GABA(A) receptor activation at medullary sympathetic neurons contributes to postexercise hypotension.

Am J Physiol Heart Circ Physiol. 2002 May;282(5):H1615-24.

Kajekar R, Chen CY, Mutoh T, Bonham AC.

Department of Internal Medicine, University of California at Davis, Davis, California 95616, USA.

A single bout of mild or moderate exercise in a hypertensive individual leads to post exercise hypotension (PEH). Two important features of PEH are a reduction in sympathetic nerve activity (SNA) and an intact baroreflex system. In this study the authors investigated the possible mechanisms underlying PEH. The experiments were performed in male spontaneously hypertensive rats (SHR) seperated in two groups, PEH group were subjected to single bout of exercise on a motor driven treadmill at 15m/min, 10 degree for 40 min or to a sham exercise group (sham-PEH) placed in treadmill with no exercise for 40 min. This study provides some interesting findings, during PEH the spontaneous firing activity of the cardiovascular sympathetic neurons in the RVLM are significantly decreased along with a reduced lumbar SNA. The reduced neuronal activity were mediated at least in part by a GABAa receptor mechanism, which was tested by injection of muscimol and bicuculine on RVLM. Muscimol and bicuculine produced a current-related decrease and increase in unit activity respectively supporting the above findings. Finally they also found that during PEH the baroreceptor control of RVLM activity is reduced. These findings suggest the possibility that increased signaling of GABA at RVLM neurons may contribute to PEH by decreasing sympathetic outflow.

- Madhan

http://ajpheart.physiology.org/content/282/5/H1615.full.pdf+html