Cuneiform nucleus stimulation produces activation of medullary sympathoexcitatory neurons in rats

Activation of the cuneiform nucleus (CNF) of the midbrain produces elevation of arterial blood pressure. This study examined the influence of the CNF on arterial blood pressure, sympathetic vasomotor outflow, and the discharges of barosensitive sympathoexcitatory neurons of the rostral ventrolateral medulla (RVLM) in halothane-anesthetized, paralyzed rats. Electrical stimulation (50 Hz, 25-75 microA, 10 s) of the CNF elicited intensity-dependent elevations in arterial blood pressure associated with excitation of the sympathetic vasomotor discharge (elevated discharge of the lumbar sympathetic nerve). Intermittent paired-pulse electrical stimulation of the CNF elicited an excitatory response in the discharge of the lumbar sympathetic outflow that consisted of an early peak (onset latency 84 +/- 4 ms) and a smaller late peak (onset latency 217 +/- 6 ms). Seventeen of 22 RVLM sympathoexcitatory neurons tested were excited by stimulation of the CNF. Twelve of 14 units tested projected to the thoracic spinal cord, and of these, 10 units were excited by CNF stimulation with an onset latency of 16 +/- 1 ms. These findings support the hypothesis that the sympathoexcitatory and pressor responses elicited by activation of the CNF are mediated by RVLM sympathoexcitatory neurons.