This research project explores the role of catecholaminergic systems in the control of the adaptive physiological and behavioral responses to stress. It has long been known that the sympathoadrenal system in the periphery plays a critical role in maintaining homeostasis during stress. More recent work has suggested that central dopaminergic and noradrenergic neurons have a parallel role in the mediation of the appropriate behavioral responses to stimulation. For the past 12 years, we have been examining the effects of stress on the biosynthesis of catecholamines (CAs), the relation between alterations in CA biosynthesis and CA release, and the functional impact of those released CAs, both in the periphery and in the brain. During the next 5 years, we hope to determine each of the following: (a) Whether the increase in tyrosine hydroxylase (TH) activity that has been observed in the sympathetic nerves and adrenal glands of rats exposed to chronic cold stress or insulin-induced hypoglycemia is associated with an increased capacity for CA release, and if so, whether this enhanced release results in physiologically significant effects on cardiovascular function. (b) Whether acute stress activates TH in the sympathoadrenal system of rats that previously had been exposed to chronic stress, and if so, whether this is associated with an enhanced capacity for CA release. (c) Whether chronic insulin-induced hypoglycemia increases the activity of phenylethanolamine N-methyltransferase (PNMT) in the adrenal medulla of rats, and if so, whether this is associated with an enhanced capacity for epinephrine secretion. (d) Whether chronic stress is associated with an increase in the amount of messenger RNA for TH and PNMT in the adrenal medulla of rats and if so, whether the time course of this effect parallels the observed changes in enzyme activity. (e) Whether activation and induction of TH occurs in central noradrenergic neurons when rats are exposed to cold stress or insulin-induced hypoglycemia, and if so, whether this results in an increase in the capacity for norepinephrine release. (f) Whether hypothalamic lesions affect the changes in sympathoadrenal TH activity that otherwise occur when rats are exposed to cold stress or insulin-induced hypoglycemia.
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