Plasma catecholamine and cardiovascular responses following hypothalamic stimulation in the awake cat

Ninety-three hypothalamic sites were electrically stimulated, using constant parameters, in awake, restrained cats to determine those regions which maximally activated the sympatho-adrenal (SA) and cardiovascular (CV) systems. Plasma catecholamine levels were measured over time following hypothalamic stimulation; levels of norepinephrine (NE) and epinephrine (E) served as indices of adrenergic neural and adrenal medullary activities, respectively. CV parameters of heart rate (HR) and mean intra-arterial blood pressure (MAP) were continuously monitored. The greatest elevation in plasma catecholamines was elicited by stimulation of sites in the perifornical area, ventromedial nucleus, and medial forebrain bundle. Several sites were identified which preferentially elevated one of the sympatho-adrenal neurotransmitters. A differential increase in plasma E was most frequently obtained from sites around the border of the ventromedial nucleus and in the medial forebrain bundle. Differential elevation of plasma NE was observed following stimulation of sites in the anterior commissure, central preoptic area, and dorsal perifornical region posterior to the ventromedial nucleus. Sites which activated the CV and SA systems were not always coincident; those sites which activated the CV system alone tended to be located in the lateral hypothalamus.