3.0 mg/kg) additionally reduced open-arm entries and total head-dipping, and increased closed-arm returns. These anxiogenic-like effects were observed in the absence of significant changes in general activity levels. Although AM-251 had a very similar profile in maze-experienced animals, significant drug effects on open-arm avoidance measures were precluded by experientially-induced changes in behavioural baselines (i.e. 'ceiling' effects). Nevertheless, AM-251 again significantly reduced total head-dipping and increased grooming (3.0 mg/kg) and, unlike effects in naïve animals, both doses markedly reduced time spent on the centre platform and increased time spent in the enclosed arms. Against a baseline of almost total open-arm avoidance, the pattern of behavioural change in maze-experienced mice would also be consistent with an anxiogenic-like action of AM-251. Data are discussed in relation to previous findings with rimonabant, the putative existence of a novel non-CB1 neuronal cannabinoid receptor and, more generally, the behavioural pharmacology of plus-maze 'trial 2'.

The use of sudden darkness in mice: a behavioural and pharmacological approach

Sudden darkness is a non-invasive behavioural analysis tool which increases motor activity and decreases anxiety in rats. It has been shown in previous studies that in rats, dark test conditions can also modify behavioural responses to drugs acting on the dopaminergic system. The increasing use of transgenic mice in behavioural research has raised interest in developing new tests for phenotyping mice. Hence, the aim of the present study was to adapt the sudden darkness paradigm for mice. In the first part of this study, effects of sudden darkness on the performance of mice in the elevated plus maze test were evaluated. Both genders of two mouse strains (Swiss and Balb/c) were tested either in high light intensity conditions or were exposed to sudden darkness. In the second part, responses to the 5-HT(1A) receptor agonist 8-OH-DPAT (0.5 and 1.0 mg/kg) and 5-HT(2C) receptor agonist mCPP (1.0 and 2.0 mg/kg) were investigated in male Swiss mice. Sudden darkness induced a clear anxiolytic effect in male and female Swiss mice. In Balb/c mice, anxiety-related behaviour was only decreased in females, whereas in males the anxiety state remained unchanged. An increase in motor activity was only observed in male Swiss mice; in the other groups, sudden darkness did not affect locomotion. Depending on the light conditions used, the behavioural response to receptor agonists was more evident: 8-OH-DPAT (1.0 mg/kg) only significantly decreased the anxiety state when mice were tested under high levels of illumination, whereas the anxiogenic effect of mCPP (1.0 and 2.0 mg/kg) was only evident in the dark. This study suggests that the sudden darkness paradigm is also a useful tool for the analysis of mice and can be used to modulate the anxiety level without administering drugs. Depending on the mouse strain tested, the same effects on anxiety and motor activity were observed as have been shown for rats.

Bidirectional effects of benzodiazepine binding site ligands in the elevated plus-maze: differential antagonism by flumazenil and beta-CCt

Recent research using genetically modified mice has pointed to the specific contribution of individual receptor subtypes to the various effects of benzodiazepines. The aim of this study was to examine the relative significance of alpha(1)-containing GABA(A) receptors in the effects of modulators at the benzodiazepine site in the elevated plus-maze (EPM) under dim red light in rats. We tested the effects of the non-selective antagonist flumazenil (0-20.0 mg/kg), the preferential alpha(1)-subunit selective antagonist beta-carboline-3-carboxylate-t-butyl ester (beta-CCt, 0-30.0 mg/kg), the non-selective agonist midazolam (0-2.0 mg/kg), the preferential alpha(1)-subunit selective agonist zolpidem (0-2.0 mg/kg) and the non-selective inverse agonist methyl 6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM, 0-2.0 mg/kg). The influence of flumazenil (10.0 mg/kg) and beta-CCt (30.0 mg/kg) on the effects of both kinds of agonists were also examined. The standard spatio-temporal parameters reflecting anxiety (percentage of open arm entries and time) and locomotion (closed and total arm entries) were analyzed. beta-CCt did not affect behavior, while flumazenil at the highest dose (20.0 mg/kg) decreased indices of open arm activity and total arm entries. Midazolam at the dose of 1.0 mg/kg significantly increased the percentage of open arm time, whereas at 2.0 mg/kg both anxiety-related parameters were increased. In contrast to the open arm entries, the open arm time was independent of the decreased closed arm entries, observed at 2.0 mg/kg. Flumazenil abolished these effects, whereas beta-CCt partially potentiated the anxiolytic actions of midazolam. Zolpidem significantly increased both open-arm indices at 1.0 mg/kg, but the effect was dependent on the decreased closed arm entries. The selectivity of the anxiolytic-like effects of zolpidem was further checked under brighter white illumination. In these settings, the influence on anxiety-related, but not activity-related parameters, was absent. All of the activity-related effects of midazolam and zolpidem were mainly counteracted by both antagonists. DMCM produced significant anxiogenic effects at 1.0 mg/kg (open arm time) and 2.0 mg/kg (both parameters). beta-CCt (30.0 mg/kg) and flumazenil at higher dose (20.0 mg/kg) antagonized the effects of DMCM. The results indicate the anxiolytic effects of a non-selective benzodiazepine site agonist involve a predominant role of subunits other than alpha(1), whereas the behavioral indices of the anxiolytic-like properties of an alpha(1)-selective ligand, if observed, depend on the experimental settings and the changes in locomotor activity, and hence were behaviorally non-specific. The present results generally correspond well to the behavioral findings with the genetically modified mice. On the other hand, the relative significance of the alpha(1)-subunit in the anxiogenic effects of DMCM could not be clearly deduced.

Mouse grooming microstructure is a reliable anxiety marker bidirectionally sensitive to GABAergic drugs

Grooming is an important part of rodent behavioural repertoire, representing a complex hierarchically ordered cephalo-caudal sequence of patterns sensitive to stress and various drugs. Gamma-aminobutyric acid (GABA) is involved in the regulation of both anxiety and grooming behaviours. This study investigated the predictive validity of grooming behavioural microstructure as a marker of anxiety, by examining the effects of two GABAergic reference compounds, anxiolytic diazepam (0.1 and 0.5 mg/kg i.p.) and anxiogenic pentylenetetrazole (5 and 10 mg/kg i.p.) on mouse grooming. Our data suggest that the percentage of pattern transitions not fitting to the cephalo-caudal progression, and the percentage of interrupted grooming bouts are more reliable behavioural markers of stress bidirectionally sensitive to GABAergic anxiogenic and anxiolytic drugs, compared to the frequency and duration scores. Our study also confirms that detailed ethological analyses of grooming microstructure can be a useful tool in behavioural pharmacology of anxiety.

Anxiogenic treatments do not increase fear-potentiated startle in mice

BACKGROUND

In rodents, the fear-potentiated startle paradigm (FPS; exaggerated startle as a measure of the conditioned fear response to cues associated with footshock) has demonstrated predictive validity for anxiolytic drugs. The predictive validity of the model for anxiogenic drugs, however, remains unclear. Therefore, we evaluated the bi-directionality of the FPS model for anxiety-modulating compounds in mice.

METHODS

The clinical anxiogenics FG-7142 (1-20 mg/kg), yohimbine (.1-10 mg/kg), and m-Chlorophenylpiperazine (mCPP; .3-3 mg/kg), and the putative anxiogenics atipamezole (.3-3 mg/kg) and corticotropin-releasing factor (h/r-CRF; .03-1 microg) were tested in DBA/1J mice trained for FPS.

RESULTS

Contrary to predictions, FG-7142 (10 and 20 mg/kg) and yohimbine (10 mg/kg) reduced FPS in mice without affecting baseline startle. Atipamezole (3 mg/kg), mCPP (3 mg/kg), and h/r-CRF (.3, 1 microg) did not affect FPS, but increased startle independently from the presence of the cue. FG-7142 and h/r-CRF had similar effects in 129SvEv mice.

CONCLUSIONS

Murine FPS is not bi-directionally predictive for anxiety-modulating compounds, although murine baseline startle may have some utility as a bi-directional model of anxiety. These data corroborate the recent hypothesis that systems mediating FPS are independent from systems mediating increased startle from unconditioned and putatively anxiogenic stimuli.

Differential effects of infralimbic vs. ventromedial orbital PFC lidocaine infusions in CD-1 mice on defensive responding in the mouse defense test battery and rat exposure test

The ventromedial prefrontal cortex (vmPFC) is extremely sensitive to a variety of stressful situations and threatening events, and has been suggested to be an associative cortical brain system processing the integration of anxiety-related cognitive, affective and motivated behavior in rodents, primates and humans. In addition, recent evidence suggests that (a) anxiety-related affective processing appears to be lateralized to the right hemisphere vmPFC; and (b) there appears to be functional heterogeneity within the rodent vmPFC. The present study evaluated the possibility that distinct sub-areas of the right hemisphere ventral PFC might differentially influence anxiety-like defensive responding in two different predator stress situations following transient inactivation of the ventromedial orbital (vMO) or infralimbic (IL) vmPFC in CD-1 mice. In week 1, IL vmPFC lidocaine infusions reduced anxiety-like defensive responding in mice (enhanced approach and contact) confronted with a hand-held anesthetized rat stimulus in the mouse defense test battery (vMO inactivation exerted minimal effects). In week 2, vMO lidocaine infusions enhanced anxiety-like defensive responding (enhanced avoidance and protected risk assessment) toward a barricaded live rat in the rat exposure test (IL inactivation exerted minimal effects). Although it is unclear whether week 1 mouse defense test battery testing influenced week 2 rat exposure test results, these preliminary data suggest functional differences within the mouse right hemisphere ventral PFC related to cautious evaluation of predator threat. Given the dense unilateral reciprocal connectivity between the IL and vMO subregions of the PFC, both associative ventromedial cortical areas may exert complimentary yet dissociable roles in the processing of threat stimuli. This suggests that while the IL vmPFC may mediate cautious evaluation of threat situations (risk assessment), the vMO PFC may inhibit prepotent avoidance responses to facilitate such IL-mediated adaptive behavioral responses.

Detailed analysis of the behavior of Lister and Wistar rats in anxiety, object recognition and object location tasks

The present study, examines some issues in the measure and analysis of behavior in animals. Two strains of rats of both genders were used to illustrate and discuss these issues. We examined to what extent various behavioral measures reflect different or identical emotional or cognitive factors and, how sensitive are the various parameters of a task to differences between strains and genders. Wistar and Lister males and females rats were tested in an anxiety test then in the object recognition task followed by the object location task. Taking advantage of a simple computer program it is possible to: (1) record several parameters of theses tasks and examine the pattern of animal responses toward novelty and/or familiarity; (2) examine whether different measurements of the same response would reflect anxiety response to novelty and, can they discriminate between novelty and familiarity responses to objects; and (3) examine if changes in the pattern of animal responses are reflected by these measurements and, whether anxiety or discrimination is evident mainly during the first minute of the test. The results on the anxiety test show that different measures of the same response proved concordant and revealed significant differences between Lister males and Wistar males. Lister males approached more frequently an object and spent more time on an object in each approach compared to Wistar males in the first 5 min of test and in the total 10 min. They have also shorter latencies between approaches compared to Wistar males. The examination of performance over different time bins was significant with the measure of frequency. Lister male rats approached less frequently the object in the last 5 min of the test compared to the first 5 min. Their performance, however, did not differ from that of the other groups in this last 5 min. In the memory tasks, the measure of the frequency of approaches suggests that Lister male rats were able to discriminate between novel and familiar objects and, between novel and familiar location of objects. The measure of latency of first approach shows that Wistar female rats were able to discriminate between objects only in the spatial memory test. Discrimination in the object recognition task was observed in the first and second minute, and in the total 3 min sessions. Discrimination in the object location task was observed with the measure of frequency of approaches, in the first minute, and in the total 3 min sessions. Results from the total 3 min sessions were more concordant between the different measures of discrimination than results from separate 1 min bins. The results from the two memory tasks show that novelty prevented habituation to re-exposure to the testing environment. In many cases, novelty increased exploration of the objects in the choice phase compared to the sample phase. However, this lack of habituation or increased exploration in the choice phase is not concordant with most results of discrimination between novelty and familiarity from the same type of measurements.

Long-term effects of social stress on brain and behavior: a focus on hippocampal functioning

In order to study mechanisms involved in the etiology of human affective disorders, there is an abundant use of various animal models. Next to genetic factors that predispose for psychopathologies, environmental stress is playing an important role in the etiology of these mental diseases. Since the majority of stress stimuli in humans that lead to psychopathology are of social nature, the study of consequences of social stress in experimental animal models is very valuable. The present review focuses on one of these models that uses the resident-intruder paradigm. In particular the long-lasting effects of social defeat in rats will be evaluated. Data from our laboratory on the consequences of social defeat on emotional behavior, stress responsivity and serotonergic functionality are presented. Furthermore, we will go into detail on hippocampal functioning in socially stressed rats. Very recent results show that there is a differential effect of a brief double social defeat and repetitive social defeat stress on dendritic remodeling in hippocampal CA3 neurons and that this has repercussions on hippocampal LTP and LTD. Both the structural and electrophysiological changes of principal neurons in the hippocampal formation after defeat are discussed as to their relationship with the maintenance in cognitive performance that was observed in socially stressed rats. The results are indicative of a large dynamic range in the adaptive plasticity of the brain, allowing the animals to adapt behaviorally to the previously occurred stressful situation with the progression of time.

Changes in motoric, exploratory and emotional behaviours and neuronal acetylcholine content and 5-HT turnover in histidine decarboxylase-KO mice

Histamine has been implicated, inter alia, in mechanisms underlying arousal, exploratory behaviour and emotionality. Here, we investigated behavioural and neurochemical parameters related to these concepts, including open-field activity, rotarod performance and anxiety, as well as brain acetylcholine and 5-HT concentrations of mice deficient for the histidine decarboxylase (HDC) gene. These mice are unable to synthesize histamine from its precursor histidine. The HDC-knockout mice showed reduced exploratory activity in an open-field, but normal habituation to a novel environment. They behaved more anxious than the controls, as assessed by the height-fear task and the graded anxiety test, a modified elevated plus-maze. Furthermore, motor coordination on the rotarod was superior to controls. Biochemical assessments revealed that the HDC-knockout mice had higher acetylcholine concentrations and a significantly higher 5-HT turnover in the frontal cortex, but reduced acetylcholine levels in the neostriatum. These results are suggestive of important interactions between neuronal histamine and these site-specific neurotransmitters, which may be related to the behavioural changes found in the HDC-deficient animals.

Anxiolytic properties of the antipsychotic alkaloid alstonine

Anxiolytic properties may be a crucial feature of newer antipsychotics associated with the improvement of negative symptoms in schizophrenic patients. The indole alkaloid alstonine acts as an atypical antipsychotic in behavioral models, but differs in its dopamine and serotonin binding profile. The purpose of this study was to verify if alstonine possesses anxiolytic properties in mice. The hole-board and light/dark models were used; moreover, the participation of D(1), 5-HT(2), NMDA and gamma-aminobutyric acid (GABA) receptors was likewise investigated. Alstonine clearly behaves as anxiolytic in both hole-board and light/dark situations. Pretreatment with the 5-HT(2A/2C) serotonin receptor antagonist ritanserin reverted the effects of alstonine in both the hole-board and light/dark models, suggesting the involvement of these receptors in the alstonine mechanism of action. The involvement of glutamate NMDA receptors should also be considered, given that alstonine partially reversed the increase in locomotion induced by MK-801 in the hole board, as well as MK-801-induced hyperlocomotion in motor activity apparatus.

Early weaning induces anxiety and aggression in adult mice

Early environmental stimuli have been shown to affect many aspects of physiological and behavioral development in humans and other mammals. In this study, we investigated the effects of early weaning on behavioral traits in adulthood. Male and female Balb/c mice were divided into two groups, one weaned from the dam at 14 days of age (early-weaned group) and the other weaned at 21 days of age (normally weaned group), as a control. At 8 and 22 weeks of age, animals of both groups were subjected to the plus maze test to assess their anxiety levels. The early-weaned mice showed lower frequency of entry into the open arms of the maze. Although a subsequent isolation-induced aggression test revealed no clear differences between the two groups, when males from each of the two weaning groups were regrouped after 1 month of isolation, the early-weaned animals showed a great number of wounds on their tails and hindquarters. These results suggest that the deprivation of mother-pup interaction from 14 through 21 postnatal days augments anxiety and aggressiveness.

Effects of bacterial superantigens on behavior of mice in the elevated plus maze and light-dark box

Bacterial superantigens, such as staphylococcal enteroxins A and B (SEA/SEB) stimulate T cells to produce high levels of cytokines in blood. Previously it had been shown that these toxins were capable of stimulating increased neuroendocrine activity and enhanced behavioral reactivity to novel gustatory and non-gustatory stimuli. Therefore, it was suggested that these superantigens may promote anxiety-like behavior. In the current set of experiments, BALB/cByJ and C57BL/6J male mice were challenged with either SEB (50 microg) or SEA (5 or 10 microg) and tested for behavior in the elevated plus maze (EPM). Results suggested an absence of increased anxiety-like behavior, with exploration of the open arms being enhanced by SEA or SEB treatment. In another test of anxiety, the light-dark box, SEB challenge of BALB/cByJ mice 90 min prior to testing, did not alter exit latency, activity nor time spent in the dark. However, in a second experiment, it was found that if animals were first tested for consumption, followed by testing in the light-dark box, SEB challenged animals displayed increased exit latency and reduced exploration. These studies suggest that in standard tests of rodent anxiety-like behavior, evidence for the induction of anxiety-like processes subsequent to challenge with SEA or SEB is not patently discernable. However, neurobiological events induced by immunological challenge might synergize with reactivity to psychogenic and/or gustatory stimuli, thereby resulting in increased anxiety-like behavior that could be unmasked by standard behavioral tests such as the light-dark box or EPM.

The neurochemical effects of anxiolytic drugs are dependent on rearing conditions in Fawn-Hooded rats

There is a vast literature examining the neurochemical effects of anxiolytics throughout the rat brain; however, although the behavioural actions of anxiolytic drugs are routinely assessed in animal models of anxiety, the majority of neurochemical studies have been performed in rats with relatively 'normal' behavioural phenotypes. Since there is significant evidence that an anxious phenotype is associated with numerous neurochemical alterations, it is feasible that the central effects of anxiolytics may vary depending on the underlying behavioural state (and corresponding neuropathology) of the experimental animal. For this reason, the aim of the present study was to examine the effect of chronic anxiolytic drug administration on the central CCK and dopamine systems in anxious (isolated from weaning) and nonanxious (group-housed) Fawn-Hooded (FH) rats. It is important to note that these studies were performed in rats with continued access to ethanol, which may affect the responses to anxiolytic treatment. Chronic anxiolytic treatment with the selective CCK-B (CCK(2)) receptor antagonist, Ci-988 (0.3 mg/kg/day ip) or diazepam (2 mg/kg/day ip), induced numerous effects throughout the central nervous system (CNS), with Ci-988 inducing significant changes in the density of dopamine D(2) receptors, and diazepam producing marked changes in both dopamine D(2) and CCK-B receptor binding density as well as preproCCK mRNA expression. Interestingly, the neurochemical effects of these anxiolytic drugs varied significantly depending on the rearing conditions of the rats, demonstrating the importance of using adequate animal models when correlating the behavioural and central effects of drugs acting throughout the CNS.

Infralimbic D2 receptor influences on anxiety-like behavior and active memory/attention in CD-1 mice

Ventromedial prefrontal cortical (vmPFC) dopamine (DA) influences attentional aspects of cognition and anxiety-like behavioral responding in rodents. The present study investigated the role of D2 receptors on spontaneous alternation in the Y-maze and anxiety-like behavior in a two-trial elevated plus-maze (EPM) procedure in CD-1 mice following vmPFC infusions of the D2 antagonist, sulpiride, and the D2 agonist, quinpirole. Pretrial 1 quinpirole infusions did not influence any anxiety measure (with the exception that the lowest dose increased protected stretch attends), but reduced protected exploration activity (closed-arm entry/time ratios and wall rearing). In Trial 2 24 h later (no injection), quinpirole exerted an anxiolytic behavioral profile relative to Trial 2 control mice (enhanced open-arm entry/time ratios, unprotected head dips), with no effects on protected exploration or risk assessment activity. Pretrial 1 sulpiride infusions enhanced unprotected exploration (open-arm entry/time ratios, unprotected stretch attend, and head dips), but did not influence protected exploration or risk assessment in the EPM. In Trial 2, 24 h later (no injection), sulpiride extended this anxiolytic profile to reduced protected exploration and risk assessment activity (closed-time ratio, protected stretch attend, and head dips). In the Y-maze, whereas quinpirole disrupted alternation performance (5- and 10-nmol dose) concomitant with marked repetitive same-arm returns (SAR) at the highest dose, sulpiride disrupted alternation performance concomitant with marked repetitive SAR behavior at the lowest dose only. These data indicate that although infralimbic (IL) quinpirole and sulpiride infusions similarly disrupted alternation performance in the Y-maze and reduced Trial 2 anxiety-like responding in the EPM, these drugs differentially produced these effects.

Prior exposure to the elevated plus-maze sensitizes mice to the acute behavioral effects of fluoxetine and phenelzine

A single undrugged experience of the elevated plus-maze modifies future drug responses in the test. The present study investigated the effects of maze-experience on the acute behavioral effects of the monoamine oxidase inhibitor phenelzine and the serotonin reuptake inhibitor fluoxetine. Phenelzine (2.5-12.5 mg/kg) had no clear effect on plus-maze behavior in test-naive Swiss Webster mice, but dose-dependently increased anxiety-like behavior in maze-experienced subjects. Similarly, fluoxetine (5-20 mg/kg) produced non-significant trends for increased anxiety-like behavior in maze-naive mice, but significantly and dose-dependently increased anxiety-like behavior and suppressed locomotor activity in maze-experienced mice. The anxiogenic effects of the benzodiazepine receptor inverse agonist N-methyl-beta-carboline-3-carboxamide (FG 7142) (20 mg/kg) was abolished by prior test experience, suggesting an alteration in gamma-aminobutyric acid (GABA)/benzodiazepine receptor function with maze-experience. However, the benzodiazepine receptor antagonist flumazenil (5-20 mg/kg) produced a silent profile regardless of maze-experience. Present findings provide further evidence demonstrating that prior test history is a critical consideration in mouse studies of anxiety-related behavior.

Anxiogenic-like activity of L-655,708, a selective ligand for the benzodiazepine site of GABA(A) receptors which contain the alpha-5 subunit, in the elevated plus-maze test

GABA(A) receptor is a transmembrane hetero-oligomeric protein which consists of five subunits, the combination of which confers unique pharmacological properties to the receptor. L-655,708 is a new ligand selective for GABA(A) receptors containing an alpha-5 subunit. It is a partial inverse agonist that exhibits a 100-fold higher affinity for alpha-5 containing receptors, compared with alpha-1 containing receptors. The aim of this study was to examine the effects of L-655,708 (0.625-5 mg/kg i.p.) on anxiety tested in the elevated plus-maze in male mice. A number of classical parameters were collected: (a) Open arm duration; (b) Closed arm duration; (c) Central platform duration; (d) Open arm frequency; (e) Closed arm frequency; and (f) Total number of entries in the arms. Likewise, different ethological measures were also obtained (rears, head-dipping [HD], stretched attend posture [SAP] and grooming). Mice treated with L-655,708 showed a marked increase in the frequency of entries and the time spent in closed arms, as well as a reduction in the frequency of entries and the time spent in open arms, as compared with the control group. Unprotected HDs were also significantly decreased after treatment with the drug. Overall, these results indicate that L-655,708 could exhibit an anxiogenic-like profile in the elevated plus-maze test. This ligand is selective for GABA(A) receptors containing an alpha-5 subunit, which is mainly expressed over the hippocampal formation, a region which has been involved in the modulation of anxiety.

Further evidence for the predictive validity of the unstable elevated exposed plus-maze, a behavioural model of extreme anxiety in rats: differential effects of fluoxetine and chlordiazepoxide

The unstable elevated exposed plus-maze (UEEPM) is a novel model of extreme anxiety which elicits unconditioned flight/escape behaviour in rats. The current studies aimed to investigate further the predictive validity of the paradigm, by examining the effects on UEEPM behaviour of both clinically effective (chronic fluoxetine) and ineffective (acute fluoxetine and chlordiazepoxide) treatments for panic disorder. In the first experiment, male Brown Norway rats received a single injection of fluoxetine (1.0-10.0 mg/kg p.o.) or chlordiazepoxide (CDP, 1.0-10.0 mg/kg i.p.) 30 min prior to UEEPM exposure. In the second experiment, in order to assess the effects of chronic dosing or handling on baseline UEEPM behaviour, subjects received either 21 days vehicle injection (p.o.) or handling, before being exposed to the test. Finally, rats received 21 days fluoxetine (1.0-10.0 mg/kg) in their food, before being tested in the UEEPM. Acute CDP and fluoxetine had no effect on UEEPM behaviour. Chronic handling and vehicle administration (p.o.) significantly reduced escape in the UEEPM, hence preventing the effects of chronic fluoxetine administration from being investigated by p.o. dosing. Chronic fluoxetine in subjects' food (10.0 mg/kg) significantly attenuated animals' propensity to escape from the UEEPM. The results further support the pharmacological similarity between symptoms of panic in humans and escape in the UEEPM and suggest that the UEEPM may represent a paradigm to facilitate investigation into the neurochemical basis of extreme anxiety disorders.

Behavioral and neuroanatomical characterization of the Fmr1 knockout mouse

Previous studies showed the Fmr1 knockout (KO) mouse to be an excellent animal model for human fragile-X syndrome. The aim of this study was to further characterize the phenotype of these animals. Neuroanatomically, KO male mice were compared to wild-types (littermates) with respect to their sizes of hippocampal intra- and infrapyramidal mossy fiber (IIPMF) terminal fields. Behaviorally, they were tested in four different paradigms, each measuring different aspects of cognitive and emotional behavior: elevated plus maze (anxiety), neutral cage (aggression), open field (exploration), and radial maze (spatial memory). The results showed a diminished ability for radial maze learning associated with smaller sizes of IIPMF terminal fields. In addition, Fmr1 knockout animals exhibited increased locomotor activity, while no differences were found for aggression and anxiety. These data suggest the involvement of FMRP protein in the development of spatial learning and the sprouting of IIPMF terminal fields.

Evaluation of the elevated plus-maze and open-field tests for the assessment of anxiety-related behaviour in inbred mice

The elevated plus-maze test (PM) and open-field test (OF) are routinely used to study anxiety-related behaviour in mouse. However, the data obtained with these tests have often been contradictory, probably because of differences between laboratories in the selection and analysis of behavioural parameters. We have characterised the pattern of mouse anxiety by analysing a number of behavioural parameters with both PM and OF in BALB/c and C57BL/6 mice, two behaviourally distant mouse strains. Twenty-eight variables (15 analysed with PM and 13 with OF) were selected by correlation analysis from those initially recorded with both tests. The scores of the selected variables were first analysed by MANOVAs, and then by principal component analysis (PCA). PCA extracted five factors for PM and four factors for OF. These factors were subjected to a correlation analysis, which showed significant correlation between four of them. The factorial scores of BALB/c and C57BL/6 mice were analysed by MANOVAs, which showed significant effects of both the strain and test used. Our results confirm the multidimensional structure of mouse anxiety-related behaviour as regards both simple components and functional interactions, and comprehensively represent strain- and test-specific features of mouse anxiety-related behaviour.

Anxiogenic properties of Ptychopetalum olacoides Benth. (Marapuama)

Alcohol infusions of roots of Ptychopetalum olacoides Benth. (PO), known as Marapuama or Muirapuama, are used in the Brazilian Amazon as a 'nerve tonic'. Over the years PO has been found increasingly in phytoformulations and regarded as a stimulant, claimed to enhance physical and mental performances. This study determined that a P. olacoides ethanol extract (30, 100 and 300 mg/kg) decreased exploratory behaviour in the hole-board test, without interfering with locomotion or motor coordination (rota-rod test). The data are comparable to that obtained with pentylenetetrazol (40 mg/kg), suggesting an anxiogenic effect of P. olacoides.

GIRK2 deficient mice. Evidence for hyperactivity and reduced anxiety

G-protein activated inwardly rectifying potassium channel (GIRK2)-deficient (null mutant) mice were examined in three tests for anxiety: the elevated plus-maze, light/dark box and "canopy" test. In the elevated plus-maze test, GIRK2 null mutant mice spent a higher percentage of time in the open arms and showed a higher number of total entries. A short (6 days) period of social isolation decreased anxiety and also increased the total activity in GIRK2 mutant mice. However, the increase of total activity in GIRK2 null mutant mice was mostly due to an increase in the number of entries into the open arms. The behavior of the wild-type animals was not substantially changed after social isolation. In the light/dark box, GIRK2 homozygous (-/-) mice demonstrated a higher level of locomotion and a higher number of rearings in the light area. In the "canopy" test, GIRK2 mutant mice displayed an increased locomotion in the exposed area and a strong trend to decrease in the number of stretched attend postures (SAP) in the most secure "canopy" area. GIRK2 heterozygous (+/-) animals showed behavioral changes intermediate between wild-type and null mutants only in the elevated plus-maze test after social isolation. In all other tests, GIRK2 heterozygous (+/-) animals did not differ from wild-type mice. Taken together, this data demonstrates that GIRK2 null mutant mice have reduced anxiety with signs of hyperactivity. We suggest that the functional block of dopamine D3 receptors may be a reason for this phenotype.

Anxiolytic-like actions of toluene in the burying behavior and plus-maze tests: differences in sensitivity between 5-HT(1B) knockout and wild-type mice

This paper compares the anxiolytic-like actions of toluene in two anxiety paradigms, the burying behavior and plus-maze tests, in 5-HT(1B) knockout (KO) and 129/Sv-ter wild-type (WT) mice. Static exposures were conducted in 29-l gas chromatographic jars. Animals were exposed to toluene (0, 1000, 2000 or 4000 ppm; n=8-12, each) for 30 min, and immediately after, tested in one of the anxiety paradigms. Motor coordination was evaluated in the rota-rod test in independent groups of mice. Toluene produced a dose-dependent decrease in anxiety-like levels in both anxiety paradigms and in both the strains. However, toluene exerted its effects at lower concentrations in KO mice than in the WT strain. These results cannot be attributed to a decrease in motor coordination since all the animals behaved similarly in the rota-rod test, regardless of the treatment. To discard any inherent difference in the nociception threshold between strains, mice were tested in the hot plate immediately after being exposed to either air or toluene. Toluene increased nociception in a similar fashion in both the strains. Our results suggest that 5-HT(1B) KO mice are more sensitive to those of toluene's actions related to anxiety, but not to those related with motor coordination or nociception. Data are discussed in terms of toluene's mechanisms of action and on differences between WT and KO animals.

Ethological confirmatory factor analysis of anxiety-like behaviour in the murine elevated plus-maze

The elevated plus-maze has been used in animal research to measure anxiety since 1985 and is currently the most widely used animal model of anxiety. Since this paradigm has been the subject of several principal components analyses, it is well qualified for confirmatory factor analysis research. The current report builds on the substantial theoretical knowledge and empirical data obtained from these structural analyses with a view to obtain further progress in the evolution of our understanding of animal anxiety in the elevated plus-maze. The purpose of the present report was two-fold: (a) to test if the a piori imposition of a 3-factor model, or a competing 2-factor elevated plus-maze model, would fit our sample (n=200 CD-1 mice) data in each of two trials within an inferential confirmatory factor analytic framework; (b) provide a well-fitting model that confers indicator variables that can most effectively and parsimoniously measure underlying constructs of elevated plus-maze behaviour. Multiple model-fitting criteria were used, and issues related to data non-normality, outliers, replicability of the model, sampling error and error of approximation in the estimation of final model fit were addressed. The final 2-factor model, with estimated error covariance between two different pairs of indicator variables, was a good fit on the trial-1 data, although it was necessary to allow unprotected stretch attends to non-significantly cross-load on factor-2. A 2-factor model also fit the trial-2 data from the present analysis, although it was necessary to allow closed arm time ratio to negatively cross-load on factor-1. These results indicate that inferential hypothesis testing and model building procedures within a confirmatory factor analysis framework produces interpretable animal anxiety indices in the elevated plus-maze. Moreover, a 2-factor, rather than a 3-factor model, parsimoniously and unambiguously explained the underlying constructs of anxiety-like mouse behaviour in the elevated plus-maze in the present study. Taken together, a reduction in the growing number of behavioural indices reported in elevated plus-maze pharmacological studies is suggested.

Concurrent modulation of anxiety and memory

We have previously shown that the ventromedial prefrontal cortex (vmPFC) is involved in spontaneous working memory and anxiety-related behaviour in CD-1 mice. Specifically, pretrial microinjection of the kappa(1) agonist, U-69,593, in the infralimbic (IL) area of the vmPFC produced a robust anxiolytic behavioural profile in the elevated plus-maze and enhanced spontaneous working memory in the Y-maze. In the present study we sought to determine whether these effects were specific to IL kappa receptors. We hypothesized that microinjection of the kappa antagonist, norBNI, in the IL cortex would influence anxiety and spontaneous memory in an opposite direction to the effects produced by the kappa(1) agonist. In week 1, transfer-latency reference memory and anxiety were tested in the elevated plus-maze in two separate trials with an intertrial interval of 24 h. In week 2, spontaneous working memory was tested in the Y-maze followed immediately by defensive/withdrawal anxiety in the open field for one half of the animals in each group, and the other half was tested in reverse order. Pretreatment with one injection of vehicle, 1, 5 or 10 nmol/0.5 microl norBNI in the IL cortex dose-dependently reduced transfer-latencies and produced an anxiogenic behavioural profile in the first elevated plus-maze trial. Following a 24 h delay, transfer-latency reference memory was not influenced, but a robust anxiogenic behavioural profile was observed in the second no-injection anxiety trial in the elevated plus-maze relative to control animals. In week 2, the same groups of mice were again pretreated with one injection of the same doses of norBNI in the IL cortex and tested in the open field and Y-maze. NorBNI pretreatment was anxiogenic in the defensive/withdrawal anxiety test and disrupted spontaneous working memory regardless of testing order. The present results show the influence of kappa receptor modulation on anxiety induction and spontaneous working memory. These results also support the hypothesis that immediate memory processing may modulate the induction of anxiety-related behaviours.

U-69,593 microinjection in the infralimbic cortex reduces anxiety and enhances spontaneous alternation memory in mice

The present report investigated the contributions of the ventromedial prefrontal cortex to the control of spontaneous alternation/working memory and anxiety-related behaviour. In Experiment 1, we examined the effects of microinjections of the selective kappa(1) receptor agonist, U-69,593, in the infralimbic cortex (IL) of CD-1 mice on several ethologically-derived anxiety indices in the elevated plus-maze (EPM) and defensive/withdrawal (D/W) anxiety in the open field, as well as on memory in the EPM transfer-latency (T-L) test and implicit spontaneous alternation memory (SAP) in the Y-maze. In week 1, pretreatment with one injection of vehicle, 1, 10 or 25 nmol/1.0 microliter U-69,593 in the IL dose-dependently prolonged T-L and produced a dose-dependent anxiolytic behavioural profile in the first EPM trial. Following a 24-h delay, the same mice were given a drug-free second trial in the EPM tests of T-L memory and anxiety. Whereas T-L memory was not disturbed, small but detectable carry-over effects were observed in trial-2 EPM behaviour relative to vehicle-treated animals. In week 2, the same groups of mice were again pretreated with one injection of the same doses of U-69,593 in the IL and given a D/W test in an open field, followed immediately by an 8-min SAP trial in the Y-maze. The smallest U-69,593 dose was anxiolytic in the D/W test, and SAP/working memory was dose-dependently enhanced in the Y-maze. In Experiment 2, we evaluated whether 0.5 microliter volume microinjections would produce comparable behavioural and carry-over effects in the IL of three new groups of CD-1 mice, in the event that the 1.0 microl volume injections used in Experiment 1 diffused beyond the IL and therefore may have confounded some effects. Experiment 2 procedures were carried out in the same manner as in Experiment 1, except the animals were tested in reverse order. Thus in week 1, SAP memory was tested in the Y-maze followed by D/W anxiety in the open field for half of the animals in each group, and the other half was tested in reverse order. In week 2, T/L memory and anxiety were tested in the EPM in 2 trials as described in Experiment 1. Pretreatment with one injection of vehicle, 10 or 25 nmol/0.5 microliter U-69,593 in the IL reduced D/W anxiety and enhanced SAP memory regardless of testing order in week 1. In week 2, the same groups of mice were again pretreated with one injection of the same doses of U-69,593 in 0.5 microliter volumes in the IL and tested in the EPM. In a similar fashion to Experiment 1, U-69,593 dose-dependently prolonged T/L and produced an anxiolytic behavioural profile in the first EPM trial. Following a 24-h delay, T/L recall memory was again not significantly influenced, but a robust anxiolytic behavioural profile was observed in the second drug-free anxiety trial in the EPM relative to vehicle-treated animals. Results are discussed relative to a) injection volumes and testing order, b) the possible influence kappa receptors may exert on neurochemical responsivity to anxiety-provoking environments in the IL area of the mPFC, c) the possibility that kappa-mediated anxiolysis from the IL in CD-1 mice results from interactions with neurochemical systems involved in the blunting of incoming anxiety-provoking information, d) evidence that SAP memory may be an implicit subtype of working memory, and e) the possibility that IL implicit working memory processes may modulate the induction and expression of anxiety-related behaviour.

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.

Behavioral profiles displayed by rats in an elevated asymmetric plus-maze: effects of diazepam

When rats are exposed to unknown environments where novelty and fear-inducing characteristics are present (conflictive environments), some specific behaviors are induced and exploration is apparently modulated by fear. In our laboratory, a new type of plus-maze was designed as a model of conflictive exploration. The maze is composed of four arms with different geometrical characteristics, differing from each other by the presence or absence of walls. The degree of asymmetry was as follows: NW, no wall arm; SW, a single high wall present; HL, a low and a high wall present, and HH, two high walls present. The four arms were arranged at 90 degrees angles and the apparatus was called the elevated asymmetric plus-maze (APM). The purpose of the present study was to assess the behavioral profile of rats exposed for a single time to the APM with or without treatment with benzodiazepine. Increasing doses of diazepam were injected intraperitoneally in several groups of male, 90-day-old Holtzman rats. Distilled water was injected in control animals. Thirty minutes after treatment all rats were exposed singly to a 5-min test in the APM. Diazepam induced a biphasic modification of exploration in the NW and SW arms. The increase in the exploration score was evident at low doses of diazepam (0.25-1.0 mg/kg body weight) and the decrease in exploration was found with the higher doses of diazepam (2.0-3.0 mg/kg body weight). Non-exploratory behaviors (permanency) were not affected by benzodiazepine treatment. In the HL arm, exploration was not modified but permanency was increased in a dose-dependent manner. In the HH arm, exploration and permanency were not affected. Results are compatible with the idea that exploration-processing mechanisms in conflictive environments are modulated by fear-processing mechanisms of the brain.

Generalization of fear responses in C57BL/6N mice subjected to one-trial foreground contextual fear conditioning

C57BL/6N mice were trained in a foreground contextual fear conditioning paradigm by a single exposure to a context (context 1) paired with an electric shock. Conditioned mice exhibited a strong fear response, indicated by increased freezing and low locomotor activity after subsequent re-exposure to context 1, which had been used for conditioning as well as in a novel context (context 2). The fear responses to contexts 1 or 2 required the temporal sequence of the conditioned (CS) and unconditioned (US) stimuli and did not differ significantly. The intensity of the fear response was maximal 24 h after conditioning, when long-term memory was fully established. The response to context 2 was interpreted as conditioned generalization, which was also observed in the elevated plus-maze representing an environment which differed in its spatial design significantly from contexts 1 and 2. Contextual discrimination of C57BL/6N mice was enhanced after extinction of the generalized fear. Strain studies employing C57BL/6J and Balb/c mice in addition to the C57BL/6N strain revealed that Balb/c and C57BL/6J mice acquired significantly weaker conditioned fear and generalized significantly less than C57BL/6N mice. It was concluded that the intensities of the context-specific and generalized fear responses were interlinked in a strain-specific manner.

Anxiety and cardiovascular reactivity: the basal forebrain cholinergic link

The relations between anxiety states and autonomic functions are considered from the vantage of a model of the neural systems underlying anxiety and autonomic control. An important component of this model is the involvement of the basal forebrain cortical cholinergic system that is seen to play a crucial role in the cognitive aspects of anxiety, and the links between anxiety and autonomic regulation. An additional aspect of the model is the detailing of the routes by which autonomic reactivity and associated visceral afference can modulate more rostral components of the system. The proposed model offers a more comprehensive framework for research on the neurobiology of anxiety and autonomic control.

Cardiovascular and somatic startle and defense: concordant and discordant actions of benzodiazepine receptor agonists and inverse agonists

Benzodiazepine receptor (BZR) agonists and inverse agonists yield generally opposing effects on GABAergic transmission, and the functional consequences of these ligands are often bidirectional. BZR agonists exert anxiolytic effects, whereas the BZR partial inverse agonist FG 7142 has been reported to have anxiogenic actions in a variety of paradigms. In keeping with this literature, we found that the cardioacceleratory defensive response is enhanced by FG 7142, and attenuated by the BZR agonist chlordiazepoxide. In contrast, both compounds attenuated basal and fear-potentiated somatic startle responses. This did not appear to reflect a global reduction of startle reactivity, however, as the cardiac startle response was not significantly altered. These findings support the view that multiple substrates underlie distinct aspects or features of fear and anxiety. The results are consistent with the suggestion that FG 7142 may selectively enhance those aspects of anxiety that depend on cortical-cognitive processing.

D3 dopamine receptor-deficient mouse: evidence for reduced anxiety

Mice without functional D3 dopamine receptors were examined in two animal models for anxiety: the open-field test and the elevated plus-maze test. In the open field, D3 receptor-deficient mice (D3-/-) entered the center significantly more often than normal (D3+/+) littermates, suggesting an anxiolytic-like effect of the D3 receptor mutation. Consistent with this finding, D3-/- mice entered open arms of the plus maze significantly more often and longer than D3+/+ littermates, but did not differ in closed-arm entries, an index of general activity. Heterozygous (D3 +/-) animals showed intermediate behavioral changes. We interpret these results as indicative of reduced anxiety in mice without D3 receptors. Our findings thus suggest that D3 dopamine receptors are involved in the regulation of anxiety.

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.

Resistance of experientially-induced changes in murine plus-maze behaviour to altered retest conditions

Prior exposure to the elevated plus-maze results in profound behavioural alterations in rats and mice, with 24 h retest profiles indicative of fear sensitization. The present study was designed to examine the influence of retest cues on this phenomenon in male DBA/2 mice. Results confirmed the potent influence of prior maze experience on subsequent behavioural patterns, and showed that this was not affected by manipulations of extra-maze cues (90 degrees re-orientation of the maze or use of a different laboratory) on Trial 2. Data are discussed in relation to experientially-induced shifts in behavioural strategy and the apparent involvement of simple proximal cues (probably thigmotactic) in this enduring and adaptive form of spatial learning.

Behavioural effects in mice of subchronic chlordiazepoxide, maprotiline and fluvoxamine. II. The elevated plus-maze

In view of apparent commonalities in the aetiology, symptomatology, and pharmacotherapy of anxiety and depressive disorders, the present study compares the effects of the benzodiazepine, chlordiazepoxide (1.0-8.0 mg/kg), the selective noradrenaline (NA) reuptake inhibitor, maprotiline (0.5-10.0 mg/kg), and the serotonin (5-HT)-selective reuptake inhibitor, fluvoxamine (2.0-8.0 mg/kg), on the behaviour of mice in the elevated plus-maze test of anxiety. To more accurately reflect the clinical situation, subjects were treated daily for 21 days prior to testing, and comprehensive behavioural profiles were obtained through the application of an ethological scoring technique. Results show that subchronic treatment with chlordiazepoxide produced clear anxiolytic-like effects at the highest dose tested, coupled with an inhibition of risk assessment over the entire dose range. With the exception of risk assessment measures, anxiolytic-like effects were also seen with a low dose (0.5 mg/kg) of maprotiline: these effects were lost at higher doses. In contrast to these data, fluvoxamine produced minimal behavioural change under present test conditions. Findings are discussed in relation to the relative efficacy of selective monoamine. reuptake inhibitors in the treatment of anxiety disorders, and the nature of anxiety evoked in mice by exposure to the elevated plus-maze.

Animal models of anxiety: an ethological perspective

In the field of anxiety research, animal models are used as screening tools in the search for compounds with therapeutic potential and as simulations for research on mechanism underlying emotional behaviour. However, a solely pharmacological approach to the validation of such tests has resulted in distinct problems with their applicability to systems other than those involving the benzodiazepine/GABAA receptor complex. In this context, recent developments in our understanding of mammalian defensive behaviour have not only prompted the development of new models but also attempts to refine existing ones. The present review focuses on the application of ethological techniques to one of the most widely used animal models of anxiety, the elevated plus-maze paradigm. This fresh approach to an established test has revealed a hitherto unrecognized multidimensionality to plus-maze behaviour and, as it yields comprehensive behavioural profiles, has many advantages over conventional methodology. This assertion is supported by reference to recent work on the effects of diverse manipulations including psychosocial stress, benzodiazepines, GABA receptor ligands, neurosteroids, 5-HT1A receptor ligands, and panicolytic/panicogenic agents. On the basis of this review, it is suggested that other models of anxiety may well benefit from greater attention to behavioural detail.

Modulation of plus-maze behaviour in mice by the preferential D3-receptor agonist 7-OH-DPAT

Differences in the behavioural profiles of dopamine D2 receptor antagonists (e.g., haloperidol vs. sulpiride) in a animal models of anxiety have prompted speculation concerning the importance of their relative affinities for D2-like receptor populations. In an initial attempt to investigate the involvement of D3 receptors in anxiety, the present study examined the effects of the preferential D3-receptor agonist, (+/-)7-OH-DPAT (0.01-10.0 mg/kg), on behaviours displayed by male mice in the elevated plus-maze paradigm. An ethological approach incorporating measurement of a range of defensive acts and postures in addition to conventional parameters was used to provide a comprehensive behavioural profile for the compound. Data analysis indicated a significant increase in percentage of open-arm entries at 10 mg/kg and an altered temporal distribution of behaviour at 1-10 mg/kg. Furthermore, risk-assessment measures (stretched attend postures, closed-arm returns) were dose dependently reduced by drug treatment. Although these behavioural changes would be consistent with anxiety reduction, such an interpretation is negated by dose-dependent decreases in all active behaviours (arm entries, rearing, and head-dipping) and by marked increases in entry latencies and nonexploratory behaviour at the highest dose tested. Overall, these effects are remarkably similar to those previously reported for quinpirole, suggesting either that D2 and D3 receptors exert similar behavioural control or that the agents employed are sufficiently potent at D2 receptors to prevent a resolution of D2 and D3 responses.

Ethological analysis of cholecystokinin (CCKA and CCKB) receptor ligands in the elevated plus-maze test of anxiety in mice

The literature on the effects of CCK receptor manipulations in animal models of anxiety is rife with inconsistency, and the data subject to a variety of methodological and interpretative difficulties. In the present paper, the effects of a range of CCK receptor ligands on anxiety in male mice have been assessed using an ethological version of the elevated plus-maze test. Compounds selected for study were the agonists, CCK-4 and CCK-8s (12.5-100 micrograms/kg), and the antagonists, devazepide, L-365, 260 and PD 135158 (1.0 microgram/kg-1.0 mg/kg). CCK-4 failed to produce any significant behavioural effects over the dose range tested, while treatment with the sulphated octapeptide, CCK-8s, induced signs of behavioural inhibition at 100 microgram/kg without altering anxiety-related indices. Furthermore, in contrast to the clear anxiolytic profile of diazepam (1 mg/kg), and despite the comprehensive behavioural profiles yielded by ethological analysis, all three CCK receptor antagonists studied (devazepide, L-365, 260 and PD 135158) were found to be without significant effect under present test conditions. Together, present findings provide little support for the involvement of CCK receptor mechanisms in anxiety and, in particular, the form of anxiety evoked in mice by exposure to a plus-maze.