Neurons within the rostro ventromedial medulla control cutaneous vasomotion.

Recent research proposes that putative sympathetic premotor neurons controlling cutaneous vasomotion are located within the rostral ventromedial medulla (RVMM), an area delimited rostrally by the nucleus of the facial nerve (RVMM(fn)) and caudally by the rostral pole of the inferior olive (RVMM(io)). Data from several experiments have shown that cutaneous blood flow is increased by the inhibition and reduced by the activation of neurons within the RVMM(fn), but no data are available on the role of the RVMM(io) on cutaneous vasomotion. To clarify the role of RVMM(fn) and RVMM(io) neurons in controlling cutaneous vasomotion, microinjection of the GABAA agonist muscimol and GABAA antagonist bicuculline methiodide were performed within the RVMM(fn) or the RVMM(io). A massive peripheral vasodilatation was evoked by muscimol injection within both the two areas, while disinhibition of either RVMM(fn) or RVMM(io) neurons produced, respectively, a reversal of the increase in cutaneous blood flow induced by warm exposure and an unexpected rapid cutaneous vasodilatation. The results show that two intermingled sets of neurons are located within the RVMM: a vasoconstrictory and thermoregulatory set, which is tonically active, is located in both the RVMM(io) and the RVMM(fn), while a vasodilatatory and non-thermoregulatory set, which is tonically inhibited, is located in the RVMM(io).