Chronic handling modifies the anxiolytic effect of diazepam in the elevated plus-maze

The gold standard control groups in physiological and pharmacological research are not that shiny: Intraperitoneal saline injection and needle pricking affect prepubescent mice's behavior in a sex-specific manner

Study design and experimental tools are crucial for good quality science, and an essential part of it is the choice of control groups to best test the hypothesis. Two of the standard control groups in physiological and pharmacological research are needle pricking without substance injection (Sham) and/or vehicle injection (Saline). However, both needle pricking and saline injection can act as stressors, potentially influencing the analyzed outcome. This raises the question of whether the dependent variable remains unaffected by the stress induced by these procedures. Despite the significance of this issue, very few studies have investigated the behavioral effects of a single intraperitoneal (I.P.) Sham and/or single I.P. Saline injection in mice, and those that have used mostly adult males. In this study, we investigated if a single I.P. Sham and/or I.P. Saline injection affects female and male prepubertal (4-weeks-old) mice behavior. After Sham or Saline injection, we examined exploratory/motor behavior (open field test - OFT), anxiety-like behavior (elevated plus-maze - EPM), and behavioral despair/depressive-like behavior (forced swimming test - FST). We observed that both Sham prepubertal females and males showed behavioral alterations in OFT and EPM, and Saline males showed behavioral alterations in OFT and FST. On the other hand, prepubertal Saline females showed an increase in exploratory behavior, risk assessment/anxiety-like behavior, and behavioral despair/depressive-like behavior. Thus, our findings indicate that control procedures commonly used in physiological and pharmacological experimental designs affect the behavior of prepubescent mice, with more pronounced effects in females than in males. This study suggests considering Naïve animals together with Sham and/or Vehicle for a better and more honest interpretation of the data.

Anti-obesity potential of almond (Prunus dulcis) in experimental animals under cafeteria and atherogenic diets

Background & objectives

Natural dietary supplements are progressively getting famous to supplant synthetic substances particularly in chronic morbidities. The aim of this study was to evaluate the anti-obesity potential of almond on the normal, Cafeteria, and Atherogenic diets.

Materials and methods

Parameters such as change in body weight, body temperature, lipid profile, organ weights, and fat pad weights were assessed. Central Nervous System related studies (Despair Swim test and Elevated Plus maze test) were also performed to comprehend the effect of the diets, and almond on the brain. All of the experimental animals were randomly assigned to one of three diet categoriesregular, cafeteria, or atherogenic, and fed those diets for 40 days. Each diet had the control group, standard drug group and three almond groups (low dose: 50; medium dose: 100 and high dose: 200 mg/kg body weight). Body weight was recorded every alternate day. On 40th day, body temperature was measured. On day 41, lipid parameters, organ weights, fat pad weights and the CNS parameters were evaluated. ANOVA followed by Duncans Multiple Range Test were used for statistical analysis.

Results

Treatment of animals with either a low or high dose of almond as well as a standard herb prevented a rise in body weight significantly (p = 0.01) in all three diet groups. When a regular diet was replaced with a cafeteria and atherogenic diet, the serum levels of triglycerides and LDL increased significantly, while HDL levels decreased significantly. Overall, almond preparation reduced lipid parameters, organ weights, fat-pad weights, and stabilized CNS parameters substantially.

Interpretation & conclusion

The almond high dose was the most effective of all the almond preparations. Our study suggests that chronic administration of almond independently reduces the body weight in experimental animals.

The effects of age, sex, and handling on behavioral parameters in the multivariate concentric square field™ test

The multivariate concentric square field™ (MCSF) is a complex and ethologically relevant apparatus that is designed to measure several behavioral parameters within the same test session including risk-taking, risk-assessment, shelter-seeking (anxiety relieving), exploration, and general activity. While several studies have behaviorally and pharmacologically validated the use of the MCSF in adults, far fewer have used adolescents. Given the well-established link between adolescence and risk-taking, it is important to validate use of the MCSF in adolescence. The present study compared the effects of age, sex, and handling on behavioral categories in the MCSF. In addition, principal component analyses were used to compare the underlying behavioral components in adolescent and adult Sprague-Dawley rats. Results revealed that handling increased risk-taking and reduced shelter-seeking. Females were more exploratory than males, but no compelling age differences in risk-taking or risk-assessment were found. Principal component analyses revealed six major principal components for both adolescents and adults with the first and second components consisting mainly of center/center circle, risk-assessment, and shelter-seeking variables in adolescence, and general activity and center/center circle variables in adults. These results confirm age differences in the underlying behavioral components in the MCSF.

Effects of aging on the motor, cognitive and affective behaviors, neuroimmune responses and hippocampal gene expression

The known effects of aging on the brain and behavior include impaired cognition, increases in anxiety and depressive-like behaviors, and reduced locomotor activity. Environmental exposures and interventions also influence brain functions during aging. We investigated the effects of normal aging under controlled environmental conditions and in the absence of external interventions on locomotor activity, cognition, anxiety and depressive-like behaviors, immune function and hippocampal gene expression in C57BL/6 mice. Healthy mice at 4, 9, and 14 months of age underwent behavioral testing using an established behavioral battery, followed by cellular and molecular analysis using flow cytometry, immunohistochemistry, and quantitative PCR. We found that 14-month-old mice showed significantly reduced baseline locomotion, increased anxiety, and impaired spatial memory compared to younger counterparts. However, no significant differences were observed for depressive-like behavior in the forced-swim test. Microglia numbers in the dentate gyrus, as well as CD8+ memory T cells increased towards late middle age. Aging processes exerted a significant effect on the expression of 43 genes of interest in the hippocampus. We conclude that aging is associated with specific changes in locomotor activity, cognition, anxiety-like behaviors, neuroimmune responses and hippocampal gene expression.

Antidepressant responsiveness in adulthood is permanently impaired after neonatal destruction of the neurogenic pool

The dynamic turnover of hippocampal neurons is implicated in the regulation of cognitive and affective behavior. Extending our previous demonstration that administration of dexamethasone (ND) to neonatal rats depletes the resident population of neural precursor cells (NPC) and restrains the size of the neurogenic regions, we now show that the adverse effects of ND persist into adulthood. Specifically, ND impairs repletion of the neurogenic pool and neurogenesis; ND also compromises cognitive performance, the ability to actively adapt to an acute stressor and, the efficacy of glucocorticoid (GC) negative feedback. Interestingly, although ND depletes the neurogenic pool, it does not permanently abolish the proliferative machinery of the residual NPC population; however, ND increases the susceptibility of hippocampal granule neurons to apoptosis. Although the antidepressant fluoxetine (FLX) reverses the latter phenomenon, it does not replenish the NPC pool. Treatment of ND-treated adult rats with FLX also improves GC negative feedback, albeit without rescuing the deleterious effects of ND on behavior. In summary, ND leads to protracted disruption of mental functions, some of which are resistant to antidepressant interventions. We conclude that manipulation of the NPC pool during early life may jeopardize the therapeutic potential of antidepressants in adulthood.

Preclinical animal anxiety research - flaws and prejudices

The current tests of anxiety in mice and rats used in preclinical research include the elevated plus-maze (EPM) or zero-maze (EZM), the light/dark box (LDB), and the open-field (OF). They are currently very popular, and despite their poor achievements, they continue to exert considerable constraints on the development of novel approaches. Hence, a novel anxiety test needs to be compared with these traditional tests, and assessed against various factors that were identified as a source of their inconsistent and contradictory results. These constraints are very costly, and they are in most cases useless as they originate from flawed methodologies. In the present report, we argue that the EPM or EZM, LDB, and OF do not provide unequivocal measures of anxiety; that there is no evidence of motivation conflict involved in these tests. They can be considered at best, tests of natural preference for unlit and/or enclosed spaces. We also argued that pharmacological validation of a behavioral test is an inappropriate approach; it stems from the confusion of animal models of human behavior with animal models of pathophysiology. A behavioral test is developed to detect not to produce symptoms, and a drug is used to validate an identified physiological target. In order to overcome the major methodological flaws in animal anxiety studies, we proposed an open space anxiety test, a 3D maze, which is described here with highlights of its various advantages over to the traditional tests.

Age-related changes in behavior in C57BL/6J mice from young adulthood to middle age

Background

Aging is considered to be associated with progressive changes in the brain and its associated sensory, motor, and cognitive functions. A large number of studies comparing young and aged animals have reported differences in various behaviors between age-cohorts, indicating behavioral dysfunctions related to aging. However, relatively little is known about behavioral changes from young adulthood to middle age, and the effect of age on behavior during the early stages of life remains to be understood. In order to investigate age-related changes in the behaviors of mice from young adulthood to middle age, we performed a large-scale analysis of the behavioral data obtained from our behavioral test battery involving 1739 C57BL/6J wild-type mice at 2–12 months of age.

Results

Significant behavioral differences between age groups (2–3-, 4–5-, 6–7-, and 8–12-month-old groups) were found in all the behavioral tests, including the light/dark transition, open field, elevated plus maze, rotarod, social interaction, prepulse inhibition, Porsolt forced swim, tail suspension, Barnes maze, and fear conditioning tests, except for the hot plate test. Compared with the 2–3-month-old group, the 4–5- and 6–7-month-old groups exhibited decreased locomotor activity to novel environments, motor function, acoustic startle response, social behavior, and depression-related behavior, increased prepulse inhibition, and deficits in spatial and cued fear memory. For most behaviors, the 8–12-month-old group showed similar but more pronounced changes in most of these behaviors compared with the younger age groups. Older groups exhibited increased anxiety-like behavior in the light/dark transition test whereas those groups showed seemingly decreased anxiety-like behavior measured by the elevated plus maze test.

Conclusions

The large-scale analysis of behavioral data from our battery of behavioral tests indicated age-related changes in a wide range of behaviors from young adulthood to middle age in C57BL/6J mice, though these results might have been influenced by possible confounding factors such as the time of day at testing and prior test experience. Our results also indicate that relatively narrow age differences can produce significant behavioral differences during adulthood in mice. These findings provide an insight into our understanding of the neurobiological processes underlying brain function and behavior that are subject to age-related changes in early to middle life. The findings also indicate that age is one of the critical factors to be carefully considered when designing behavioral tests and interpreting behavioral differences that might be induced by experimental manipulations.

Electronic supplementary material

The online version of this article (doi:10.1186/s13041-016-0191-9) contains supplementary material, which is available to authorized users.

Better Utilization of Mouse Models of Neurodegenerative Diseases in Preclinical Studies: From the Bench to the Clinic

The major symptom of Alzheimer's disease is dementia progressing with age. Its clinical diagnosis is preceded by a long prodromal period of brain pathology that encompasses both formation of extracellular amyloid and intraneuronal tau deposits in the brain and widespread neuronal death. At present, familial cases of dementia provide the most promising foundation for modeling neurodegenerative tauopathies, a group of heterogeneous disorders characterized by prominent intracellular accumulation of hyperphosphorylated tau protein. In this chapter, we describe major behavioral hallmarks of tauopathies, briefly outline the genetics underlying familial cases, and discuss the arising implications for modeling the disease in transgenic mouse systems. The selection of tests performed to evaluate the phenotype of a model should be guided by the key behavioral hallmarks that characterize human disorder and their homology to mouse cognitive systems. We attempt to provide general guidelines and establish criteria for modeling dementia in a mouse; however, interpretations of obtained results should avoid a reductionist "one gene, one disease" explanation of model characteristics. Rather, the focus should be directed to the question of how the mouse genome can cope with the over-expression of the protein coded by transgene(s). While each model is valuable within its own constraints and the experiments performed are guided by specific hypotheses, we seek to expand upon their methodology by offering guidance spanning from issues of mouse husbandry to choices of behavioral tests and routes of drug administration that might increase the external validity of studies and consequently optimize the translational aspect of preclinical research.

Effects of chronic fluoxetine treatment on anxious behaviour of BALB/c mice in a 3-dimensional maze

Here we used a 3-dimensional (3D) maze, a modification of the radial maze, to assess the effects of treatment for two weeks with a single daily dose of fluoxetine (20 mg/kg, i.p.) on anxiety in male BALB/c mice. We examined whether anxiolytic effects of fluoxetine can be detected over three daily test sessions. We examined also whether repeated handling associated with chronic treatment interferes with effects of fluoxetine on anxiety responses. The 3D maze comprises nine arms, each connected to an upward inclined bridge radiating from a central platform. In this maze, BALB/c mice cross frequently into the bridges but avoid the arms. This avoidance is used as an index of anxiety. Two separate groups received once a day either saline (SALCH, n = 8) or fluoxetine (FLUCH, n = 8) for 14 days, and up to 30 min before the test during the subsequent 3 days. A third group received saline (SALAC, n = 8) 30 min before the test, once a day for 3 days. SALAC mice did not cross into the arms, and continued this avoidance over 3 sessions. SALCH mice avoided the arms in session 1 whereas FLUCH mice did cross into the arms, and like SALCH mice, increased number of crossings into and time on the arms in subsequent sessions. Fluoxetine evidently had an anxiolytic effect but only in the first session. These results indicate that handling experience decreased fear and anxiety in the mice, which may have masked the anxiolytic effect of fluoxetine in the second and third test sessions.

Short-term full kindling of the amygdala dissociates natural and periaqueductal gray-evoked flight behaviors of the rat

Panic attacks present a high comorbidity with agoraphobia, separation anxiety and generalized anxiety disorder. Nevertheless, while panic attacks have been frequently equated to fear, the relationship of panic disorder with specific phobias remains uncertain. The combination of experimental models of panic and phobias could but afford valuable information about both the comorbidity and causation of these disorders. As it regards, while the defensive behaviors produced by stimulation of dorsal periaqueductal gray matter (DPAG) resemble a panic attack, resistance to capture (RC) behaviors that ensue the kindling of the amygdala (AMY) are reminiscent of a phobic reaction. Therefore, this study examined the thresholds of DPAG-evoked panic-like behaviors in rats showing RC behaviors. Rats bearing electrodes in the DPAG and right AMY were subjected to either the full- (Kin-F) or sham- (Kin-S) kindling of AMY. RC behaviors were evaluated throughout both kindling procedures. Thresholds of DPAG-evoked defensive behaviors were recorded before and after the kindling. Moreover, performances of Kin-F and Kin-S rats in the elevated plus-maze were compared to those of intact controls. Data showed that Kin-F and Kin-S rats perform similarly in the elevated plus-maze, thereby making AMY-kindled rats unlikely as a model of generalized anxiety disorder. On the other hand, whereas the RC is characterized by a marked facilitation of natural freezing and flight behaviors, DPAG-evoked freezing (immobility and exophthalmus) and flight (galloping) behaviors were unexpectedly attenuated. Data suggest that RC is mediated by circuits distinct from those of DPAG-evoked defensive behaviors. Consequently, panic and phobic attacks may be mediated by different mechanisms as well.

Marked for life? Effects of early cage-cleaning frequency, delivery batch, and identification tail-marking on rat anxiety profiles

Daily handling of preweanling rats reduces their adult anxiety. Even routine cage-cleaning, involving handling, reduces adult anxiety compared with controls. Cage-cleaning regimes differ between animal breeders, potentially affecting rodent anxiety and experimental results. Here, 92 adult male rats given different cage-cleaning rates as pups, were compared on plus-maze, hyponeophagia, corticosterone, and handling tests. They were pair-housed and half were tail-marked for identification. Anxiety/stress profiles were unaffected by cage-cleaning frequency, suggesting that commercial-typical differences in husbandry contribute little variance to adult rat behavior. However, delivery batch affected some elevated plus-maze measures. Also, tail-marked rats spent three times longer on the plus-maze open arms than their unmarked cagemates, suggesting reduced anxiety, yet paradoxically they showed greater chromodacryorrhoea responses to handling, implying increased aversion to human contact. A follow-up study showed that rats avoided the odor released from the marker pen used. Thus, apparently trivial aspects of procedure can greatly affect experimental results.

The use of the elevated plus maze as an assay of anxiety-related behavior in rodents

The elevated plus maze is a widely used behavioral assay for rodents and it has been validated to assess the anti-anxiety effects of pharmacological agents and steroid hormones, and to define brain regions and mechanisms underlying anxiety-related behavior. Briefly, rats or mice are placed at the junction of the four arms of the maze, facing an open arm, and entries/duration in each arm are recorded by a video-tracking system and observer simultaneously for 5 min. Other ethological parameters (i.e., rears, head dips and stretched-attend postures) can also be observed. An increase in open arm activity (duration and/or entries) reflects anti-anxiety behavior. In our laboratory, rats or mice are exposed to the plus maze on one occasion; thus, results can be obtained in 5 min per rodent.

Lithium administration to preadolescent rats causes long-lasting increases in anxiety-like behavior and has molecular consequences

Lithium (Li) is frequently used in the treatment of bipolar disorder (BPD), a debilitating condition that is increasingly diagnosed in children and adolescents. Because the symptoms of BPD in children are different from the typical symptoms in adulthood and have significant overlap with other childhood psychiatric disorders, this disorder is notoriously difficult to diagnose. This raises the possibility that some children not affected by BPD are treated with Li during key periods of brain development. The objective of this investigation was to examine the long-term effects of Li on the developing brain via a series of behavioral and molecular studies in rats. Rat pups were reared on Li chow for 3 weeks. Parallel groups were tested while on Li chow or 2 and 6 weeks after discontinuation of treatment. We found increased measures of anxiety-like behavior at all times tested. Gene microarray studies of the amygdala revealed that Li affected the expression of gene transcripts of the synapse and the cytoskeleton, suggesting that the treatment induced synaptic adjustments. Our study indicates that Li can alter the trajectory of brain development. Although the effects of Li on the normal brain seems unfavorable, effects on the abnormal brain cannot be determined from these studies alone and may well be therapeutic. Our results indicate that Li administration to the normal brain has the potential for lasting adverse effects.

Ethological and temporal analyses of anxiety-like behavior: the elevated plus-maze model 20 years on

As well as being considered a reliable measurement instrument of animal anxiety-like behavior, the elevated plus-maze (EPM) is also used as a post-hoc test to evaluate emotionality in genetically modified rodents. The present review considers factors which may further improve the validity (predictive/face/construct) of the EPM model: (1) the importance of measuring defensive patterns of response such as risk assessment in addition to traditional measures such as open arm time; (2) other methodological refinements such as min-by-min scoring and use of a test/retest protocol; and (3) the identification and control of major sources of variability in this test. To estimate whether current use of the EPM by researchers takes the above factor into account, a survey of the recent literature was conducted. Results showed that the majority of studies have not yet assimilated these important considerations into their use of the EPM. For example, although risk assessment measures may be more sensitive to anxiety modulating drugs than traditional measures, only a quarter of studies have adopted them. It is hoped that this review can provide insights into the optimal use of the EPM, a simple task that can be very complex in terms of behavioral analysis.

Decreased anxiety levels related to aging

The present experiment investigated the effects of aging on emotional behavior, without concomitant influences from any previous behavioral manipulation apart from weighing the rats. Anxiety-related behaviors were measured in the elevated plus-maze (EPM). Performance in the open field (OF) was also assessed to control for any effect of aging on exploratory behavior that could account for changes in emotional behavior. Fifty-two naïve male Wistar rats of 3 (3MO), 17 (17MO), or 24 (24MO) months, were submitted to two sessions (5 min each) of EPM, followed by two sessions (2 min each) of OF, on 4 consecutive days. The main emotional indices (open arm entries, ratio of open arm entries to total entries, time spent in open arms, ratio of time in open arms to time in four arms, open arm ends, and head dips) measured in the EPM indicated a lower level of anxiety in aged (24MO) than in young (3MO) rats, whereas middle-aged (17MO) rats showed intermediate values between those of 3MO and 24MO rats; 3MO rats showed higher general motor activity (number of rearings in closed arms of EPM and in OF, and higher number of areas crossed in OF) than 17MO and 24MO rats. We conclude that aging is associated with a decrease in anxiety and in general motor activity.

CER to discrete and contextual stimuli: effects of stimulus modality depend on strain of rat

Strain differences in perception, cognition and affect have been found to interact with the effect of experimental treatments on learning. The present study tested Dark Agouti (DA) and Wistar rats in conditioning to discrete and contextual stimuli, for strain differences in conditioned emotional response (CER) and effects of stimulus modality. A Pavlovian trace-conditioning procedure was used in which a discrete target stimulus (flashing light or tone, counterbalanced across groups) was paired either contiguously or at a 30-s trace with footshock. Contextual conditioning was assessed using a background (continuously presented) experimental stimulus (alternate to that used as target). Experiment 1 used 5 x 0.5 mA, 0.5-s footshock and Experiment 2 used 2 x 0.5 mA, 1-s footshock. In both experiments, conditioning to the discrete (target) and background stimuli interacted with strain of rat and stimulus modality. For conditioning to the target stimulus, the trace-conditioning effect (of relatively greater suppression in contiguously conditioned than trace-conditioned groups) differed by stimulus and strain. It was greater for the Wistar strain with the flashing light stimulus and for the DA strain with the click stimulus (although the latter was not significant in Experiment 1). In addition, suppression to the background stimulus was affected by stimulus modality for the DA but not Wistar strain in both experiments. DAs conditioned more to the click than the light as background, whereas there was no difference by stimulus modality for Wistars, although the exact pattern of how this stimulus modality effect was mediated differed between experiments. These results demonstrate that stimulus modality can be an issue when considering apparent strain differences in conditioning.

The effects of MDMA pretreatment on the behavioural effects of other drugs of abuse in the rat elevated plus-maze test

Few preclinical studies have found long-term behavioural consequences of the serotonergic neurotoxicity produced by 3,4-methylenedioxymethamphetamine (MDMA). This study investigated whether pretreatment with MDMA altered the behavioural effects of other drugs of abuse. Adult male Lister hooded rats (n=10/group) were pretreated with 10 mg/kg MDMA or 1 ml/kg saline vehicle intraperitoneally every 2 h for 6 h. Fourteen days later, the behavioural effects of d-amphetamine (2 mg/kg), cocaine (10 mg/kg), ethanol (2.0 g/kg), heroin (0.5 mg/kg), or MDMA (10 mg/kg) were assessed in the elevated plus-maze test. MDMA pretreatment produced approximately 20-25% decrease in hippocampal 5-HT and 5-HIAA concentrations, and [(3)H]paroxetine binding when analysed 2 weeks later. Despite inducing neurotoxicity, this regimen had no effect upon the plus-maze behaviour induced by ethanol, heroin, and MDMA. Acutely, and independent of neurotoxic pretreatment, MDMA produced a clear anxiogenic-like behavioural profile with a reduction of open arm entries and suppression of explorative behaviours. Despite being acutely anxiogenic, pretreatment with a neurotoxic regimen of MDMA has little effect on the anxiety-related effects of other drugs of abuse. It is possible that extended time points would produce significant changes, although the available evidence suggests that the plus-maze may not be a suitable model for detection of behavioural dysfunction after neurotoxic MDMA.

Improvement of shuttle-box performance by anterodorsal medial septal lesions in rats

Septal lesions impair a variety of tasks, including inhibitory avoidance and one way active avoidance. In contrast, these lesions improve two-way active avoidance, probably by reducing anxiety. The present work aimed to study whether anterodorsal medial septal lesion (a) improves performance of two-way active avoidance task (Experiment I), as it has been observed with wider septal lesion, and (b) affect anxiety and/or locomotor activity (Experiment II). This precise region was chosen because some evidences suggest that its lesion do not lead to a reduction of anxiety. Lesioned rats tended to make a higher, but statistically non-significant (P=0.074), number of avoidances regardless of the session, being this difference statistically significant on the retention session (RT). The same lesion did not appear to have an anxiolytic effect, and did not affected basal locomotor activity. Different possible explanations of our results are discussed.

Excitotoxic lesions of the medial prefrontal cortex attenuate fear responses in the elevated-plus maze, social interaction and shock probe burying tests

Previous research investigating the effects of medial prefrontal cortex (MPFC) lesions on fear- and anxiety-related behavior has yielded an inconsistent body of findings. Behavioral studies have reported increases, decreases, and no effect on anxiety. In addition, many studies are complicated by the use of lesioning techniques that destroy fibers of passage, and the use of conditioned fear tests, which may introduce the confounding effects of learning and memory. Therefore, the present study examined the effects of ibotenic acid lesions of the MPFC (including prelimbic, infralimbic and anterior cingulate) on three wide-ranging and well-validated behavioral assays of anxiety: the elevated plus maze (EPM), social interaction (SI) and the shock-probe tests (SP). In the EPM test, lesioned rats showed a significantly higher percentage of open arm entries and open arm time than controls. In a version of the SI test sensitive to anxiolytic effects, lesioned rats were found to spend a significantly greater amount of time in active interaction with a conspecific; while another version of the SI test sensitive to anxiogenic effects did not show any differences between lesioned and non-lesioned controls. In the SP test, lesioned rats exhibited significantly lower rates of burying. In contrast, retention of shock probe avoidance was not affected. No effects of lesions on measures of locomotor activity or shock reactivity were found. The concordant anxiolytic-like effects found in the three behavioral assays strongly suggests a general reduction in fear responsiveness in MPFC lesioned rats.

Potentiation of the effect of an anesthetic, chloral hydrate, by stress and corticosterone: a behavioral study in the mouse

Many studies have demonstrated that stressors can modify the physiological action of drugs, mainly morphine. The present study investigated the effects of a mild stressor on chloral hydrate (Chl)-induced sedation in mice. For 4 consecutive days, NaCl and Chl-treated mice (300 mg kg(-1)) were stressed (S) either by a 5 min exposure to a brightly lit inescapable open field, or i.p. injected with corticosterone (Cor) (15 mg kg(-1)). Then, their spontaneous motor activity was recorded on an actisystem during 20 min and compared with that of the unstressed (US) NaCl and Chl-treated mice. On day 1 and 4, neither stressor nor i.p. administered Cor had any influence on the spontaneous motor activity of NaCl-treated mice. In Chl-treated mice, the spontaneous motor activity was very low. On day 1, it was similar in S mice, Cor-injected mice, and US mice. On the contrary, on day 4, both stress and Cor enhanced the anesthetic-induced hypoactivity, showing that the magnitude of sedation increased. It can then be stated that stressor, provided it was repeatedly administered, potentiated the sedative action of chloral hydrate and that such a potentiation was probably, but not only, Cor-dependent. Given that stress and Chl both produce dopamine overflow, it can be hypothesized that S, potentiates the sedative action of Chl through a dopaminergic link.

Diazepam has no beneficial effects on stress-induced behavioural and endocrine changes in male tree shrews

The present study evaluated the effect of subchronic oral treatment of psychosocially stressed male tree shrews with diazepam on locomotor activity, marking behavior, avoidance behavior, and urinary cortisol and noradrenaline. To mimic a realistic situation of anxiolytic intervention, the treatment started 14 days after the beginning of psychosocial stress; at that time, the stress-induced behavioral and endocrine alterations had been established. The drug (5 mg/kg/day) was administered orally in the morning, while the psychosocial stress continued during the whole treatment period; the therapeutic action of diazepam treatment was followed across 7 days. Twenty-four hours after the last application serum concentrations of diazepam and its major metabolites were determined via HPLC. The results revealed concentrations of 7 ng/ml for diazepam, 106 ng/ml for nordiazepam, 22 ng/ml for temazepam, and 30 ng/ml for oxazepam. Treatment of subordinate animals with diazepam did not reveal a beneficial effect to any of the parameters studied. This contrasts to earlier findings showing that the behavioral and neuroendocrine alterations produced by this stress paradigm are sensitive to chronic treatment with the tricyclic antidepressant clomipramine. The present results support the view that in male tree shrews the state induced by psychosocial stress might be more depression related than anxiety related.

Previous maze experience required to increase open arms avoidance in rats submitted to the elevated plus-maze model of anxiety

Studies have shown an increased open arm avoidance in rats re-exposed to the elevated plus-maze (EPM), which suggests a qualitative shift in emotional states from an unconditioned (Trial 1) to a learned (Trial 2) form of fear response, but a precise source of aversion has not been determined. Using rats submitted to the EPM or various EPM-derived configurations, this study was designed to investigate what previous maze experiences in Trial 1 are required to increase avoidance of open arms in EPM Trial 2. Results obtained from rats submitted to the EPM or EPM-derived configurations confirmed the increased open arms avoidance in Trial 2. Rats confined to either open or enclosed arms failed to show the increased avoidance of open arms in Trial 2. The results are discussed in terms of the minimum prerequisite in Trial 1 to elicit an avoidance learning response to open arms in Trial 2, and also the implications of an acquired fear response in rats for the study of the biological basis of anxiety.

Immediate increase in benzodiazepine binding in rat brain after a single brief experience in the plus maze: a paradoxical effect

A single drug-free experience in the elevated plus-maze is well documented to reduce the behavioral effects of benzodiazepines (BZs) in subsequent tests. To ascertain the possible role of altered BZ receptor binding to in this phenomenon, rats received a 5-min exposure to the elevated plus maze and were immediately sacrificed. Receptor autoradiography revealed that [3H]flunitrazepam binding was significantly elevated in several amygdaloid and hippocampal nuclei (range: 13-23%); [3H]muscimol binding in adjacent sections was not significantly altered. These results suggest that BZ receptors can change very rapidly in response to anxiogenic conditions. However, the unexpected finding that [3H]flunitrazepam binding is increased by maze exposure suggests that the subsequent loss of BZ anxiolytic effects in the plus-maze is probably unrelated to alterations in BZ binding in brain.

Tolerance to acute anxiolysis but no withdrawal anxiogenesis in mice treated chronically with 5-HT1A receptor antagonist, WAY 100635

Anxiolytic-like activity in the mouse elevated plus-maze has recently been demonstrated for a range of compounds varying in degree of selectivity as 5-HT1A receptor antagonists. As tolerance and dependence liability are among the major clinical disadvantages of benzodiazepine therapy, the present study examined the effects of acute drug challenge on the plus-maze profiles of mice following daily treatment for 20 days with saline, chlordiazepoxide (CDP; 10.0 mg/kg) or the selective 5-HT1A receptor antagonist, WAY 100635 (0.1-1.0 mg/kg). To assess the development of physical dependence (withdrawal anxiogenesis), the study incorporated independent groups of animals tested on the maze 24 h after the final dose. Challenge with CDP or WAY 100635 produced behavioural changes indicative of anxiety reduction in mice that had received daily handling/saline for 20 days, thereby demonstrating that the chronic injection regimen per se had not compromised the acute efficacy of either agent. The absence of a similar response to acute drug challenge in mice treated chronically with CDP or WAY 100635 suggested the development of tolerance to the acute anxiolytic effects of both compounds under present test conditions. Despite these observations, however, no signs of enhanced anxiety were evident 24 h following discontinuation of chronic treatment with either compound. In a further experiment, the absence of withdrawal anxiogenesis at 24 h was replicated and extended to discontinuation periods of 36 and 48 h for both drugs. Although present results show that tolerance develops to the acute anxiolytic effects of CDP and WAY 100635 in the murine plus-maze, they also suggest that enhanced anxiety is not an inevitable consequence of abrupt cessation of chronic treatment with either compound.

Combination of open field and elevated plus-maze: a suitable test battery to assess strain as well as treatment differences in rat behavior

1. A test battery consisting of a standard open field, an enriched open field and an elevated plus maze was used to study behavior in rats. 2. Male rats of the strains PVG/OlaHsd (PVG) and Sprague-Dawley-Hsd (SPRD) (150-200 g body wt) were used to assess interstrain differences as well as handling effects. In a subsequent experiment an other set of male PVG rats (150-200 g body wt) treated either with diazepam or zolpidem was used to evaluate the test battery for pharmacological purposes. 3. SPRD rats displayed higher motor activity levels and also higher levels of exploratory behavior than the PVG rats. In contrast plus-maze activity indicated more anxiety of SPRD than PVG rats. One week pre-test handling increased the activity of both strains but it increased explorative behavior in the enriched open field only in SPRD rats. Diazepam had a substantial anxiolytic effect. Zolpidem enhanced the explorative activity in a differently to diazepam and exerted only minor anxiolytic properties. 4. We concluded that the test battery used here enables to reveal differentially strain, and treatment effects in rats.

Strain differences in open-field and elevated plus-maze behavior of rats without and with pretest handling

Behavior of two rat strains was analyzed with and without 1-week pretest handling. Male rats (150-200 g body weight) of the strains PVG/OlaHsd (PVG) and Hsd:Sprague-DawleySD (SPRD) were tested once in a standard open field and an enriched open field and twice in an elevated plus-maze. Behavioral analysis revealed significant differences between the two strains and differential effects of the pretest handling procedure. SPRD rats displayed higher levels of activity and exploratory behavior than the PVG rats, whereas PVG rats were obviously less anxious. One-week pretest handling had an "anxiolytic" effect and changed activity and exploration-related behavior of the animals in both strains. Activity-related parameters were mainly affected in SPRD rats and anxiety-related ones in PVG rats. The data give evidence that differences in behavior of rats are not only determined genetically but also by preceding handling procedures. Because the two rat strains responded differentially to the pretest handling, we recommend to use a well-defined handling procedure before starting a behavioral test, especially when drug applications are included.

The influence of 5-HT2 and 5-HT4 receptor antagonists to modify drug induced disinhibitory effects in the mouse light/dark test

1. The ability of 5-HT2 and 5-HT4 receptor antagonists to modify the disinhibitory profile of diazepam and other agents was investigated in male BKW mice in the light/dark test box. 2. The 5-HT2A/2B/2C receptor antagonists ritanserin, MDL11939 and RP62203 and also methysergide, which failed to modify mouse behaviour when administered alone, caused dose-related enhancements (4 to 8 fold) in the potency of diazepam to disinhibit behavioural responding to the aversive situation of the test box. 3. Ritanserin was shown to enhance the disinhibitory potency of other benzodiazepines, chlordiazepoxide (4 fold), temazepam (10 fold) and lorazepam (10 fold), the 5-HT1A receptor ligands, 8-OH-DPAT (25 fold), buspirone (100 fold) and lesopitron (500 fold), the 5-HT3 receptor antagonists, ondansetron (100 fold) R(+)-zacopride (100 fold) and S(-)-zacopride (greater than a 1000 fold), the substituted benzamides, sulpiride (10 fold) and tiapride (5 to 10 fold) and the cholecystokinin (CCK)A receptor antagonist, devazepide (100 fold). It also reduced the onset of action of disinhibition following treatment with the 5-HT synthesis inhibitor parachlorophenylalanine. Ritanserin failed to enhance the disinhibitory effects of the CCKB receptor antagonist CI-988, the angiotensin AT1 receptor antagonist losarten or the angiotensin converting enzyme inhibitor ceranapril. 4. The 5-HT4 receptor antagonists SDZ205-557, GR113808 and SB204070 caused dose-related reductions in the disinhibitory effect of diazepam, returning values to those shown in vehicle treated controls. The antagonists failed to modify mouse behaviour when administered alone. 5. GR113808 was also shown to cause a dose-related antagonism of the disinhibitory effects of chlordiazepoxide, lorazepam, 8-OH-DPAT, buspirone, lesopitron, ondansetron, R(+)-zacopride, sulpiride, tiapride, devazepide, CI-988, losarten, ceranapril and parachlorophenylalanine. 6. It was concluded that in BKW mice (a) the failure of 5-HT2 and 5-HT4 receptor antagonists when administered alone to modify behaviour in the light/dark test indicates an absence of an endogenous 5-HT tone at the 5-HT2 and 5-HT4 receptors and (b) the enhancement by the 5-HT2 receptor antagonists and attenuation by the 5-HT4 receptor antagonists of drug-induced disinhibition indicates a plurality of 5-HT receptor involvement in the mediation of drug-induced disinhibitory profiles in the mouse.

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.

The effects of abused inhalants on mouse behavior in an elevated plus-maze

Previous research has shown that abused inhalants (i.e., the volatile solvents) share some of the pharmacological properties of drugs used in the treatment of anxiety. In an attempt to further examine commonalities in the effects of inhalants and central nervous system depressant drugs, the behavioral effects of inhaled 1,1,1-trichloroethane, toluene, methoxyflurane and the convulsant vapor flurothyl were examined and compared to those of diazepam in the elevated plus-maze, a test used to predict antianxiety effects. After inhalant exposure or diazepam injection, mice were placed in the center of an elevated plus-maze and the number of entries and time spent in each type of arm (open versus closed) were measured during 5-min tests. Exposure to increasing concentrations of toluene produced concentration-related increases in the total number of open arm entries and the total time spent on the open arms, a pattern of behavioral effects similar to that produced by diazepam. A similar pattern was observed for increasing concentrations of 1,1,1-trichloroethane and methoxyflurane but changes in open arm activity were only observed at concentrations that increased locomotor activity. Conversely, only decreases in open arm time and number of entries were observed for flurothyl. The increasing evidence for commonalities in the behavioral effects of volatile solvents and depressant drugs may provide a foundation for understanding the neurobehavioral basis of inhalant abuse.

Neuronal mechanisms mediating drug-induced cognition enhancement: cognitive activity as a necessary intervening variable

The conceptual foundations of a research aimed at the determination of potential neuronal, neuropharmacological, and behavioral/cognitive mechanisms mediating drug-induced cognition enhancement are discussed. The available evidence justifies a focus on attentional processes as a target for drug-induced cognition enhancement. Neuropharmacological mechanisms that may mediate drug-induced enhancement of attentional functions are proposed to interact necessarily with attention-associated neuronal activity. The elements of a transsynaptic approach to increase the excitability of basal forebrain cholinergic neurons and hence, attentional functions are discussed. Experimental tests of this hypothesis require the demonstration of interactions between cognition-induced increases in the activity of cortical cholinergic afferents and the effects of putative cognition enhancers. The available data illustrate that the effects of benzodiazepine receptor (BZR) agonists and inverse agonists on cortical acetylcholine (ACh) efflux interact with the state of activity in this system. The feasibility, potential heuristic power, and the experimental and conceptual problems of studies attempting to simultaneously assess drug effects on behavioral/cognitive abilities, ACh efflux, and neuronal activity have been revealed by an experiment intended to correlate performance in a task measuring sustained attention with medial prefrontal ACh efflux and medial prefrontal single-unit activity. The rational development of a psychopharmacology of cognition enhancers requires a union among behavioral/cognitive pharmacology, neuropharmacological and electrophysiological approaches.

A review of the validity and variability of the elevated plus-maze as an animal model of anxiety

Despite or possibly by virtue of the fact that it is one of the most commonly used animal models of anxiety the Elevated Plus-Maze (EPM) results in a wide range of, often contradictory, results following pharmacological experiments. The responses from a questionnaire distributed to 65 groups that have published studies using the EPM in the past 3 years has, along with reference to published reports, enabled some conclusions regarding the influencing factors to be drawn. Some evidence for differential sensitivities between strains exists, with albino rats being more sensitive to the anxiolytic effects of 5-HT3 receptor antagonists and 5-HT1A receptor agonists than pigmented animals. Most important, however, is the manipulation of the animals prior to testing and the aversiveness of the test conditions themselves. Stressing animals before testing (e.g., by moving from holding to test room) or using more aversive test conditions (e.g., elevated light levels) increases sensitivity to potential anxiolytics. Animals that are habituated to gentle handling or tested in less aversive conditions (e.g., EPM with ledges) show reduced likelihood of anxiolytic responses with administration of 5-HT3 antagonists, 5-HT1A agonists, and benzodiazepines.

The behavioural and neuronal effects of the chronic administration of benzodiazepine anxiolytic and hypnotic drugs

Benzodiazepine anxiolytic and hypnotic drugs are some of the most widely prescribed drugs in the Western world. Despite this fact, the mechanisms that underlie the development of tolerance to, and dependence upon, benzodiazepines are poorly understood. The aim of this review is to summarize and critically evaluate the experimental evidence relating to the chronic behavioural and neuronal effects of benzodiazepines. Behavioural studies in animals generally indicate that tolerance gradually develops to the muscle relaxant, ataxic, locomotor and anticonvulsant effects of benzodiazepines. The evidence relating to the development of tolerance to the anxiolytic effects of benzodiazepines is less clear. The literature on the possible mechanisms of benzodiazepine tolerance and dependence is large, highly complex and difficult to interpret. The effect of chronic benzodiazepine treatment varies enormously as a function of the benzodiazepine used and the treatment schedule employed. Many studies have demonstrated a down-regulation of benzodiazepine binding sites, although affinity is usually unchanged. The evidence relating to the number and affinity of GABAA binding sites is unclear. Some studies suggest that chronic benzodiazepine administration results in a reduction in the number of Cl- channels associated with the GABAA receptor complex, although it is not clear that the efficacy of the GABA binding site in operating the Cl- channel necessarily changes. There is, however, substantial evidence to support the hypothesis that chronic benzodiazepine treatment results in a reduction in the coupling between the GABAA and benzodiazepine binding sites (the "functional uncoupling hypothesis"). Although some electrophysiological studies suggest that chronic benzodiazepine treatment results in a subsensitivity to GABA, this effect seems to be highly area-specific.

The elevated plus-maze is not sensitive to the effect of stressor controllability in rats

The present experiments examined the sensitivity of the elevated plus-maze to the effects of stressor controllability. Previous work had established that inescapable but not an equal amount of escapable electric tail shock reduced social interaction. The present experiments demonstrate that prior exposure to shock alters elevated plus-maze behavior, but that this effect is not sensitive to the escapability of the shock. These experiments include a replication of the usual pharmacologic effects of benzodiazepine ligands (2 mg/kg diazepam; 0.4 mg/kg methyl 6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate) to demonstrate the sensitivity of the elevated plus-maze procedures used. The results provide additional support for the idea that the social interaction and elevated plus-maze measures of "anxiety" are sensitive to different processes.

Changes in benzodiazepine-GABA receptor coupling in an accumbens-habenula circuit after chronic diazepam treatment

1. The effects of subacute and of chronic diazepam treatment upon binding to the GABAA receptor have been examined by use of receptor autoradiography for determining flunitrazepam (FNZP) binding, GABA enhancement of FNZP binding. SR 95531 2-(3'-carboxy-2',propyl)-3-amino-6-p-methoxyphenylpyridazinium bromide) binding and GABA binding in parallel sections from rat brain. Prior to the autoradiographic procedures, a behavioural assessment of the rats was made in the elevated plus-maze test of anxiety. 2. Rats receiving diazepam either subacutely (3 days) or chronically (28 days) by both continuous release, from previously implanted subcutaneous silastic capsules, or by daily injection (5 mg kg-1) did not display changes in FNZP or GABA binding in any of the 47 brain structures analysed. Similarly, there were no significant effects of treatment upon mean total entries or on the open:total ratio for entries in the elevated plus-maze. 3. There were reductions in the GABA enhancement of FNZP binding in the nucleus accumbens and central grey after subacute diazepam treatment. This effect persisted in the nucleus accumbens after chronic treatment. Less marked effects occurred in the lateral habenula, dorsal raphe and substantia nigra pars compacta. In the dorsal tegmental nucleus, GABA enhancement of FNZP binding was enhanced after chronic treatment and this was accompanied by reductions in SR 95531 binding. Treatment did not otherwise affect SR 95531 binding, with the exception of the dorsal raphe where binding was decreased after subacute treatment. 4. In general, the patterns of binding produced by the two different treatment routes were very similar. However, SR 95531 binding was lower in certain hippocampal fields in the i.p. treated animals compared to the rats implanted with silastic capsules. 5. It is concluded that repeated administration of diazepam evokes changes in benzodiazepine and GABA receptor coupling, and to a lesser extent changes in low affinity GABA binding, in certain interrelated brain structures of which an accumbens-habenula circuit is a central feature. These changes occur soon after the initiation of diazepam treatment, suggesting that they are unlikely to account for tolerance to the anxiolytic effects of diazepam but may trigger and/or accompany other critical neurochemical events.

Only controls: effect of handling, sham injection, and intraperitoneal injection of saline on behavior of mice in an elevated plus-maze

In male NIH-Swiss mice intraperitoneal injection of physiological saline significantly diminished (vs. naive mice) the ratio of the number of entries into open arms over the sum of entries into open and closed arms, and significantly prolonged time spent in closed arms. These two effects are considered to be typical for anxiety-inducing drugs (anxiogens). The time spent in open arms and at the intersection was unaffected. An equal number of entries into closed and also open arms was observed among fast- and slow-moving individuals. This is an argument against using the number of entries into arms as a measure of locomotor activity of mice. Additional measurement of locomotor activity in actometers is needed to check whether drugs used in experiments with elevated plus-maze alter locomotor activity. Injection of saline significantly shortened the latency of reaching one of the closed arms from the free end of an open arm. Handling, sham injection, and injection significantly diminished the shortening of latency in a second experiment (vs the latency in the first one), a parameter used as a criterion of memory and learning. Thus, saline-treated groups taken as controls in pharmacological experiments possess the behavioral profile of stressed and anxious animals in an elevated plus-maze, a device used as a model of anxiety and a model for studying memory and learning in mice and rats.

Differential effect of buspirone and diazepam on negative contrast in one-way avoidance learning

The main aim of the present work was to investigate the effect of buspirone, a 5-HT1A receptor agonist, on successive negative contrast in one-way avoidance learning. Successive negative contrast was induced by shifting rats from a large reward (30 s spent in the safe compartment) to a small reward (1 s). Acute administration of buspirone (0.25, 0.5, 0.75 and 1.0 mg/kg i.p.) did not attenuate the contrast effect, as opposed to that observed for diazepam (1 mg/kg i.p.). The highest dose of buspirone used, however, did interfere with the learning of the avoidance response itself. Chronic buspirone (20 days, 0.5 and 0.75 mg/kg i.p.) did not have any effect on successive negative contrast either. Overall, these results could suggest that the 5-HT1A receptor is not involved in the negative contrast effect studied, quite different to that observed for the gamma-aminobutyric acid (GABA) system. The findings are compared to results obtained with animal models selectively sensitive to some anxiolytic drugs, as are the so-called 'conflict models'.

Increased dopamine and norepinephrine release in medial prefrontal cortex induced by acute and chronic stress: effects of diazepam

We have examined the effects of diazepam on the stress-induced increase in extracellular dopamine and norepinephrine in the medial prefrontal cortex using in vivo microdialysis. In naive rats, acute tail pressure (30 min) elicited an increase in the concentrations of dopamine and norepinephrine in extracellular fluid of medial prefrontal cortex (+54 and +50%, respectively). Diazepam (2.5 mg/kg, i.p.) decreased the basal concentration of extracellular dopamine and norepinephrine. Diazepam also attenuated the stress-evoked increase in the absolute concentrations of extracellular dopamine (+17%), but did not alter the stress-induced increase in norepinephrine (+41%). However, when the drug-induced decrease in basal dopamine and norepinephrine concentration was taken into account, the stress-induced net increase in dopamine above the new baseline was equivalent to that obtained in vehicle pretreated rats, whereas the net increase in norepinephrine was almost twice that obtained in control subjects. In rats previously exposed to chronic cold (three to four weeks at 5 degrees C), tail pressure again produced an increase in the concentrations of dopamine and norepinephrine in the medial prefrontal cortex (+42% and +92%, respectively). However, in these chronically stressed rats, diazepam no longer decreased basal dopamine or norepinephrine in extracellular fluid, nor did it affect the stress-induced increase in the concentrations of these catecholamines. These data indicate that diazepam has complex effects on the extracellular concentrations of dopamine and norepinephrine which vary depending upon whether the rat is undisturbed or stressed during the period of drug exposure as well as the rat's prior history of exposure to stress. Moreover, these data raise questions regarding the role of catecholamines in the mechanism by which diazepam exerts its anxiolytic properties.

Continuous exposure to FG 7142: behavioural sensitisation is not accompanied by changes in benzodiazepine/GABA receptor coupling

Chronic intermittent high-dose treatment with N-methyl-β-carboline-3-carboxamide (FG 7142) leads to kindling accompanied by reduction in γ-aminobutyric acid (GABA) receptor function, whereas chronic continuous administration may result in behavioural effects in the opposite direction from those of acute FG 7142. In the present study, we have investigated the effects of continuous administration of low doses of FG 7142 on the response to an acute challenge dose of FG 7142 in an ethologically based model of anxiety. Rats treated continuously for 14 days with FG 7142 delivered by osmotic minipump at a rate of 1.2-1.5 mg/kg/day showed sensitisation to the anxiogenic effects of a challenge dose of FG 7142 (6 mg/kg), as measured in the elevated plus-maze. This was not accompanied by any change in benzodiazepine/GABA receptor coupling, as assessed by the 'GABA shift'. These results indicate that continuous low-dose treatment with FG 7142 can elicit sensitisation to the behavioural effects of FG 7142, but that this is unlikely to be mediated by changes in benzodiazepine/GABA receptor coupling.

Handling alters habituation and response to stimulus change in the holeboard

The responses of rats that had been extensively handled for 18 days were compared in the holeboard with those of rats that had received handling for only 4 days before the test. The extensively handled group showed slower between-day habituation of exploratory head-dipping. They did not differ in the number of head-dips, but spent longer head-dipping, at holes with objects than at those without. The less-handled group did not differ in the time spent head-dipping, but made more head-dips at empty holes. Both groups reacted similarly to the removal of the objects on day 4. However, the extensively handled rats showed a greater response of increased head-dipping when a novel object was introduced on day 5. The groups did not differ in their locomotor activity, but the extensively handled group made more rears. The results are discussed with respect to the neurochemical changes that have been found after repeated handling.

Effects of early protein malnutrition and environmental stimulation upon the reactivity to diazepam in two animal models of anxiety

In order to investigate the effects of early protein malnutrition and environmental stimulation upon the response to the anxiolytic properties of diazepam, two animal models of anxiety (elevated plus-maze and light-dark transition tests) were used. Rats were malnourished by feeding their dams a 6% protein diet during the lactation period (0-21 days of age) while well-nourished controls received a 16% protein diet. From 21 to 70 days of age all rats received a balanced lab chow diet. Environmental stimulation consisted of 3-min daily handling from birth to 70 days of age. Additional stimulation was provided from 21 to 70 days of age by rearing the rats in an enriched living cage. Eight groups of rats were studied in a 2 (malnourished or well-nourished) x 2 (stimulated or nonstimulated) x 2 (diazepam or vehicle) design. At 70 days of age, independent groups of rats treated with diazepam (2.5 mg/kg, IP) or vehicle were submitted to testing in the elevated plus-maze or light-dark transition procedures. The results showed that both diazepam and environmental stimulation reduced anxiety in the elevated plus-maze; stimulation changed the anxiolytic response to diazepam and the two diet conditions altered differentially the response to both pharmacological and stimulation procedures. These results suggest that environmental stimulation can affect differentially the behavioral response of malnourished and well-nourished rats treated with diazepam.

Ethological evaluation of the effects of acute and chronic buspirone treatment in the murine elevated plus-maze test: comparison with haloperidol

Buspirone is renowned for its highly inconsistent effects in animal models of anxiety. In the present study, the effects of acute (0.63-5.0 mg/kg) and chronic (1.25-5.0 mg/kg, daily, 15 days) buspirone treatment on the behaviour of mice in the elevated plus-maze test were assessed using a recently developed ethological scoring method. On acute administration, a selective reduction in risk assessment behaviours was observed at 1.25 mg/kg; these mild anxiolytic-like effects were maintained at higher doses (2.5-5.0 mg/kg) which also reduced measures of general activity. Similar, though more potent, effects were observed with chronic administration; the lowest dose tested (1.25 mg/kg) reduced open arm entries and total stretch attend postures while higher doses profoundly reduced all major indices of anxiety (traditional and novel) and, concomitantly, suppressed total entries and rearing. Acute administration of haloperidol (0.0125-0.1 mg/kg) appeared to mimic the behavioural suppressant effects of buspirone without selectively affecting anxiety-related measures at any dose. It is suggested that the anti-anxiety and behavioural suppressant profile of buspirone may reflect combined action at 5-HT1A and D2 receptors, respectively. Results are discussed in relation to the utility of risk assessment as a sensitive index of anxiety in models based upon unconditioned behaviour.

Comparison of potencies of 5-HT3 receptor antagonists at inhibiting aversive behavior to illumination and the von Bezold-Jarisch reflex in the mouse

The inhibitory effects of ondansetron and R and S zacopride on aversive behavior to light and the von Bezold-Jarisch reflex have been compared in mouse. The potencies (ID50, microgram/kg i.v.) of compounds at inhibiting the von Bezold-Jarisch reflex, elicited by 2-methyl-5-HT (mouse 100 micrograms/kg, i.v.; rat 10-80 micrograms/kg i.v.) were: S zacopride (0.02), granisetron (0.17), R zacopride (0.30) ondansetron (3.16). A similar rank order of ID50 values was observed in rat, i.e. S zacopride (0.02), granisetron (0.36), R zacopride (0.25) and ondansetron (2.65). These data suggest that the activity of compounds at 5-HT3 receptors mediating this effect was similar in both mouse and rat. In mouse behavioral studies, ondansetron and R and S zacopride potently inhibited aversive behavior to light (0.0003-30 micrograms/kg, p.o.), when the amount of time spent in the dark and locomotor activity were measured. Thus, at 0.3 ng/kg, the mean percentage time spent in the dark significantly decreased from 84 to 72, for both R and S zacopride, respectively. The maximal effects of these compounds were modest in comparison to the 'anxiolytic' effects of diazepam (0.3-1.4 mg/kg, i.p.; at 0.3 mg/kg the mean percentage time spent in the dark significantly decreased from 84 to 36) or chlordiazepoxide (3-40 mg/kg, i.p.; at 3 mg/kg, the mean percentage time spent in the dark significantly decreased from 85 to 40). The doses of the 5-HT3 antagonists were approx 1000-fold lower than those effective inhibitory doses determined in the von Bezold-Jarisch reflex studies, in either mouse or rat.(ABSTRACT TRUNCATED AT 250 WORDS)

An assessment of the elevated X-maze for studying anxiety and anxiety-modulating drugs

The elevated X-maze has strong claims to validity as an animal model of anxiety, both in theoretical basis and drug responses. The model is sensitive to actual and putative anxiolytics, but because insufficient time has elapsed since its discovery, no agent first predicted to be anxiolytic in the elevated X-maze has been brought into general use yet. It has an advantage in detecting anxiolytic and anxiogenic agents under the same operating conditions. The design and execution of experiments with the model is discussed and it is shown that baseline arm preference and the size or direction of drug effects differ in the procedural factors affecting them. Because it presents features of both passive and active avoidance and approach/avoidance conflict, it may prove able to detect drug effects in different forms of human anxiety and aid in understanding their neurobiology.

Anxiogenic stimuli in the elevated plus-maze

Untreated rats normally avoid the open arms of the "elevated plus-maze," preferring instead the closed arms, whereas rats treated with antianxiety drugs (e.g., diazepam) show far less open-arm avoidance. Although it has often been assumed that rats avoid the open arms because of novelty, height, or open space, the anxiogenic role of these stimuli in the plus-maze has not been systematically examined. In Experiment 1, rats were repeatedly exposed to the elevated plus-maze with the expectation that their "fear" of the open arms would habituate over trials. Instead, open-arm avoidance actually increased on the second trial and showed no evidence of habituating after 18 trials. In Experiment 2, three 30-min sessions of confinement to the open arms ("flooding") failed to decrease rats' open-arm avoidance. Instead, rats that had received flooding avoided the open arms significantly more than control rats during the first test. Experiment 3 showed that although diazepam-treated rats avoided the open arms less than vehicle-controls on the first test this difference dissipated across test trials. Further, diazepam had no carryover effect on rats' subsequent avoidance of the open arms in a nondrugged state. In Experiment 4, plus-maze height was varied from 50 to 6 cm, but rats did not display more open-arm activity as maze height decreased. In Experiment 5, height cues were manipulated by placing a "floor" 8 cm beneath one open arm while leaving the floor of the other open arm at 50 cm. Rats did not avoid the "low" open arm less than the "high" open arm.(ABSTRACT TRUNCATED AT 250 WORDS)