Voluntary exercise alters GABA(A) receptor subunit and glutamic acid decarboxylase-67 gene expression in the rat forebrain.

Voluntary exercise improves stress coping and lowers anxiety. Because of the role of GABA in these processes, we investigated changes in the central GABAergic system in rats with free access to a running wheel for 4 weeks. The control animals had no access to a running wheel. Using insitu hybridisation histochemistry, we studied changes in gene expression of various GABA(A) receptor subunits as well as the GABA-synthesising enzyme glutamic acid decarboxylase-67 (GAD67) in the forebrain. There were region-specific decreases in alpha2, beta3 and gamma2 subunit mRNA expression and region-specific increases in beta1 subunit expression. The alpha5 and delta subunits, in the forebrain specifically associated with extrasynaptic GABA(A) receptors in the hippocampus, showed differential increases in expression levels. Expression of GAD67 mRNA was increased in many forebrain regions including all hippocampal cell layers, peri-paraventricular nucleus, bed nucleus stria terminalis, nucleus accumbens core and motor cortex, suggesting that long-term voluntary exercise enhances forebrain GABA synthesis capacity but in a region-specific manner. Thus, regular performance of exercise results in extensive changes in the forebrain GABAergic system that may be implicated in the changes in stress sensitivity and emotionality observed in exercising subjects.

The ultradian and circadian rhythms of free corticosterone in the brain are not affected by gender: an in vivo microdialysis study in Wistar rats.

Recently, we described that free corticosterone levels in the brain of male Wistar rats, as assessed by in vivo microdialysis, show an ultradian rhythm with a pulse frequency of 1.2 pulses/h. To establish whether gender influences brain free corticosterone rhythms, we studied free corticosterone levels in the female Wistar rat under baseline and stressful conditions using microdialysis in the hippocampus. Analysis of the data with the PULSAR algorithm revealed that hippocampal free corticosterone levels show a clear ultradian pattern in female rats with a pulse frequency of 1.16+/-0.05 pulses/h between 09.00 h and 21.00 h. Further analysis showed that the pulse amplitude is significantly higher during the late afternoon/early night (15.00-21.00 h) than during the morning/early afternoon (09.00-15.00 h) phase (0.13+/-0.03 versus 0.07+/-0.01 microg/dl, respectively, P < 0.05). Pulse characteristics were extremely reproducible as demonstrated by the almost identical pulse parameters derived from two consecutive 24-h periods [pulse frequency: 1.13+/-0.09 and 1.19+/-0.08 pulses/h; pulse amplitude: 0.11+/-0.05 and 0.10+/-0.02 microg/dl for day 1 and day 2 (09.00-21.00 h) respectively, P > 0.05]. Both exposure to a novel environment and forced swim stress increased hippocampal free corticosterone levels. However, the stress-induced rise reached higher levels and was more prolonged after forced swimming (area under the curve: 46.84+/-9.25 and 12.08+/-1.69 arbitrary units for forced swimming and novelty stress respectively, P = 0.01). Importantly, the ultradian rhythm was rapidly restored after termination of the stress response. This is the first demonstration that the female rat brain is exposed to free corticosterone levels that follow a circadian as well as an ultradian pattern and show almost identical pulse characteristics as recently reported in male animals. These observations are of significance for further investigations into the dynamics of glucocorticoid action in the brain of both genders.

Stress and hypothalamic-pituitary-adrenal axis function in experimental autoimmune encephalomyelitis and multiple sclerosis - a review.

Multiple sclerosis (MS) is an inflammatory and degenerative disease of the CNS with an assumed autoimmune-mediated pathogenesis. Stressful life events have been hypothesized as potential triggers of disease exacerbation. Animal studies using experimental autoimmune encephalomyelitis (EAE), as a model for MS, suggest that decreased hypothalamic-pituitary-adrenal (HPA) function may play a role in the increased susceptibility and severity of the disease. Histopathological studies of the hypothalamus point to disturbances in corticotropin-releasing hormone (CRH) regulation as a result of MS lesions in this area. Functional endocrine tests (e.g., the combined Dexamethasone-CRH test) showed a disturbed negative feedback after steroid application in MS patients. Hyper- and hypoactivity of the HPA axis, have been described to be associated with more severe courses. This paper presents an overview of the evidence for a role of HPA dysfunction in EAE and MS based on stress-experimental studies.

Long-term voluntary exercise and the mouse hypothalamic-pituitary-adrenocortical axis: impact of concurrent treatment with the antidepressant drug tianeptine.

We investigated whether voluntary exercise and concurrent antidepressant treatment (tianeptine; 20 mg/kg/day; 4 weeks) exert synergistic effects on the mouse hypothalamic-pituitary-adrenocortical (HPA) axis. Animals had access to a running wheel, were treated with the antidepressant, or received both conditions combined. Control mice received no running wheel and no drug treatment. Exercise resulted in asymmetric changes in the adrenal glands. Whereas sedentary mice had larger left adrenals than right ones, this situation was abolished in exercising animals, mainly due to enlargement of the right adrenal cortex. However, antidepressant treatment alone was ineffective whereas the combination of antidepressant treatment and exercise resulted in an enlargement of both adrenal cortices. In these respective conditions, the levels of tyrosine hydroxylase (TH) mRNA expression in the left and right adrenal medullas varied greatly in parallel to the changes observed in the adrenal cortex sizes. TH mRNA expression in the locus coeruleus of exercising mice was significantly increased irrespective of concomitant tianeptine treatment. Corticotrophin-releasing factor mRNA levels in the hypothalamic paraventricular nucleus were decreased after voluntary exercise but were unaffected by tianeptine. Exercise, particularly in combination with tianeptine treatment, resulted in decreased early morning baseline plasma levels of corticosterone. If animals were exposed to novelty (i.e. a mild psychological stressor), a decreased response in plasma corticosterone levels was observed in the exercising mice. By contrast, after restraint, a mixed physical and psychological stressor, exercising mice showed an enhanced response in plasma corticosterone compared to the controls; a response which was even further boosted in exercising mice concomitantly treated with tianeptine. Under either condition, plasma adrenocorticotrophic hormone levels were not different between groups. Thus, voluntary exercise impacts substantially on HPA axis regulation. Concurrent tianeptine treatment results in synergistic actions, mainly at the adrenal level, affecting both its structure and function.

Forced swimming evokes a biphasic response in CREB phosphorylation in extrahypothalamic limbic and neocortical brain structures in the rat.

The transcription factor cAMP response element-binding protein (CREB) plays a critical role in plasticity processes underlying learning and memory. We investigated the phosphorylation of CREB in rat brain after forced swimming, a stressor known to impact on higher limbic and neocortical brain areas. As shown by immunohistochemistry, forced swimming increased phosphorylated CREB (P-CREB) levels in the dentate gyrus, all neocortical areas, the medial, lateral and basolateral nuclei of the amygdala, cerebellum but not in the hypothalamic paraventricular nucleus. Distinct differences in the P-CREB pattern were observed in the deeper vs. superficial layers of the neocortex. The response in P-CREB was stressor type-specific because exposure to either ether or a cold environment was ineffective. The forced swimming-induced changes in P-CREB levels showed a biphasic time-course: an early peak detected at 15 min was followed by a marked drop at 60 min; a second rise starting after 1-2 h, reached maximal values between 6 and 8 h, and remained elevated for at least 48 h. Examination of the neuroanatomical induction pattern of the CRE-inducible immediate early gene product c-fos revealed that it was only partly overlapping with that of P-CREB. Western analyses showed that only the 43-kDa CREB protein (an enhancer of CRE-containing promotors) was phosphorylated after forced swimming, while other members of the CREB/ATF family (CREM, ATF-1 and ATF-2) remained unaffected. The NF-kappaB pathway was not activated, indicating that forced swimming does not unspecifically evoke transcription factor activation. Thus, in contrast to physical stressors, such as ether or cold exposure, forced swimming, a stressor with a strong psychological component, elicits the recruitment of the CREB pathway in a widespread manner in the limbic system and neocortex; brain regions known to be implicated in various forms of (stress-related) learning and memory.

Corticotropin-releasing hormone receptor type 1-deficiency enhances hippocampal serotonergic neurotransmission: an in vivo microdialysis study in mutant mice.

Corticotropin-releasing hormone plays an important role in the coordination of various responses to stress. Previous research has implicated both corticotropin-releasing hormone and the serotonergic system as causative factors in the development and course of stress-related psychiatric disorders such as major depression. To delineate the role of the corticotropin-releasing hormone receptor type 1 (CRH-R1) in the interactions between corticotropin-releasing hormone and serotonergic neurotransmission, in vivo microdialysis was performed in CRH-R1-deficient mice under basal (home cage) and stress (forced swimming) conditions. Hippocampal dialysates were used to measure extracellular levels of serotonin and its metabolite 5-hydroxyindoleacetic acid, and free corticosterone levels to monitor the status of the hypothalamic-pituitary-adrenocortical axis. Moreover, behavioural activity was assessed by visual observation and a scoring paradigm. Both wild-type and heterozygous mutant mice showed a clear diurnal rhythm in free corticosterone. Free corticosterone concentrations were, however, lower in heterozygous mutant mice than in wild-type animals and undetectable in homozygous CRH-R1-deficient mice. Homozygous CRH-R1-deficient mice showed enhanced hippocampal levels of 5-hydroxyindoleacetic acid but not of serotonin during the light and the dark phase of the diurnal cycle, which may point to an enhanced synthesis of serotonin in the raphe-hippocampal system. Moreover, the mutation resulted in higher behavioural activity in the home cage during the light but not during the dark period. Forced swimming caused a rise in hippocampal serotonin followed by a further increase after the end of the stress paradigm in all genotypes. Homozygous and heterozygous mutant mice showed, however, a significantly amplified serotonin response to the forced swimming as compared to wild-type control animals. We conclude that CRH-R1-deficiency results in reduced hypothalamic-pituitary-adrenocortical axis activity, in enhanced synthesis of serotonin during basal conditions, and in an augmented response in extracellular levels of serotonin to stress. These data provide further evidence for the intricate relationship between corticotropin-releasing hormone and serotonin and the important role of the CRH-R1 herein.