Chronic mild stress (CMS) revisited: consistency and behavioural-neurobiological concordance in the effects of CMS

Notch1 signaling, hippocampal neurogenesis and behavioral responses to chronic unpredicted mild stress in adult ischemic rats

Accumulating evidence indicates that the Notch signaling pathway fulfills important roles in ischemia-stimulated neurogenesis, which may be regarded as an etiological factor in post-stroke depression. Here we explored Notch(1) signaling, hippocampal neurogenesis and behavioral responses to chronic unpredicted mild stress (CUMS) in adult ischemic rats. Animals were treated with permanent middle cerebral artery occlusion followed by an 18 day CUMS procedure. Proliferating cells in the hippocampus and their cell fate were investigated on days 19 and 28 after ischemic surgery. Additionally, expression of the Notch(1) intracellular domain (NICD) and its downstream targets Hes1 and Hes5 was examined. A sucrose preference test and forced swim test were used to assess behavioral responses. CUMS produced depressive-like behaviors and decreased the number of proliferating cells on day 19 (both p<0.001), accompanied by a decreased expression of both Hes1 and Hes5 in the hippocampus of ischemic animals (p<0.001). On day 28, CUMS resulted in a decreased number of neurogenically-differentiating cells in the subgranular zone (p<0.001) while permitting differentiation into astrocytes in the hilus (p<0.05). Hes1 and Hes5 protein expression levels were increased. The expression of the NICD was significantly decreased at both time-points. CUMS led to expression changes in the Notch(1) signaling cascade in ischemic rats, most of which concerned hippocampal neurogenesis. This suggests that variation in Notch(1) activity and subsequent expression of its downstream targets, including Hes1 and Hes5, may, at least in part, contribute to modulation of ischemia-related hippocampal neurogenesis by CUMS.

Learning and extinction of a passive avoidance response in mice with high levels of predisposition to catalepsy

This report presents results obtained from comparative analysis of learning and the dynamics of extinction of a conditioned passive avoidance response in ASC mice, which were bred for a high level of predisposition to catalepsy, and in CBA and AKR mice. The following findings were obtained: 1) impairments to the extinction of the memory of fear represent an important symptom of depression in ASC mice; 2) extinction is delayed in CBA mice; and 3) new inhibitory learning occurs quickly in AKR mice. Prolonged retention of the fear memory in ASC mice appears to be related to increased anxiety on prolonged testing without a punishment. The deficit of inhibition of the fear reaction in ASC mice allows this strain to be regarded as a genetic model of depression.

Interest of using genetically manipulated mice as models of depression to evaluate antidepressant drugs activity: a review

Among the multiple possibilities to study human depressive disorders, animal models remain important preclinical tools. They allow the understanding of the mechanisms of action of antidepressant drugs. Primarily developed in rat, animal models of depression have been adapted to the mouse, an easy-to-use mammal with better genetic possibilities than rats. As an example, genetic manipulation of the serotoninergic 5-hydroxytryptamine-HT; (5-HT) system provided important opportunities to investigate the role of this monoamine in mood disorders. The contribution of either constitutive knockout (KO), tissue specific, or inducible KO mice and animal models in the current knowledge of the pathophysiology and treatment of depression is unanimously recognized. The phenotype of genetically manipulated animals is strongly influenced by both the genetic background of the animal as well as environmental factors. For these reasons, it is necessary to underline that KO mice have been generated on various genetic backgrounds, which strongly influence the behavioral and neurochemical responses to the tests. The present review will thus focus on KO mice lacking G protein-coupled monoaminergic receptors (e.g; 5-HT1B, 5-HT1A, and 5-HT4 receptors) and the 5-HT serotonin transporter, which is the main target of antidepressant drugs (or strategies). The importance of KO mice for neurotrophic factors, particularly for brain-derived neurotrophic factor and its main receptor displaying a tyrosine kinase activity, will also be addressed to illustrate the fact that in preclinical studies, combination of genetic manipulations with pharmacological ones should allow further progress in the field of neuropsychopharmacology.

The 3beta-hydroxysteroid dehydrogenase inhibitor trilostane shows antidepressant properties in mice

Changes in neuro(active)steroid levels are involved in depressive states and mood disorders. For instance, dehydroepiandrosterone or pregnenolone sulfate showed anti-stress and antidepressant activity in rodents and regulation of allopregnanolone levels appeared to be one of the consequence of an effective antidepressant therapy in patients. 4alpha,5-Epoxy-17beta-hydroxy-3-oxo-5alpha-androstane-2alpha-carbonitrile (trilostane) inhibits the activity of 3beta-hydroxysteroid dehydrogenase (3beta-HSD) that, in particular, converts pregnenolone into progesterone. We examined whether systemic administration of trilostane affects the response to stress and depression. An acute treatment with trilostane (6.3-50mg/kg SC injected twice -16 and -2h before the measure) increased 3beta-HSD mRNA levels in the hippocampus and adrenals, but had little effect on protein levels. The trilostane treatment failed to affect open-field, locomotor or exploratory behaviors, but significantly reduced the immobility duration in the forced swimming test, measuring antidepressant-like activity, and increased the time spent in open arm in the elevated plus-maze, measuring anxiety response. The antidepressant-like effect of trilostane was effective after a repeated treatment (2.5-20mg/kgSC twice-a-day during 7 days) or in mice submitted to a restraint stress during 21 days and showing several behavioral and physiological parameters of depression (decreased body weight, increased adrenal glands weight and anhaedonia). Trilostane also reduced stress-induced increase in plasma corticosterone and ACTH levels, showing direct effect on HPA axis activity. These observations suggest that the 3beta-HSD inhibitor trilostane present antidepressant-like activity, putatively by regulating brain and peripheral levels of neuroactive steroids.

CNS disorders--current treatment options and the prospects for advanced therapies

The development of new pharmaceutical products has successfully addressed a multitude of disease states; however, new product development for treating disorders of the central nervous system (CNS) has lagged behind other therapeutic areas. This is due to several factors including the complexity of the diseases and the lack of technologies for delivery through the blood-brain barrier (BBB). This article examines the current state of six major CNS disease states: depression, epilepsy, multiple sclerosis (MS), neurodegenerative diseases (specifically Alzheimer's disease [AD]), neuropathic pain, and schizophrenia. Discussion topics include analysis of the biological mechanisms underlying each disease, currently approved products, and available animal models for development of new therapeutic agents. Analysis of currently approved therapies shows that all products depend on the molecular properties of the drug or prodrug to penetrate the BBB. Novel technologies, capable of enhancing BBB permeation, are also discussed relative to improving CNS therapies for these disease states.

Differential effects of chronic unpredictable stress on hippocampal CB1 receptors in male and female rats

Chronic unpredictable mild stress (CMS), an animal model of depression, downregulates hippocampal CB1 receptors in adult male rats. Given that endocannabinoids are implicated in modulating stress and anxiety and that women are vulnerable to stress-related disorders, we tested the effects of CMS on both female and male rats. Gonadectomized (gndx) and gonadally intact male and female rats were exposed to a three-week chronic stress protocol. Following CMS, CB1 receptor and fatty-acid-amide-hydrolase (FAAH) expression levels in the hippocampus were assessed by western blot analysis. CMS reliably produced a downregulation of CB1 receptors ( approximately 50%) in the hippocampus of both gndx and intact males. This effect was more robust in the dorsal than in the ventral hippocampus. Conversely, CMS produced an upregulation of CB1 receptors ( approximately 150%) in the hippocampus of both gndx and intact females. This upregulation was only observed in the dorsal hippocampus of female animals. CMS produced an upregulation of FAAH levels in both male and female animals. In non-stress control animals, males were observed to have higher CB1 levels than females, but no differences in FAAH were found. These findings suggest that the endocannabinoid (eCB) system is preferentially organized in male and female animals to respond differentially to chronic stress. These sex differences in the eCB system may help development of novel treatments for stress and depression that are designed specifically for women and men.

Corticolimbic transcriptome changes are state-dependent and region-specific in a rodent model of depression and of antidepressant reversal

Gene microarrays may enable the elucidation of neurobiological changes underlying the pathophysiology and treatment of major depression. However, previous studies of antidepressant treatments were performed in healthy normal rather than 'depressed' animals. Since antidepressants are devoid of mood-changing effects in normal individuals, the clinically relevant rodent transcriptional changes could remain undetected. We investigated antidepressant-related transcriptome changes in a corticolimbic network of mood regulation in the context of the unpredictable chronic mild stress (UCMS), a naturalistic model of depression based on socio-environmental stressors. Mice subjected to a 7-week UCMS displayed a progressive coat state deterioration, reduced weight gain, and increased agonistic and emotion-related behaviors. Chronic administration of an effective (fluoxetine) or putative antidepressant (corticotropin-releasing factor-1 (CRF1) antagonist, SSR125543) reversed all physical and behavioral effects. Changes in gene expression differed among cingulate cortex (CC), amygdala (AMY) and dentate gyrus (DG) and were extensively reversed by both drugs in CC and AMY, and to a lesser extent in DG. Fluoxetine and SSR125543 also induced additional and very similar molecular profiles in UCMS-treated mice, but the effects of the same drug differed considerably between control and UCMS states. These studies established on a large-scale that the molecular impacts of antidepressants are region-specific and state-dependent, revealed common transcriptional changes downstream from different antidepressant treatments and supported CRF1 targeting as an effective therapeutic strategy. Correlations between UCMS, drug treatments, and gene expression suggest distinct AMY neuronal and oligodendrocyte molecular phenotypes as candidate systems for mood regulation and therapeutic interventions.

Morphological, physiological and behavioural evaluation of a 'Mice in Space' housing system

Environmental conditions likely affect physiology and behaviour of mice used for life sciences research on Earth or in Space. Here, we analysed the effects of cage confinement on the weightbearing musculoskeletal system, behaviour and stress of wild-type mice (C57BL/6JRj, 30 g b.wt., total n = 24) housed for 25 days in a prototypical ground-based and fully automated life support habitat device called "Mice in Space" (MIS). Compared with control housing (individually ventilated cages) the MIS mice revealed no significant changes in soleus muscle size and myofiber distribution (type I vs. II) and quality of bone (3-D microarchitecture and mineralisation of calvaria, spine and femur) determined by confocal and micro-computed tomography. Corticosterone metabolism measured non-invasively (faeces) monitored elevated adrenocortical activity at only start of the MIS cage confinement (day 1). Behavioural tests (i.e., grip strength, rotarod, L/D box, elevated plus-maze, open field, aggressiveness) performed subsequently revealed only minor changes in motor performance (MIS vs. controls). The MIS habitat will not, on its own, produce major effects that could confound interpretation of data induced by microgravity exposure during spaceflight. Our results may be even more helpful in developing multidisciplinary protocols with adequate scenarios addressing molecular to systems levels using mice of various genetic phenotypes in many laboratories.

Anhedonia and activity deficits in rats: impact of post-stroke depression

Animal models may allow investigation into the aetiology and treatment of various human disorders. In the present study, a rat model for post-stroke depression (PSD) has been developed using middle cerebral artery occlusion (MCAO), followed by an 18-day chronic mild stress (CMS) paradigm in conjuncture with isolation rearing. The open-field test (OFT) and the sucrose consumption test were used to assess depression-like behaviour and the effects of the antidepressant citalopram. CMS induced behavioural changes in the ischemic animals, including decreased locomotor and rearing activity and reduced sucrose preference (compared with baseline, control and stroke groups respectively), all these behaviours were reversed by chronic administration of citalopram. During the recovery period for the PSD models, the open-field activity and preference for sweet sucrose solution decreased continually, opposed to rats subjected to stress only. Decreased locomotor and rearing represents activity deficits, whereas reduced sucrose preference may indicate desensitisation of the brain reward mechanism (anhedonia). Our findings suggest that anhedonia, one of the core symptoms in patients with PSD, and activity deficits can be found in the MCAO+CMS group of animals. Furthermore, citalopram can ameliorate the behavioural abnormalities observed in these animals. With high validity, good operability and repeatability, our findings suggest that the ischemic rat CMS model is an appropriate model for further PSD research.

Ketamine treatment reverses behavioral and physiological alterations induced by chronic mild stress in rats

Several studies have supported the idea that ionotropic glutamate N-methyl-d-aspartate receptor (NMDA) is an important player in the etiology of psychopathologies, such as anxiety disorders and major depression. Additionally, studies have shown that ketamine induces antidepressant effects in humans as well as in rodents subjected to animal models of depression. In this context, the present study was aimed to evaluate behavioral and physiological effects of acute and chronic administration of ketamine, a NMDA receptor antagonist, in rats exposed to chronic mild stress (CMS). After 40 days of CMS, rats were treated with ketamine (15 mg/kg) and sweet food consumption, body and adrenal gland weight, corticosterone and adrenocorticotropic (ACTH) hormone levels, and hippocampal BDNF protein levels were assessed. Our findings demonstrated that CMS evoked anhedonia, induced hypertrophy of adrenal gland, impaired gain of body weight and increased corticosterone and ACTH circulating levels in rats. Acute and chronic treatment with ketamine reversed the increase in adrenal gland weight, promoted regain of body weight, and normalized corticosterone and ACTH circulating levels. Repeated, but not acute, administration of ketamine reversed anhedonia-like behavior, although the treatment with ketamine per se increased sweet food consumption in non-stressed rats. Finally, acute and chronic ketamine treatment did not alter hippocampal BDNF protein levels in stressed rats. In conclusion, these findings support the idea of a putative role of NMDA receptors in mood-related symptoms, and rapid and robust effects of ketamine in reverting mainly physiological alterations induced by chronic mild stressful situations in rats.

Chronic treatment with celecoxib reverses chronic unpredictable stress-induced depressive-like behavior via reducing cyclooxygenase-2 expression in rat brain

Recent clinical trails reported that adjunctive cyclooxygenase (COX)-2 inhibition with celecoxib is beneficial in treating depression. However, another clinical study showed celecoxib did not have inhibitory effect of COX-2 in human brain when given at a therapeutic dose. Therefore, whether celecoxib is exerting its influence through COX inhibition or by some other mechanism remains unclear. The present study further investigated the effect of celecoxib on COX-2 expression, prostaglandin E(2) (PGE2, a major COX-2-mediated inflammatory mediator) concentration and the depressive-like behaviors in rats. Celecoxib was administrated by oral gavage to naive rats (16 mg/kg) or stressed rats (2, 8, 16 mg/kg, respectively) for 21 days, or to stressed rats for a single dose (16 mg/kg). The results showed that 21 days chronic unpredictable stress induced depressive-like behaviors and increased the COX-2 expression and PGE2 concentration in rat brain. Chronic treatments with celecoxib alleviated the depressive-like behavior and reversed the levels of COX-2 expression and PGE2 concentration in stressed rat in a dose-dependent manner. Celecoxib also improved the emotional state and decreased COX-2 expression and PGE2 concentration in naive rats. In addition, a single dose of celecoxib treatment reversed COX-2 expression and PGE2 concentration, but didn't alter the depressive-like behavior in stressed rat. These results suggest that COX-2 enzyme might play a key role in pathophysiology of depression. Furthermore, these data indicate that chronic celecoxib treatment reverse chronic unpredictable stress-induced depressive-like behavior might via reducing COX-2 enzyme in brain, and the selective COX-2 inhibitors could be developed as potential remedies for the management of depression.

Invivo antioxidant status: a putative target of antidepressant action

Oxidative stress is a critical route of damage in various psychological stress-induced disorders, such as depression. Antidepressants are widely prescribed to treat these conditions; however, few animal studies have investigated the effect of these drugs on endogenous antioxidant status in the brain. The present study employed a 21-day chronic regimen of random exposure to restraint stress to induce oxidative stress in brain, and behavioural aberrations, in rodents. The forced swimming (FST) and sucrose preference tests were used to identify depression-like phenotypes, and reversal in these indices indicated the effectiveness of treatment with fluoxetine (FLU; 20 mg/kg/day, p.o.; selective serotonin reuptake inhibitor), imipramine (IMI; 10 mg/kg/day, p.o.; tricyclic antidepressant) and venlafaxine (VEN; 10 mg/kg/day, p.o.; dual serotonin/norepinephrine reuptake inhibitor) following restraint stress. The antioxidant status was investigated in the brain of these animals. The results evidenced a significant recovery in the activities of superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST), glutathione reductase (GR) and glutathione (GSH) levels by antidepressant treatments following a restraint stress-induced decline of these parameters. The severely accumulated lipid peroxidation product malondialdehyde (MDA) and protein carbonyl contents in stressed animals were significantly normalized by antidepressant treatments. The altered oxidative status is implicated in various aspects of cellular function affecting the brain. Thus, it is possible that augmentation of in vivo antioxidant defenses could serve as a convergence point for multiple classes of antidepressants as an important mechanism underlying the neuroprotective pharmacological effects of these drugs observed clinically in the treatment of various stress disorders. Consequently, pharmacological modulation of stress-induced oxidative damage as a possible stress-management approach should be an important avenue of further research.

Adaptations of striatal endocannabinoid system during stress

The endocannabinoid system (ECS) plays a fundamental role in the regulation of synaptic transmission. Exposure to stressful events triggers synaptic adaptations in many brain areas. The activity of the ECS in stress-responsive neural circuits suggests that it may be involved in the behavioral responses and synaptic effects typical of stress. In this review, we discuss evidence demonstrating that striatal ECS is modulated by stress. Chronic stress exposure alters endocannabinoid levels, cannabinoid CB1 receptor binding and cannabinoid CB1 receptor-mediated control of inhibitory synaptic transmission in the striatum. Recent studies have shown that impairment of endocannabinoid signalling is associated with inability to adapt to chronic stress and to the development of maladaptive behaviors. The ECS represents a novel potential pharmacological target to treat stress-associated neuropsychiatric conditions.

Mutant mouse models and antidepressant drug research: focus on serotonin and brain-derived neurotrophic factor

Several lines of knockout (KO) mice have been evaluated as models of depression-related behavioral and neurobiological changes, and used to investigate molecular and cellular mechanisms underlying the activity of antidepressant drugs. Adult neurogenesis and brain 5-hydroxytryptamine (5-HT)/neurotrophic factor interactions have recently attracted great interest in relation to the mechanism of action of antidepressant drugs. The present review focuses primarily on genetic manipulation of the serotoninergic (5-HT) system. Basal neurochemical and behavioral changes occurring in mice lacking the 5-HT transporter (SERT), which is the main target of antidepressant drugs, as well as in those lacking G protein-coupled serotonin receptors (e.g. 5-HT1B, 5-HT1A, and 5-HT4 receptors) are described and evaluated. The importance of KO mice for neurotrophic factors, particularly for brain-derived neurotrophic factor and its high-affinity receptor (R-TrkB), is also addressed. Constitutive KO, tissue specific, or inducible KO mice targeting both 5-HT and brain-derived neurotrophic factor systems may potentially make an important contribution to knowledge of the pathophysiology and treatment of depression.

Decline in serotonergic firing activity and desensitization of 5-HT1A autoreceptors after chronic unpredictable stress

Chronic stressful life events are risk factors for contracting depression, the pathophysiology of which is strongly associated with impairments in serotonergic (5-HT) neurotransmission. Indeed, in rodents, exposure to chronic unpredictable stress (CUS) produces depressive-like behaviours such as behavioural despair and anhedonia. To date, there have not been many studies that especially explore in vivo changes in 5-HT neurotransmission associated with CUS in the rat. Therefore, using in vivo electrophysiology, we evaluated whether CUS that induces anhedonia-like behaviours concurrently impairs midbrain raphe 5-HT neuronal activity. Unlike unstressed and acutely stressed rats, CUS produced progressive reductions in sucrose intake and preference (anhedonia-like). These were associated with a decrease in the spontaneous firing activity (35.4%) as well as in the number of spontaneously active 5-HT neurons, and a desensitization of somatodendritic 5-HT1A autoreceptors in the dorsal raphe. These results suggest that CUS dramatically decreases 5-HT neural activity and 5-HT1A autoreceptor sensitivity, and may represent endophenotypic features of depressive-like states.

Prenatal alcohol exposure increases vulnerability to stress and anxiety-like disorders in adulthood

Children and adults with fetal alcohol spectrum disorder (FASD) have elevated rates of depression and anxiety disorders compared to control populations. The effects of prenatal alcohol exposure (PAE) on anxiety, locomotor activity, and hormonal reactivity in male and female rats tested on the elevated plus maze (EPM), a task commonly used to assess anxiety-like behaviors in rodents, were examined. Pregnant dams were assigned to PAE, pair-fed (PF), or ad libitum-fed control (C) groups. At adulthood, half of all male (N= 60) and female (N= 60) PAE, PF, and C offspring were exposed to 10 days of chronic mild stress (CMS); the other half remained undisturbed. Animals were then tested on the EPM, and blood collected 30 min posttest for analysis of corticosterone (CORT), testosterone, estradiol, and progesterone. Overall, CMS exposure produced a significant anxiogenic profile. Moreover, CMS increased anxiety-like behavior in PAE males and females compared to controls and eliminated the locomotor hyperactivity observed in nonstressed PAE females. CMS also increased post-EPM CORT, testosterone, and progesterone levels in all groups, with CORT and progesterone levels significantly higher in PAE than in C females. By contrast, CMS selectively lowered estradiol levels in PAE and PF, but not C, females. CMS exposure reveals sexually dimorphic behavioral and endocrine alterations in PAE compared to C animals. Together, these data suggest the possibility that fetal reprogramming of hypothalamic-pituitary-adrenal (HPA) and -gonadal (HPG) systems by alcohol may underlie, at least partly, an enhanced susceptibility of fetal alcohol-exposed offspring to depression/anxiety-like disorders in adulthood.

Vaccination as a novel approach for treating depressive behavior

BACKGROUND

Depressive behavior in animals is often associated with reduced levels of brain-derived neurotrophic factor (BDNF) and impaired neurogenesis in the hippocampus. Recent studies showed that T cells recognizing central nervous system (CNS)-specific antigens can regulate adult hippocampal neurogenesis and expression of BDNF. On the basis of these findings, we hypothesized that controlling CNS specific immune activity by immunization with a myelin-related peptide may have an antidepressant effect.

METHODS

We investigated the impact of immunization with a CNS related peptide, on the behavioral and cellular outcomes of chronic mild stress (CMS; an animal model for depression) in rats.

RESULTS

Immunization with a weak agonist of a myelin-derived peptide ameliorated depressive behavior such as anhedonia (measured by sucrose preference), induced by CMS in rats. The behavioral outcome was accompanied by restoration of hippocampal BDNF levels and neurogenesis.

CONCLUSIONS

The results of this study introduce a novel approach of immunization with CNS-related antigens as a therapeutic means for fighting depression. Vaccination, as an antidepressant therapy, may invoke several molecular and cellular pathways that are known to be regulated by antidepressant drugs. Therefore, we suggest that immune-based therapies should be considered for treatment of depression.

Chronic mild stress induces widespread decreases in thyroid hormone alpha1 receptor mRNA levels in brain--reversal by imipramine

While considerable clinical evidence implicates thyroid hormones (THs) in depressive illness, the specific nature of this involvement remains unclear. The alpha1 subtype (TR-alpha1) is the most abundant TH receptor in brain. Here we investigated changes in TR-alpha1 mRNA in the chronic mild stress (CMS) model of depression. Rats were exposed to a CMS schedule for 3 weeks, which resulted in a progressive decreases in sucrose preference (an index of anhedonia). They were then treated daily with either imipramine (IMI, 10mg/kg) or vehicle (VEH) for 2 weeks before being sacrificed for quantitative in situ hybridization analyses of TR-alpha1 mRNA throughout the brain. Results indicated that CMS followed by VEH induced widespread decreases in TR-alpha1 mRNA in brain. In contrast, CMS-exposed rats receiving IMI for the last 2 weeks prior to sacrifice showed full recovery of sucrose preference. Furthermore, brain TR-alpha1 mRNA levels in these animals were similar to those of non-stressed controls receiving either SAL or IMI. These results reveal that TR-alpha1 mRNA brain levels are very sensitive to CMS effects. The reversal of both anhedonic and TR-alpha1 effects of CMS by IMI suggests that TR-alpha1 may play a role both in stress-induced depressive symptoms and in their reversal by antidepressant interventions.

Chronic mild stress (CMS) in mice: of anhedonia, 'anomalous anxiolysis' and activity

Background

In a substantial proportion of depressed patients, stressful life events play a role in triggering the evolution of the illness. Exposure to stress has effects on different levels in laboratory animals as well and for the rat it has been shown that chronic mild stress (CMS) can cause antidepressant-reversible depressive-like effects. The adoption of the model to the mouse seems to be problematic, depending on the strain used and behavioural endpoint defined. Our aim was to evaluate the applicability of CMS to mice in order to induce behavioural alterations suggested to reflect depression-like symptoms.

Methodology/Principal Findings

A weekly CMS protocol was applied to male mice of different mouse strains (D2Ola, BL/6J and BL/6N) and its impact on stress-sensitive behavioural measures (anhedonia-, anxiety- and depression-related parameters) and body weight was assessed. Overnight illumination as commonly used stressor in CMS protocols was particularly investigated in terms of its effect on general activity and subsequently derived saccharin intake. CMS application yielded strain-dependent behavioural and physiological responses including ‘paradox’ anxiolytic-like effects. Overnight illumination was found to be sufficient to mimic anhedonic-like behaviour in BL/6J mice when being applied as sole stressor.

Conclusions/Significance

The CMS procedure induced some behavioural changes that are compatible with the common expectations, i.e. ‘anhedonic’ behaviour, but in parallel behavioural alterations were observed which would be described as ‘anomalous’ (e.g. decreased anxiety). The results suggest that a shift in the pattern of circadian activity has a particular high impact on the anhedonic profile. Changes in activity in response to novelty seem to drive the ‘anomalous’ behavioural alterations as well.

A trans-dimensional approach to the behavioral aspects of depression

Depression, a complex mood disorder, displays high comorbidity with anxiety and cognitive disorders. To establish the extent of inter-dependence between these behavioral domains, we here undertook a systematic analysis to establish interactions between mood [assessed with the forced-swimming (FST) and sucrose consumption tests (SCT)], anxiety [elevated-plus maze (EPM) and novelty suppressed feeding (NSF) tests] and cognition (spatial memory and behavioral flexibility tests) in rats exposed to unpredictable chronic-mild-stress (uCMS). Expectedly, uCMS induced depressive-like behavior, a hyperanxious phenotype and cognitive impairment; with the exception of the measure of anxiety in the EPM, these effects were attenuated by antidepressants (imipramine, fluoxetine). Measures of mood by the FST and SCT were strongly correlated, whereas no significant correlations were found between the different measures of anxiety (EPM and NSF); likewise, measures of cognition by spatial memory and behavioral flexibility tests were poorly correlated. Inter-domain analysis revealed significant correlations between mood (FST and SCT) and anxiety-like behavior (NSF, but not EPM). Furthermore, significant correlations were found between cognitive performance (reverse learning task) and mood (FST and SCT) and anxiety-like behavior (NSF). These results demonstrate interactions between different behavioral domains that crosscut the disciplines of psychiatry and neurology.

Chronic stress and individual vulnerability

Over the last decades the burden of disease in Western countries has shifted from comparably easily treated infectious diseases to more complex diseases, such as the metabolic syndrome, cardiovascular disease, and psychiatric disorders. A common characteristic of these illnesses is the interplay of multiple genetic and nongenetic factors, which eventually results in the manifestation of disease symptoms. Large-scale epidemiological studies in humans have resulted in the identification of various environmental and genetic risk factors, which contribute to the onset, duration, and severity of disease. While tremendous progress has been made, it is still impossible to predict which combination of risk factors will result in the manifestation of a specific illness. This lack of knowledge is also frequently reflected in inadequate treatment strategies, which mainly focus on symptom reversal rather than targeting the cause of the diseases. One of the most prominent environmental risk factors described for numerous diseases is chronic exposure to stressful situations. In this paper we address clinical and preclinical evidence of chronic stress as a risk factor for disease and introduce a novel, high-throughput mouse model for chronic social stress. We can show that this model has a high degree of construct, face, and predictive validity in terms of physiological, behavioral, and gene expression changes. We further illustrate how novel animal models of chronic social stress can help to unravel the complex interaction of individual genetic vulnerability and environmental risk factors.

Limbic regulation of hypothalamo-pituitary-adrenocortical function during acute and chronic stress

The hypothalamo-pituitary-adrenocortical (HPA) axis is responsible for initiation of glucocorticoid stress responses in all vertebrate animals. Activation of the axis is regulated by diverse afferent input to the hypothalamic paraventricular nucleus (PVN). This review discusses brain mechanisms subserving generation and inhibition of stress responses focusing on the contribution of the limbic system and highlighting recent conceptual advances regarding organization of stress response pathways in the brain. First, control of HPA axis responses to psychogenic stimuli is exerted by a complex neurocircuitry that involves oligosynaptic networks between limbic forebrain structures and the PVN. Second, individual stress-modulatory structures can have a heterogeneous impact on HPA axis responses, based on anatomical micro-organization and/or stimulus properties. Finally, HPA axis hyperactivity pursuant to chronic stress involves a substantial functional and perhaps anatomical reorganization of central stress-integrative circuits. Overall, the data suggest that individual brain regions do not merely function as monolithic activators or inhibitors of the HPA axis and that network approaches need be taken to fully understand the nature of the neuroendocrine stress response.

Effects of chronic mild stress on the oxidative parameters in the rat brain

Major depression is characterized for symptoms at the psychological, behavioral and physiological levels. The chronic mild stress model has been used as an animal model of depression. The consumption of sweet food, locomotor activity, body weight, lipid and protein oxidation levels and superoxide dismutase and catalase activities in the rat hippocampus, prefrontal cortex and cortex were assessed in rats exposed to chronic mild stress. Our findings demonstrated a decrease on sweet food intake, no effect on locomotor activity, lack of body weight gain, increase in protein (prefrontal, hippocampus, striatum and cortex) and lipidic peroxidation (cerebellum and striatum), and an increase in catalase (cerebellum, hippocampus, striatum, cortex) and a decrease in superoxide dismutase activity (prefrontal, hippocampus, striatum and cortex) in stressed rats. In conclusion, our results support the idea that stress produces oxidants and an imbalance between superoxide dismutase and catalase activities that contributes to stress-related diseases, such as depression.

Role of endocannabinoid signaling in anxiety and depression

Cannabinoid receptors and their endogenous ligands are located throughout the limbic, or "emotional," brain, where they modulate synaptic neurotransmission. Converging preclinical and clinical data suggest a role for endogenous cannabinoid signaling in the modulation of anxiety and depression. Augmentation of endocannabinoid signaling (ECS) has anxiolytic effects, whereas blockade or genetic deletion of CB₁ receptors has anxiogenic properties. Augmentation of ECS also appears to have anti-depressant actions, and in some assays blockade and genetic deletion of CB₁ receptors produces depressive phenotypes. These data provide evidence that ECS serves in an anxiolytic, and possibly anti-depressant, role. These data suggest novel approaches to treatment of affective disorders which could include enhancement of endogenous cannabinoid signaling, and warrant cautious use of CB₁ receptor antagonists in patients with pre-existing affective disorders.

Removing obstacles in neuroscience drug discovery: the future path for animal models

Despite great advances in basic neuroscience knowledge, the improved understanding of brain functioning has not yet led to the introduction of truly novel pharmacological approaches to the treatment of central nervous system (CNS) disorders. This situation has been partly attributed to the difficulty of predicting efficacy in patients based on results from preclinical studies. To address these issues, this review critically discusses the traditional role of animal models in drug discovery, the difficulties encountered, and the reasons why this approach has led to suboptimal utilization of the information animal models provide. The discussion focuses on how animal models can contribute most effectively to translational medicine and drug discovery and the changes needed to increase the probability of achieving clinical benefit. Emphasis is placed on the need to improve the flow of information from the clinical/human domain to the preclinical domain and the benefits of using truly translational measures in both preclinical and clinical testing. Few would dispute the need to move away from the concept of modeling CNS diseases in their entirety using animals. However, the current emphasis on specific dimensions of psychopathology that can be objectively assessed in both clinical populations and animal models has not yet provided concrete examples of successful preclinical-clinical translation in CNS drug discovery. The purpose of this review is to strongly encourage ever more intensive clinical and preclinical interactions to ensure that basic science knowledge gained from improved animal models with good predictive and construct validity readily becomes available to the pharmaceutical industry and clinical researchers to benefit patients as quickly as possible.

Interleukin-1 (IL-1): a central regulator of stress responses

Ample evidence demonstrates that the pro-inflammatory cytokine interleukin-1 (IL-1), produced following exposure to immunological and psychological challenges, plays an important role in the neuroendocrine and behavioral stress responses. Specifically, production of brain IL-1 is an important link in stress-induced activation of the hypothalamus-pituitary-adrenal axis and secretion of glucocorticoids, which mediate the effects of stress on memory functioning and neural plasticity, exerting beneficial effects at low levels and detrimental effects at high levels. Furthermore, IL-1 signaling and the resultant glucocorticoid secretion mediate the development of depressive symptoms associated with exposure to acute and chronic stressors, at least partly via suppression of hippocampal neurogenesis. These findings indicate that whereas under some physiological conditions low levels of IL-1 promote the adaptive stress responses necessary for efficient coping, under severe and chronic stress conditions blockade of IL-1 signaling can be used as a preventive and therapeutic procedure for alleviating stress-associated neuropathology and psychopathology.

Stress, depression and cardiovascular dysregulation: a review of neurobiological mechanisms and the integration of research from preclinical disease models

Bidirectional associations between mood disorders and cardiovascular diseases are extensively documented. However, the precise physiological and biochemical mechanisms that underlie such relationships are not well understood. This review focuses on the neurobiological processes and mediators that are common to both mood and cardiovascular disorders. The discussion places an emphasis on the role of exogenous stressors in addition to: (a) neuroendocrine and neurohumoral changes involving dysfunction of the hypothalamic-pituitary-adrenal axis and the activation of the renin-angiotensin-aldosterone system, (b) immune alterations including activation of pro-inflammatory cytokines, (c) autonomic and cardiovascular dysregulation including increased sympathetic drive, withdrawal of parasympathetic tone, cardiac rate and rhythm disturbances, and altered baroreceptor reflex function, (d) central neurotransmitter system dysfunction involving the dopamine, norepinephrine and serotonin systems, and (e) behavioral changes including fatigue and physical inactivity. The review also discusses experimental investigations using preclinical disease models to elucidate the neurobiological mechanisms underlying the link between mood disorders and cardiovascular disease. These include: (a) the chronic mild stress model of depression, (b) a model of congestive heart failure, (c) a model of cardiovascular deconditioning, (d) pharmacological manipulations of body fluid and sodium balance, and (e) pharmacological manipulations of the central serotonergic system. In combination with an extensive human research literature, the investigation of mechanisms underlying mood and cardiovascular regulation using animal models will enhance understanding the association between depression and cardiovascular disease. This will ultimately promote the development of better treatments and interventions for individuals with co-morbid psychological and somatic pathologies.

Chronic unpredictable stress enhances cocaine-conditioned place preference in type 1 cannabinoid receptor knockout mice

Cannabinoid signaling via the type 1 cannabinoid (CB1) receptor modulates the effects of drugs of abuse and the response to exposure to stressors. In addition, exposure to stressors can alter the effects of drugs of abuse. This study examined the effects of exposure to chronic unpredictable stress (CUS) in CB1 receptor knockout (CB1 KO) mice and their wild-type (WT) littermates, using cocaine-conditioned place preference (CPP) to compare their response to cocaine. Mice were untreated or exposed to 2 weeks of CUS. After this period, the acquisition of a cocaine CPP was examined with one of three doses (3.2, 10.0, or 17.0 mg/kg) of cocaine. Untreated CB1 KO and WT mice both acquired the cocaine CPP; however, exposure to CUS enhanced the acquisition of the cocaine CPP in CB1 KO mice, but did not significantly alter the effects of cocaine in WT mice. Taken together, these findings support earlier evidence suggesting a role for the CB1 receptor in the response to stress as well as in the effects of cocaine.

Aging increases the susceptibility to develop anhedonia in male rats

The objective of this study was to establish the effect of aging on the development of anhedonia, a core feature of depression. Young and old male Wistar rats (of around 3-5 and 12-15 months, respectively) were exposed to a chronic variable stress (CVS) schedule for 3 weeks. CVS produced anhedonia, indicated by a reduction in the intake of a sucrose solution (1%), in 8 out of 23 (35%) young rats and in 19 out of 26 (73%) old rats, implying that old animals are more susceptible to stress and develop anhedonia more readily than young animals. Young and old anhedonic rats showed a similar temporal course in the reduction of sucrose consumption, reaching the anhedonic state after 2 weeks of CVS exposure. Compared with young animals, old rats had lower basal serum testosterone and estradiol levels. The systemic levels of corticosterone did not vary between both age groups. No significant pathological condition was detected in old animals. It is suggested that the higher susceptibility to develop anhedonia in male rats could be associated to neuroendocrine changes consequent to aging.

Behavioral effects of CB2 cannabinoid receptor activation and its influence on food and alcohol consumption

Consumers of marijuana typically feel a strong, compulsive desire to consume food. Although past research revealed that the CB1 cannabinoid receptor is a potent regulator of food intake, the functional presence of neuronal CB2 cannabinoid receptors in the brain has been controversial. The role of CB2 receptors in food and alcohol consumption and the behavioral effects of CB2 receptor ligands are not well characterized. This is because CB2 cannabinoid receptors were thought to be absent from the brain and expressed primarily in immune cells and in the periphery. We tested the effects of peripheral injections of CB2 antagonist AM 630, CB2 agonist PEA, and CB1 antagonist AM 251 on male C57BL/6, Balb/c, and DBA/2 mice at the beginning of the night cycle and after overnight 12-hour fasts. We also investigated the effects of the putative CB2 agonist, JWH015, and CB2 antagonist, SR144528, in mouse motor function tests and in the two-compartment black and white box. Under standard conditions, the CB2 antagonist AM 630 inhibited food consumption in C57BL/6 mice and DBA/2 mice, but failed to block food intake of Balb/c mice. The CB2 agonist PEA had no significant effect on food consumption in Balb/c mice, and reduced food intake in C57BL/6 and DBA mice. The CB1 antagonist AM 251 inhibited food ingestion in the three mouse strains at variable times. After 12-hour food deprivation, the CB2 antagonist AM 630 increased food consumption in C57Bl/6 mice, but failed to produce significant changes in food intake for Balb/c and DBA/2 mice. The CB2 agonist PEA also reduced food consumption in all three mice strains at variable times. In comparison to the CB2 ligands, CB1 antagonist AM 251 inhibited food ingestion in the mouse strains. A general pattern of depression in locomotor activity was induced by JWH 015 in both males and females in the three mouse strains tested as the dose was increased. The development and enhancement of alcohol preference was observed after chronic treatment with CB2 agonist JWH 015 in stressed mice, but not in controls. In the DBA/2 strain, the spontaneous locomotor activity and stereotype behavior was enhanced by acute administration of low doses of SR144528. There was a reduction in CNR2 gene expression in the ventral mid-brain region of mice that developed alcohol preference, but not in those that did not develop alcohol preference. These effects of CB2 cannabinoid receptor ligands in in vivo behavioral tests are provided as functional evidence that CB2-Rs in the brain play a role in food and alcohol consumption and in the modification of mouse behavior.

Functional expression of brain neuronal CB2 cannabinoid receptors are involved in the effects of drugs of abuse and in depression

Major depression and addiction are mental health problems associated with stressful events in life with high relapse and recurrence even after treatment. Many laboratories were not able to detect the presence of CB2 cannabinoid receptors (CB2-Rs) in healthy brains, but CB2-R expression has been demonstrated in rat microglial cells and other brain-associated cells during inflammation. Thus, neuronal expression of CB2-Rs has been ambiguous and controversial, and its role in depression and substance abuse is unknown. In this study we tested the hypothesis that genetic variants of the CB2 gene might be associated with depression in a human population and that alteration in CB2 gene expression may be involved in the effects of abused substances, including opiates, cocaine, and ethanol, in rodents. Here we demonstrate that a high incidence of Q63R but not H316Y polymorphism in the CB2 gene was found in Japanese depressed subjects. CB2-Rs and their gene transcripts are expressed in the brains of naïve mice and are modulated after exposure to stressors and administration of abused drugs. Mice that developed an alcohol preference had reduced CB2 gene expression, and chronic treatment with JWH015 a putative CB2-R agonist, enhanced alcohol consumption in stressed but not in control mice. The direct intracerebroventricular microinjection of CB2 antisense oligonucleotide into the mouse brain reduced mouse aversions in the plus-maze test, indicating the functional presence of CB2-Rs in the brain that modifies behavior. Using electron microscopy we report the subcellular localization of CB2-Rs that are mainly on postsynaptic elements in rodent brain. Our data demonstrate the functional expression of CB2-Rs in the brain that may provide novel targets for the effects of cannabinoids in depression and substance abuse disorders beyond neuroimmunocannabinoid activity.

Chronic treatment with electroconvulsive shock may modulate the immune function of macrophages

OBJECTIVE

To determine the effect of single and chronic electroconvulsive shock (ECS) administration on the immunoregulatory functions of macrophages.

METHODS

Male Wistar rats received single or chronic treatment with ECS (150 mA, 50 Hz, 0.5 seconds) delivered through ear clips, once a day for 10 consecutive days, or sham ECS administered likewise. The rats were killed 24 hours after the last treatment, and peritoneal macrophages were cultured in vitro for 3 or 36 hours for a subsequent determination of their metabolic activity. The ability of macrophages to reduce Alamar Blue, 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT), and nitrotetrazolium blue chloride and pinocytosis, adherence, and vitality, as well as synthesis of nitric oxide and arginase activity, was assessed.

RESULTS

We found statistically significant changes in the biological properties of macrophages which occurred after 36 hours of incubation, especially in cultures stimulated with lipopolysaccharide; in contrast, no differences were observed between groups assessed after 3 hours of incubation. Rats receiving chronic 10-fold ECS showed a substantial increase in the metabolic activity of macrophages, reflected as their ability to reduce Alamar Blue and MTT and to increase arginase activity, accompanied with a marked but statistically insignificant decrease in nitric oxide synthesis compared with respective controls.

CONCLUSIONS

Our results suggest that chronic treatment with ECS may induce long-lasting changes in the activity of peritoneal macrophages. Attenuation of their proinflammatory properties indicates that ECS can change the primarily immunoregulatory functions of macrophages.

Changes in brain G proteins and colonic sympathetic neural signaling in chronic-acute combined stress rat model of irritable bowel syndrome (IBS)

The role of the brain-gut axis interaction in the pathogenesis of irritable bowel syndrome (IBS) is not well understood. To examine this possibility, a novel rat model of IBS subjected to both chronic and acute stress (CAS) was established. G proteins play a crucial role in the pathophysiology of depression. The alpha 2A adrenoceptor (alpha(2A)-AR) and the norepinephrine reuptake transporter (NET) determine the sympathetic signal activity. It is conceivable that stress may induce brain G proteins, colonic alpha(2A)-ARs, and NET abnormal expression, which may be responsible for the abnormalities in IBS. Colonic motility, visceral sensation, and secretion were assessed by counting fecal pellets, abdominal muscle contractions in response to colorectal balloon distension (CRD), and short-circuit current study, respectively. Western blot analysis was used to investigate the expression of G proteins, alpha(2A)-ARs, and NET. Compared with control animals, the colonic epithelial secretion, fecal pellets, and numbers of abdominal muscle contraction induced by CRD were significantly higher in both acute stress only (AS) and CAS rats. However, the G proteins, alpha(2A)-AR, and NET expression changed differently in AS and CAS rats. We showed that exposure to either AS or CAS would cause the increase of secretion, motility, and sensation, but the change of protein expression in brain-gut axis was different. It may be responsible for the pathogenesis of IBS.

Glial loss in the prefrontal cortex is sufficient to induce depressive-like behaviors

BACKGROUND

Postmortem studies have repeatedly found decreased density and number of glia in cortical regions, including the prefrontal and cingulate areas, from depressed patients. However, it is unclear whether this glial loss plays a direct role in the expression of depressive symptoms.

METHODS

To address this question, we characterized the effects of pharmacologic glial ablation in the prefrontal cortex (PFC) of adult rats on behavioral tests known to be affected by stress or antidepressant treatments: sucrose preference test (SPT), novelty suppressed feeding test (NSFT), forced swim test (FST), and two-way active avoidance test (AAT). We established the dose and time course for the actions of an astrocyte specific toxin, L-alpha-aminoadipic acid (L-AAA), and compared the behavioral effects of this gliotoxin with the effects of an excitotoxic (ibotenate) lesion and to the effects of chronic stress.

RESULTS

The results demonstrate that L-AAA infusions induced anhedonia in SPT, anxiety in NSFT, and helplessness in FST and AAT. These effects of L-AAA were similar to chronic unpredictable stress (CUS)-induced depressive-like behaviors in these tests. However, ibotenate-induced neurotoxic lesion of the PFC had no effect in these behavioral tests.

CONCLUSIONS

The results demonstrate that glial ablation in the PFC is sufficient to induce depressive-like behaviors similar to chronic stress and support the hypothesis that loss of glia contributes to the core symptoms of depression.

AKT signaling within the ventral tegmental area regulates cellular and behavioral responses to stressful stimuli

BACKGROUND

The neurobiological mechanisms by which only a minority of stress-exposed individuals develop psychiatric diseases remain largely unknown. Recent evidence suggests that dopaminergic neurons of the ventral tegmental area (VTA) play a key role in the manifestation of stress vulnerability.

METHODS

Using a social defeat paradigm, we segregated susceptible mice (socially avoidant) from unsusceptible mice (socially interactive) and examined VTA punches for changes in neurotrophic signaling. Employing a series of viral vectors, we sought to causally implicate these neurotrophic changes in the development of avoidance behavior.

RESULTS

Susceptibility to social defeat was associated with a significant reduction in levels of active/phosphorylated AKT (thymoma viral proto-oncogene) within the VTA, whereas chronic antidepressant treatment (in mice and humans) increased active AKT levels. This defeat-induced reduction in AKT activation in susceptible mice was both necessary and sufficient to recapitulate depressive behaviors associated with susceptibility. Pharmacologic reductions in AKT activity also significantly raised the firing frequency of VTA dopamine neurons, an important electrophysiologic hallmark of the susceptible phenotype.

CONCLUSIONS

These studies highlight a crucial role for decreases in VTA AKT signaling as a key mediator of the maladaptive cellular and behavioral response to chronic stress.

Early weaning results in less active behaviour, accompanied by lower 5-HT1A and higher 5-HT2A receptor mRNA expression in specific brain regions of female pigs

In rodents and humans stressful events in early life e.g. maternal deprivation, can increase sensitivity to stress in later life. Humans may become more susceptible to mood disorders, e.g. depression. In livestock species, such as pigs, early weaning is a form of maternal deprivation. We investigated behavioural consequences in 99 female pigs weaned at three different ages (12, 21 and 42 days; d12, d21, d42). Pigs were habituated to an open field arena over 6 days before being given 5-min open-field tests over three subsequent days (days 77-79). Early-weaned pigs (d12) showed behavioural inhibition (reduced vocalisations and lower activity) compared with later-weaned pigs, although in all groups these measures declined over the three tests, so this treatment difference might reflect more rapid habituation to the test in d12 pigs. Long-term effects on mood-related 5-HT receptor subtypes were measured in the brain at 90 days in a random sample of the d12 (n=8) and d42 pigs (n=8), using (3)H-ligand-binding and autoradiography and in situ hybridisation histochemistry. There were no differences between weaning ages in binding of (3)H-8-OH-DPAT (5-HT(1A) receptor agonist) or of (3)H-ketanserin (5-HT(2A) receptor antagonist) to any brain region studied. In d12 pigs, 5-HT(1A) receptor mRNA expression per unit area was 29%, 63%, 52% and 64% lower than in d42 pigs in the parvocellular PVN, amygdala and hippocampal dentate gyrus and pyramidal cell layer, respectively. The ratio of expression per cell to expressing cells per unit area was also lower, by 31%, in the pars horizontalis of the PVN in d12 pigs. Conversely, 5-HT(2A) receptor mRNA was expressed at a 25% and 28% higher density per unit area in the amygdala and pyramidal cell layer of the hippocampus, respectively, in these d12 pigs. In individual pigs, across brain regions, 5-HT(1A) receptor mRNA data were 70-79% correlated with binding data but no correlation was found for 5-HT(2A) data, suggesting different regulatory mechanisms. The behavioural and neurobiological responses to early weaning might represent either dysfunction or adaptation. Further investigation is required.

Age-dependent effects of chronic stress on brain plasticity and depressive behavior

Exposure to chronic mild stress (CMS) is known to induce anhedonia in adult animals, and is associated with induction of depression in humans. However, the behavioral effects of CMS in young animals have not yet been characterized, and little is known about the long-term neurochemical effects of CMS in either young or adult animals. Here, we found that CMS induces anhedonia in adult but not in young animals, as measured by a set of behavioral paradigms. Furthermore, while CMS decreased neurogenesis and levels of brain-derived neurotrophic factor (BDNF) in the hippocampus of adult animals, it increased these parameters in young animals. We also found that CMS altered alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptor GluR1 subunit levels in the hippocampus and the nucleus accumbens of adult, but not young animals. Finally, no significant differences were observed between the effects of CMS on circadian corticosterone levels in the different age groups. The substantially different neurochemical effects chronic stress exerts in young and adult animals may explain the behavioral resilience to such stress young animals possess.

Calcium-sensitive adenylyl cyclases in depression and anxiety: behavioral and biochemical consequences of isoform targeting

BACKGROUND

Adenylyl cyclases (ACs) represent a diverse family of enzymes responsible for the generation of cyclic adenosine monophosphate (cAMP), a key intracellular second messenger. The Ca(2+)/calmodulin-stimulated AC1 and AC8 isoforms as well as the calcium-inhibited AC5 isoform are abundantly expressed within limbic regions of the central nervous system. This study examines the contribution of these AC isoforms to emotional behavior.

METHODS

Male and female AC1/8 double knockout mice (DKO) and AC5 knockout mice (AC5KO) were examined on a series of standard laboratory assays of emotionality. Mice were also assayed for hippocampal cell proliferation and for changes in brain-derived neurotrophic factor signaling in the nucleus accumbens, amygdala, and hippocampus, three forebrain structures involved in the regulation of mood and affect.

RESULTS

The AC5KO mice showed striking anxiolytic and antidepressant phenotypes on standard behavioral assays. In contrast, AC1/8 DKO mice were hypoactive, exhibited diminished sucrose preference, and displayed alterations in neurotrophic signaling, generally consistent with a prodepressant phenotype. Neither line of mice displayed alterations in hippocampal cell proliferation.

CONCLUSIONS

These data illustrate the complex manner in which Ca(2+)/calmodulin-stimulated ACs contribute to emotional behavior. In addition, they support the possibility that a selective AC5 antagonist would be of therapeutic value against depression and anxiety disorders.