Spontaneous activity and barosensitivity of the barosensitive neurons in the rostral ventrolateral medulla of hypertensive rats induced by transection of aortic depressor nerves.

In order to determine the role of the rostral ventrolateral medulla (RVLM) in the development of neurogenic hypertension, the aortic depressor nerves of rats were transected (tADN) to produce neurogenic hypertension. The rate and pattern of firing of the barosensitive RVLM neurons of the treated rats were studied. In neurogenic hypertensive rats, the RVLM barosensitive neurons exhibited a faster firing rate and a shorter interspike interval (ISI) than the corresponding values of the control and sham groups, indicating an enhanced spontaneous activity of these neurons in the hypertensive rats. The coefficient of variation (cv) and skewness (sk) of the ISI histogram, parameters reflecting the regularity of neuronal firing, were smaller in neurogenic hypertensive than in the control and sham-operated rats. Following tADN, the responsiveness of these neurons to blood pressure changes was attenuated, suggesting a reduced intrinsic barosensitivity of neurons and/or a reduced baroreceptor input. The increase in spontaneous activity and firing regularity of RVLM barosensitive neurons imply an enhancement in the efficacy of outflow from these neurons. The increased efficacy of the outflow from the RVLM barosensitive neurons and the resetting of the baroreflex may contribute to the genesis of neurogenic hypertension.