[Role of sympatho-activating structures of the ventrolateral surface of the medulla oblongata in vasomotor regulation]

Abstract

In anesthetized cats, the cold block or coagulation of intermediate zones of the bulbar ventro-lateral surface (BVLS) resulted in profound decrease of the blood pressure (BP) level. The descending tonic activation of spinal vasomotor mechanism in formed by spontaneous discharges of antidromically identified output sympatho-activating neurons with mean firing rate about 14.4/sec. After coagulation of the intermediate zone, pressure reflexes of the BP and late somato-sympathetic response in white rami disappear whereas the spino--bulbo--spinal somato--somatic reflex remains unchanged. The reflex discharges of single sympatho--activating neurons were within the time limits of the late somato--sympathetic response and followed by the silent period. The preferable inhibition of the long-latency white rami discharges elicited by BVLS stimulation arise 200-250 msec after R-wave of the ECG. The inhibition of long-latency discharges was observed during the increase of the BP level induced with vasoconstrictor drugs. The intermediate zone structures of BVLS seem to play the key role in supporting of the BP level and organization of pressure reflexes. These structures are suggested to be the actual elements of the bulbar vasomotor center.