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

Ischemic stimulation of cardiac receptors reflexly excites the cardiovascular system. However, the supraspinal mechanisms involved in this reflex are not well defined. This study examined the responses of barosensitive neurons in the rostral ventrolateral medulla (RVLM) to stimulation of cardiac receptors and the afferent pathways involved in these responses. Single-unit activity of RVLM neurons was recorded in alpha-chloralose-anesthetized rats. Cardiac receptors were stimulated by epicardial application of 10 microg/ml of bradykinin (BK). Barosensitive neurons were silenced by stimulation of baroreceptors. Application of BK increased the mean arterial pressure from 65.2 +/- 1.9 to 89.3 +/- 2.9 mmHg and excited RVLM barosensitive neurons from 6.2 +/- 0.7 to 10.7 +/- 0.9 impulses/s (P < 0.05, n = 40). BK had no effect on 21 nonbarosensitive neurons. Blockade of stellate ganglia abolished the 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 stimulation of cardiac receptors selectively activates RVLM barosensitive neurons through sympathetic afferent pathways. This information suggests that the RVLM barosensitive neurons are likely involved in the sympathetic control of circulation during myocardial ischemia.