Functional anatomy of sympathetic premotor cell groups in the medulla.

Pre- and postganglionic sympathetic neurons are organized into discrete functional channels, according to the target they supply. The activity patterns which they show differ between channels, implying that the CNS pathways driving them are not the same. Premotor neurons probably play a key role. This article focuses on what recent evidence tells us about the organization of premotor neurons which control specific sympathetic outflows. Cells that drive muscle vasoconstrictor (MVC), cutaneous vasoconstrictor (CVC), visceral vasoconstrictor (VVC) and renal sympathetic (RSN) outflows have been identified among the premotor neurons of the rostral ventrolateral medulla (RVLM). Other vasomotor, cardiac or adrenal drives are also represented in that cell group. Neurons driving sudomotor responses have been localized in the rostral ventromedial medulla. Evidence on the specific functions of other premotor cell groups is briefly discussed.