A model of sustained activation of the symphatetic nervous system (SNS) using anterior hypothalamic cooling in the baboon

Abstract

A model has been developed to simulate central activation of the sympathetic nervous system (SNS) in unanesthetized baboons. By continuously cooling the preoptic anterior hypothalamus with an implanted thermode, a chronic heat production response is generated. In the primate, SNS activation is a major feature of the response to cold stress. During central cooling, oxygen consumption and catecholamine excretion doubled. These responses have been sustained for 30 days. Metabolic and endocrine changes accompanying chronic SNS activation include (1) an early period of basal hyperinsulinemia followed by restoration of normal insulin sensitivity, (2) an unexpected maintenance of normal (or even increased) responsiveness to isoproterenol (heart rate, insulin secretion and lipolysis, (3) increased glucagon levels throughout, (4) a persistent and progressive fall in T3 without change in T4 which was not explained by decreased food intake since this did not diminish, and weight was maintained. The model may prove useful in characterizing the adaptations and maladaptations which accompany sustained increases in central SNS activity in primates.