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      Differential Stress Reactivity in Intact and Ovariectomized Prepubertal and Adult Female Rats

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          Abstract

          The pubertal development of the hypothalamic-pituitary-adrenal (HPA) axis has received relatively little experimental attention. As puberty is marked by an increase in the susceptibility to various psychiatric disorders that may be related to HPA dysfunction, it is imperative to elucidate the pubertal development of this neuroendocrine axis. To date, the limited research in this area has been conducted primarily on males. Presently, we investigated stress responsiveness, as measured by both stress hormones (e.g., corticotropin (ACTH) and corticosterone) and gonadal steroids, in intact and ovariectomized prepubertal and adult female rats before and after a 30-min session of restraint stress. We report here that intact prepubertal females exhibit an extended corticosterone stress response (30–45 min longer) compared to intact adults. Moreover, ovariectomized prepubertal females continue to exhibit a prolonged stress-induced corticosterone and progesterone response compared to ovariectomized adults, indicating these protracted responses prior to puberty are independent of ovarian hormones. ACTH levels were not significantly different between intact and ovariectomized prepubertal and adult animals at all the post-stress time points measured, suggesting that the prolonged corticosterone response in prepubertal females is due to an enhanced sensitivity to ACTH at the level of the adrenal cortex. Taken together, these data indicate that stress reactivity changes dramatically during puberty in females. Furthermore, these data demonstrate additional development of the HPA axis during pubertal maturation, resulting in a more quickly terminated stress response in adulthood.

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          Most cited references 24

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          Functional cross-talk between the hypothalamic-pituitary-gonadal and -adrenal axes.

           V Viau (2002)
          Under normal conditions, the adrenal glucocorticoids, the endproduct of the hypothalamic-pituitary-adrenal (HPA) axis, provide a frontline of defence against threats to homeostasis (i.e. stress). On the other hand, chronic HPA drive and glucocorticoid hypersecretion have been implicated in the pathogenesis of several forms of systemic, neurodegenerative and affective disorders. The HPA axis is subject to gonadal influence, indicated by sex differences in basal and stress HPA function and neuropathologies associated with HPA dysfunction. Functional cross-talk between the gonadal and adrenal axes is due in large part to the interactive effects of sex steroids and glucocorticoids, explaining perhaps why several disease states linked to stress are sex-dependent. Realizing the interactive nature by which the hypothalamic-pituitary-gonadal and HPA systems operate, however, has made it difficult to model how these hormones act in the brain. Manipulation of one endocrine system is not without effects on the other. Simultaneous manipulation and assessment of both endocrine systems can overcome this problem. This dual approach in the male rat reveals that testosterone can act and interact on different aspects of basal and stress HPA function. Basal adrenocorticotropic hormone (ACTH) release is regulated by testosterone-dependent effects on arginine vasopressin synthesis, and corticosterone-dependent effects on corticotropin-releasing hormone (CRH) synthesis in the paraventricular nucleus (PVN) of the hypothalamus. In contrast, testosterone and corticosterone interact on stress-induced ACTH release and drive to the PVN motor neurones. Candidate structures mediating this interaction include several testosterone-sensitive afferents to the HPA axis, including the medial preoptic area, central and medial amygdala and bed nuclei of the stria terminalis. All of these relay homeostatic information and integrate reproductive and social behaviour. Because these modalities are affected by stress in humans, a dual systems approach holds great promise in establishing further links between the neuroendocrinology of stress and the central bases of sex-dependent disorders, including psychiatric, cardiovascular and metabolic disease.
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            Variations in the hypothalamic-pituitary-adrenal response to stress during the estrous cycle in the rat.

             V Viau,  M. Meaney (1991)
            To investigate the role of gonadal steroids in the hypothalamic-pituitary-adrenal (HPA) response to stress, we studied adrenocorticotrophin (ACTH) and corticosterone (B) responses to 20-min restraint stress in cycling female rats, and in ovariectomized (OVX) rats replaced with physiological levels of estradiol (E2) and progesterone (P). In cycling rats, we found significantly higher peak ACTH (P less than 0.01) and B (P less than 0.05) responses to stress during proestrus compared to the estrous and diestrous phases. No differences were found in either basal ACTH and B levels across the cycle phases. In a separate study, OVX rats were maintained on low, physiological levels of E2 and P with silastic implants for 3 days, and injected either with oil (O'), 10 micrograms of E2 (E') 24 h before stress testing, or with E2 and 500 micrograms P 24 and 4 h, respectively, prior to stress (EP'). These treatments mimicked endogenous profiles of E2 and P occurring during diestrous, proestrous, and late proestrous-early estrous phases, respectively. In response to stress, ACTH levels were higher (P less than 0.01) in the E' group compared to the EP' and O' groups. Although the peak B response was similar in all groups, the E' and EP' groups secreted more B after the termination of stress than did the O' group. Within the 20 min stress period, ACTH levels in the E' group were significantly (P less than 0.05) higher at 5, 10, and 15 min after the onset of stress, compared to the EP' and O' groups. Plasma B levels were significantly higher in the E' group at 5 and 10 min (P less than 0.05 and P less than 0.01, respectively) compared to the EP' and O' group. beta-endorphin-like immunoreactive responses to restraint stress were also significantly higher in the E' group compared to the EP' (P less than 0.05) and O' (P less than 0.01) groups. In contrast to the effect seen at 24 h, ACTH responses to stress 48 h after E2 injection in the E' group were comparable to O' animals. There was no effect of E2 on ACTH clearance, whereas B clearance was enhanced in E' treated animals vs. O'-treated animals. These results indicate that the HPA axis in the female rat is most sensitive to stress during proestrous. Such enhanced HPA responses to stress are limited to the early portion of proestrous, as progesterone appears to inhibit the facilitatory effects of estrogen on ACTH release during stress. Taken together, these results suggest an ovarian influence on both activational and inhibitory components of HPA activity.
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              Testosterone Cannot Activate an Adult-Like Stress Response in Prepubertal Male Rats

              The pubertal maturation of the hypothalamic-pituitary-adrenal (HPA) axis has received relatively little experimental attention. The present set of experiments sought to extend our understanding of the pubertal stress response by measuring corticotropin (ACTH), corticosterone, and testosterone levels in prepubertal and adult male rats exposed to a single 30-min session of restraint stress. We show that ACTH and corticosterone levels in prepubertal males take significantly longer to return to baseline after termination of the stressor compared to adults. These data indicate that prepubertal males demonstrate a more prolonged stress response compared to adults after a single acute stressor with both psychogenic and neurogenic components. As testosterone has been shown to reduce the stress response in adulthood, we next investigated whether the relatively low levels of circulating testosterone in prepubertal males mediated their protracted stress response. Data collected from additional experiments revealed that prepubertal males treated with adult-like physiological levels of testosterone still exhibited an extended stress response compared to similarly treated adults. These results indicate that the stress response demonstrated by adult males cannot be mimicked or activated in prepubertal males by mere supplementation of testosterone. Thus, we conclude that the HPA neuroendocrine axis is further shaped during pubertal development to allow for the emergence of a more tightly regulated stress response in adulthood.
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                Author and article information

                Journal
                NEN
                Neuroendocrinology
                10.1159/issn.0028-3835
                Neuroendocrinology
                S. Karger AG
                0028-3835
                1423-0194
                2004
                May 2005
                25 May 2005
                : 80
                : 6
                : 387-393
                Affiliations
                Laboratory of Neuroendocrinology, Rockefeller University, New York, N.Y., USA
                Article
                84203 Neuroendocrinology 2004;80:387–393
                10.1159/000084203
                15741744
                © 2004 S. Karger AG, Basel

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                Page count
                Figures: 4, Tables: 2, References: 29, Pages: 7
                Categories
                Original Paper

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