REDUCED GLUCOCORTICOID RESPONSE TO CORTICOTROPIN SECRETAGOGUES IN THE AGED SPRAGUE-DAWLEY RAT

Aging, as well as some frequently associated pathological conditions (depression, dementia, Alzheimer's disease, etc.), has been shown to have a profound impact on the normal functioning of the hippocampus-hypothalamo-pituitary-adrenocortical axis system. The hypothalamo-pituitary-adrenocortical axis in the aged rat is characterized by an increase in the basal level of circulating corticosterone, an impaired ability to recover from the adrenocortical stress response, and a reduced sensitivity to the dexamethasone suppression test. All these alterations may arise from a reduced hippocampal negative feedback control of the axis, as suggested by the age-dependent loss of hippocampal adrenocorticoid receptors. Among the hypothalamic corticotropin secretagogues, corticotropin-releasing hormone (CRH) and arginine-vasopressin (AVP) are considered the main physiological mediators of hypothalamic control of ACTH release. Thus, we have investigated the dynamic and the temporal course of the adrenocortical. response to CRH and AVP in the aged rat. Freely moving jugular-catheterized male Sprague-Dawley rats (3- and 24-month-old) were injected with CRH (0.5, 0.05 and 0.01 mu g/kg i.v.), or AVP (1.0, 0.1 and 0.05 mu g/kg i.v.), or CRH and AVP in combination. In addition, adrenocortical sensitivity to corticotropin has been studied by injecting ACTH (10 ng/kg i.v.). Our study has (1) indicated that the response td ACTH secretagogues is dampened with aging, and (2) shown in the aged rat a slower recovery. Moreover, the results had confirmed the age-dependent increase in the basal level of corticosterone in the rat, and shown no age-related differences in the glucocorticoid response to ACTH

Neurotoxicity of Kainate to the hippocampus is not accrued by aging, stress and exogenous corticosterone in wistar kyoto and spontaneously hypertensive rats.

It has been reported that a high corticosterone milieu can exacerbate various experimental insults to the nervous system, in particular to the hippocampus. However, in many of these studies the above milieu was attained by injecting corticosterone in doses (e.g. 10 mg/rat) producing supraphysiological concentrations. In the present study we have investigated whether high plasma corticosterone levels, such as those associated with aging or stress, potentiate a hippocampal excitotoxic insult. Male Wistar Kyoto (WKY) and Spontaneously Hypertensive Rats (SHR) at the age of 6, 12, 18 and 24 months (only WKY for the oldest age) were used. As in other strains, aging in these rats was marked by an increase in basal plasma corticosterone levels. Rats were infused in the dorsal hippocampus with kainic acid (0.035 µg/hippocampus) and the neuronal injury was evaluated within the areas CA3 and CA4. Results indicated that neither aging nor the hypertensive condition affected kainic acid neurotoxicity. In order to study the effect of stress, rats were stressed twice a day, with alternate types of stressors to avoid possible habituation, 3 days prior to and 3 days following the kainic acid infusion. Using this experimental paradigm the hippocampal damage in stressed rats was of the same degree as in non-stressed controls. In a complementary set of experiments, 6 month old WKY and SHR rats were injected with corticosterone (10 mg/rat s.c.). Four hours after administration plasma corticosterone levels in the range of 60-70 µg/100 ml were found. Moreover, a time-course study showed a plasma corticosterone peak in the range of 240 µg/100 ml. Daily corticosterone administration for 3 days before and 3 days after kainic acid infusion potentiated the hippocampal damage in 6 months old SHR but not in the WKY. These results demonstrate that elevation of corticosterone levels within physiological range does not exacerbate hippocampal kainate neurotoxicity and that pharmacological doses of glucocorticoid hormone, which produces plasma levels well above those observable in any physiopathological condition, might, with some strain dependency, potentiate a hippocampal neurotoxic insult

Effect of increased maternal corticosterone during lactation on hippocampal corticosteroid receptors, stress response and learning in offspring in the early stages of life

The influence of maternal corticosterone during lactation on the development of the hippocampal corticosteroid receptor system, hypothalamus-pituitary-adrenal axis activity and spatial learning/retention performance was investigated in the rat during postnatal days 11 to 30. We increased the plasma levels of corticosterone by adding the hormone (200 μg/ml) to the drinking water of the dams. When compared to controls corticosterone-nursed offspring displayed: i) higher number of hippocampal type I and type II corticosteroid receptors at 30 days of life, but no changes at 11 and 16 days; ii) higher plasma levels of corticosterone in the basal condition and after 15 min of maternal separation at 11 but not at 16 days; iii) lower adrenal weights at 11 and 16 days, but which were no longer present at the age of 30 days; iv) no difference in performance in the place learning version of the Morris water task and T aquatic maze at 16 days. The present results, together with our previous findings showing that 90-day-old corticosterone-nursed rats have lower basal and restraint stress corticosterone levels and improved learning performance, indicate that the effects of maternal treatment appears only after weaning, thereby suggesting that increased corticosteroid receptors may be responsible, at least partially, for the endocrine and learning modifications induced by pre-weaning corticosterone exposure. The role played by maternal circulating corticosterone during the period of lactation in shaping the characteristics of the hypothalamus-pituitary-adrenal axis and brain of the offspring is outlined

Opposite strain-dependent effects of post-training corticosterone in a passive avoidance task in mice: role of dopamine

Post-training administration of corticosterone (0.1–1 mg/kg) dose-dependently improves retention of an inhibitory avoidance response in C57BL/6 mice, whilst impairing it in the DBA/2 strain. The effects on retention performance induced by the hormone in C57BL/6 and DBA/2 mice appear to be due to an effect on memory consolidation. In fact, they were observed when the drug was given at short, but not long, periods of time after training, ie, when the memory trace is susceptible to modulation. In the absence of pharmacological ..

MATERNAL PLASMA AND MILK FREE CORTISOL DURING THE 1ST 3 DAYS OF BREAST-FEEDING FOLLOWING SPONTANEOUS DELIVERY OR ELECTIVE CESAREAN-SECTION

In a view of the increased clinical interest in the presence of hormones in human milk, the objective of this study was to evaluate maternal plasma and milk cortisol levels in early puerperium and their relationship in breast-feeding in women who underwent elective cesarean section or who delivered vaginally. During the first 3 days of breast-feeding, plasma and milk cortisol levels declined significantly both in women who underwent elective cesarean section and in women who had spontaneous deliveries. Moreover, the breast-feeding procedure did not affect maternal plasma and milk hormonal levels, since no differences between the cortisol levels measured immediately before and after morning daily breast-feeding were detected. Furthermore, a very high positive correlation (p < 0.001) was found between plasma and milk cortisol concentrations. Therefore, maternal plasma cortisol levels can be considered a very reliable measure to predict the hormonal concentration in breast milk