The role of hypothalamic catecholamines in stress hormone release in rats exposed to acute cold

Abstract

The parvocellular neurons of the hypothalamic paraventricular nucleus (PVN) are under the catecholaminergic influence of the medial preoptic area (MPOA) which is supposed to be the thermoregulation centre. About 50% of PVN parvocellular neurons coexpress vasopressin (VP) and corticotrophin-releasing hormone (CRH), which have synergistic action on adrenocorticotropic hormone (ACTH) secretion. Consequent rise in blood corticosterone (CORT) levels is the key for successful coping with that threat. The aim of this study was to reveal the correlation among aforementioned hormones and neurotransmitters after exposure to cold for different periods of time. The Rattus norvegicus (Wistar strain), were exposed to cold (+4°C) for a 30 or 60 min. The circulating hormones were determined by an ELISA test (CORT, VP), chemiluminescence’s method (ACTH) or radioenzymatic assay (catecholamines). The pituitary morphology was examined by fluorescent immunohistochemistry. The results obtained show the decrease in hypothalamic catecholamine levels after exposure to cold regardless of the exposure duration, unlike the ACTH levels which were increased, being higher after 30 min of exposure than after 60 min. The blood CORT concentrations followed the ACTH changes. The blood VP levels were statistically unchanged in comparison to control, regardless of the exposure duration. Those results suggest that catecholamines are not the only neurotransmitters involved in regulation of HPA activity, since their pattern of changes is different from those of ACTH.