Brain organic cation transporter 2 controls response and vulnerability to stress and GSK3β signaling

Interactions between genetic and environmental factors, like exposure to stress, have an important role in the pathogenesis of mood-related psychiatric disorders, such as major depressive disorder. The polyspecific organic cation transporters (OCTs) were shown previously to be sensitive to the stress hormone corticosterone in vitro, suggesting that these transporters might have a physiologic role in the response to stress. Here, we report that OCT2 is expressed in several stress-related circuits in the brain and along the hypothalamic-pituitary-adrenocortical (HPA) axis. Genetic deletion of OCT2 in mice enhanced hormonal response to acute stress and impaired HPA function without altering adrenal sensitivity to adrenocorticotropic hormone (ACTH). As a consequence, OCT2(-/-) mice were potently more sensitive to the action of unpredictable chronic mild stress (UCMS) on depression-related behaviors involving self-care, spatial memory, social interaction and stress-sensitive spontaneous behavior. The functional state of the glycogen synthase kinase-3β (GSK3β) signaling pathway, highly responsive to acute stress, was altered in the hippocampus of OCT2(-/-) mice. In vivo pharmacology and western blot experiments argue for increased serotonin tonus as a main mechanism for impaired GSK3β signaling in OCT2(-/-) mice brain during acute response to stress. Our findings identify OCT2 as an important determinant of the response to stress in the brain, suggesting that in humans OCT2 mutations or blockade by certain therapeutic drugs could interfere with HPA axis function and enhance vulnerability to repeated adverse events leading to stress-related disorders.

Rescuing prefrontal cAMP-CREB pathway reverses working memory deficits during withdrawal from prolonged alcohol exposure

Both human and animal studies indicate that alcohol withdrawal following chronic alcohol consumption (CAC) impairs many of the cognitive functions which rely on the prefrontal cortex (PFC). A candidate signaling cascade contributing to memory deficits during alcohol withdrawal is the protein kinase A (PKA)/cAMP-responsive element binding (CREB) cascade, although the role of PKA/CREB cascade in behavioral and molecular changes during sustained withdrawal period remains largely unknown. We demonstrated that 1 week (1W) or 6 weeks (6W) withdrawal after 6-month CAC impairs working memory (WM) in a T-maze spontaneous alternation task and reduces phosphorylated CREB (pCREB) in the PFC but not the dorsal CA1 region (dCA1) of the hippocampus compared with CAC and water conditions. In contrast, both CAC-unimpaired and withdrawn-impaired mice exhibited decreased pCREB in dCA1 as well as reduced histone H4 acetylation in PFC and dCA1, compared with water controls. Next, we showed that enhancing CREB activity through rolipram administration prior to testing improved WM performance in withdrawn mice but impaired WM function in water mice. In addition, WM improvement correlates positively with increased pCREB level selectively in the PFC of withdrawn mice. Results further indicate that direct infusion of the PKA activator (Sp-cAMPS) into the PFC significantly improves or impairs, respectively, WM performance in withdrawn and water animals. In contrast, Sp-cAMPS had no effect on WM when infused into the dCA1. Collectively, these results provide strong support that dysregulation of PKA/CREB-dependent processes in prefrontal neurons is a critical molecular signature underlying cognitive decline during alcohol withdrawal.

Social rank and responses to feeding competition in rhesus monkeys

A group of rhesus monkeys (Macaca mulatta) living in a large enclosure received food which varied in desirability and spatial distribution. Feeding and agonistic behaviour of four hierarchical subgroups were analyzed. In general, there was less aggression and improved feeding rates with dispersed food than with piled food. The behaviour of high-ranking subjects was the most stable: they usually ate first, ate most, and showed little agonistic behaviour. The most subordinate subjects were also involved in few agonistic episodes, since they tended to remain on the periphery and eat little. However, subordinates obtained access earlier to a pile of the most highly prized food (banana pieces) than to piles of less attractive foods. Subordinates also obtained their highest feeding score when banana pieces were dispersed. This latter condition was associated with increased aggression. The feeding behaviour of intermediate-ranking subjects lay between that of dominants and subordinates, and the former were involved in more aggression. Behaviour in situations involving restricted food reflects cognitive processes in which several factors including attractiveness of the food, social status, and risks involved are evaluated.

Gabra5-gene haplotype block associated with behavioral properties of the full agonist benzodiazepine chlordiazepoxide

The gabra5 gene is associated with pharmacological properties (myorelaxant, amnesic, anxiolytic) of benzodiazepines. It is tightly located (0.5 cM) close to the pink-eyed dilution (p) locus which encodes for fur color on mouse chromosome 7. We tested the putative role of the gabra5 gene in pharmacological properties of the full non specific agonist chlordiazepoxide (CDP), using behavioral and molecular approaches in mutated p/p mice and wild type F2 from crosses between two multiple markers inbred strain ABP/Le and C57BL/6By strain. From our results, using rotarod, light-dark box, elevated maze and radial arm maze tests, we demonstrate that p/p mice are more sensitive than WT to the sensory motor, anxiolytic and amnesic effect of CDP. This is associated with the presence of a haplotypic block on the murine chromosome 7 and with an up regulation of gabra5 mRNAs in hippocampi of p/p F2 mice.

Antidepressants recruit new neurons to improve stress response regulation

Recent research suggests an involvement of hippocampal neurogenesis in behavioral effects of antidepressants. However, the precise mechanisms through which newborn granule neurons might influence the antidepressant response remain elusive. Here, we demonstrate that unpredictable chronic mild stress in mice not only reduces hippocampal neurogenesis, but also dampens the relationship between hippocampus and the main stress hormone system, the hypothalamo-pituitary-adrenal (HPA) axis. Moreover, this relationship is restored by treatment with the antidepressant fluoxetine, in a neurogenesis-dependent manner. Specifically, chronic stress severely impairs HPA axis activity, the ability of hippocampus to modulate downstream brain areas involved in the stress response, the sensitivity of the hippocampal granule cell network to novelty/glucocorticoid effects and the hippocampus-dependent negative feedback of the HPA axis. Remarkably, we revealed that, although ablation of hippocampal neurogenesis alone does not impair HPA axis activity, the ability of fluoxetine to restore hippocampal regulation of the HPA axis under chronic stress conditions, occurs only in the presence of an intact neurogenic niche. These findings provide a mechanistic framework for understanding how adult-generated new neurons influence the response to antidepressants. We suggest that newly generated neurons may facilitate stress integration and that, during chronic stress or depression, enhancing neurogenesis enables a dysfunctional hippocampus to restore the central control on stress response systems, then allowing recovery.

Acute inescapable stress exposure induces long-term sleep disturbances and avoidance behavior: a mouse model of post-traumatic stress disorder (PTSD)

The experience of traumatic stress often leads to long-lasting alteration in sleep quality and behavior. The objective of the present experiment was to investigate the short- and long-term effects of acute inescapable stress (i.e. two electric foot-shocks of 1.5 mA; 2s) on sleep/wakefulness parameters and behavior in Swiss mice using electroencephalographic (EEG) analysis. Baseline EEG recording was performed in the home cage for 6h prior to the application of the foot-shocks in the presence of an object (i.e. a plastic prism). One, 7, 14 or 21 days later, a second 6h EEG recording session was performed after mice had been exposed or not to the same object for 5 min in their home cage. Results showed that at day 1, 7, 14 and 21 post-stress, shocked mice displayed sleep fragmentation as shown by an increase in the number of sleep episodes, regardless the presence of the object or not. In animals exposed to the object, the total duration of wakefulness over 6h was significantly increased at days 7, 14 and 21 post-stress, and rapid eye movement (REM) sleep was significantly decreased at day 14 post-shock. Moreover, in the behavioral experiment, conditioned avoidance to a shock-paired object, which appeared as soon as 24h after shock application, turned into generalized avoidance towards an unknown object 21 days after stress. These findings demonstrate that an acute inescapable stress exposure may cause long-lasting alterations in sleep patterns and behavior. Such modifications may be reminiscent of the profound changes observed in patients suffering from post-traumatic stress disorder.

Central auditory processing in aging: the dichotic listening paradigm

OBJECTIVE

Aging is associated with cognitive changing. Central auditory processing dysfunction may explain some understanding difficulties in elderly. It may be evaluated with the dichotic listening (DL) test, a widely-used experimental paradigm for studying inter-hemispheric interactions and attentional processes. This study examines central auditory language processing with a dichotic listening task in right-handed old subjects according to their age.

DESIGN

Cross sectional-study.

SETTING

memory clinic and geriatric unit.

PARTICIPANTS

Adult group (Ad) consisted in 26 subjects (21 women and 5 men) aged 50-69 years and an old adults group (Old-Ad) consisted in 20 subjects (19 women and 1 man) aged 70 to 89 years.

MEASUREMENTS

DL consisted in a free-recall word task and a digit forced-attention task (forced-right: FR and forced-left: FL) in order to study central auditory language processing. In addition, we used neuropsychological tests to study executive functions and cognitive control, sustained by the prefrontal cortex.

RESULTS

In the free recall condition, we confirmed the classic right ear advantage (REA) in both groups, particularly in older subjects. In the forced condition, we observed an ear advantage with a change in ear asymmetry as a consequence of instruction: REA in FR and a left-ear advantage (LEA) in FL. We compared contaminations by the contra-lateral inattentive ear: reports of the left ear (LE) in the FR condition and reports of the right ear (RE) in the FL condition. Contaminations by the RE in the FL condition were more pronounced in Old-Ad suggesting difficulties in competition between the natural tendency for the RE and the instruction. In the Old-Ad group, the correlation between the RE score in FL and TMT B-A/A suggests an impairment in mental flexibility.

CONCLUSION

DL may be helpful to study central auditory dysfunction in aging. Our results suggest difficulties in attentional control and executive functions. Central auditory dysfunction should be evaluated in elderly because it potentially contributes to difficulty of hearing in noisy environment with consequences in the rehabilitation of presbyacousic subjects. More studies are needed to investigate the predictive value of DL as a marker of cognitive decline, particularly executive functions.

Open questions in current models of antidepressant action

Research on depression and antidepressant drugs is necessary, as many patients display poor response to therapy. Different symptomatic and pathophysiological features have been proposed as end points of the depressive phenotype and of the antidepressant action, including anhedonia, depressed mood, alterations in morphology and activity of some brain areas (amygdala, nucleus accumbens, hippocampus, prefrontal cortex and cingulate cortex), modifications in the connectivity between brain structures, changes in neurotransmitters (serotonin, noradrenaline, glutamate and neuropeptides), brain plasticity (neurogenesis, neurotrophins) and abnormal function of the hypothalamic-pituitary adrenal axis. However, few models have been proposed to describe how these end points could induce the depressive phenotype and are involved in the mechanism of action of antidepressants. Here we propose a connectionist-inspired network of depression and antidepressant action, in which the different aetiological factors participating in the release of a depressive episode are represented by input nodes, the different symptomatic as well as pathophysiological end points are represented by an intermediate layer, and the onset of depression or of comorbid disease is represented by the output node. The occurrence of depression and the mechanism of the antidepressant action thus depend upon the weight of the interactions between the different end points, none of them being per se crucial to the onset of a depressive phenotype or to the antidepressant action. This model is heuristic to draw future lines of research concerning new antidepressant therapies, designing new animal models of depression and for a better understanding of the depressive pathology and of its comorbid pathology such as anxiety disorders.

Lack of serotonin1B receptor expression leads to age-related motor dysfunction, early onset of brain molecular aging and reduced longevity

Normal aging of the brain differs from pathological conditions and is associated with increased risk for psychiatric and neurological disorders. In addition to its role in the etiology and treatment of mood disorders, altered serotonin (5-HT) signaling is considered a contributing factor to aging; however, no causative role has been identified in aging. We hypothesized that a deregulation of the 5-HT system would reveal its contribution to age-related processes and investigated behavioral and molecular changes throughout adult life in mice lacking the regulatory presynaptic 5-HT(1B) receptor (5-HT(1B)R), a candidate gene for 5-HT-mediated age-related functions. We show that the lack of 5-HT(1B)R (Htr1b(KO) mice) induced an early age-related motor decline and resulted in decreased longevity. Analysis of life-long transcriptome changes revealed an early and global shift of the gene expression signature of aging in the brain of Htr1b(KO) mice. Moreover, molecular changes reached an apparent maximum effect at 18-months in Htr1b(KO) mice, corresponding to the onset of early death in that group. A comparative analysis with our previous characterization of aging in the human brain revealed a phylogenetic conservation of age-effect from mice to humans, and confirmed the early onset of molecular aging in Htr1b(KO) mice. Potential mechanisms appear independent of known central mechanisms (Bdnf, inflammation), but may include interactions with previously identified age-related systems (IGF-1, sirtuins). In summary, our findings suggest that the onset of age-related events can be influenced by altered 5-HT function, thus identifying 5-HT as a modulator of brain aging, and suggesting age-related consequences to chronic manipulation of 5-HT.

Prucalopride and donepezil act synergistically to reverse scopolamine-induced memory deficit in C57Bl/6j mice

It is known that 5-HT(4) receptor agonists increase sAPPalpha levels in the cortex and hippocampus of mice as well as in a model of Alzheimer's disease (AD). As sAPPalpha is thought to have pro-mnesic properties, we assessed whether its increase induces cognitive improvement in a spatial memory task and whether it reverses a scopolamine-induced memory deficit. Mice treated or not treated with scopolamine were trained in the Morris water maze for 3 days. Before the probe test, they received an injection of either a 5-HT(4) receptor agonist (prucalopride or RS 67333), or an acetylcholinesterase inhibitor (donepezil), or both drugs. As expected, scopolamine decreased performance, an effect that was not reversed by the drugs tested when injected alone. However, prucalopride (5 mg kg(-1), s.c.) acted synergistically with donepezil (0.75 mg kg(-1), s.c.) to counteract completely scopolamine-induced amnesia. Western blot analysis of tissue homogenates in the cortex and hippocampus shows that sAPPalpha levels did not differ between saline- and scopolamine-treated mice. Furthermore, a region-dependent drug action was observed since the scopolamine-treated mice display a tendency to increase sAPPalpha levels in the hippocampus after donepezil or in the cortex after prucalopride. Our results suggest that a combined treatment with a 5-HT(4) receptor agonist with an acetylcholinesterase inhibitor has beneficial effects on memory in mice. Moreover, it seems to enhance sAPPalpha levels in two brain regions highly affected in AD. Thus, a drug polytherapy could be interesting not only to enhance cognitive performance and decrease drawbacks but also to get the best action in each brain region.

Functional implications of decreases in neurogenesis following chronic mild stress in mice

Numerous data from human and animal studies suggest that hippocampal plasticity might be a key element in depression. However, the connection remains loose at best and further data are needed. Human studies are of necessity limited, but animal models can help providing further insight. Unpredictable chronic mild stress (UCMS) is a commonly used model because it mimics depression-like phenotypes satisfactorily. Its rationale is based on the underlying stress-induced difficulties found in many depressed patients. We therefore studied learning and hippocampal neurogenesis in mice from three different inbred strains subjected to UCMS. Learning was assessed in different hippocampus-dependent and independent tasks. The rate of survival of newly generated brain cells was determined in behaviorally-naive animals. Results demonstrated a dramatic reduction of surviving new brain cells in both the hippocampus and the subventricular zone of UCMS-treated animals. This reduction was observed both for neurons and for other cells of the hippocampus. Behavioral data demonstrated an impairment of hippocampus-dependent learning, whereas hippocampus-independent learning was spared. However, the specific results were strongly dependent on strain and sex so that there does not appear to be a direct causative relationship between the deficits in neurogenesis and behavior.

Neuropeptides in psychiatric diseases: an overview with a particular focus on depression and anxiety disorders

This paper aimed at reviewing the involvement of neuropeptides in various psychiatric diseases, particularly in depression, and anxiety disorders. General features of neuropeptides are first described, including the history of their discovery, their definition, classification, biosynthesis, transport, release, inactivation, as well as their interaction with specific neuronal receptors. The differences with classical neurotransmitters are mentioned, as well as the different patterns of co-transmission. Finally, different mechanisms, both at the cellular and at the systemic level, are proposed that may explain the involvement of these molecules in various psychiatric diseases. Indeed, at the cellular level, a neuropeptide can be involved in a psychiatric disease, either because it is co-localized with a classical neurotransmitter involved in a disease, or because the neuropeptide-containing neuron projects on a target neuron involved in the disease. At the systemic level, a neuropeptide can play a direct role in the expression of a symptom of the disease. This is illustrated by different examples.

Ethological validation and the assessment of anxiety-like behaviours: methodological comparison of classical analyses and structural approaches

The research on emotional reactivity usually implies the use of standardised behavioural tests that provide a quick idea of the effect of a treatment on the reactivity of subjects to potentially dangerous situations. Many validity criteria have been considered to evaluate these tests. This validity concept supports the idea that animals' behaviour in these tests model human anxiety. Generally, those criteria repeatedly labelled as "ethological validation" refer to the analogy between animals and human in the meaning of the test situation. Although the content of the ethological validation concept is heterogeneous, it is steadily related to a fixed interpretation of the behavioural items produced in a given experimental setting. The basic assumption of such reasoning is that the behavioural items would always be expressed in the same behavioural context whatever the subject, its gender, strain or species, thoroughly asserting a predefined subjective state. Using multivariate and textual analysis, we found evidence that the "ethological validation" recourse to an a priori interpretation for a given behavioural variable may be deceptive. We defend the idea that the meaning of a behavioural variable should be restricted to the general context where it arose. Theoretical propositions and methodological options are discussed.

Susceptibility to subchronic unpredictable stress is related to individual reactivity to threat stimuli in mice

As in many complex behavioral responses, inter-individual variability can be observed in the responses to a chronic mild stress. While some subjects exhibit more resilient behaviours, others appear more susceptible to stress. This study hypothesizes that this variability relies on the individual appraisal of the stressful event. To study this assumption, mice were first subjected to a conditioned task occurring in a circular arena. In this task, a mild air-puff (i.e. stressor) in a given quadrant of the arena was coupled with the presence or the absence of a light in the same quadrant. Half of mice were then submitted to a 15-day subchronic stress consisting in various environmental and social mild stressors randomly applied two or three times a day. At the end of this procedure, the occurrence of depressive-like behaviours in stressed mice was assessed using measures of the stress regime (i.e. physical state, choice test, grooming test). The physical state assessed the physical appearance of mice. The grooming test consisted in measuring the time spent in grooming after mice were sprayed upon with a viscous solution. The choice test consisted in measuring the time spent in an uncomfortable place (i.e. whose floor was covered with damp sawdust) versus a more comfortable one (i.e. with dry sawdust) to evaluate the reactivity to a negative stimulus previously encountered during the subchronic stress. Multiple regression analyses revealed a relationship between attention toward salient stressful stimuli in the conditioned task and susceptibility to the subchronic stress procedure. These results are discussed regarding their relevance for the understanding of aetiologies of depressive illnesses.

Correlations between behaviours in the elevated plus-maze and sensitivity to unpredictable subchronic mild stress: evidence from inbred strains of mice

This study aimed at investigating the relationship between anxiety-like and depressive-like behaviour in mice. Therefore, we assessed the behaviour of mice from eight different strains (FVB/NA, BALB/c, C57BL/6, DBA/2, 129/Sv, C3H/He, CBA and BA) confronted first to anxiety models (the elevated plus-maze and the free exploratory test) and then to tests of depressive-like behaviours (forced swim test and unpredictable subchronic mild stress). In the forced swim test, mice from the DBA/2, the BA and the C3H/He strains displayed higher immobility than mice from the 129/Sv, the BALB/c, the C57BL/6 and the CBA strains. In the subchronic mild stress, mice from the C57BL/6 and the CBA strains displayed low sensitivity when compared with mice from all the others strains. A stepwise multiple regression analysis suggests that behaviour in the elevated plus-maze is associated with the time of immobility in the forced swim test (20%) and with the susceptibility to the unpredictable subchronic stress procedure (31%). The behaviour in the free exploratory paradigm is slightly associated with behaviours in the two tests of depression. These results suggest that anxiety may be a factor contributing, among others, to the susceptibility to depressive-like behaviours.

Emotional reactivity in mice may not be inherited but influenced by parents

Heredity is often assimilated to genetic transmission of traits. However, some traits may be socially inherited. This has been described for maternal behaviour as well as for emotional reactivity in rodents such as rats or mice. The aim of the present study was to investigate further this idea using two backcrosses between CB6 or B6C females and C57BL/6 males. Indeed, the experimental groups are genetically identical but may be exposed to very different mothering types. When adults, the offspring were subjected to rodent emotional reactivity tests such as elevated plus maze and free exploration paradigm. Results show that CB6xB6 males exhibit higher emotional reactivity than B6CxB6 and B6 males in all behavioural situations, but these effects are not seen in females. Contrarily to their offspring that show different reactivity even if sharing the same genetical background, CB6 and B6C females display quite identical emotional reactivity. A possible explanation is that emotional reactivity is induced by maternal behaviour rather than transmitted by the parents.

Behaviour in the elevated plus-maze predicts coping after subchronic mild stress in mice

This study was aimed at investigating the coping style of mice subjected to a subchronic unpredictable mild stress procedure and its relationship to initial emotional reactivity. Two inbred strains of mice, the BALB/c ByJ and the C57BL/6 J, known to exhibit distinct emotionality, have been used. They were first observed in the elevated plus-maze and the free exploratory paradigm, each provides a separation of the population in high and low emotional mice. Half of the mice of each strain were then confronted to a 2-week subchronic unpredictable mild stress and tested for their responses in different behavioural situations (consumption of a palatable food, physical state, grooming behaviours and reactivity to a conflict situation). Mice were also tested in the light/dark procedure to assess the effect of the subchronic stress on emotional reactivity. First, a relationship between initial emotional reactivity in the elevated plus-maze and behavioural coping style in response to stress was found, high emotional mice (i.e., BALB mice) displaying inhibited behaviours and less emotional mice (i.e., BL/6 mice) exhibiting few behavioural changes. Furthermore, emotional reactivity was increased in stressed mice compared with nonstressed ones.

Emotional behaviour as the result of stochastic interactions. A process crucial for cognition

This paper is aimed at exhibiting two striking features of the usual approach of emotional expression in science and philosophy, suggesting a different perspective. One is the generally shared belief that emotions are a state of utter disarray, which hampers objective knowledge; the other is the search for causal explanation, along a wide range of categorized approaches (psychology, neurosciences, developmental biology) each proposing its own theoretical framework. In both cases the result is to play down emotional expression. Alternatively, we propose to view emotions as something crucial in the choice of our conceptual tools, ideas and involvements, in the genesis of which various explanations interact in a complex stochastic way. Rather than being a harmful disruption of the mind calling for identification of a definite causality, emotional behaviour appears as a necessary process in cognition, which is irreducible to a unique origin.

Measuring normal and pathological anxiety-like behaviour in mice: a review

Measuring anxiety-like behaviour in mice has been mostly undertaken using a few classical animal models of anxiety such as the elevated plus-maze, the light/dark choice or the open-field tests. All these procedures are based upon the exposure of subjects to unfamiliar aversive places. Anxiety can also be elicited by a range of threats such as predator exposure. Furthermore, the concepts of "state" and "trait" anxiety have been proposed to differentiate anxiety that the subject experiences at a particular moment of time and that is increased by the presence of an anxiogenic stimulus, and anxiety that does not vary from moment to moment and is considered to be an "enduring feature of an individual". Thus, when assessing the behaviour of mice, it is necessary to increase the range of behavioural paradigms used, including animal models of "state" and "trait" anxiety. In the last few years, many mice with targeted mutations have been generated. Among them some have been proposed as animal models of pathological anxiety, since they display high level of anxiety-related behaviours in classical tests. However, it is important to emphasise that such mice are animal models of a single gene dysfunction, rather than models of anxiety, per se. Inbred strains of mice, such as the BALB/c line, which exhibits spontaneously elevated anxiety appear to be a more suitable model of pathological anxiety.

The genetic basis of the pharmacological effects of anxiolytics: a review based on rodent models

Anxiolytic drugs exert their pharmacological actions by binding to molecular targets, such as benzodiazepine receptors or 5-hydroxytryptamine (5-HT) receptors. Specific genes encode these receptors, or the subunits of which they are formed. Therefore, genetic factors may influence strongly the ability of anti-anxiety agents to produce their behavioural effects. The literature on this subject is reviewed here, with emphasis on data derived from studies with rodents. We present in a critical way the animal models used in the studies aimed at investigating the genetic basis of the action of anxiolytic compounds, including inbred mice, selected lines, linkage strains or mice generated by targeted mutation. Data show that increased anxiety-like behaviour is not a predictive factor for increased sensitivity to anxiolytic treatment, and it is possible that gene deletion might not be isomorphic to pharmacological antagonism. It is suggested that the strain differences in anxiety-like behaviour may be used as a tool in assaying anxiolytic activity of new drugs.

Emotional reactivity in mice, a case of nongenetic heredity?

Nongenetic heredity cases have been described in man, as well as in animals, and relationships between parents and offspring seem to play an important role in this transmission. In mice, mothering type could be nongenetically heritable by a latent learning close to mechanism. As mothering style clearly influences emotional reactivity, this reactivity could be nongenetically transmitted over generations. To clarify this question, the mother's influence on adult offspring reactivity must be established (whatever its basis, genetic, social or other). Thus, two reciprocal F1 hybrids (CB6 from a BALB/c mother and B6C from a C57BL/6 mother) have been compared using an ethological analysis in animal tests of emotional reactivity such as the free exploration paradigm and the light/dark box. First results show a sharp influence of the mother's strain and that suggests an effect of mothering style. The offspring from C57BL/6 mothers display less reactivity in the free exploration paradigm than the offspring from BALB/c mothers. In the light/dark box, no difference has been found between the two hybrids. Moreover, the mother's influence is greater in males than in females.

Environmental enrichment in BALB/c mice: effects in classical tests of anxiety and exposure to a predatory odor

Early stimulation by environmental enrichment generally leads to improved learning abilities in rodents. However, the effects of environmental enrichment on emotional reactivity remain more questionable and were mostly studied by using classical tests of anxiety based on confrontation with a novel environment. The main goal of our study was to use different tests of anxiety to compare BALB/c mice reared in either a standard condition (SC) or enriched condition (EC). Exposure to cat feces was used to assess anxiety according to an ethoexperimental approach and a comparison was made with the elevated plus maze and the open field as classical tests of anxiety. In accordance with previous works, our results show that EC mice were more active than SC mice in the elevated plus maze and the open field. Thus, possibly as a direct consequence of frequent changes in their breeding conditions, reactivity to a novel environment was reduced in EC mice. However, the cat odor test revealed no intergroup differences for behavior, although corticosterone levels were reduced in EC mice. These results indicate that classical (i.e. reaction to novel environments) and ethoexperimental-based tests (i.e. exposure to predator cues) measure different aspects of emotional reactivity. Further studies using ECs should be useful for the delineation of the neurobiological substrates of these different reactions.

Behavioral and neurochemical changes following predatory stress in mice

This article had several objectives. First it aimed at investigating the anxiogenic-like behaviors elicited by unavoidable cat exposure and/or cat odor across nine strains of mice (BALB/c, C57BL/6, C3H, CBA, DBA/2, NMRI, NZB, SJL, Swiss) in a modified version of the free-exploration test. The second objective was to investigate possible neurochemical changes following cat exposure in Swiss mice by measuring the turnover of dopamine (DA), noradrenaline (NA) and serotonin (5-HT) in several brain regions known to be involved in the modulation of emotional processes (hippocampus, hypothalamus and striatum). Finally, the third objective was to examine the effects of anxiolytic drug treatments on the anxiogenic responses elicited by a cat odor (i.e. a feces) in Swiss mice previously exposed to a cat using the free-exploration test. Results from the strain comparison showed that mice could be divided into three distinct groups: two non-reactive strains (NZB and SJL) which were relatively insensitive to predatory exposure and/or odor; five intermediate-reactive strains (Swiss, NMRI, CBA, C3H and BALB/c) which displayed clear anxiogenic-like responses only when exposed to both cat and, subsequently, to feces; and two high reactive strains (C57BL/6 and DBA/2) which showed anxiogenic-like reactions following cat exposure, regardless of the stimulus (clay or feces) present in the free-exploration cage. Neurochemical data revealed that, while brain levels of NA, DA, 5-HT in cat exposed Swiss mice were not significantly different from those of control animals, turnover rates of these monoamines were increased in the hippocampus (NA and 5-HT), hypothalamus and striatum (DA) after cat exposure. Results from pharmacological experiments indicated that repeated administration of the 5-HT reuptake inhibitor fluoxetine (5-20 mg/kg, twice a day, for 5 days) completely abolished avoidance of the cat feces in Swiss mice previously exposed to the predator. Neither acute nor repeated administration of the classical anxiolytic diazepam was able to reduce avoidance behavior of the anxiogenic stimulus in the free-exploration test. Taken together, these findings indicate that the exposure of mice to unavoidable predatory stimuli is associated with behavioral and neurochemical changes consistent with increased anxiety.

Rodent models of anxiety-like behaviors: are they predictive for compounds acting via non-benzodiazepine mechanisms?

An overview of the preclinical literature on the effects of the most studied clinically effective or putative non-benzodiazepine anxiolytics in existing animal models of anxiety-like behavior indicates that, with the exception of 5-HT1A agonists, these compounds display highly variable effects. Because these drugs have been shown (selective 5-HT reuptake inhibitors) or proposed (CCK(B) and CRF antagonists) to have a different spectrum of therapeutic activity in anxiety disorders than benzodiazepines, agents mainly used against generalized anxiety disorder, the screening of such compounds clearly requires the validation of new techniques that may model aspects of these conditions.

An investigation of the mechanisms responsible for acute fluoxetine-induced anxiogenic-like effects in mice

Although selective 5-hydroxytryptamine (5-HT) reuptake inhibitors (SSRIs) are widely used in the chronic treatment of several anxiety disorders, increased anxiety has been observed in some patients at the beginning of treatment with these compounds. Similar increases in anxiety-related behaviors have been observed in animal studies following a single injection with SSRIs. The mechanism underlying this effect is unclear. The aim of the present study was to investigate the effects of a variety of psychoactive compounds on the anxiogenic-like activity of fluoxetine. The drugs used included the benzodiazepine diazepam, the 5-HT1A receptor partial agonist buspirone, the 5-HT1A receptor antagonists pindolol and WAY-100635, the non-selective 5-HT2 receptor antagonists methiothepin, mianserin and ritanserin, the non-selective dopamine (DA) receptor antagonist haloperidol, the D1 antagonist SCH23390, the selective D2 antagonist raclopride, the D2/3 agonist quinelorane, the cholecystokininB (CCK(B)) receptor antagonist LY 288513, and the corticotropin-releasing factor1 (CRF1) receptor antagonist CP-154,526. Experiments were performed in the free-exploration test. This model is based on the strong neophobic reactions exhibited by BALB/c mice when confronted simultaneously with a familiar and a novel environment. When administered alone, diazepam (1 and 2 mg/kg), buspirone (1 mg/kg) and mianserin (0.3 mg/kg) produced anxiolytic-like effects as they significantly increased exploratory activity of the novel compartment. In contrast, fluoxetine (20 mg/kg) almost completely suppressed exploration of the novel area. Diazepam reversed the anxiogenic-like as well as the locomotor impairment induced by fluoxetine, while quinelorane blocked only the anxiogenic action of fluoxetine. None of the other compounds was able to counteract this effect. Taken together, these results suggest that dopaminergic mechanisms may underlie, at least in part, the behavioral effects of fluoxetine in the free-exploration test, whereas 5-HT1A 5-HT2, CCK(B) and CRF1 receptors may not be involved primarily in these effects.

The effects of the lurcher mutation on object localization, T-maze discrimination, and radial arm maze tasks

The Lurcher mutation is characterized by degeneration of the cerebellar cortex and cerebellar ataxia. The mutants were compared to littermate controls of the same background strain in three spatial tasks: 1) left-right discrimination in a water-filled T-maze, a reference memory task requiring a win-stay strategy; 2) the radial arm maze, a working memory task requiring a win-shift strategy; 3) object localization, a reference memory task requiring the use of cognitive mapping. Lurcher mutants were impaired in the object localization and radial arm maze tasks but not in the left-right discrimination task. These results indicate that trial-independent tasks and reference memory tasks using cognitive mapping may be particularly vulnerable to cerebellar degeneration.

Absence of cocaine-induced place conditioning in serotonin 1B receptor knock-out mice

A large body of evidence suggests that genetic factors may affect the reinforcing properties of drugs of abuse. This study investigated the involvement of the serotonin 1B (5-HT1B) receptor in modulating cocaine-induced place conditioning by comparing the response of 5-HT1B receptor gene knock-out mice with wild type 129/Sv-ter mice. The rewarding effects of various doses of cocaine (0, 2.5, 5, 10, 20, and 40 mg/kg) were examined in both strains. Results clearly show that 5-HT1B receptor knock-out mice failed to display a conditioned place preference for stimuli paired with cocaine while wild type mice exhibited a conditioned place preference for the compartment paired with cocaine (5 and 20 mg/kg). As other studies showed that 5-HT1B knock-out mice self-administer cocaine, these results suggest a dissociation between the psychologic state linked to self-administration and the one measured in conditioned place preference.

Naloxone potentiates anxiolytic-like actions of diazepam, pentobarbital and meprobamate but not those of Ro19-8022 in the rat

The elevated plus-maze test was used to determine if the opiate antagonist naloxone could potentiate the anxiolytic-like effects of the benzodiazepine diazepam, the barbiturate pentobarbital, the propanediol carbamate meprobamate and the partial benzodiazepine receptor agonist [R]-1-[(10-chloro-4-oxo-3-phenyl-4H-benzo[a]quinolizin-1-yl) carbonyl]-2-pyrrolidine-methanol (Ro19-8022) in the rat. A subeffective dose of each of these compounds was combined with naloxone, 10 mg/kg. Naloxone had no effect by itself, but potentiated all drugs except Ro19-8022. The proportion of entries on the open arm increased while the total number of arms entries was not modified. These results coincide with and extend data previously obtained in the mouse. One possible explanation for naloxone's effect could be that it blocks opioid inhibition of GABAergic (gamma-aminobutyric acid) neurons thereby enhancing the effects of benzodiazepines. Another possibility is that naloxone blocks opioid effects on adenosinergic systems.

Beta-CCT, a selective BZ-omega1 receptor antagonist, blocks the anti-anxiety but not the amnesic action of chlordiazepoxide in mice

The aim of this study was to test further the hypothesis that different benzodiazepine (BZ-omega) receptor subtypes may mediate anxiolytic and amnesic effects of BZ agonists, using the selective BZ-omega1 receptor antagonist beta-CCT (beta-carboline-3-carboxylate t-butyl-ester). Experiments were performed in Swiss mice using the elevated plus-maze anxiety test and two learning tasks - passive avoidance and the radial arm maze. In the elevated plus-maze test, beta-CCT (30 mg/kg, i.p.) completely abolished the increase in open-arm entries induced by the BZ chlordiazepoxide (5mg/kg, i.p.). Chlordiazepoxide decreased retention latency in the passive avoidance step-through procedure, and increased the number of errors in the radial arm maze. These effects were not modified by beta-CCT. Except for a slight, albeit significant, amnesic effect in the passive avoidance test, beta-CCT was devoid of intrinsic activity when administered alone. These results are in agreement with previous studies using selective BZ-omega1 agonists, and thus provide further evidence that BZ-omega1 receptors may be involved in the anxiolytic but not in the amnesic effects of BZ agonists.

Anxiolytic-like effects of meprobamate. Interactions with an opiate antagonist in Swiss and BALB/c mice

Naloxone has previously been shown to block the effects of benzodiazepines in the Swiss but not in the BALB/c strain. We have also reported that naloxone potentiates subeffective doses of benzodiazepines in Swiss mice. In the present studies we first determined whether naloxone could block anxiolytic-like effects of meprobamate in Swiss and BALB/c mice. Then we evaluated if subeffective doses of meprobamate could be potentiated in Swiss as well as in BALB/c mice. The elevated plus-maze test and the light/dark choice procedure were used. The lowest dose of meprobamate with anxiolytic-like effects was 60 mg/kg in the BALB/c mice. This dose was effective in both the plus-maze and in the light/dark choice procedure. In Swiss mice the same dose was effective in the plus-maze, whereas 120 mg/kg was required in the light/dark choice procedure. When an effective dose of meprobamate was combined with naloxone, 10 mg/kg, no blockade of anxiolytic-like effects was obtained in any strain in any procedure. To the contrary, when a subeffective dose of meprobamate was combined with naloxone, 10 mg/kg, an anxiolytic-like effect was obtained in both strains in both procedures. The present series of experiment shows that the ability of naloxone to block anxiolytic-like drug effects do not apply to meprobamate. However, the naloxone-induced potentiation of subeffective doses previously observed after treatment with benzodiazepines or buspirone was present also after treatment with meprobamate. Moreover, although blockade of anxiolytic-like drug effects with naloxone has not been observed in BALB/c mice, potentiation was as evident in that strain as in the Swiss. This suggests that the mechanisms behind naloxone's blockade of anxiolytic-like effects are independent from those behind its potentiation of such effects.

Differences in drug-induced place conditioning between BALB/c and C57Bl/6 mice

The influence of genotype on the rewarding effects of morphine (0, 1, 3, and 9 mg/kg), amphetamine (0, 0.5, 1, and 2 mg/kg), and cocaine (0, 2.5, 5, and 10 mg/kg) was examined in a place-conditioning paradigm. Two strains of mice, the BALB/cByJIco and the C57BL/6JIco, were used, notably because of their high difference in novelty-seeking behavior. Indeed, high novelty seeking has been associated with an increased risk for using drugs of abuse. Results clearly show that C57BL/6 mice display a conditioned place preference for stimuli paired with morphine, amphetamine, or cocaine. In contrast, BALB/c mice demonstrated place preference to morphine and place aversion to amphetamine, while cocaine was ineffective at the doses tested. No treatment induced differences in the locomotion measured in a drug-free condition. Results may be related to differences at the behavioral (difference in novelty seeking) or neurochemical level (differences in catecholaminergic or opioidergic neurotransmission).

Differences in anxiety-related behaviours and in sensitivity to diazepam in inbred and outbred strains of mice

RATIONALE

Natural strain differences exist in mice for behavioural traits such as emotional reactivity.

OBJECTIVE

The present experiments compared the behavioural profiles of nine strains of mice (BALB/c, C57BL/6, C3H, CBA, DBA/2, NMRI, NZB, SJL, Swiss) in two models of anxiety after the administration of the benzodiazepine diazepam.

METHODS

The tests used were the light/dark choice task and the elevated plus-maze, two well-validated anxiolytic screening tests.

RESULTS

In vehicle-treated animals, differences on variables designed to measure anxiety-related behaviours were observed in both tests. In the light/dark test, the strains could be divided into three distinct groups: two non-reactive strains (NZB and SJL), an intermediate-reactive group (C3H, CBA, DBA/2, NMRI, C57BL/6 and Swiss), and one highly reactive strain (BALB/c). In the elevated plus-maze, SJL, NMRI, CBA and, to a lesser extent, C3H strains of mice, consistently showed low levels of anxiety-related behaviours. Intermediate levels were seen in the Swiss and BALB/c strains, and high levels of emotional reactivity were seen in C57BL/6, DBA/2 and NZB. The strain distribution between the light/dark and the elevated plus-maze tests shows similarities and differences, suggesting that each of these experimental procedures represents a different set of behaviours. Marked differences between a number of strains of mice in their sensitivity to the anxiolytic-like action of diazepam were observed in both the light/dark and the elevated plus-maze tests. Mice of the BALB/c, Swiss and, to a lesser extent, CBA and C3H strains were responsive to diazepam in both tests, although in the case of CBA mice, effects may have been contaminated by behavioural suppression. SJL mice were largely unresponsive to the action of the benzodiazepine in both tests, whereas in C57, DBA/2, NMRI and NZB mice, diazepam produced positive effects only in the elevated plus-maze.

CONCLUSION

The finding of differential strain distributions both with and without diazepam treatment in the light/dark and the elevated plus-maze tests, indicates that not all strains of mice are suitable for investigating the effects of GABA/BZ receptor ligands. This study may thus provide a useful guide for choosing the best strain of mice for studying the pharmacology of fear-related behaviours.

Flumazenil induces benzodiazepine partial agonist-like effects in BALB/c but not C57BL/6 mice

RATIONALE

Some anxiety disorders may be treated in a different way than normal anxiety.

OBJECTIVE

This study was aimed at investigating the action of the benzodiazepine receptor antagonist flumazenil, compared to that of the benzodiazepine receptor full agonist chlordiazepoxide, in an animal model of generalised anxiety disorder (the BALB/c mouse).

METHODS

Flumazenil (0.0001, 0.001, 0. 01, 0.1 and 1 mg/kg) or chlordiazepoxide (5 mg/kg) were administered to BALB/c or C57BL/6 mice subjected to the light/dark test, the elevated plus maze or a passive avoidance step-through paradigm.

RESULTS

Chlordiazepoxide and flumazenil (at all doses tested in the elevated plus maze and at the doses of 0.001 and 0.01 mg/kg in the light/dark test) induced a strong anxiolytic effect in BALB/c mice. Flumazenil did not induce anxiolysis in C57BL/6 mice, whatever the behavioral test or the dose used. However, chlordiazepoxide elicited anxiolysis in this strain in both procedures. In the passive avoidance test, chlordiazepoxide was amnesic in both strains but flumazenil had no effect.

CONCLUSION

Flumazenil induces partial agonist-like effects in BALB/c and not in C57BL/6 mice, suggesting a possible benzodiazepine receptor set point shift toward the agonistic direction in some pathological anxiety states such as generalised anxiety disorder.

Decreased GABAA-receptor clustering results in enhanced anxiety and a bias for threat cues

Patients with panic disorders show a deficit of GABAA receptors in the hippocampus, parahippocampus and orbitofrontal cortex. Synaptic clustering of GABAA receptors in mice heterozygous for the gamma2 subunit was reduced, mainly in hippocampus and cerebral cortex. The gamma2 +/- mice showed enhanced behavioral inhibition toward natural aversive stimuli and heightened responsiveness in trace fear conditioning and ambiguous cue discrimination learning. Implicit and spatial memory as well as long-term potentiation in hippocampus were unchanged. Thus gamma2 +/- mice represent a model of anxiety characterized by harm avoidance behavior and an explicit memory bias for threat cues, resulting in heightened sensitivity to negative associations. This model implicates GABAA-receptor dysfunction in patients as a causal predisposition to anxiety disorders.

Rearing environmental enrichment in two inbred strains of mice: 1. Effects on emotional reactivity

The effects of an enriched rearing environment on two types of anxiety-like behavior (designated "trait" and "state" anxiety) and on spontaneous activity were investigated in two inbred strains of mice, BALB/c (C) and C57BL/6(B6). Subjects were socially reared from birth to 56 days of age under enriched or standard rearing conditions. The enriched environment consisted of an assembly of plastic boxes in which a various number of objects (running wheels, pieces of plastic, etc.) offered the possibility of multiple activities. The subjects were subsequently tested in three situations: a spontaneous activity recorder, an elevated plus-maze test (a model of state anxiety), and a free exploration test (a model of trait anxiety). No group differences could be found in spontaneous activity. Environmental enrichment, however, decreased the level of both types of anxiety-like behavior in the C strain. In contrast, the level of trait anxiety of the B6 mice was not modified. The results were discussed in relation to possible CNS modifications, especially in the limbic system.

Dietary fish oil affects monoaminergic neurotransmission and behavior in rats

We studied the effects of a fish oil enriched diet on fatty acid composition of cerebral membranes and on several neurochemical and behavioral variables of monoaminergic function in rats. The frontal cortex, striatum, hippocampus and cerebellum were studied in rats fed fish oil (FPO, 50% salmon oil + 50% palm oil), which provided an (n-6)/(n-3) polyunsaturated fatty acid (PUFA) ratio of 0.14 versus 6. 19 in controls fed a diet containing a mixture of African peanut oil and rapeseed oil. In the FPO group compared to the control group, the major modifications in fatty acid composition of cerebral membranes included the following: higher levels in 22:6(n-3), lower levels in 20:4(n-6) and a significantly greater proportion of phosphatidylserine. Dopamine levels were 40% greater in the frontal cortex of rats fed FPO than from those fed the control diet. In this cerebral region there was also a reduction in monoamine oxidase B (MAO-B) activity and greater binding to dopamine D2 receptors. By contrast, a lower binding to dopamine D2 receptors (-7%) was observed in the striatum. Ambulatory activity was also reduced in FPO-fed rats, possibly related to observed changes in striatal dopaminergic receptors. This suggested that the level of (n-6) PUFA, which was considerably lower in the FPO diet than in the control diet, could act on locomotion through an effect on striatal dopaminergic function, whereas the high level of (n-3) PUFA could act on cortical dopaminergic function.

Naloxone potentiates the anxiolytic but not the amnestic action of chlordiazepoxide in C57BL/6 mice

This study aimed to investigate the effects of the opiate antagonist naloxone (10 mg/kg) on the action of a subeffective dose of chlordiazepoxide. C57BL/6 mice were tested for either anxiety, using an elevated plus maze, emotional memory in a passive avoidance paradigm or spatial memory in a radial maze. In the elevated plus maze, chlordiazepoxide 2.5 mg/kg was ineffective per se but, when combined with naloxone, it increased the proportion of open-arm entries, as did a higher dose of chlordiazepoxide (5 mg/kg). Closed-arm entries were increased with chlordiazepoxide (2.5 mg/kg) injected alone but naloxone, alone or combined with chlordiazepoxide, did not modify this measure. In the passive avoidance test, chlordiazepoxide 2.5 mg/kg decreased the latency to enter a compartment associated with an electric foot-shock, while a dose of 1.25 mg/kg, alone or in combination with naloxone, was ineffective. Finally, in the radial arm maze, chlordiazepoxide (5 mg/kg) induced amnesia. However, a dose of 2.5 mg/kg, alone or with naloxone, had no effect on learning. Naloxone elicited no intrinsic action in any of these behavioural models. It can be concluded that naloxone potentiates the anxiolytic but not the amnestic action of chlordiazepoxide.

Modulation of mice anxiety in response to cat odor as a consequence of predators diet

The effectiveness of predator odours as repellents was assessed, and the behavioral antipredatory responses were characterized. Mice had free access to an unfamiliar runway containing different olfactory stimuli: modelling clay, or feces of a cat subjected either to a vegetarian or a carnivorous diet. The first experiment revealed various indices of a spontaneous behavioral pattern that included exploratory activity, different kinds of emotionality, and a range of active or passive defensive reactions until the appearance of absence of risk assessment strictly related to presence or absence of anxiety. These reactions differ with larger responses to feces resulting from a carnivorous as opposed to vegetarian diets. In the second experiment, chlordiazepoxide (0, 2.5, 5, or 7.5 mg/kg) had a dose-related anxiolytic effect on exploration in mice of both vegetarian and carnivorous groups but could not totally reverse the strong anxiogenic effect of carnivorous stimulus on defensive mechanisms. These differences are related to the nature of the mammalian cues. This paradigm may be a fear-motivated model of animal anxiety.

Alpha-linolenic acid deficiency modifies distractibility but not anxiety and locomotion in rats during aging

In rodents, chronic dietary alpha-linolenic acid deficiency decreases learning and memory and alters dopaminergic and serotoninergic neurotransmission. However, these two neurotransmitter systems are related mainly to attention, emotion and locomotion. Therefore, we decided to investigate the effects of dietary alpha-linolenic acid deficiency in rats tested with animal models of distractibility (the distractometer procedure), anxiety (the elevated plus maze) and ambulatory activity (a circular corridor). Moreover, because these neurochemical modifications persist during aging, we decided to study the effects of aging on these behaviors by using rats aged 2, 6, 12 and 24 mo. An age-related decline in distractibility was observed that was accelerated by linolenic acid deficiency. Indeed, an age-related reduction in distractibility was found in so far as distraction time was reduced at the age of 12 mo in controls and at the age of 24 mo in deficient groups compared with 2-mo-old rats. Moreover, distraction time was significantly lower in 6- and 24-mo-old rats fed a deficient diet compared with age-matched controls. Anxiety was not modified by diet or age. Finally, a parallel decrease in locomotion was exhibited by rats fed both diets between 6 and 12 mo of age. Locomotion was not modified by diet. These results show that dietary alpha-linolenic deficiency alters behavior in a very specific way; distractibility is modified by diet, whereas anxiety and locomotion are not, suggesting that particular brain areas may be altered.

The role of subtypes of the opioid receptor in the anxiolytic action of chlordiazepoxide

Previous studies have shown that the opiate antagonist naloxone blocks the anxiolytic-like effects of benzodiazepines in several models of anxiety, including the elevated plus-maze. Although naloxone preferentially binds to the mu opioid receptor, its selectivity is rather low. The opioid receptor subtype important for anxiolytic-like actions of benzodiazepines in the plus-maze remains, therefore, unknown. In the present experiments, the ability of antagonists selective for subtypes of the opioid receptor to block the anxiolytic-like effects of chlordiazepoxide in the elevated plus-maze was evaluated in Swiss mice. Chlordiazepoxide, 5 mg/kg, increased the proportion as well as the number of open arms entries without modifying closed arms entries. Lower doses of the benzodiazepine were ineffective. The mu receptor antagonist beta-funaltrexamine, 10 and 20 mg/kg, the delta antagonist naltrindole, 10 mg/kg, and the kappa antagonist nor-binaltorphimine, 2.5 and 5 mg/kg, were then combined with chlordiazepoxide, 5 mg/kg. beta-funaltrexamine, 10 mg/kg, reduced the effects of the benzodiazepine while the dose of 20 mg/kg completely blocked the effects. Nor-binaltorphimine was ineffective at a dose of 2.5 mg/kg, but completely inhibited the actions of chlordiazepoxide when the dose was 5 mg/kg. Naltrindole was ineffective. None of the antagonists affected plus-maze behavior when administered alone. It was concluded that the mu and kappa receptors are important for the anxiolytic-like actions of chlordiazepoxide in the elevated plus maze.

Toxicity, mutagenicity, and behavioral effects of beta-CIT, a ligand for dopamine transporter exploration by SPECT

The cocaine analog beta-CIT is one of the most used compounds for SPET examination of the dopamine transporter in drug abuse and Parkinson's disease. However, the toxicity of this agent has not yet been studied. We report here acute toxicity, mutagenicity, and effect on locomotor activity of beta-CIT. Acute toxicity experiments were performed in mice and rats. The LD50 values were about 20 mg and 5 mg for mice and rats, respectively. There was no sex difference. The mutagenicity was evaluated using the Ames' test. No mutagenic effect was observed for beta-CIT. Effects on locomotor activity were measured in mice using the open-field test. beta-CIT increased locomotion (+65%) when injected at a dose of 0.312 mg/kg; the maximal increase (+205%) was observed at a dose of 1.25 mg/kg; at higher doses, the effect was decreased slightly. These pharmacological findings are in agreement with an inhibitory effect of beta-CIT at the dopamine transporter. We conclude that with no mutagenic effects and LD50 more than 6 orders of magnitude higher than the routinely used doses in PET or SPET, it can be assumed that beta-CIT can be safely used as a radioligand in humans.

Cholecystokinin receptors mediate the development of a preference for the mother by newly born lambs

The aim of this study was to investigate the effect of selective cholecystokinin (CCK) antagonists on the development of a preference for the mother by newly born lambs. At birth lambs received an injection of the CCK-A antagonist devazepide (0.01 or 0.1 mg/kg), the CCK-B antagonist PD135158 (0.01 or 0.1 mg/kg), or saline for the controls (1 ml/kg). No major side effects were observed in the first 4 postnatal hours except that lambs receiving PD135158 displayed more exploratory behavior towards the maternal body than lambs from the other groups. When tested in a 2-choice test situation at 24 hr of age, lambs treated with PD135158 or saline spent significantly more time near their dams than near the alien ewes, whereas lambs treated with devazepide did not show any discrimination. The effect of devazepide persisted at 48 hr of age. The use of a CCK-A antagonist, but not a CCK-B antagonist, was concluded to prevent the formation of a preferential relationship between the lamb and its mother, most probably by impairing neonatal learning.

Interactions between dopamine and GABA in the control of ambulatory activity and neophobia in the mouse

Ambulatory activity in a familiar and novel environment as well as the time spent in a novel environment were evaluated using the free exploratory paradigm. Male mice treated with D-amphetamine, 2 mg/kg, displayed enhanced ambulatory activity in the familiar environment. The time spent in the novel environment was reduced by amphetamine, 1 and 2 mg/kg. The GABA transaminase inhibitor gamma-acetylen GABA (GAG) reduced ambulatory activity and rearing as well as the time spent in the novel environment. The mixed GABA(A)/GABA(B) agonist progabide, 200 mg/kg, reduced rearing both in the familiar and novel environments without affecting the time spent in the novel environment. Amphetamine, 1 mg/kg, was then combined with ineffective doses of GAG and progabide (50 and 100 mg/kg, respectively). The GABAergics did not reliably modify the effects of amphetamine on the time spent in the novel environment. Ambulatory activity and rearing were reduced both in comparison to amphetamine + saline and to control. These data show that GABAergic drugs are potentiated by enhanced dopaminergic neurotransmission with regard to their actions on ambulatory activity and rearing. The effects of progabide + amphetamine were then evaluated after treatment with the GABA(A) antagonist bicuculline or the GABA(B) antagonist CGP 35348. Neither bicuculline, 1 mg/kg, nor CGP 35348, 100 mg/kg, blocked the actions of progabide. The combined treatment with both antagonists was also unable to reduce the effects of progabide. These data suggest that the interaction between amphetamine and progabide with regard to motor effects depends on a non-GABA(A), non-GABA(B) receptor.

Cholecystokinin receptors mediate the development of a preference for the mother by newly born lambs

The aim of this study was to investigate the effect of selective cholecystokinin (CCK) antagonists on the development of a preference for the mother by newly born lambs. At birth lambs received an injection of the CCK-A antagonist devazepide (0.01 or 0.1 mg/kg), the CCK-B antagonist PD135158 (0.01 or 0.1 mg/kg), or saline for the controls (1 ml/kg). No major side effects were observed in the first 4 postnatal hours except that lambs receiving PD135158 displayed more exploratory behavior towards the maternal body than lambs from the other groups. When tested in a 2-choice test situation at 24 hr of age, lambs treated with PD135158 or saline spent significantly more time near their dams than near the alien ewes, whereas lambs treated with devazepide did not show any discrimination. The effect of devazepide persisted at 48 hr of age. The use of a CCK-A antagonist, but not a CCK-B antagonist, was concluded to prevent the formation of a preferential relationship between the lamb and its mother, most probably by impairing neonatal learning.

Further pharmacological validation of the BALB/c neophobia in the free exploratory paradigm as an animal model of trait anxiety

The present experiments were aimed at investigating the ability of established or putative anxiolytics to reduce the neophobia exhibited by BALB/c mice in the free exploratory paradigm. Results confirm the anxiolytic effects of the benzodiazepine receptor full agonist chlordiazepoxide (2.5-7.5 mg/kg), of meprobamate (15-60 mg/kg) and of ethanol (0.5-1.5 g/kg) and extend the pharmacological action of these compounds to a test situation devoid of anxiogenic components, that is to trait anxiety. The non-competitive NMDA antagonist MK 801 (0.04-0.16 mg/kg) elicited very similar behavioural effects. However, the alpha 2-adrenoceptor antagonists yohimbine (0.5-2 mg/kg) and idazoxan (0.3-2.7 mg/kg), the barbiturate pentobarbital (3.75-30 mg/kg), the mixed 5HT2 receptor antagonist ritanserin (0.25-4 mg/kg) and the D2 dopaminergic antagonist sulpiride (8-32 mg/kg) failed to decrease neophobia in BALB/c mice. The discussion focuses on the adequacy of this animal model of human pathology. The BALB/c neophobia may not model panic attacks because of the absence of worsening by the panic-provoking agent yohimbine and the lack of attenuation by CCK-B receptor antagonists. Because of its chronicity, this paradigm may model generalized anxiety, a pathology that has been suggested to overlap trait anxiety.