THE CAUDAL VENTROLATERAL MEDULLA IS A SOURCE OF TONIC SYMPATHOINHIBITION

The caudal ventrolateral medulla (CVLM) contains neurons that are essential for the elaboration of the sympathoinhibitory effects of baroreceptor afferent stimulation. To determine if neurons in the CVLM also mediate a tonic inhibition of sympathetic nerve activity (SNA), we examined the effects of lesioning CVLM neurons in baroreceptor-denervated rats. The sustained increases in both arterial pressure (AP; 40 mmHg) and splanchnic SNA (200%) indicate that the discharge of neurons in the CVLM maintains a tonic sympathoinhibition that contributes significantly to the maintenance of normotensive levels of SNA and AP.