Modification of the baroreceptor reflex by superfusion of the canine posterior hypothalamus with tetrodotoxin.

The role of the posterior hypothalamus in the baroreceptor reflex was investigated in dogs. The posterior hypothalamus was superfused bilaterally through push-pull cannulae with artificial cerebrospinal fluid. After bilateral superfusion with tetrodotoxin (10(-5) M) for 120 min, the increases in mean arterial pressure and heart rate induced by the electrical stimulation of the posterior hypothalamus were almost abolished, and the resting mean arterial pressure was significantly decreased. Under these circumstances the increases in mean arterial pressure and heart rate in response to bilateral carotid occlusion were significantly reduced. The decrease in mean arterial pressure induced by intravenous injection of sodium nitroprusside (5 micrograms/kg) was significantly augmented while the associated increase in heart rate was suppressed. These results suggest that the posterior hypothalamus plays an important role in maintaining the resting arterial pressure and in the baroreceptor reflex to increase the arterial pressure and heart rate.