Somatic nerve stimulation evokes qualitatively different somatosympathetic responses in the cervical and splanchnic sympathetic nerves in the rat

Full cite: S. McMullan, et al. Somatic nerve stimulation evokes qualitatively different somatosympathetic responses in the cervical and splanchnic sympathetic nerves in the rat. Brain Res., 1217 (2008), pp. 139–147 Simon McMullan, Karrnan Pathmanandavel, Paul M. Pilowsky, Ann K. Goodchild Australian School of Advanced Medicine, Macquarie University, Australia University of Sydney This study is examining the reflex responses of two different sympathetic nerves in response to somatic pressor response– from the sciatic nerve. The two sympathetic nerves that they are looking at is the splanchnic and cervical nerve. The primary technique used is this study is electrophysiology. They stimulated from the aortic depressor nerve, using antidromic action potentials to confirm that the neurons that they were recording from in RVLM were barosensitive. They found that the splanchnic nerve had a primarily biphasic response to sciatic nerve stimulation, whereas the cervical nerve was primarily monophasic. This suggests qualitatively different responses between the sympathetic nerves given the same stimulus, suggesting a difference in the pathways controlling these nerves. It was determined that the first peak in both cervical and splanchnic were mediated throughout the same pathway, however, the second peak of the splanchnic –which was not present in the cervical– was due to an additional response in the splanchnic to the stimulus. This additional response to the splanchnic might be likely due to some input from unmyelinated afferents, that are selectively absent in the cervical control. The splanchnic receives both A- and C- fibers, whereas the cervical only receives A- fibers, suggesting a non-uniform organizational scheme when it comes to the control of RVLM. This paper provides a little bit of additional evidence into the complexity of RVLM’s control of the sympathetic nervous system, and that each sympathetic nerve has different properties to its control and function. There are likely different neurons controlling the different nerve activities, but also different afferents projecting to these nerves. My presentation and the study paired with it is another piece of evidence to RVLM’s sympathetic control, showing that adrenal and splanchnic control are mediated differentially by GABA following baroreflex unloading. -MTL