Lateralisation of projections from the rostral ventrolateral medulla to sympathetic preganglionic neurons in the rat

Lateralisation of projections from the rostral ventrolateral medulla to sympathetic preganglionic neurons in the rat Elizabeth A. Moon, Ann K. Goodchild, Paul M. Pilowsky Hypertension and Stroke Research Laboratories, Departments of Physiology and Neurosurgery, University of Sydney, Block 3 Ground Floor, Royal North Shore Hospital, St. Leonards, 2065 Sydney, NSW, Australia This study contains three different techniques: anterograde tract-tracing (using Phaseolus vulgaris leucoagglutinin, PHA-L), retrograde tract-tracing(using CTB) and electrophysiology. Spinally projecting neurons (SPNs) that project to the adrenal gland or to the superior cervical ganglia were labelled retrogradely. The retrograde labeling was paired with anterograde tract-tracing from the RVLM to see if lateralization in the bulbospinal projection to SPN innervating the adrenal gland or superior cervical ganglia could be identified. Unilateral injections of the spinal cord were made with a retrograde tracer in order to determine the amount of lateralization between the upper and lower thoracic spinal cord. The last experiment they did was stimulate the RVLM with glutamate and record from the left cervical sympathetic and left adrenal nerve to test for functional lateralization. They found that the SPNs controlling the SCG were primarily bilateral, meaning that both the ipsilateral and contralateral sides were nearly equally labelled following anterograde labeling. The SPNs controlling the adrenal medulla were almost exclusively labelled on the ipsilateral side, suggesting ipsilateral control. Next in the retrograde tracing studies, they showed that CTB injected unilaterally at T2 and T8 both showed about 66%-75% ipsilateral projections to 25%-33% contralateral projections. The electrophysiological studies showed that following glutamatergic stimulation of RVLM, there are no differences in the ratio of responses to either the cervical sympathetic truck or adrenal nerve, suggesting that while there are differences in anatomical connections, the functional contribution of each RVLM to the respective nerve activity may very well be the same under the given conditions. This paper will provide helpful anatomical knowledge for my presentation where I will present my differential control data. My results corroborate with their anatomy data for the adrenal nerve, demonstrating that under normotensive conditions, that the adrenal nerve responds the primarily ipsilateral to a given injection of glutamate. It would be interesting to do a similar tract tracing study to see if the nature of the ipsilateral/contralateral connections might be altered following physical (in)-activity. -MTL