Selective enhancement of glutamate-mediated pressor responses after GABAA receptor blockade in the RVLM of sedentary versus spontaneous wheel running rats

Patrick J. Mueller* and Nicholas A. Mischel Department of Physiology, Wayne State University School of Medicine, Detroit, MI, USA I needed an excuse to read this paper again……. In this study we looked at the response of WRs and SEDs to exogenous glutamate following the removal of GABAergic tone via bicuculline. This paper is an attempt to build on Nick’s 2011 paper which looked at sympathoexcitation following a dose of exogenous glutamate and looked at the blood pressure and splanchnic sympathetic nervous activity response. This paper is examining lumbar sympathetic nervous activity and blood pressure response to different doses of glutamate, with the inclusion of pre-bic and post-bic protocols. Interestingly enough he was not able to duplicate the same dose response curve of the 2011 paper for lumbar nerve activity, suggesting that SEDS/WRs do not have different sympathoexcitatory responses to solely exogenous glutamate in regards to lumbar nerve. They were able to show sympathoexcitatory differences in the post-bic protocols 5’ and 15’ minutes after the injection of bic, suggesting that GABAergic transmission is hiding the sympathoexcitatory differences between WRs and SEDs in regards to lumbar and blood pressure. It is important to consider that bicuculline was injected unilaterally so there could have been some kind of compensation from the contralateral RVLM. I would like to see what the glutamate responses would be if the RVLMs were blocked bilaterally, that being said, the blood pressure might raise too high (190 mmHg) with a bilateral injection of bic. It would also be interesting to see if there were any differences in glutamate responses with the ipsilateral RVLM completely disinhibited with bic and the contralateral RVLM excitated with glutamate. Venturing to what I have been looking at with my endogenous input experiments, it would be important to see if there were differences in the nerve activity responses to bicuculline in regards to the lumbar nerve, or these nerves (splanchnic and lumbar) might be differentially inhibited by GABA. -M.T.L.