Temporal relationships of barosensory attenuation in conscious rabbits.

Electrical stimulation of anterior or posterior hypothalamus with 10-s trains elicited heart rate and blood pressure decreases. Presentation of anterior hypothalamic stimulation coincident with or 5, 10, or 15 s prior to 5-s train stimulation of aortic nerve (AN) summated with depressor-decelerator responses to AN stimulation. The summating effect was more pronounced for heart rate than for blood pressure. Simultaneous onset of AN and posterior hypothalamic stimulation did not influence AN responses. In contrast, when AN stimulation was delayed until 5, 10, or 15 s after onset of posterior hypothalamic stimulation, small, moderate, and full attenuation of AN responses occurred, respectively. Since AN and posterior hypothalamic stimulation each led to depressor-decelerator responses, attenuation of AN responses cannot be attributed to simple summation of cardiovascular responses elicited by intracranial and aortic nerve stimulation.