Differentiation of two cardiovascular regions within caudal ventrolateral medulla

SERGIO L. CRAVO, SHAUN F. MORRISON, AND DONALD J. REIS Am. J. Physiol. 261 (Regulatory Integrative Comp. Physiol. 30): R985-R994, 1991 The caudal ventrolateral medulla provides GABAergic input to the rostral ventrolateral medulla. We know that CVLM neurons receive glutamatergic input from the nucleus of the solitary tract (NTS) that leads to inhibition of RVLM and depressor and sympathoinhibition. However, in some studies were they lesioned the CVLM, laboratories prior to this point in time would get different results. Some reported that baroreceptor reflex remained intact another lab reported the complete opposite finding. So this laboratory hypothesized that baroreceptor and non-baroreceptor sensitive neurons in the CVLM were separated from one another. So in order to test this hypothesis they instrumented rats so they could record blood pressure, splanchnic sympathetic nerve activity and also ECG. They first did an aortic depressor nerve (AND) stimulation in order to activate the baroreceptor reflex. This resulted in decreases in bp pans sSNA. Next the blocked the rostral portion of the CVLM using kainic acid and repeated the ADN stimulus. They found that the ADN response was eliminated. However, when the kainic acid was microinjected in the caudal portion of the CVLM the response to ADN stimulation remained. These data suggest that the rostral portion of the CVLM is important phasic inhibition and the caudal for tonic inhibition. -MD