Stressful stimuli are known to affect glucocorticoid receptor (GR) mRNA levels in the rat brain. The aim of this study was to examine the duration of chronic stress-induced changes in GR gene expression in the male rat hippocampus and cerebellum. By using in situ hybridization histochemistry, we detected a statistically significant down-regulation of GR mRNA both in the hippocampus and in the cerebellum of rats stressed for 8, 10 and 14 days. The same degree of down-regulation could also be detected in the above brain areas of rats stressed for 14 days and left undisturbed for 48 h or 8 days after stress. To examine the effects of subsequent stressors on the expression of down-regulated GR mRNA in the hippocampus of chronically stressed rats, we determined, by Northern blotting, GR mRNA levels in the hippocampi of rats stressed for 14 days and subsequently exposed to either short- or long-duration stressors. The down-regulated levels of GR mRNA remained practically unaffected when a subsequent new stressor was applied. Our results show that chronic stress-induced down-regulation of GR mRNA in the rat brain can be extended for periods longer than the initial/causative stimulus, irrespective of the presence of a novel stimulus.

The two subtypes of corticosterone receptors in the rat brain play a pivotal role in the modulation of the stress response. Appropriate control of their gene expression is therefore critical for the maintenance of cellular and organism homeostasis. In this study, we investigated the contribution of gender and of the cellular environment of certain brain areas to the expression of both types of corticosteroid receptors, following restraint stress. Adult Wistar rats of both sexes were subjected to acute, chronic or to a combined chronic plus acute stress regimen, and the expression of glucocorticoid and mineralocorticoid receptors was evaluated in their hippocampus, hypothalamus, pituitary and frontal cortex, by using Northern blot analysis. Significant sex differences were observed in the first three brain areas examined as to the stress-induced expression of corticosteroid receptors. Among these, females showed a distinct mechanism of regulating glucocorticoid/mineralocorticoid receptor ratio in the hippocampus upon chronic stress, while the female hypothalamus was more prone than the male to changing corticosteroid receptor expression in response to restraint stress. In another set of experiments, we assessed the influence of ovarian steroids on stress-induced corticosteroid receptor expression in the above brain areas by analyzing ovariectomized rats exposed to short-term restraint. Our results showed that although ovarian steroids affect the stress-induced expression of receptor genes in a region-specific manner, their elimination does not appear to lead to the male pattern of expression. These findings provide further evidence for the existence of both regional and gender specificity in the regulation of brain and pituitary corticosteroid receptors following stress, and support the hypothesis of a distinct male and female neuroendocrine axis in response to stress.

Corticosteroid receptors are key mediators of the neuroendocrine response to stress. Previously, we have determined the effects of restraint stress on the regulation of corticosteroid receptor genes in the brain and pituitary of male and female rats. Significant gender- and regional-specific regulation of receptor mRNAs was observed. To further investigate the stressor specificity in the same context, we have determined glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) mRNAs following exposure to swimming stress paradigms applied alone, or in combination with restraint stress. Our data revealed stressor-specific alterations in GR or MR mRNA levels, which were more pronounced in males, the gender most affected by swimming stress. No alterations in GR or MR mRNA levels were detected in the female hippocampus and hypothalamus upon exposure to swimming paradigms, while in males the same stressors down-regulated GR mRNA in the hippocampus (chronic exposure) and up-regulated both genes in the hypothalamus (acute exposure). In the frontal cortex, acute swimming stress caused a reciprocal change in GR mRNA levels in the two sexes. The above difference is not due to circulating ovarian steroids, since ovariectomy did not change the female pattern of GR gene expression following acute stress. Our results further showed a hypothalamic-pituitary-adrenal axis facilitation to a novel superimposed stressor expressed at the level of limbic corticosteroid receptors: When chronically restrained rats of both sexes were exposed to acute swimming stress, a reduced GR/MR mRNA ratio, implying reduced feedback axis sensitivity, was detected in both the hippocampus and the hypothalamus. In conclusion, our work provides additional evidence on stressor, gender and region specificity in the regulation of brain corticosteroid receptors.

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Our study confirms the prognostic significance of K19 expression in Caucasian patients with HCCs, providing further evidence that it may be used to stratify HCC according to tumour aggressiveness.