Neuroendocrine and behavioral responses during conditioned active and passive behavior in the defensive burying/probe avoidance paradigm: effects of ipsapirone

Coping styles vary with species' sociality and life history: A systematic review and meta-regression analysis

Despite a long history of animal studies investigating coping styles, the causal connections between behavior and stress physiology remain unclear. Consistency across taxa in effect sizes would support the idea of a direct causal link maintained by either functional or developmental dependencies. Alternatively, lack of consistency would suggest coping styles are evolutionarily labile. Here, we investigated correlations between personality traits and baseline and stress-induced glucocorticoid levels using a systematic review and meta-analysis. Most personality traits did not consistently vary with either baseline or stress-induced glucocorticoids. Only aggression and sociability showed a consistent negative correlation with baseline glucocorticoids. We found that life history variation affected the relationship between stress-induced glucocorticoid levels and personality traits, especially anxiety and aggression. The relationship between anxiety and baseline glucocorticoids depended on species' sociality with solitary species showing more positive effect sizes. Thus, integration between behavioral and physiological traits depends on species' sociality and life history and suggests high evolutionary lability of coping styles.

Activity in a prefrontal-periaqueductal gray circuit overcomes behavioral and endocrine features of the passive coping stress response

The question of how the brain links behavioral and biological features of defensive responses has remained elusive. The importance of this problem is underscored by the observation that behavioral passivity in stress coping is associated with elevations in glucocorticoid hormones, and each may carry risks for susceptibility to a host of stress-related diseases. Past work implicates the medial prefrontal cortex (mPFC) in the top-down regulation of stress-related behaviors; however, it is unknown whether such changes have the capacity to buffer against the longer-lasting biological consequences associated with aversive experiences. Using the shock probe defensive burying test in rats to naturalistically measure behavioral and endocrine features of coping, we observed that the active behavioral component of stress coping is associated with increases in activity along a circuit involving the caudal mPFC and midbrain dorsolateral periaqueductal gray (PAG). Optogenetic manipulations of the caudal mPFC-to-dorsolateral PAG pathway bidirectionally modulated active (escape and defensive burying) behaviors, distinct from a rostral mPFC-ventrolateral PAG circuit that instead limited passive (immobility) behavior. Strikingly, under conditions that biased rats toward a passive coping response set, including exaggerated stress hormonal output and increased immobility, excitation of the caudal mPFC-dorsolateral PAG projection significantly attenuated each of these features. These results lend insight into how the brain coordinates response features to overcome passive coping and may be of importance for understanding how activated neural systems promote stress resilience.

Offensive Behavior, Striatal Glutamate Metabolites, and Limbic-Hypothalamic-Pituitary-Adrenal Responses to Stress in Chronic Anxiety

Variations in anxiety-related behavior are associated with individual allostatic set-points in chronically stressed rats. Actively offensive rats with the externalizing indicators of sniffling and climbing the stimulus and material tearing during 10 days of predator scent stress had reduced plasma corticosterone, increased striatal glutamate metabolites, and increased adrenal 11-dehydrocorticosterone content compared to passively defensive rats with the internalizing indicators of freezing and grooming, as well as to controls without any behavioral changes. These findings suggest that rats that display active offensive activity in response to stress develop anxiety associated with decreased allostatic set-points and increased resistance to stress.

Anteroventral bed nuclei of the stria terminalis neurocircuitry: Towards an integration of HPA axis modulation with coping behaviors - Curt Richter Award Paper 2017

A network of interconnected cell groups in the limbic forebrain regulates hypothalamic-pituitary-adrenal (HPA) axis activation and behavioral responses to emotionally stressful experiences, and chronic disruption of these systems chronically is implicated in the pathogenesis of psychiatric illnesses. A significant challenge has been to unravel the circuitry and mechanisms providing for regulation of HPA activity, as these limbic forebrain regions do not provide any direct innervation of HPA effector cell groups in the paraventricular hypothalamus (PVH). Moreover, information regarding how endocrine and behavioral responses are integrated has remained obscure. Here we summarize work from our laboratory showing that anteroventral (av) bed nuclei of the stria terminalis (BST) acts as a point of convergence between the limbic forebrain and PVH, receiving and coordinating upstream influences, and restraining HPA axis output in response to inescapable stressors. Recent studies highlight a more expansive modulatory role for avBST as one that coordinates HPA-inhibitory influences while concurrently suppressing passive behavioral responses via divergent pathways. avBST is uniquely positioned to convey endocrine and behavioral alterations resulting from chronic stress exposure, such as HPA axis hyperactivity and increased passive coping strategies, that may result from synaptic reorganization in upstream limbic cortical regions. We discuss how these studies give new insights into understanding the systems-level organization of stress response circuitry, the neurobiology of coping styles, and BST circuit dysfunction in stress-related psychiatric disorders.

Habitat complexity, environmental change and personality: A tropical perspective

Tropical rainforests are species-rich, complex ecosystems. They are increasingly being negatively affected by anthropogenic activity, which is rapidly and unpredictably altering their structure and complexity. These changes in habitat state may expose tropical animals to novel and unpredictable conditions, potentially increasing their extinction risk. However, an animal's ability to cope with environmental change may be linked to its personality. While numerous studies have investigated environmental influences on animal personalities, few are focused on tropical species. In this review, we consider how behavioural syndromes in tropical species might facilitate coping under, and adapting to, increasing disturbance. Given the complexity of tropical rainforests, we first discuss how habitat complexity influences personality traits and physiological stress in general. We then explore the ecological and evolutionary implications of personality in the tropics in the context of behavioural flexibility, range expansion and speciation. Finally, we discuss the impact that anthropogenic environmental change may have on the ecological integrity of tropical rainforests, positing scenarios for species persistence. Maintaining tropical rainforest complexity is crucial for driving behavioural flexibility and personality type, both of which are likely to be key factors facilitating long term persistence in disturbed habitats.

Active coping toward predatory stress is associated with lower corticosterone and progesterone plasma levels and decreased methylation in the medial amygdala vasopressin system

An active coping style displayed under stress - which involves proactive investigatory responses toward environmental threats - has been associated with reduced vulnerability to psychiatric illness. However, the neurobiological determinants of coping styles are not well understood. When rats are exposed to a naturalistic stressor (cat fur) in a group, some individuals in the group show robust active investigation of the stimulus while others show a passive response involving retreat, immobility and close aggregation with conspecifics. Here we explored endocrine and epigenetic correlates of these contrasting coping styles. Male Wistar rats (n=48) were exposed to cat fur in groups of 4 and the passive and active responders were identified and assessed for endocrine and epigenetic differences. Three days after the final cat fur exposure, active responders had substantially lower plasma levels of corticosterone and progesterone than passive responders. Plasma and testicular testosterone levels did not differ between active and passive responders. Active responders had markedly less methylation of the AVP CGCG promoter region located at base 4970 in the posterodorsal region of the medial amygdala but did not differ in the methylation status of the CCGG sequence located at base 2243. This is in agreement with prior research suggesting that AVP and progesterone act in opposition within the medial amygdala to modulate stress-related behaviors. The present study reports striking endocrine and epigenetic differences between active and passive responders, providing insight into potential systems involved in the manifestation of differing coping styles.

Memory enhancement produced by post-training exposure to sucrose-conditioned cues

A number of aversive and appetitive unconditioned stimuli (such as shock and food) are known to produce memory enhancement when they occur during the post-training period. Post-training exposure to conditioned aversive stimuli has also been shown to enhance memory consolidation processes. The present study shows for the first time that post-training exposure to conditioned stimuli previously paired with consumption of a sucrose solution also enhances memory consolidation. Male Long Evans rats were trained on a one-session conditioned cue preference (CCP) task on a radial arm maze. Immediately or 2 hours after training, rats consumed a sucrose solution or were exposed to cues previously paired with consumption of sucrose or cues previously paired with water. Twenty-four hours later, the rats were tested for a CCP. Immediate, but not delayed, post-training consumption of sucrose enhanced memory for the CCP. Immediate, but not delayed, post-training exposure to cues previously paired with sucrose, but not with water, also enhanced CCP memory. The possibility that rewarding and aversive conditioned stimuli affect memory by a common physiological process is discussed.

Sex differences in the burying behavior test in middle-aged rats: effects of diazepam

The full behavioral profile displayed during the burying behavior test was studied in middle aged (11-14 months) males, females with irregular estrous cycles, and females in persistent diestrus, with and without diazepam (0.5-2.0mg/kg). Ambulation and motor coordination were also tested to discern behavioral changes from general motor alterations. Without diazepam treatment, middle-aged males showed longer burying behavior latencies, more prod explorations and less freezing than both groups of females. Untreated middle aged males also showed less cumulative burying and more immobility compared to females with irregular cycles. None of the parameters showed any difference between the female groups. Diazepam (0.5 and 1.0mg/kg) increased burying behavior latency in females, but had no effect on any parameter in middle aged males. However, a higher dose (2.0mg/kg) of diazepam increased immobility, freezing and the number of prod shocks and decreased prod explorations and groomings, but impaired motor coordination in males. In contrast with young males and females, diazepam at any dose reduced cumulative burying. Data are discussed on the bases of (1) sex and age differences in burying behavior and on (2) the anxiolytic-like action of diazepam and its side effects.

Early adolescence as a critical window during which social stress distinctly alters behavior and brain norepinephrine activity

Many neural programs that shape behavior become established during adolescence. Adverse events at this age can have enduring consequences for both adolescent and adult mental health. Here we show that repeated social stress at different stages of adolescent development differentially affects rat behavior and neuronal activity. Early-adolescent (PND 28, EA), mid-adolescent (PND 42, MA), and adult (PND 63) rats were subjected to resident-intruder social stress (7 days) and behavior was examined 24-72 h later. In EA rats selectively, resident-intruder stress increased proactive responses in the defensive burying and forced swim tests. In adult rats, resident-intruder stress decreased burying behavior regardless of whether the animal was stressed as an adult or during early adolescence. As the locus coeruleus (LC)-norepinephrine system has been implicated in proactive defense behaviors, LC neuronal activity was quantified in separate cohorts. Stressed EA rats had elevated spontaneous LC discharge rates and diminished responses to sensory stimuli compared with controls. Microinjection of a CRF antagonist into the LC selectively inhibited neurons of stressed EA rats, suggesting that EA social stress induces tonic CRF release onto LC neurons, shifting the mode of discharge to an activated state that promotes active defensive behaviors. In all adult groups, resident-intruder stress resulted in an increased phasic response to sensory stimuli with no change in spontaneous rates. MA was a transition period during which social stress did not affect behavior or LC activity. The results suggest that social stress interacts with the brain norepinephrine system to regulate defensive strategies in an age-dependent manner.

Neuroendocrinology of coping styles: towards understanding the biology of individual variation

Individual variation in behavior and physiology is a widespread and ecologically functional phenomenon in nature in virtually all vertebrate species. Due to domestication of laboratory animals, studies may suffer from a strong selection bias. This paper summarizes behavioral, neuroendocrine and neurobiological studies using the natural individual variation in rats and mice. Individual behavioral characteristics appear to be consistent over time and across situations. The individual variation has at least two dimensions in which the quality of the response to a challenging condition (coping style) is independent from the quantity of that response (stress reactivity). The neurobiology reveals important differences in the homeostatic control of the serotonergic neuron and the neuropeptides vasopressin and oxytocin in relation to coping style. It is argued that a careful exploitation of the broad natural and biologically functional individual variation in behavior and physiology may help in developing better animal models for understanding individual disease vulnerability.

Application of a naturalistic psychogenic stressor in periadolescent mice: effect on serum corticosterone levels differs by strain but not sex

Background

As a first step in determining whether psychogenic stressors might be incorporated into periadolescent mouse models of stress, we evaluated whether a commonly used psychogenic stressor, exposure to red fox urine, alters serum corticosterone levels in periadolescent C57BL/6J and DBA/2J mice.

Findings

In a 1-day experiment, forty-eight 38-day-old C57BL/6J (N = 12 males; N = 12 females) and DBA/2J (N = 12 males; N = 12 females) mice were exposed to 10-min of red fox urine via cotton ball (N = 12 C57BL/6J mice; N = 12 DBA/2J mice) or to a non-saturated cotton ball (N = 12 C57BL/6J mice; N = 12 DBA/2J mice). All mice were sacrificed 15-min after cotton ball exposure and serum was collected for corticosterone assessment. Overall, there was a main effect for strain such that C57BL/6J male and female mice displayed higher corticosterone levels than did male and female DBA/2J mice. There were no main effects for sex or odor exposure. However, there was a significant strain by odor exposure interaction, whereby, within odor-exposed mice, DBA/2J mice displayed lower corticosterone levels (ng/mL) compared to C57BL/6J mice, regardless of sex. Further, among DBA/2J mice, predator odor exposure reduced corticosterone levels compared to no odor exposure.

Conclusions

Findings indicate that mouse strain, but not sex, may play an important role in the efficacy of a predator odor among periadolescent mice.

Strain differences in coping behaviour, novelty seeking behaviour, and susceptibility to socially conditioned fear: a comparison between Wistar and Sprague Dawley rats

The aim of the current study was to generate socially conditioned fear in two different strains of rat (Wistar, W and Sprague Dawley, SD) using social conflict, in order to investigate whether the magnitude of the conditioned fear responses in each strain was related to behaviour exhibited prior to or during fear induction (i.e. social conflict). On day one of the study, all intruders were assessed for exploratory activity in a novel environment. Twenty four hours following the novel environment test the locomotor activity of the intruders was assessed, while they underwent a single familiarisation exposure to the arena in which the conflict was subsequently to occur in. Twenty-four hours following familiarisation, intruders underwent either a 10 min social conflict or sham conflict session. One day later we examined the response of the intruders when they were returned to the vacant resident's cage. Upon return to the conflict context, we examined the intruder's ultrasonic distress vocalisations and the extent to which locomotor activity was inhibited. We found that W rats displayed significantly more immobility (i.e. conditioned fear) upon return to context than did SD rats (p < 0.05). Importantly, we observed that the differences in the two strains behaviour upon return to context appeared to be related to their quite different patterns of coping behaviour. The results of the current study indicate that preclinical between-strain comparisons potentially have much to offer in regard to understanding the basis of resilience to social stress.

Behavioural assays to model cognitive and affective dimensions of depression and anxiety in rats

Animal models have been used extensively to investigate neuropsychiatric disorders, such as depression, and their treatment. However, the aetiology and pathophysiology of many such disorders are largely unknown, which makes validation of animal models particularly challenging. Furthermore, many diagnostic symptoms are difficult to define, operationalize and quantify, especially in experimental animals such as rats. Thus, rather than attempting to model complex human syndromes such as depression in their entirety, it can be more productive to define and model components of the illness that may account for clusters of co-varying symptoms, and that may share common underlying neurobiological mechanisms. In preclinical investigations of the neural regulatory mechanisms linking stress to depression and anxiety disorders, as well as the mechanisms by which chronic treatment with antidepressant drugs may exert their beneficial effects in these conditions, we have employed a number of behavioural tests in rats to model specific cognitive and anxiety-like components of depression and anxiety disorders. In the present study, we review the procedures for conducting four such behavioural assays: the attentional set-shifting test, the elevated-plus maze, the social interaction test and the shock-probe defensive burying test. The purpose is to serve as a guide to the utility and limitations of these tools, and as an aid in optimising their use and productivity.

Differential blockade of CRF-evoked behaviors by depletion of norepinephrine and serotonin in rats

RATIONALE

Central administration of corticotropin-releasing factor (CRF) elicits a specific pattern of behavioral responses resembling a stress-like state and is anxiogenic in rodent models of anxiety.

OBJECTIVES

Specific behaviors evoked by the administration of CRF were measured. The roles of CRF receptor subtypes and that of serotonergic and noradrenergic systems in mediating these responses were studied.

MATERIALS AND METHODS

Burying, grooming, and head shakes were quantified in rats following intracerebroventricular administration of CRF and urocortin II and after pretreatment with antagonists. The role of forebrain norepinephrine in the behavioral responses to CRF (0.3 microg) was examined following pretreatment with the neurotoxin DSP-4 and that of serotonin after depletion using systemic administration of para-chlorophenylalanine (p-CPA).

RESULTS

CRF at 0.3 and 3.0 microg caused robust increases in burying, grooming, and head shakes, but urocortin II was ineffective. Pretreatment with either antalarmin or propranolol significantly attenuated the CRF-evoked behaviors. Destruction of forebrain norepinephrine pathways blocked spontaneous burying behavior elicited by CRF and conditioned burying directed towards an electrified shock probe. In contrast, depletion of 5-HT selectively attenuated CRF-evoked grooming.

CONCLUSIONS

Overt behavioral responses produced by CRF, burying, grooming, and head shakes appeared to be mediated through the CRF(1) receptor. Spontaneous burying behavior evoked by CRF or conditioned burying directed towards a shock probe was disrupted by lesion of the dorsal noradrenergic bundle and may represent anxiety-like behavior caused by CRF activation of the locus ceruleus. In contrast, CRF-evoked increases in grooming were dependent on serotonin.

Differential MR/GR activation in mice results in emotional states beneficial or impairing for cognition

Corticosteroids regulate stress response and influence emotion, learning, and memory via two receptors in the brain, the high-affinity mineralocorticoid (MR) and low-affinity glucocorticoid receptor (GR). We test the hypothesis that MR- and GR-mediated effects interact in emotion and cognition when a novel situation is encountered that is relevant for a learning process. By adrenalectomy and additional constant corticosterone supplement we obtained four groups of male C57BL/6J mice with differential chronic MR and GR activations. Using a hole board task, we found that mice with continuous predominant MR and moderate GR activations were fast learners that displayed low anxiety and arousal together with high directed explorative behavior. Progressive corticosterone concentrations with predominant action via GR induced strong emotional arousal at the expense of cognitive performance. These findings underline the importance of a balanced MR/GR system for emotional and cognitive functioning that is critical for mental health.

Individual Variation in Coping with Stress: A Multidimensional Approach of Ultimate and Proximate Mechanisms

Ecological studies on feral populations of mice, fish and birds elucidate the functional significance of phenotypes that differ individually in their behavioral and neuroendocrine response to environmental challenge. Within a species, the capacity to cope with environmental challenges largely determines individual survival in the natural habitat. Recent studies indicate that individual variation within a species may buffer the species for strong fluctuations in the natural habitat. A conceptual framework will be presented that is based on the view that individual variation in aggressive behavior can be considered more generally as a variation in actively coping with environmental challenges. Highly aggressive individuals adopt a proactive coping style whereas low levels of aggression indicate a more passive or reactive style of coping. Coping styles have now been identified in a range of species and can be considered as trait characteristics that are stable over time and across situations. The dimension of coping style seems to be independent of an emotionality dimension. Hence, in the analysis of the proximate mechanisms of stress and adaptation, one has to consider the possibility that the mechanisms which determine the type of stress response might be independent from those underlying the magnitude of the response. The two coping styles differ in a number of important neurobiological and neuroendocrine systems. For example, proactive males differ significantly from reactive males in the homeostatic control of serotonergic activity resulting in completely opposite dose response relationships of various serotonergic drugs. The results so far show that proactive coping is characterized by a strong inhibitory control of the 5-HT neuron via its somatodendritic 5-HT(1A) autoreceptor. It is hypothesized that the regulation of serotonin release is causally related to coping style rather than emotionality. Understanding the functional individual variation as it occurs in nature and the underlying neurobiology and neuroendocrinology is fundamental in understanding individual vulnerability to stress related disease.

Noradrenergic facilitation of shock-probe defensive burying in lateral septum of rats, and modulation by chronic treatment with desipramine

We have previously shown that acute stress-induced release of norepinephrine (NE) facilitates anxiety-like behavioral responses to stress, such as reduction in open-arm exploration on the elevated-plus maze and in social behavior on the social interaction test. Since these responses represent inhibition of ongoing behavior, it is important to also address whether NE facilitates a response that represents an activation of behavior. Correspondingly, it is unknown how a chronic elevation in tonic steady-state noradrenergic (NA) neurotransmission induced by NE reuptake blockade might alter this acute modulatory function, a regulatory process that may be pertinent to the anxiolytic effects of NE reuptake blockers such as desipramine (DMI). Therefore, in this study, we investigated noradrenergic modulation of the shock-probe defensive burying response in the lateral septum (LS). In experiment 1, shock-probe exposure induced an acute 3-fold increase in NE levels measured in LS of male Sprague-Dawley rats by microdialysis. Shock-probe exposure also induced a modest rise in plasma ACTH, taken as an indicator of perceived stress, that returned to baseline more rapidly in rats that were allowed to bury the probe compared to rats prevented from burying by providing them with minimal bedding, indicating that the active defensive burying behavior is an effective coping strategy that reduces the impact of acute shock probe-induced stress. In experiment 2, blockade of either alpha(1)- or beta-adrenergic receptors in LS by local antagonist microinjection immediately before testing reduced defensive burying and increased immobility. In the next experiment, chronic DMI treatment increased basal extracellular NE levels in LS, and attenuated the acute shock probe-induced increase in NE release in LS relative to baseline. Chronic DMI treatment decreased shock-probe defensive burying behavior in a time-dependent manner, apparent only after 2 weeks or more of drug treatment. Moreover, rats treated chronically with DMI showed no significant rise of plasma ACTH in response to shock-probe exposure. Thus, acute stress-induced release of NE in LS facilitated defensive burying, an active, adaptive behavioral coping response. Chronic treatment with the NE reuptake blocker and antidepressant drug DMI attenuated acute noradrenergic facilitation of the active burying response, and also attenuated the level of perceived stress driving that response. These results suggest that long-term regulation of the acute modulatory function of NE by chronic treatment with reuptake blockers may contribute to the mechanisms by which such drugs exert their anxiolytic effects in the treatment of stress-related psychiatric conditions, including depression and anxiety.

Stress and welfare: two complementary concepts that are intrinsically related to the animal's point of view

The closely associated concepts of welfare and stress may be considered as opposites since welfare cannot be achieved under stress and vice versa. Stress was first considered as an unspecific response to any challenge taxing the organism's resources where the HPA axis plays a central role [Selye H. A syndrome produced by diverse nocuous agents. Nature 1936:32]. Along the same lines, welfare was considered as the state of an individual on a continuum between poor and good depending on the efforts required to adapt to the environment [Broom DM. Animal welfare: concepts and measurement. J Anim Sci 1991;69:4167-75]. However, these views cannot explain opposite results such as up- vs. down-regulation of the HPA axis and hypo- vs. hyper-behavioural reactivity under chronic stress. Later, it was shown that aversive situations trigger stress responses only if the individual perceives them as aversive. Mason [Mason JW. A re-evaluation of the concept of 'non-specificity' in stress theory. J Psychiatr Res 1971;8:323-33] suggested that the unspecificity of stress responses originates from a common emotion that produces them. Welfare has also been defined in terms of emotional states by Dawkins [Dawkins MS. Animal suffering, the science of animal welfare. London: Chapman and Hall Ltd.; 1980] and Duncan [Duncan IJH. Welfare is to do with what animals feel. J Agric Environ Ethics 1993;6:8-14]. Hence, both concepts are linked to mental states. Recent advances in psychology suggest that the very nature of an emotion results from a series of evaluations of the triggering situation that the individual makes based on criteria including novelty, predictability, controllability, and others [Scherer KR. Appraisal considered as a process of multi-level sequential checking. In: Scherer KR, Schorr A, Johnstone T, editors. Appraisal processes in emotion: theory, methods, research. New York: Oxford University Press; 2001. p. 92-120]. It is therefore suggested that the discrepancies found in the literature in terms of responses of the HPA axis or modification of behaviour under aversive conditions may stem from differences in the way a situation is evaluated. It is argued that stress comes from the animal's evaluation of the outcome of a situation, and that welfare is the state resulting from that evaluation.

Hippocampal Mek/Erk signaling mediates extinction of contextual freezing behavior

Fear memories elicit multiple behavioral responses, encompassing avoidance, or behavioral inhibition in response to threatening contexts. Context-specific freezing, reflecting fear-induced behavioral inhibition, has been proposed as one of the main risks factors for the development of anxiety disorders. We attempted to define the key hippocampal mediators of extinction in a mouse model of context-dependent freezing. Nine-week-old male C57BL/6J mice were trained and tested for contextual fear conditioning and extinction. Freezing behavior scored by unbiased sampling, was used as an index of fear. Proteomic, immunoblot, and immunohistochemical approaches were employed to identify, verify, and analyze the alterations of the hippocampal extracellular signal-regulated kinases 1 and 2 (Erk-1/2). Targeted pharmacological inhibition of the Erk-1/2 activating kinase, the mitogen activated and extracellular signal-regulated kinase (Mek), served to establish the role of Mek/Erk signaling in extinction. When compared to acquisition, extinction of contextual freezing triggered a rapid activation of Erk-1/2 showing a distinctive time-course, nuclear localization, and subcellular isoform distribution. These differences suggested that the upstream regulation and downstream effects of this pathway might be specific for each process. Dorsohippocampal injections of the Mek inhibitors U0126 (0.5 microg/site) and PD98059 (1.5 microg/site) immediately after the nonreinforced trials prevented Erk-1/2 activation and significantly impaired extinction. This effect was dissociable from potential actions on memory retrieval or reconsolidation. On the basis of these findings, we propose that hippocampal Mek/Erk signaling might serve as one of the key mediators of contextual fear extinction.

Lineage is an epigenetic modifier of QTL influencing behavioral coping with stress

A genome-wide scan was carried out on a segregating F2 population of rats derived from reciprocal intercrosses between two inbred strains of rats, Fisher 344 (F344) and Wistar Kyoto (WKY) that differ significantly in their behavioral coping responses to stress measured by the defensive burying (DB) test. The DB test measures differences in coping strategies by assaying an animal's behavioral response to an immediate threat. We have previously identified three X-linked loci contributing to the phenotypic variance in behavioral coping. Here we report on six significant autosomal quantitative trait loci (QTL) related to different behaviors in the DB test:one for the number of shocks received, three for number of prod approaches, one for latency to bury, and one pleiotropic locus affecting both approach and latency. These QTL contributing to different aspects of coping behaviors show that the effect of genotype on phenotype is highly dependent on lineage. The WKY lineage was particularly influential, with five out of the six QTL affecting coping behavior only in rats of the WKY lineage, and one locus affecting only those in the F344 lineage. Thus, epigenetic factors, primarily of WKY origin, may significantly modulate the genetic contribution to variance in behavioral responses to stress in the DB test.

The Darwinian concept of stress: benefits of allostasis and costs of allostatic load and the trade-offs in health and disease

Why do we get the stress-related diseases we do? Why do some people have flare ups of autoimmune disease, whereas others suffer from melancholic depression during a stressful period in their life? In the present review possible explanations will be given by using different levels of analysis. First, we explain in evolutionary terms why different organisms adopt different behavioral strategies to cope with stress. It has become clear that natural selection maintains a balance of different traits preserving genes for high aggression (Hawks) and low aggression (Doves) within a population. The existence of these personality types (Hawks-Doves) is widespread in the animal kingdom, not only between males and females but also within the same gender across species. Second, proximate (causal) explanations are given for the different stress responses and how they work. Hawks and Doves differ in underlying physiology and these differences are associated with their respective behavioral strategies; for example, bold Hawks preferentially adopt the fight-flight response when establishing a new territory or defending an existing territory, while cautious Doves show the freeze-hide response to adapt to threats in their environment. Thus, adaptive processes that actively maintain stability through change (allostasis) depend on the personality type and the associated stress responses. Third, we describe how the expression of the various stress responses can result in specific benefits to the organism. Fourth, we discuss how the benefits of allostasis and the costs of adaptation (allostatic load) lead to different trade-offs in health and disease, thereby reinforcing a Darwinian concept of stress. Collectively, this provides some explanation of why individuals may differ in their vulnerability to different stress-related diseases and how this relates to the range of personality types, especially aggressive Hawks and non-aggressive Doves in a population. A conceptual framework is presented showing that Hawks, due to inefficient management of mediators of allostasis, are more likely to be violent, to develop impulse control disorders, hypertension, cardiac arrhythmias, sudden death, atypical depression, chronic fatigue states and inflammation. In contrast, Doves, due to the greater release of mediators of allostasis (surplus), are more susceptible to anxiety disorders, metabolic syndromes, melancholic depression, psychotic states and infection.

X-linked and lineage-dependent inheritance of coping responses to stress

Coping-or how one routinely deals with stress-is a complex behavioral trait with bearing on chronic disease and susceptibility to psychiatric disorders. This complexity is a result of not only underlying multigenic factors, but also important non-genetic ones. The defensive burying (DB) test, although originally developed as a test of anxiety, can accurately measure differences in coping strategies by assaying an animal's behavioral response to an immediate threat with ethological validity. Using offspring derived from reciprocal crosses of two inbred rat strains differing in DB behaviors, we provide convergent phenotypic and genotypic evidence that coping styles are inherited in an X-linked fashion. We find that first-generation (F(1)) males, but not females, show maternally derived coping styles, and second-generation (F(2)) females, but not males, show significant differences in coping styles when separated by grandmaternal lineage. By using a linear modeling approach to account for covariate effects (sex and lineage) in QTL analysis, we map three quantitative trait loci (QTL) on the X Chromosome (Chr) ( Coping-1, Approach-1, and Approach-2) associated with coping behaviors in the DB paradigm. Distinct loci were associated with different aspects of coping, and their effects were modulated by both the sex and lineage of the animals, demonstrating the power of the general linear modeling approach and the important interplay of allelic and non-allelic factors in the inheritance of coping behaviors.

Amygdala inactivation blocks expression of conditioned memory modulation and the promotion of avoidance and freezing

Rats were exposed to shock-paired cues immediately after training on an appetitive preference task. Elevated levels of freezing in and active avoidance of the shock-paired compartment were observed, and memory for the appetitive task was improved when tested 24 hr later. Intra-amygdala muscimol injected before the posttraining exposure eliminated freezing, avoidance, and memory modulation. The blockade of both freezing and active avoidance, which involve competing behavioral tendencies, makes it unlikely that the amygdala itself generates either behavior. The elimination of conditioned memory modulation suggests that conditioned neurohormonal responses were blocked. These conditioned internal responses may comprise the intervening variable of "conditioned fear" and may promote observable behaviors, the form of which is determined by the environment in which they occur.

Stress-induced hyperthermia and anxiety: pharmacological validation

When mammals, including man, are confronted with a stressful event, their core body temperature rises, stress-induced hyperthermia. In mice, the stress-induced hyperthermia procedure has been developed to measure antistress or anxiolytic-like effects of psychoactive drugs. Group-housed and singly housed versions of the stress-induced hyperthermia generate comparable results. Because the number of animals needed to perform an experiment is much lower in the singly housed versus the group-housed procedure, the former is the test of choice for pharmacological testing. A typical stress-induced hyperthermia test starts with an injection 60 min before the first rectal temperature measurement (T(1)), followed by a second temperature measurement (T(2)) 10-15 min later. The difference DeltaT (=T(2)-T(1)) is the stress-induced hyperthermia. The procedure also measures the intrinsic activity of drugs on the basal body temperature and DeltaT is relatively independent from the intrinsic temperature effects of drugs. Anxiolytic drugs (benzodiazepines, 5-HT(1A) receptor agonists, alcohol) reduce DeltaT suggestive of anxiolytic-like effects. Because the parameter measured for anxiety in the stress-induced hyperthermia procedure is not dependent on locomotor activity, like in almost all other anxiety tests, the stress-induced hyperthermia procedure is an attractive addition to tests in the anxiety field. Because the stress-induced hyperthermia is also present with a comparable pharmacological profile in females, this procedure has a wide species and gender validity. The procedure was applied in various genetically modified mice [5-HT(1A) and 5-HT(1B) receptor knockout (KO) mice and corticotropin-releasing hormone overexpressing (CRH-OE) mice] to study phenotypic influences of the various mutations on aspects of anxiety. The stress-induced hyperthermia test in singly housed male and female mice appears a useful and extremely simple test to measure effects of drugs on certain aspects of anxiety or to help to determine phenotypic differences in mutant mice.

Defensive burying in rodents: ethology, neurobiology and psychopharmacology

Defensive burying refers to the typical rodent behavior of displacing bedding material with vigorous treading-like movements of their forepaws and shoveling movements of their heads directed towards a variety of noxious stimuli that pose a near and immediate threat, such as a wall-mounted electrified shock-prod. Since its introduction 25 years ago by Pinel and Treit [J. Comp. Physiol. Psychol. 92 (1978) 708], defensive (shock-prod) burying has been the focus of a considerable amount of research effort delineating the methodology/ethology, psychopharmacology and neurobiology of this robust and species-specific active avoidance or coping response. The present review gives a summary of this research with special reference to the behavioral (face and construct) and pharmacological (predictive) validity of the shock-prod burying test as an animal model for human anxiety. Emphasis is also placed on some recent modifications of the paradigm that may increase its utility and reliability as to individual differences in expressed emotional coping responses and sensitivity to pharmacological treatments. Overall, the behavioral and physiological responses displayed in the shock-prod paradigm are expressions of normal and functionally adaptive coping patterns and the extremes of either active (i.e., burying) or passive (i.e., freezing) forms of responding in this test cannot simply be regarded as inappropriate, maladaptive or pathological. For this reason, the shock-prod paradigm is not an animal model for anxiety disorder or for any other psychiatric disease, but instead possesses a high degree of face and construct validity for normal and functionally adaptive human fear and anxious apprehension. However, the apparent good pharmacological validation (predictive validity) of this test reinforces the view that normal and pathological anxiety involves, at least partly, common neurobiological substrates. Therefore, this paradigm is not only suitable for screening potential anxiolytic properties of new drugs, but seems to be especially valuable for unraveling the neural circuitry and neurochemical mechanisms underlying the generation of active and passive coping responses as different expressions of anxiety.

Stress responses during milking; comparing conventional and automatic milking in primiparous dairy cows

A comparative study was performed to evaluate the differences in behavioral and physiological stress responses during milking between cows that were milked by an automated milking system (AM-cows) and cows that were milked in a conventional tandem parlor (TM-cows). In a randomized design, 36 primiparous Holstein-Friesian dairy cows were observed and blood sampled (1-min intervals) individually during milking. AM-cows spent less time standing with their heads outside the feeding trough than TM-cows and had a lower heart rate. In addition, AM-cows had lower maximum plasma adrenaline and noradrenaline concentrations during milking. No differences were found in the number of steps. After tactile stimulation of the teats either by hand or by the cleaning brush, mean oxytocin concentrations did not differ. In AM-cows, however, elevated oxytocin levels were prolonged at the end of milking. Averaged over the first five blood samples, AM-cows tended to have higher plasma cortisol concentrations than TM-cows, but median fecal concentrations of the cortisol metabolite dioxoandrostane were comparable. Maximum quarter milk flow, maximum udder milk flow and residual milk as a percentage of the total milk volume was comparable. From this study it is concluded that behavioral and physiological responses, both in automatically and in conventionally milked cows, were relatively low and were typical for cows being milked. We therefore conclude that, as far as the welfare of the dairy cow during milking is concerned, automatic milking and conventional milking are equally acceptable.

Individual response profiles of male Wistar rats in animal models for anxiety and depression

Previous work has shown that systematic individual differences between male Wistar rats can be detected in tasks like the elevated plus-maze, or the open field. Here, we investigated whether individual profiles of anxiety, as measured with the plus-maze, may predict behavioral response profiles in other tasks where anxiety, aversion, or depressive behaviors are important. Male Wistar rats were initially screened: (A) in an open field; and (B) in an elevated plus-maze. Based on their plus-maze behavior, that is, the time spent in the open arms, the animals were divided into two subgroups with either 'low' or 'high' anxiety (LA or HA) levels. These subgroups were exposed to other experimental anxiety paradigms, namely object burying and two-way active avoidance, and an animal model of depression, the forced swim test. In the plus-maze, the percentage of time spent on, and the number of entries into the open arms were lower in HA than in LA rats. In the object burying task, HA rats showed more burying behavior of Tabasco-coated marbles, and in the active avoidance task, they showed slower acquisition of avoidance learning and higher escape latency as compared to LA rats. Finally, LA and HA rats behaved similarly in the forced swim test; however, the percentage changes of immobility time between test days 1 and 2 were negatively correlated to open field behavior, namely locomotor activity and center entries. On the other hand, the frequencies of rearing in the open field, which can also gauge functional differences between rats (for example responsiveness to novelty, psychomotor activation), were not substantially related to the behavioral profiles in the tests of anxiety and depression. These results show that individual differences of anxiety in the plus-maze can be predictive of behavior in other anxiety models, but not in forced swim test, indicating that they may be determined partly by similar functional and physiological mechanisms.

Relationship of anhedonia and anxiety to social rank, defeat and entrapment

There is good evidence to suggest that depression is highly correlated with perceptions of low rank and subordinate status (i.e. feeling inferior, low-self esteem, feeling that others look down on the self, and submissive behaviour). However, it is possible for people to feel inferior and anxious, and behave submissively but not necessarily be depressed. More recently two other processes, defeat and entrapment, have attracted attention as possible processes linked specifically to depression and anhedonia. This research explored the relationship of these variables (social rank variables and defeat and entrapment) to two measures of hedonic tone (low positive affectivity and anhedonia) and anxiety in both a clinical and student population. All variables were strongly associated with lowered hedonic tone and anxiety. However, partial correlations, and a structural equation model fitted to the data from combined groups, suggests that perceptions of defeat play a specifically important role in anhedonia as measured by low positive affect. Framed within an evolutionary model the data suggest that the mechanisms which evolved to help animals accommodate and respond to defeats may have important regulatory effects over positive affect, reducing exploration of and engagement with the environment.

Conditioned memory modulation, freezing, and avoidance as measures of amygdala-mediated conditioned fear

Three conditioned aversive responses were used to infer the existence of an unobservable central state of "conditioned fear," and the roles of certain amygdala subregions in producing these responses were investigated. Rats received tone-shock pairings in one compartment of a shuttle box and no tones or shocks in the other, distinctive, compartment. They were then trained to find food in one arm of a Y-maze. After the final training trial they were exposed to different sets of stimuli in the shuttle box with no shock. Twenty-four hours later rats that had received immediate posttraining exposure to the conditioned stimuli (in the shock-paired compartment) made significantly more correct responses on the Y-maze than rats that had been exposed to the neutral stimuli (in the no-shock compartment) or rats that had received delayed posttraining exposure to the conditioned stimuli. This constitutes a demonstration of posttraining memory modulation by conditioned aversive stimuli. Freezing increased during posttraining exposure to the conditioned stimuli compared to the neutral stimuli. When subsequently allowed to move freely between the two compartments, the rats in all groups also showed significant conditioned avoidance of the compartment containing the conditioned stimuli. In a second experiment the effects of lesions confined to specific parts of the amygdala on the three conditioned responses (memory modulation, freezing, avoidance) were tested. Lesions of the central nucleus impaired all three conditioned responses; lesions of the medial nucleus impaired conditioned modulation and avoidance. These lesions had no effect on freezing during the training trials. Lesions of the lateral and basolateral nuclei attenuated freezing during both training and testing. The findings suggest that the central and medial nuclei of the amygdala may be important parts of neural circuits mediating conditioned responses that constitute conditioned aversive states, but that conditioned freezing may be mediated independently.

A Mouse is Not Just a Mouse

In this paper we describe the existence and consequences of subspecific and individual variation in the genetic make-up of house mice. The purpose is to illustrate forms of variation that are often neglected in discussions about animal care and experimental design. Towards this end, different inbred mouse strains as well as genetically selected mouse lines are compared in relation to their ecological origin. Firstly, the behaviour of BALB/c, C57BL/6J and CBA mice is described in relation to different habitats. Furthermore, their aggression is compared, as measured by two paradigms. It appears that some inbred lines (eg BALB/c and C57BL/6J) clearly show behaviour that reflects the functional adaptation to the natural habitats in which their ancestors lived. Other strains (eg CBA) show a lack of such behavioural adaptation and their phenotypes appear to be very unstable over time. Secondly, two fundamentally different characters, both present in populations of wild house mice and under genetic control, are described: on the one hand, active copers are characterized by aggressive behaviour; on the other hand, passive copers are reluctant to attack. The active, aggressive animals (manipulators) are well adapted to an invariant environment like their own territory, whereas the passive, non-aggressive copers (adjustors) are well adapted to a changing environment, eg when roaming. We discuss to what extent these coping styles are present in laboratory strains of mice. The major conclusion with regard to both phenomena is that individual and subspecific variation may have significant implications for experimental design and the welfare of the experimental animals.

Regulation of monoamine receptors in the brain: dynamic changes during stress

Monoamine receptors are membrane-bound receptors that are coupled to G-proteins. Upon stimulation by agonists, they initiate a cascade of intracellular events that guide biochemical reactions of the cell. In the central nervous system, they undergo diverse regulatory processes, among which are receptor desensitization, internalization into the cell, and downregulation. These processes vary among different types of monoamine receptors. alpha 2-Adrenoceptors are often downregulated by agonists, and beta-adrenoceptors are internalized rapidly. Others, such as serotonin1A-receptors, are controlled tightly by steroid hormones. Expression of these receptors is reduced by the "stress hormones" glucocorticoids, whereas gonadal hormones such as testosterone can counterbalance the glucocorticoid effects. Because of this, the pattern of monoamine receptors in certain brain regions undergoes dynamic changes when there are elevated concentrations of agonists or when the hormonal milieu changes. Stress is a physiological situation accompanied by the high activity of brain monoaminergic systems and dramatic changes in peripheral hormones. Resulting alterations in monoamine receptors are considered to be in part responsible for changes in the behavior of an individual.

Y chromosomal and sex effects on the behavioral stress response in the defensive burying test in wild house mice

Genetically selected short attack latency (SAL) and long attack latency (LAL) male wild house mice behave differently in the defensive burying test. When challenged, SAL males respond actively with more time spent on defensive burying, whereas LAL males are more passive with more time remaining immobile. The first aim of this study was to find out whether the nonpairing part of the Y chromosome (Y(NPAR)) affects the behavioral stress response in this paradigm. Second, to determine if the differential behavioral profile found in males is also present in females, SAL and LAL females were tested. Third, nonattacking and attacking LAL males were compared. Five behavioral elements were recorded: defensive burying, immobility, rearing, grooming, and exploration. Males were first tested for attack latency. The results show that the Y(NPAR) influences defensive burying. However, the size of this effect is overshadowed by the background of the mice. Furthermore, although females differed from males, they tended to demonstrate the same behavioral profile as males. Nongenetic factors may also play a role, as attacking LAL males showed more defensive burying than nonattacking LAL males.

The 5-HT1A receptor and its ligands: structure and function

An overview is presented on progress made in research on 5-HT1A receptors and their ligands since their discovery in 1983. Molecular biology has offered new tools, for example cloned 5-HT1A receptors, their mutants and chimeras to study structure and function. Many compounds, belonging to different chemical classes, display high affinity and selectivity for 5-HT1A receptors. The majority of these compounds are agonists or partial agonists, full antagonists are still scarce. Agonists and partial agonists are active in various animal models of anxiety and depression. Partial receptor agonists have been proven to be effective in general anxiety disorder and depression in man. Potential therapeutic applications for 5-HT1A receptor antagonists are evaluated, for example, in cognition disorders.

Blockade of the anxiolytic-like action of ipsapirone and buspirone, but not that of 8-OH-DPAT, by adrenalectomy in male rats

The effect of the 5-HT1A agonists ipsapirone (5 mg/kg), buspirone (5 mg/kg) and 8-OH-DPAT (0.5 mg/kg) on experimental anxiety was examined in sham-operated, adrenalectomized and adrenally demedullated male rats. The animal model of anxiety used was the defensive burying test. At the doses selected, all 5-HT1A compounds produced an anxiolytic-like action by reducing the burying behavior in both sham-operated and demedullated rats. However, in adrenalectomized subjects, while 8-OH-DPAT still reduced burying behavior, ipsapirone and buspirone lost their action. Data suggest that adrenocortical secretions play a role in the anxiolytic-like actions of buspirone and ipsapirone, but not in those of 8-OH-DPAT. Buspirone and ipsapirone also produced a reduction in burying behavior latency in sham-operated animals that was not observed in adrenalectomized or adrenally demedullated rats. These data suggest that adrenaline may be participating in the action of these compounds on the burying behavior latency. Present findings support possible direct relationships between the stimulation of 5-HT1A receptors and adrenal secretions.

Heart rate variability during manual restraint in chicks from high- and low-feather pecking lines of laying hens

The purpose of this investigation was to determine whether there is a difference in coping style in chicks from a high (HFP)- and low-feather pecking (HFP) line of laying hens. Active and passive coping styles can be distinguished by differences in sympathetic and parasympathetic activities on the heart. We studied heart rate during baseline conditions and during manual restraint in HFP and LFP hens. Heart rate and locomotor activity were successfully monitored around the clock with a biotelemetric implant. During the light period, the values for locomotor activity and heart rate were highest, whereas during the dark period they were the lowest. These values did not differ in LFP and HFP hens. However, during manual restraint (restraining the bird on its side by hand for 8 min) HFP birds had somewhat faster heart rate than LFP birds (at 4 min, p = 0.066). Studying heart rate variability during manual restraint showed that LFP chickens had a significant higher parasympathetic activity at 5 min (p = 0.023) and at 6 min (p = 0.002) as compared to HFP hens. The results showed that in terms of coping style, LFP chickens are passive, whereas HFP birds are active.

The antagonism of ipsapirone induced biobehavioral responses by +/- pindolol in high and low impulsives

The present study was conducted to investigate whether +/- pindolol antagonizes ipsapirone induced biobehavioral changes in a personality dependent way. Our previous work demonstrated that high impulsives show higher immune cell responses than low impulsive subjects upon treatment with ipsapirone. A total number of 80 healthy male volunteers received placebo (N = 20) or 10 mg ipsapirone (N = 20), 30 mg +/- pindolol (N = 20), or a combination of 30 mg +/- pindolol and 10 mg ipsapirone (N = 20). Each group consisted of 10 low and 10 high impulsive subjects. Since 5-HT related drugs induce thermoregulatory responses, the study took place in a climate chamber with a constant ambient temperature. Blood samples (for measurement of CD4+ cell counts) were drawn from an indwelling catheter invisibly for the subjects. The results clearly demonstrate that the ipsapirone induced decreases in body temperature and number of peripheral CD4+ cells are more pronounced in high impulsives. +/- Pindolol antagonizes thermoregulatory and CD4+ cell responses. The results are discussed with respect to mechanisms of alteration in 5-HT function related to impulsivity.

Mineralocorticoid and glucocorticoid receptor antagonists in animal models of anxiety

The behavioral effects of intracerebroventricular (i.c.v.) administration of a specific mineralocorticoid receptor (MR) antagonist [RU28318 (10-50 ng/2 microliters)], a glucocorticoid receptor (GR) antagonist [RU38486 (1-50 ng/2 microliters)], or both antagonists (50 ng/2 microliters), were studied in two different animal models of fear and anxiety in rats. In the defensive burying paradigm simultaneous blockade of MR and GR increased immobility behavior, whereas a small decrease in defensive burying was seen. In the fear-potentiated startle test concurrent MR and GR blockade led to an increase in fear-potentiated startle at the highest loudness level (105 dB). In both tests the antagonists were not effective when given separately. The findings are discussed in terms of the involvement of GR and MR in neural mechanisms of fear and anxiety.

Neuroendocrine effects of diazepam and flesinoxan in the stress-induced hyperthermia test in mice

In the stress-induced hyperthermia (SIH) paradigm in mice, both a benzodiazepine receptor agonist, diazepam, and a 5-HT1A receptor agonist, flesinoxan, reduced the stress-induced increase in rectal temperature. The SIH procedure itself enhanced plasma ACTH and corticosterone levels but not plasma glucose levels. Diazepam (3, 6, and 12 mg/kg p.o.) did neither affect basal plasma ACTH, corticosterone, or glucose levels, nor did it suppress the stress-induced rises in these parameters. Flesinoxan (1, 3, and 10 mg/kg p.o.) enhanced plasma ACTH and corticosterone concentrations under nonstress conditions but did not affect the stress-induced increases in ACTH and corticosterone secretion. No clear effects of flesinoxan on plasma glucose levels were found. Our results indicate that in mice the anxiolytic effects of diazepam and flesinoxan in the SIH paradigm are not paralleled by a blockade of stress-induced increases in plasma ACTH, corticosterone, and glucose levels.

Hypoxia and brain development

Hypoxia threatens brain function during the entire life-span starting from early fetal age up to senescence. This review compares the short-term, long-term and life-spanning effects of fetal chronic hypoxia and neonatal anoxia on several behavioural paradigms including novelty-induced spontaneous and learning behaviours. Furthermore, it reveals that perinatal hypoxia is an additional threat to neurodegeneration and decline of cognitive and other behaviours during the aging process. Prenatal hypoxia evokes a temporary delay of ingrowth of cholinergic and serotonergic fibres into the hippocampus and neocortex, and causes an enhanced neurodegeneration of 5-HT-ir axons during aging. Neonatal anoxia suppresses hippocampal ChAT activity and up-regulates muscarinic receptor sites for 3H-QNB and 3H-pirenzepine binding in the hippocampus in the early postnatal age. The altered development of axonal arborization and pre- and postsynaptic cholinergic functions may be an important underlying mechanism to explain the behavioural deficits. As far as the cellular mechanisms of perinatal hypoxia is concerned, our primary aim was to study the putative importance of Ca2+ homeostasis of developing neurons by means of pharmacological interventions and by measuring the development of immunoexpression of Ca(2+)-binding proteins. We assessed that nimodipine, an L-type calcium channel blocker, prevented or attenuated the adverse behavioural and neurochemical effects of perinatal hypoxias, while it enhanced the early postnatal development of ir-Ca(2+)-binding proteins. The results are discussed in the context of different related research areas on brain development and hypoxia and ischaemia.

Behavioral stress response of genetically selected aggressive and nonaggressive wild house mice in the shock-probe/defensive burying test

Genetically selected aggressive and nonaggressive male wild house mice were tested in the shock-probe/defensive burying test: Five distinct behaviors (burying, immobility, rearing, grooming, and exploration) were recorded in two environmental situations: fresh and home cage sawdust. Nonaggressive animals, characterized by a Long Attack Latency (LAL), showed more immobility in both test situations than animals having Short Attack Latencies (SAL), whereas SAL males displayed more defensive burying than LAL ones when tested with fresh sawdust. Testing with home cage sawdust, however, resulted in the same duration of defensive burying in SAL and LAL. These results support earlier findings about the existence of two heritable, fundamentally different strategies to cope with aversive situations. Aggressive (SAL) animal react actively to environmental challenges, whereas nonaggressive animals react actively or passively, depending on the characteristics of the stressful environment. These mouse lines, selected for attack latency, i.e., aggression, may, therefore, be important tools to unravel the genetic architecture underlying the physiological and neuronal mechanisms of behavioral strategies towards stressful events.

The anxiolytic effects of flesinoxan, a 5-HT1A receptor agonist, are not related to its neuroendocrine effects

The effects of flesinoxan, a selective 5-HT1A receptor agonist, were studied under basal non-stress conditions and in the shock-probe burying paradigm. Flesinoxan (1 and 3 mg/kg s.c.) significantly reduced burying and freezing behaviour, indicating clear anxiolytic properties. Under non-stress conditions, injection of 3 mg/kg flesinoxan significantly enhanced plasma corticosterone and glucose levels, whereas prolactin secretion was significantly enhanced after both 1 mg/kg and 3 mg/kg flesinoxan. Flesinoxan (1 and 3 mg/kg) did not suppress shock-probe stress-induced rises in plasma corticosterone and glucose levels. The enhanced plasma prolactin levels induced by flesinoxan were not further affected by shock-probe exposure. Our data show that the anxiolytic effects of flesinoxan in the shock-probe burying paradigm are not related to increases in plasma corticosterone and glucose levels.

5-Hydroxytryptamine-interacting drugs in animal models of anxiety disorders: more than 30 years of research

An overview of the behavioral data arising from the vast literature concerning the involvement of 5-hydroxytryptamine (5-HT) neurotransmission in the regulation of anxiety is presented. More than 1300 experiments were carried out in this area and they provide evidence that: (1) results obtained in ethologically based animal models of anxiety with drugs stimulating 5-HT transmission are most consistent with the classic 5-HT hypothesis of anxiety in that they show an increase in animals' emotional reactivity; (2) no category of anti-anxiety models are selectively sensitive to the anxiolytic-like effects of drugs targetting 5-HT1A, 5-HT2A or 5-HT2C receptor subtypes; (3) anxiolytic-like effects of 5-HT3 receptor antagonists, in the great part, are revealed by models based on spontaneous behaviors. Taken together, these observations lead to the conclusion that different 5-HT mechanisms, mediated by different receptor subtypes, are involved in the genesis of anxiety.