Sympathoinhibitory pathway from caudal midline medulla to RVLM is independent of baroreceptor reflex pathway

J.R. Potas and R.A.L Dampney

The authors of this paper were interested in whether the caudal midline medulla was causing sympathoinhibitory effects in response to glutamate stimulation by either causing activation of CVLM neurons or direct inhibition of RVLM neurons. In order to iinvestigate this question they injected kynurenate into CVLM and looked at responses to glutamate stimulation of CMM. they found that the sympathoinhition caused by activation of CMM was not inhibited. Next they wanted to see if blockade of GABA receptors in the RVLM would blunt the response. So they blocked the left RVLM so they would not get profound drops in bp and SNA and then they injected bicuculline into the RVLM and looked at responses to CMM stimulation. They found that the response was significantly blunted.

Conclusion: The sympathoinhibitory effects of CMM on the cardiovascular system is not due to activation of CVLM neurons but due to another pathway that ultimately leads to inhibition of RVLM neurons.
-M.D.