HYPOTHALAMIC HISTAMINE-RELEASE, NEUROENDOCRINE AND CARDIOVASCULAR-RESPONSES DURING TUBEROMAMMILLARY NUCLEUS STIMULATION IN THE CONSCIOUS RAT

Neuronal histamine (HA) in the central nervous system (CNS) has been i mplicated in control of peripheral cardiovascular and neuroendocrine r esponses. The tuberomammillary nucleus (TMN) of the posterior hypothal amus contains all CNS HA cell bodies. In these experiments, the TMN wa s electrically stimulated in conscious rats and HA release in the regi on of the supraoptic nucleus (SON) was estimated using in vivo microdi alysis. In addition, mean arterial blood pressure (MAP), heart rate (H R), and plasma concentrations of norepinephrine (NE) and vasopressin ( VP) were measured before, during and following TMN stimulation. Stimul ation of the TMN resulted in a significant increase in extracellular H A (110 +/- 29% control) in the region of the SON. MAP, HR and plasma N E concentration were also significantly elevated during TMN stimulatio n. However, plasma VP concentrations were unchanged. These results sho w that TMN stimulation in conscious animals releases HA in the region of the SON and is associated with a pressor response, tachycardia, and increased plasma concentration of NE, but not release of VP.