Airjet and FG-7142-induced Fos expression differs in rats selectively bred for high and low anxiety-related behavior

A pontomesencephalic PACAPergic pathway underlying panic-like behavioral and somatic symptoms in mice

Panic disorder is characterized by uncontrollable fear accompanied by somatic symptoms that distinguish it from other anxiety disorders. Neural mechanisms underlying these unique symptoms are not completely understood. Here, we report that the pituitary adenylate cyclase-activating polypeptide (PACAP)-expressing neurons in the lateral parabrachial nucleus projecting to the dorsal raphe are crucial for panic-like behavioral and physiological alterations. These neurons are activated by panicogenic stimuli but inhibited in conditioned fear and anxiogenic conditions. Activating these neurons elicits strong defensive behaviors and rapid cardiorespiratory increase without creating aversive memory, whereas inhibiting them attenuates panic-associated symptoms. Chemogenetic or pharmacological inhibition of downstream PACAP receptor-expressing dorsal raphe neurons abolishes panic-like symptoms. The pontomesencephalic PACAPergic pathway is therefore a likely mediator of panicogenesis, and may be a promising therapeutic target for treating panic disorder.

Selective breeding of rats for high (HAB) and low (LAB) anxiety-related behaviour: A unique model for comorbid depression and social dysfunctions

Animal models of selective breeding for extremes in emotionality are a strong experimental approach to model psychopathologies. They became indispensable in order to increase our understanding of neurobiological, genetic, epigenetic, hormonal, and environmental mechanisms contributing to anxiety disorders and their association with depressive symptoms or social deficits. In the present review, we extensively discuss Wistar rats selectively bred for high (HAB) and low (LAB) anxiety-related behaviour on the elevated plus-maze. After 30 years of breeding, we can confirm the prominent differences between HAB and LAB rats in trait anxiety, which are accompanied by consistent differences in depressive-like, social and cognitive behaviours. We can further confirm a single nucleotide polymorphism in the vasopressin promotor of HAB rats causative for neuropeptide overexpression, and show that low (or high) anxiety and fear levels are unlikely due to visual dysfunctions. Thus, HAB and LAB rats continue to exist as a reliable tool to study the multiple facets underlying the pathology of high trait anxiety and its comorbidity with depression-like behaviour and social dysfunctions.

Sex differences in amygdalohippocampal oscillations and neuronal activation in a rodent anxiety model and in response to infralimbic deep brain stimulation

Introduction

Depression and anxiety are highly comorbid mental disorders with marked sex differences. Both disorders show altered activity in the amygdala, hippocampus, and prefrontal cortex. Infralimbic deep brain stimulation (DBS-IL) has anxiolytic and antidepressant effects, but the underlying mechanisms remain unclear. We aimed to contribute to understanding sex differences in the neurobiology of these disorders.

Methods

In male and female rats, we recorded neural oscillations along the dorsoventral axis of the hippocampus and the amygdala in response to an anxiogenic drug, FG-7142. Following this, we applied DBS-IL.

Results

Surprisingly, in females, the anxiogenic drug failed to induce most of the changes observed in males. We found sex differences in slow, delta, theta, and beta oscillations, and the amygdalo-hippocampal communication in response to FG-7142, with modest changes in females. Females had a more prominent basal gamma, and the drug altered this band only in males. We also analyzed c-Fos expression in both sexes in stress-related structures in response to FG-7142, DBS-IL, and combined interventions. With the anxiogenic drug, females showed reduced expression in the nucleus incertus, amygdala, septohippocampal network, and neocortical levels. In both experiments, the DBS-IL reversed FG-7142-induced effects, with a more substantial effect in males than females.

Discussion

Here, we show a reduced response in female rats which contrasts with the higher prevalence of anxiety in women but is consistent with other studies in rodents. Our results open compelling questions about sex differences in the neurobiology of anxiety and depression and their study in animal models.

The role of the locus coeruleus in the generation of pathological anxiety

This review aims to synthesise a large pre-clinical and clinical literature related to a hypothesised role of the locus coeruleus norepinephrine system in responses to acute and chronic threat, as well as the emergence of pathological anxiety. The locus coeruleus has widespread norepinephrine projections throughout the central nervous system, which act to globally modulate arousal states and adaptive behavior, crucially positioned to play a significant role in modulating both ascending visceral and descending cortical neurocognitive information. In response to threat or a stressor, the locus coeruleus–norepinephrine system globally modulates arousal, alerting and orienting functions and can have a powerful effect on the regulation of multiple memory systems. Chronic stress leads to amplification of locus coeruleus reactivity to subsequent stressors, which is coupled with the emergence of pathological anxiety-like behaviors in rodents. While direct in vivo evidence for locus coeruleus dysfunction in humans with pathological anxiety remains limited, recent advances in high-resolution 7-T magnetic resonance imaging and computational modeling approaches are starting to provide new insights into locus coeruleus characteristics.

Neuronal substrates underlying stress resilience and susceptibility in rats

Background

Stress and stressful life events have repeatedly been shown as causally related to depression. The Chronic Mild Stress rat model is a valid model of stress-induced depression. Like humans, rats display great heterogeneity in their response to stress and adversity. Hence some individuals are stress-sensitive and prone to develop depression-like behaviour in response to modest stressors, while others are stress-resilient and remain essentially symptom free.

Objectives

Compared to the large body of research, which describes stress-induced maladaptive neurobiological changes, relatively little attention has been devoted to understand resiliency to stress. The aim of the present study was to identify changes in neuronal activity, associated with stress-resilient and stress-susceptible chronic mild stress endophenotypes, by examining c-Fos expression in 13 different brain areas. Changes in c-Fos expression have been reported as associated to stressful conditions.

Methods

Stress-induced modulation of neuronal activation patterns in response to the chronic mild stress paradigm was mapped using the immediate early gene expression c-Fos as a marker. Quantification of the c-Fos-like immunoreactivity responses was done by semi-automated profile counting procedures and design-based stereology.

Results

Exposure to chronic mild stress significantly altered c-Fos expression in a total of 6 out of 13 investigated areas. Chronic mild stress was found to suppress the c-Fos response within the magnocellular ventral lateral geniculate nucleus of both stress subgroups. In the the lateral and ventral orbital cortices of stress-resilient rats, the c-Fos like immunoreactivity response was also repressed by stress exposure. On the contrary the c-Fos response within the amygdala, medial habenula, and infralimbic cortex was increased selectively for the stress-susceptible rats.

Conclusions

The study was initiated to characterize neuronal substrates associated with stress-coping mechanisms. Six areas, all of which represents limbic structures, were found to be sensitive to stress exposure. The effects within these areas associate to the hedonic status of the rats. Hence, these areas might be associated to stress-coping mechanisms underlying the chronic mild stress induced segregation into stress-susceptible and stress-resilient endophenotypes.

Chronic subordinate colony housing paradigm: a mouse model to characterize the consequences of insufficient glucocorticoid signaling

Chronic, in particular chronic psychosocial, stress is a burden of modern societies and known to be a risk factor for numerous somatic and affective disorders (in detail referenced below). However, based on the limited existence of appropriate, and clinically relevant, animal models for studying the effects of chronic stress, the detailed behavioral, physiological, neuronal, and immunological mechanisms linking stress and such disorders are insufficiently understood. To date, most chronic stress studies in animals employ intermittent exposure to the same (homotypic) or to different (heterotypic) stressors of varying duration and intensity. Such models are only of limited value, since they do not adequately reflect the chronic and continuous situation that humans typically experience. Furthermore, application of different physical or psychological stimuli renders comparisons to the mainly psychosocial stressors faced by humans, as well as between the different stress studies almost impossible. In contrast, rodent models of chronic psychosocial stress represent situations more akin to those faced by humans and consequently seem to hold more clinical relevance. Our laboratory has developed a model in which mice are exposed to social stress for 19 continuous days, namely the chronic subordinate colony housing (CSC) paradigm, to help bridge this gap. The main aim of the current review article is to provide a detailed summary of the behavioral, physiological, neuronal, and immunological consequences of the CSC paradigm, and wherever possible relate the findings to other stress models and to the human situation.

Making memories of stressful events: a journey along epigenetic, gene transcription, and signaling pathways

Strong psychologically stressful events are known to have a long-lasting impact on behavior. The consolidation of such, largely adaptive, behavioral responses to stressful events involves changes in gene expression in limbic brain regions such as the hippocampus and amygdala. However, the underlying molecular mechanisms were until recently unresolved. More than a decade ago, we started to investigate the role of these hormones in signaling and epigenetic mechanisms participating in the effects of stress on gene transcription in hippocampal neurons. We discovered a novel, rapid non-genomic mechanism in which glucocorticoids via glucocorticoid receptors facilitate signaling of the ERK-MAPK signaling pathway to the downstream nuclear kinases MSK1 and Elk-1 in dentate gyrus granule neurons. Activation of this signaling pathway results in serine10 (S10) phosphorylation and lysine14 (K14) acetylation at histone H3 (H3S10p-K14ac), leading to the induction of the immediate-early genes c-Fos and Egr-1. In addition, we found a role of the DNA methylation status of gene promoters. A series of studies showed that these molecular mechanisms play a critical role in the long-lasting consolidation of behavioral responses in the forced swim test and Morris water maze. Furthermore, an important role of GABA was found in controlling the epigenetic and gene transcriptional responses to psychological stress. Thus, psychologically stressful events evoke a long-term impact on behavior through changes in hippocampal function brought about by distinct glutamatergic and glucocorticoid-driven changes in epigenetic regulation of gene transcription, which are modulated by (local) GABAergic interneurons and limbic afferent inputs. These epigenetic processes may play an important role in the etiology of stress-related mental disorders such as major depressive and anxiety disorders like post-traumatic stress disorder.

Environmental enrichment effects on the neurobehavioral profile of selective outbred trait anxiety rats

Environmental enrichment attenuates the response to psychostimulants and has been shown to reduce both anxiety and stress-related behaviors. Since stress is a major vulnerability factor for addiction, we investigated whether enrichment could reverse stress profiles in high anxious rats as well as reduce their amphetamine sensitivity. Using selectively-bred high and low anxiety males (filial 3) from enriched, social or isolated environments, we tested elevated plus maze exploration, novelty place preference and amphetamine (AMPH; 0.5mg/kg, IP)-induced hyperactivity. We measured plasma corticosterone (CORT) response after forced novel object exposure, phosphorylation of the tropomyosin-related kinase B receptor (pTrkB) in the hippocampus and striatum, and dopamine (D2) receptor mRNA levels in the striatum and nucleus accumbens. Results indicate that high anxiety animals reared in social or enriched environments spent more time on open arms of the EPM while low anxiety animals raised in enriched environments spent more time on open arms when compared to either isolated or social groups. There were no group differences or interactions found for novelty place preference. Enriched environments decreased the response to AMPH and stress-induced CORT regardless of trait but selectively decreased pTrkB and increased D2 mRNA levels in high anxiety animals. The results suggest that selectively-bred trait anxiety rats show state anxiety that is influenced by rearing environments, and D2 protein levels and BDNF/TrkB signaling may differentially contribute to integrating these effects.

Development × environment interactions control tph2 mRNA expression

Adverse early life experience is thought to increase an individual's susceptibility to mental health disorders, including anxiety and affective disorders, later in life. Our previous studies have shown that post-weaning social isolation of female rats during a critical period of development sensitizes an anxiety-related serotonergic dorsal raphe nucleus (DR) system in adulthood. Therefore, we investigated how post-weaning social isolation, in combination with a challenge with the anxiogenic drug, N-methyl-beta-carboline-3-carboxamide (FG-7142; a partial inverse agonist at the benzodiazepine allosteric site on the GABAA receptor), affects home cage behavior and serotonergic gene expression in the DR of female rats using in situ hybridization histochemistry. Juvenile female rats were reared in isolation or groups of three for a 3-week period from weaning (postnatal day (PD) 21 to mid-adolescence (PD42)), after which all rats were group-reared for an additional 16 days until adulthood. Among vehicle-treated rats, isolation-reared rats had decreased rodent tryptophan hydroxylase 2 (tph2) mRNA expression in ventral and ventrolateral subdivisions of the DR, a pattern observed previously in a rat model of panic disorder. Isolation-reared rats, but not group-reared rats, responded to FG-7142 with increased duration of vigilance and arousal behaviors. In addition, FG-7142 decreased tph2 expression, measured 4h following treatment, in multiple subregions of the DR of group-reared rats but had no effect in isolation-reared rats. No treatment effects were observed on 5-HT1A receptor or serotonin transporter gene expression. These data suggest that adolescent social isolation alters tph2 expression in specific subregions of the DR and alters the effects of stress-related stimuli on behavior and serotonergic systems.

Common brain activations for painful and non-painful aversive stimuli

BACKGROUND

Identification of potentially harmful stimuli is necessary for the well-being and self-preservation of all organisms. However, the neural substrates involved in the processing of aversive stimuli are not well understood. For instance, painful and non-painful aversive stimuli are largely thought to activate different neural networks. However, it is presently unclear whether there is a common aversion-related network of brain regions responsible for the basic processing of aversive stimuli. To help clarify this issue, this report used a cross-species translational approach in humans (i.e. meta-analysis) and rodents (i.e. systematic review of functional neuroanatomy).

RESULTS

Animal and human data combined to show a core aversion-related network, consisting of similar cortical (i.e. MCC, PCC, AI, DMPFC, RTG, SMA, VLOFC; see results section or abbreviation section for full names) and subcortical (i.e. Amyg, BNST, DS, Hab, Hipp/Parahipp, Hyp, NAc, NTS, PAG, PBN, raphe, septal nuclei, Thal, LC, midbrain) regions. In addition, a number of regions appeared to be more involved in pain-related (e.g. sensory cortex) or non-pain-related (e.g. amygdala) aversive processing.

CONCLUSIONS

This investigation suggests that aversive processing, at the most basic level, relies on similar neural substrates, and that differential responses may be due, in part, to the recruitment of additional structures as well as the spatio-temporal dynamic activity of the network. This network perspective may provide a clearer understanding of why components of this circuit appear dysfunctional in some psychiatric and pain-related disorders.

Imaging trait anxiety in high anxiety F344 rats: Focus on the dorsomedial prefrontal cortex

Functional magnetic resonance imaging (fMRI) has become an important method in clinical psychiatry research whereas there are still only few comparable preclinical investigations. Herein, we report that fMRI in rats can provide key information regarding brain areas underlying anxiety behavior. Perfusion as surrogate for neuronal activity was measured by means of arterial spin labeling-based fMRI in various brain areas of high anxiety F344 rats and control Sprague-Dawley rats. In one of these areas, the dorsomedial prefrontal cortex (dmPFC), c-Fos labeling was compared between these two strains with immunolabeling. The effects of a neurotoxic ibotenic acid lesion of the dmPFC in F344 rats were examined in a social approach-avoidance anxiety procedure and fMRI. Regional brain activity of high anxiety F344 rats was different in selective cortical and subcortical areas as compared to that of low anxiety Sprague-Dawley rats; the largest difference (i.e. hyperactivity) was measured in the dmPFC. Independently, c-Fos labeling confirmed that F344 rats show increased dmPFC activity. The functional role was confirmed by neurotoxic lesion of the dmPFC that reversed the high anxiety-like behavior and partially normalized the brain activity pattern of F344 rats. The current findings may have translational value as increased activity is reported in an equivalent cortical area in patients with social anxiety, suggesting that pharmacological or functional inhibition of activity in this brain area should be explored to alleviate social anxiety in patients.

Post-weaning social isolation attenuates c-Fos expression in GABAergic interneurons in the basolateral amygdala of adult female rats

Previous studies have found that adolescent social isolation of rats can lead to an increased anxiety state during adulthood, while chronic anxiety states are associated with dysregulated local GABAergic inhibition within the basolateral amygdala (BL). Therefore, we investigated the effects of post-weaning social isolation of female rats, in combination with a challenge with the anxiogenic drug, N-methyl-beta-carboline-3-carboxamide (FG-7142), on a subset of GABAergic interneurons in the BL in adulthood using dual immunohistochemical staining for c-Fos and parvalbumin. Juvenile female rats were reared in isolation or in groups of three for a 3-week period from weaning to mid-adolescence, after which all rats were group-housed for an additional 2 weeks. Group-reared rats and isolation-reared rats injected with FG-7142 had increased c-Fos expression in GABAergic interneurons in the anterior part of the BL compared to group-reared rats and isolation-reared rats, respectively, injected with vehicle. Isolation rearing had a main effect to decrease c-Fos expression in GABAergic interneurons in the anterior part of the BL compared to group-reared rats. These data suggest that post-weaning social isolation of female rats leads to dysregulation of a parvalbumin-containing subset of local GABAergic interneurons in the anterior part of the BL, which have previously been implicated in the pathophysiology of chronic anxiety states. These cellular changes may lead to an increased vulnerability to stress- and anxiety-related responses in adulthood.

Post-weaning social isolation of female rats, anxiety-related behavior, and serotonergic systems

Our previous studies have shown that post-weaning social isolation of male rats leads to sensitization of serotonergic systems and increases in anxiety-like behavior in adulthood. Although studies in humans suggest that females have an increased sensitivity to stress and risk for the development of neuropsychiatric illnesses, most studies involving laboratory rats have focused on males while females have been insufficiently studied. The objective of this study was to investigate the effects of post-weaning social isolation on subsequent responses of an anxiety-related dorsal raphe nucleus (DR)-basolateral amygdala system to pharmacological challenge with the anxiogenic drug, N-methyl-beta-carboline-3-carboxamide (FG-7142; a partial inverse agonist at the benzodiazepine allosteric site on the γ-aminobutyric acid (GABA)(A) receptor). Juvenile female rats were reared in isolation or in groups of three for a 3-week period from weaning to mid-adolescence, after which all rats were group-reared for an additional 2 weeks. We then used dual immunohistochemical staining for c-Fos and tryptophan hydroxylase in the DR or single immunohistochemical staining for c-Fos in the basolateral amygdala. Isolation-reared rats, but not group-reared rats, injected with FG-7142 had increased c-Fos expression within the basolateral amygdala and in serotonergic neurons in the dorsal, ventrolateral, caudal and interfascicular parts of the DR relative to appropriate vehicle-injected control groups. These data suggest that post-weaning social isolation of female rats sensitizes a DR-basolateral amygdala system to stress-related stimuli, which may lead to an increased sensitivity to stress- and anxiety-related responses in adulthood.

Selectively bred rodents as models of depression and anxiety

Stress related diseases such as depression and anxiety have a high degree of co morbidity, and represent one of the greatest therapeutic challenges for the twenty-first century. The present chapter will summarize existing rodent models for research in psychiatry, mimicking depression- and anxiety-related diseases. In particular we will highlight the use of selective breeding of rodents for extremes in stress-related behavior. We will summarize major behavioral, neuroendocrine and neuronal parameters, and pharmacological interventions, assessed in great detail in two rat model systems: The Flinders Sensitive and Flinders Resistant Line rats (FSL/FRL model), and rats selectively bred for high (HAB) or low (LAB) anxiety related behavior (HAB/LAB model). Selectively bred rodents also provide an excellent tool in order to study gene and environment interactions. Although it is generally accepted that genes and environmental factors determine the etiology of mental disorders, precise information is limited: How rigid is the genetic disposition? How do genetic, prenatal and postnatal influences interact to shape adult disease? Does the genetic predisposition determine the vulnerability to prenatal and postnatal or adult stressors? In combination with modern neurobiological methods, these models are important to elucidate the etiology and pathophysiology of anxiety and affective disorders, and to assist in the development of new treatment paradigms.

A mouse model of high trait anxiety shows reduced heart rate variability that can be reversed by anxiolytic drug treatment

Increasing evidence suggests that specific physiological measures may serve as biomarkers for successful treatment to alleviate symptoms of pathological anxiety. Studies of autonomic function investigating parameters such as heart rate (HR), HR variability and blood pressure (BP) indicated that HR variability is consistently reduced in anxious patients, whereas HR and BP data show inconsistent results. Therefore, HR and HR variability were measured under various emotionally challenging conditions in a mouse model of high innate anxiety (high anxiety behaviour; HAB) vs. control normal anxiety-like behaviour (NAB) mice. Baseline HR, HR variability and activity did not differ between mouse lines. However, after cued Pavlovian fear conditioning, both elevated tachycardia and increased fear responses were observed in HAB mice compared to NAB mice upon re-exposure to the conditioning stimulus serving as the emotional stressor. When retention of conditioned fear was tested in the home cage, HAB mice again displayed higher fear responses than NAB mice, while the HR responses were similar. Conversely, in both experimental settings HAB mice consistently exhibited reduced HR variability. Repeated administration of the anxiolytic NK1 receptor antagonist L-822429 lowered the conditioned fear response and shifted HR dynamics in HAB mice to a more regular pattern, similar to that in NAB mice. Additional receiver-operating characteristic (ROC) analysis demonstrated the high specificity and sensitivity of HR variability to distinguish between normal and high anxiety trait. These findings indicate that assessment of autonomic response in addition to freezing might be a useful indicator of the efficacy of novel anxiolytic treatments.

Identifying a network of brain regions involved in aversion-related processing: a cross-species translational investigation

The ability to detect and respond appropriately to aversive stimuli is essential for all organisms, from fruit flies to humans. This suggests the existence of a core neural network which mediates aversion-related processing. Human imaging studies on aversion have highlighted the involvement of various cortical regions, such as the prefrontal cortex, while animal studies have focused largely on subcortical regions like the periaqueductal gray and hypothalamus. However, whether and how these regions form a core neural network of aversion remains unclear. To help determine this, a translational cross-species investigation in humans (i.e., meta-analysis) and other animals (i.e., systematic review of functional neuroanatomy) was performed. Our results highlighted the recruitment of the anterior cingulate cortex, the anterior insula, and the amygdala as well as other subcortical (e.g., thalamus, midbrain) and cortical (e.g., orbitofrontal) regions in both animals and humans. Importantly, involvement of these regions remained independent of sensory modality. This study provides evidence for a core neural network mediating aversion in both animals and humans. This not only contributes to our understanding of the trans-species neural correlates of aversion but may also carry important implications for psychiatric disorders where abnormal aversive behavior can often be observed.

Animal models of depression and anxiety: What do they tell us about human condition?

While modern neurobiology methods are necessary they are not sufficient to elucidate etiology and pathophysiology of affective disorders and develop new treatments. Achievement of these goals is contingent on applying cutting edge methods on appropriate disease models. In this review, the authors present four rodent models with good face-, construct-, and predictive-validity: the Flinders Sensitive rat line (FSL); the genetically "anxious" High Anxiety-like Behavior (HAB) line; the serotonin transporter knockout 5-HTT(-/-) rat and mouse lines; and the post-traumatic stress disorder (PTSD) model induced by exposure to predator scent, that they have employed to investigate the nature of depression and anxiety.

Susceptibility to the long-term anxiogenic effects of an acute stressor is mediated by the activation of the glucocorticoid receptors

The specificity of the response of an organism is an important variable influencing stress-related parameters and psychopathological states. We have shown that trait anxiety in C57BL/6 mice, determined by their emergence latencies in the free choice open field test, positively correlates with the long-term behavioral and neuroendocrinological changes induced by a stressor. Here, we show that this interindividual variability is caused by a different reactivity of the hypothalamus-pituitary-adrenal (HPA) axis upon exposure to a stressor. Mice with high trait anxiety (long emergence latency, LEL) display a more pronounced stress-induced activation of the HPA axis than mice with low trait anxiety (short emergence latency, SEL). Moreover, stress-induced activation of tyrosine hydroxylase and corticotropin-releasing hormone occurred in LEL but not SEL mice. In search of the molecular mechanisms underlying these differences, we found that under non-stressed conditions mRNA and protein levels of the glucocorticoid receptor in the hippocampus were higher in LEL mice compared to SEL mice. Also, systemic injection of the glucocorticoid receptor antagonist RU486 decreased the stress-induced activation of the HPA axis and the long-term anxiogenic effects of stress observed in LEL mice. Finally, the rewarding properties of cocaine were enhanced in LEL mice compared to SEL mice, suggesting a causal link between trait anxiety, stress activity and the behavioral responses to drugs of addiction.

TMEM132D, a new candidate for anxiety phenotypes: evidence from human and mouse studies

The lifetime prevalence of panic disorder (PD) is up to 4% worldwide and there is substantial evidence that genetic factors contribute to the development of PD. Single-nucleotide polymorphisms (SNPs) in TMEM132D, identified in a whole-genome association study (GWAS), were found to be associated with PD in three independent samples, with a two-SNP haplotype associated in each of three samples in the same direction, and with a P-value of 1.2e-7 in the combined sample (909 cases and 915 controls). Independent SNPs in this gene were also associated with the severity of anxiety symptoms in patients affected by PD or panic attacks as well as in patients suffering from unipolar depression. Risk genotypes for PD were associated with higher TMEM132D mRNA expression levels in the frontal cortex. In parallel, using a mouse model of extremes in trait anxiety, we could further show that anxiety-related behavior was positively correlated with Tmem132d mRNA expression in the anterior cingulate cortex, central to the processing of anxiety/fear-related stimuli, and that in this animal model a Tmem132d SNP is associated with anxiety-related behavior in an F2 panel. TMEM132D may thus be an important new candidate gene for PD as well as more generally for anxiety-related behavior.

Activation patterns of cells in selected brain stem nuclei of more and less stress responsive rats in two animal models of PTSD - predator exposure and submersion stress

This study had two purposes. First: compare predator and water submersion stress cFos activation patterns in dorsal raphe (DR), locus coeruleus (LC) and periaqueductal gray (PAG). Second: identify markers of vulnerability to stressors within these areas. Rats were either predator or submersion stressed and tested 1.75 h later for anxiety-like behavior. Immediately thereafter, rats were sacrificed and cFos expression examined. In DR, serotonergic cells expressing or not expressing cFos were also counted. Predator and submersion stress increased anxiety-like behavior (in the elevated plus maze- EPM) equally over controls. Moreover, stressed rats spent equally less time in the center of the hole board than handled controls, another indication of increased anxiety-like behavior. To examine vulnerability, rats which were less anxious (LA) and more (highly) anxious (MA) in the EPM were selected from among handled control and stressed animals. LA rats in the stressed groups were considered stress non-responsive and MA stressed rats were considered stress responsive. LA and MA rats did not differ in cFos expression in any brain area, though stressors did increase cFos cell counts in all areas over controls. Intriguingly, the number of serotonergic DR neurons not activated by stress predicted degree of anxiety response to submersion stress only. LA submersion stressed rats had more serotonergic cells than all other groups, and MA submersion stressed rats had fewer serotonergic cells than all other groups, which did not differ. Moreover, these cell counts correlated with EPM anxiety. We conclude that a surplus of such cells protects against anxiogenic effects of submersion, while a paucity of such cells enhances vulnerability to submersion stress. Other data suggest serotonergic cells may exert their effects via inhibition of dorsolateral PAG cells during submersion stress. Findings are discussed with respect to serotonergic transmission in vulnerability to predator stress and relevance of findings for post traumatic stress disorder (PTSD). This article is part of a Special Issue entitled 'Post-Traumatic Stress Disorder'.

Potential anxiogenic effects of cannabinoid CB1 receptor antagonists/inverse agonists in rats: comparisons between AM4113, AM251, and the benzodiazepine inverse agonist FG-7142

Cannabinoid CB1 inverse agonists suppress food-motivated behaviors, but may also induce psychiatric effects such as depression and anxiety. To evaluate behaviors potentially related to anxiety, the present experiments assessed the CB1 inverse agonist AM251 (2.0-8.0mg/kg), the CB1 antagonist AM4113 (3.0-12.0mg/kg), and the benzodiazepine inverse agonist FG-7142 (10.0-20.0mg/kg), using the open field test and the elevated plus maze. Although all three drugs affected open field behavior, these effects were largely due to actions on locomotion. In the elevated plus maze, FG-7142 and AM251 both produced anxiogenic effects. FG-7142 and AM251 also significantly increased c-Fos activity in the amygdala and nucleus accumbens shell. In contrast, AM4113 failed to affect performance in the plus maze, and did not induce c-Fos immunoreactivity. The weak effects of AM4113 are consistent with biochemical data showing that AM4113 induces little or no intrinsic cellular activity. This research may lead to the development of novel appetite suppressants with reduced anxiogenic effects.

Activation of the septohippocampal system differentiates anxiety from fear in startle paradigms

It has been suggested that different brain areas are involved in the modulation and expression of fear and anxiety. In the present study we investigated these potential differences by using the fear-potentiated-startle (FPS) and light-enhanced-startle (LES) paradigms to differentiate between fear and anxiety, respectively. Male Wistar rats were tested in the FPS and LES paradigm and perfused 1 h after the test session. Fos immunoreactivity (IR) was quantified in 21 brain areas and compared between FPS, LES and four control conditions. Both FPS and LES procedures significantly enhanced the acoustic startle response. A principal component analysis of Fos-IR-data showed that 70% of the changes in Fos-IR could be explained by three independent components: an arousal-component, identifying brain areas known to be activated under conditions of vigilance, arousal and stress, a LES- and an FPS-component. The LES component comprised the septohippocampal system and functionally interrelated areas including nucleus accumbens, anterior cingulate cortex, lateral habenula and supramammillary areas, but not the dorsolateral part of the bed nucleus of the stria terminalis. The central amygdaloid nucleus and the dorsolateral part of the bed nucleus of the stria terminalis loaded exclusively on the FPS component. Analysis of the separate brain areas revealed significantly higher Fos-IR in LES relative to FPS in the anterior cingulate cortex, nucleus accumbens shell, lateral septum, lateral habenula and area postrema. We conclude that the neural circuitry activated during FPS and LES shows clear differences. In anxiety as induced by LES, activation of the septohippocampal system and related areas seems to play a major role. In fear as induced by FPS, the central amygdaloid nucleus and the dorsolateral part of the bed nucleus of the stria terminalis loaded on the same component, but Fos-IR observed in these brain regions did not differentiate between anxiety and fear. Furthermore, principal-component analysis appears a useful tool in detecting and describing correlated changes in patterns of neuronal activity.

Differential stress-induced neuronal activation patterns in mouse lines selectively bred for high, normal or low anxiety

There is evidence for a disturbed perception and processing of emotional information in pathological anxiety. Using a rat model of trait anxiety generated by selective breeding, we previously revealed differences in challenge-induced neuronal activation in fear/anxiety-related brain areas between high (HAB) and low (LAB) anxiety rats. To confirm whether findings generalize to other species, we used the corresponding HAB/LAB mouse model and investigated c-Fos responses to elevated open arm exposure. Moreover, for the first time we included normal anxiety mice (NAB) for comparison. The results confirm that HAB mice show hyperanxious behavior compared to their LAB counterparts, with NAB mice displaying an intermediate anxiety phenotype. Open arm challenge revealed altered c-Fos response in prefrontal-cortical, limbic and hypothalamic areas in HAB mice as compared to LAB mice, and this was similar to the differences observed previously in the HAB/LAB rat lines. In mice, however, additional differential c-Fos response was observed in subregions of the amygdala, hypothalamus, nucleus accumbens, midbrain and pons. Most of these differences were also seen between HAB and NAB mice, indicating that it is predominately the HAB line showing altered neuronal processing. Hypothalamic hypoactivation detected in LAB versus NAB mice may be associated with their low-anxiety/high-novelty-seeking phenotype. The detection of similarly disturbed activation patterns in a key set of anxiety-related brain areas in two independent models reflecting psychopathological states of trait anxiety confirms the notion that the altered brain activation in HAB animals is indeed characteristic of enhanced (pathological) anxiety, providing information for potential targets of therapeutic intervention.

Effect of chronic psychosocial stress-induced by subordinate colony (CSC) housing on brain neuronal activity patterns in mice

Chronic subordinate colony (CSC) housing has been recently validated as a murine model of chronic psychosocial stress which induces alterations of stress-related parameters including decreased body-weight gain and an increased level of anxiety in comparison with single housed control (SHC) mice. By using immunohistochemical immediate early gene (IEG) mapping we investigated whether CSC housing causes alterations in neuronal activation patterns in limbic areas including the amygdala, hippocampus, septum and the periaqueductal gray (PAG) and hypothalamic paraventricular nucleus (PVN). While CSC housing increased basal Zif-268 expression in the nucleus accumbens shell compared to SHC, IEG responses to subsequent open arm (OA) exposure were attenuated in the ventral and intermediate sub-regions of the lateral septum, parvocellular PVN and the dorsal CA3 region of the hippocampus of CSC compared with SHC mice. In contrast, a potentiated c-Fos response in CSC mice was observed in the dorsomedial PAG after OA exposure. Confirming previous findings obtained on the elevated plus-maze, an enhanced anxiety-related behavior in CSC compared with SHC mice was also observed during OA exposure. In order to investigate the appropriate control conditions for CSC housing, group housed control (GHC) mice were additionally included in the behavioral testing. Interestingly, GHC as well as CSC mice showed significantly less risk assessment/exploratory behavior during OA exposure compared with SHC mice indicating that group housing itself is stressful for mice and not an adequate control for the CSC paradigm. Overall, CSC housing is an ethologically relevant chronic psychosocial stressor which results in an elevated sensitivity to a subsequent novel, aversive challenge. However, the CSC-induced increase in anxiety-related behavior was accompanied by differences in neuronal activation, compared with SHC, in defined sub-regions of brain areas known to be involved in the processing of emotionality and stress responses.

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

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

Contact with infants modulates anxiety-generated c-fos activity in the brains of postpartum rats

The postpartum period is associated with many behavioral changes, including a reduction in anxiety, which is thought to be necessary for mothers' ability to appropriately care for infants. In laboratory rats, this reduction in anxiety requires recent contact with pups, but areas of the brain where infant contact influences neural activity to reduce anxiety are mostly unknown. We examined c-fos expression in lactating rats whose pups were removed for 4h to increase mothers' anxiety, or not removed to maintain low anxiety in mothers, followed by exposure to the anxiogenic stimuli of either brief handling or handling followed by exposure to an elevated plus maze. Control animals had their litters removed or not, but no further stimulation. A large number of neural sites traditionally implicated in regulating anxiety in male rats were examined, and similar to what is found in male rats, most showed increased Fos expression after handling and/or elevated plus-maze exposure. Litter presence before testing affected Fos expression due to handling or elevated plus-maze exposure only in the ventral bed nucleus of the stria terminalis, dorsal and ventral preoptic area, ventromedial hypothalamus, lateral habenula, and supramammillary nucleus. Contrary to expectations, prior litter presence was associated with more Fos expression in most of these sites after handling and/or elevated plus-maze stimulation, and only after such stimulation. These sites may be of particular importance for how sensory inputs from infants modulate anxiety and other mood states during the postpartum period.

The vasopressin system--from antidiuresis to psychopathology

Vasopressin is a neuropeptide with multiple functions. In addition to its predominantly antidiuretic action after peripheral secretion from the posterior pituitary, it seems to fulfill--together with its receptor subtype--all requirements for a neuropeptide system critically involved in higher brain functions, including cognitive abilities and emotionality. Following somatodendritic and axonal release in distinct brain areas, vasopressin acts as a neuromodulator and neurotransmitter in multiple and varying modes of interneuronal communication. Accordingly, changes in vasopressin expression and release patterns may have wide-spread consequences. As shown in mice, rats, voles, and humans, central vasopressin release along a continuum may be beneficial to the individual, serving to adjust physiology and behavior in stressful scenarios, possibly at the potential expense of increasing susceptibility to disease. Indeed, if over-expressed and over-released, it may contribute to hyper-anxiety and depression-like behaviors. A vasopressin deficit, in turn, may cause signs of both diabetes insipidus and total hypo-anxiety. The identification of genetic polymorphisms underlying these phenomena does not only explain individual variation in social memory and emotionality, but also help to characterize potential targets for therapeutic interventions. The capability of both responding to stressful stimuli and mediating genetic polymorphisms makes the vasopressin system a key mediator for converging (i.e., environmentally and genetically driven) behavioral regulation.

Altered brain activation pattern associated with drug-induced attenuation of enhanced depression-like behavior in rats bred for high anxiety

BACKGROUND

The enhanced depression-like behavior in the forced swim test displayed by rats selectively bred for high anxiety-related behavior (HAB) as compared with their low anxiety counterparts (LAB) is abolished by chronic paroxetine treatment. The aim of the present study was to identify neuronal substrates underlying this treatment response in HABs.

METHODS

The HAB rats received paroxetine (10 mg/kg/day) for 24 days via drinking water, and drug-induced modulation of neuronal activation patterns in response to forced swimming was mapped with the expression of the immediate early gene c-Fos as marker.

RESULTS

Chronic paroxetine treatment reduced the immobility scores during forced swimming, confirming the previously observed antidepressant-like effect in these animals, and attenuated the forced swim-induced c-Fos response in a restricted set (11 of 70) of brain areas. These included limbic areas such as the prelimbic cortex, parts of the amygdala, the bed nucleus of the stria terminalis, dorsal hippocampus, dorsal lateral septum as well as hypothalamic and hindbrain areas (dorsolateral periaqueductal gray [PAG], locus coeruleus). Untreated LAB rats, which displayed low depression-like behavior comparable to that of treated HABs, also showed low swim stress-induced c-Fos response in most of these same areas, further supporting an association of attenuated neuronal excitability in the identified areas with attenuated depression-like behavior.

CONCLUSIONS

These findings indicate that modulation of neuronal activation in a restricted set of defined, mainly limbic as well as selected hypothalamic and hindbrain areas by paroxetine treatment is associated with the reduction of enhanced depression-like behavior in a psychopathological animal model.

Interaction of AT1 receptors and V1a receptors-mediated effects in the central cardiovascular control during the post-infarct state

Experimental objectives. Because myocardial infarct is associated with overactivation of brain angiotensin II (ANG II) and vasopressin (AVP) V1a receptors we decided to determine whether AT1 and V1a receptors-mediated effects of ANG II and AVP interact in central cardiovascular control during the post-infarct state. Four groups of infarcted and four groups of sham-operated conscious rats entered the study. Results. In the infarcted rats cerebroventricular infusion of AT1 (AT1ANT, losartan) and V1a antagonist {V1aANT,d(CH(2))(5)[Tyr(Me)(2)Ala-NH(2)(9)]VP} and combined infusion of both these compounds performed 4 weeks after induction of the infarct significantly and comparably reduced mean arterial blood pressure (MABP) in comparison to control experiments (artificial cerebrospinal fluid infusion). In the sham rats MABP was not affected by any of the infusions. In control experiments MABP and HR responses to an alarming air jet stress were significantly higher in the infarcted than in the sham rats. Both responses were normalized with the same effectiveness by administration of AT1ANT, V1aANT and AT1ANT+V1aANT. In the sham rats administration of these compounds did not affect MABP and HR responses to stress.

CONCLUSION

The results provide evidence for interaction of AT1 and V1a receptors-mediated effects of ANG II and AVP in the central cardiovascular control during the post-infarct state.

Altered brain activity processing in high-anxiety rodents revealed by challenge paradigms and functional mapping

Pathological anxiety involves aberrant processing of emotional information that is hypothesized to reflect perturbations in fear/anxiety pathways. The affected neurobiological substrates in patients with different anxiety disorders are just beginning to be revealed. Important leads for this research can be derived from findings obtained in psychopathologically relevant rodent models of enhanced anxiety, by revealing where in the brain neuronal processing in response to diverse challenges is different to that in animals with lower anxiety levels. Different functional mapping methods in various rodent models, including psychogenetically selected lines or genetically modified animals, have been used for this purpose. These studies show that the divergent anxiety-related behavioral response of high-anxiety- vs. normal and/or low-anxiety rodents to emotional challenges is associated with differential neuronal activation in restricted parts of proposed fear/anxiety circuitries including brain areas thought to be important in stress, emotion and memory. The identification of neuronal populations showing differential activation depends in part on the applied emotional challenge, indicating that specific facets of elicited fear or anxiety preferentially engage particular parts of the fear/anxiety circuitry. Hence, only the use of an array of different challenges will reveal most affected brain areas. A number of the neuronal substrates identified are suggested as candidate mediators of dysfunctional brain activation in pathological anxiety. Indeed, key findings revealed in these rodent models show parallels to observations in human symptom provocation studies comparing anxiety disorder patients with healthy volunteers. Work to investigate exactly which of the changed neuronal activation patterns in high-anxiety rodents has to be modulated by therapeutic drugs to achieve effective anxiolysis and via which neurochemical pathways this can be accomplished is at its early stages but has identified a small number of promising candidates. Extending these approaches should help to provide further insight into these mechanisms, revealing new leads for therapeutic targets and strategies.

Gabrb3 gene deficient mice exhibit increased risk assessment behavior, hypotonia and expansion of the plexus of locus coeruleus dendrites

Gabrb3 gene deficient (gabrb3(-/-)) mice, control littermates (gabrb3(+/+)) and their progenitor strains C57Bl/6J and 129/SvJ were assessed for changes in the morphology of the main noradrenergic nuclei, the locus coeruleus (LC) and LC-associated behaviors including anxiety and muscle tone. While the area defined by the cell bodies of the LC was found not to differ between gabrb3(-/-) mice and controls, the pericoerulear dendritic zone of the LC was found to be significantly enlarged in gabrb3(-/-) mice. Relative to controls, gabrb3(-/-) mice were also found to be hypotonic, as was indicated by poor performance on the wire hanging task. Gabrb3(-/-) mice also exhibited a significant increase in stretch-attend posturing, a form of risk assessment behavior associated with anxiety. However, in the plus maze, a commonly used behavioral test for assessing anxiety, no significant difference was observed between gabrb3(-/-) and control mice. Lastly, relative to controls, gabrb3(-/-) mice exhibited significantly less marble burying behavior, a method commonly used to assess obsessive-compulsive behavior. However, the poor marble burying performance of the gabrb3(-/-) mice could be associated with the hypotonic condition exhibited by these mice. In conclusion, the results of this study indicate that the gabrb3 gene contributes to LC noradrenergic dendrite development with the disruption of this gene in mice resulting in an enlarged plexus of LC dendrites with a concurrent reduction in muscle tone and marble burying behavior, an increase in risk assessment behavior but no change in the plus maze parameters that are commonly used for assessing anxiety.