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

Elizabeth A. Moon, Ann K. Goodchild, Paul M. Pilowsky
Brain Res. 2002 Mar 8;929(2):181-90.

It is well known that presymapthetic neurons in the RVLM is important in tonic and reflex control of blood pressure in the arteries and sympathetic nerve activity. In this article the authors were interested in identifying how the sympathoexcitatory neurons form connections with sympathetic preganglionic neurons (SPN). They tested this by three different approaches. 1) Retrograde tracers were used to label the SPN that project to the adrenal gland or the superior cervical ganglion (SCG). Antrograde tracers were used from the pressor sites in the RVLM in order to identify whether lateral projections from the bulbospinal neurons project to the SPN that innervates the SCG and adrenal gland. 2) To identify the degree of lateralization retrograde tracers were injected unilaterally in to the spinal cord. 3) Finally they used a electrophysiological approach to stimulate RVLM with glutamate and recorded the activity from adrenal and cervical sympathetic nerves in order to examine the functional aspect of lateralization.
The significant findings of the present study are anterograde and retrograde experiments showed that the presympathetic neurons from the RVLM that form connections with SPN that innervate the SCG are bilateral. Interestingly projections to the adernal gland are ipsilateral. The second study showed that projections from RVLM to both the upper and lower level of the thoracic spinal cord (intermediolateral cell column) are predominantly ipsilateral. Inspite of this differential anatomical lateralization, the final study with glutamate microinjection showed no difference in nerve response even when different sides of the RVLM were injected.

- Madhan