Anterior hypothalamic neurons respond to blood pressure changes via gamma-aminobutyric acid and angiotensins in rats.

It has been suggested that neurons in the hypothalamus respond to baroreflex activation and deactivation. In this study, we examined whether angiotensin II-sensitive neurons in the anterior hypothalamic area (AHA) respond to baroreflex activation and deactivation, and which neurotransmitters are involved in mediating the baroreflex responses. Male Wistar rats were anesthetized and artificially ventilated. Extracellular potentials were recorded from single neurons in the AHA. Increases in blood pressure induced by intravenous phenylephrine completely inhibited the firing of AHA angiotensin II-sensitive neurons. The phenylephrine-induced inhibition of neuronal firing was blocked and enhanced by the pressure application of bicuculline and nipecotic acid, respectively, onto the same neurons. In contrast, decreases in blood pressure induced by intravenous nitroprusside increased the firing of angiotensin II-sensitive neurons. The nitroprusside-induced increase of neuronal firing was blocked by the pressure application of losartan onto the same neurons. These findings suggest that angiotensin II-sensitive neurons in the AHA respond to blood pressure changes via gamma-aminobutyric acid and angiotensins in rats.