Responses of neurons in rostral ventrolateral medulla to activation of cardiac receptors in rats

Ischemic stimulation of cardiac receptors reflexly excites the cardiovascul ar system. However, the supraspinal mechanisms involved in this reflex are not well defined. This study examined the responses of barosensitive neuron s in the rostral ventrolateral medulla (RVLM) to stimulation of cardiac rec eptors and the afferent pathways involved in these responses. Single-unit a ctivity of RVLM neurons was recorded in alpha -chloralose-anesthetized rats . Cardiac receptors were stimulated by epicardial application of 10 mug/ml of bradykinin (BK). Barosensitive neurons were silenced by stimulation of b aroreceptors. Application of BK increased the mean arterial pressure from 6 5.2 +/- 1.9 to 89.3 +/- 2.9 mmHg and excited RVLM barosensitive neurons fro m 6.2 +/- 0.7 to 10.7 +/- 0.9 impulses/s (P < 0.05, n = 40). BK had no effe ct on 21 nonbarosensitive neurons. Blockade of stellate ganglia abolished t he response of barosensitive neurons to BK. Cervical vagotomy significantly increased the baseline discharges of RVLM barosensitive neurons but had no effect on their responses to BK. Thus this study indicates that stimulatio n of cardiac receptors selectively activates RVLM barosensitive neurons thr ough sympathetic afferent pathways. This information suggests that the RVLM barosensitive neurons are likely involved in the sympathetic control of ci rculation during myocardial ischemia.