Responses of preoptic thermosensitive neurons to changes in blood pressure.

Effects of changes in arterial blood pressure were studied on the neuronal activity of 56 thermosensitive and 122 thermally insensitive neurons of the preoptic and anterior hypothalamus (PO/AH) in the urethane-anesthetized rat. Falls in blood pressure by 15 mmHg or less, which were induced by hemorrhage or by IV injection of vasoactive drug, resulted in the increased activity of warm-sensitive neurons (53.3%) and the decreased activity of cold-sensitive neurons (45.5%). However, the majority (71.3%) of thermally insensitive neurons were not affected by a rise or a fall in blood pressure by as large as 30 mmHg. Bilateral sections of glossopharyngeal, vagus and sympathetic nerves abolished the neuronal responses to blood pressure changes, indicating that the responses are mediated largely by peripheral baro/volume receptors. Increased and decreased activities of warm-sensitive neurons and cold-sensitive neurons during hypotension respectively suggest that at least a part of hypothermia observed during acute hemorrhage is a centrally induced response having a survival value.