Midbrain central gray: Influence on medullary sympathoexcitatory neurons and the baroreflex in rats

Abstract

The influence of the central gray (CG) of the midbrain on the activity of 19 barosensitive sympathoexcitatory neurons of the rostral ventrolateral medulla (RVLM) and on the sympathetic vasomotor baroreflex was studied in halothane-anesthetized rats. Eighteen RVLM barosensitive units were readily activated by train stimulation of the CG, although twin-pulse stimulation was less effective (10 of 19 neurons responded). Inhibition of neurons within the RVLM by bilateral microinjection of the GABA-mimetic drug muscimol abolished the pressor responses to CG stimulation, while the accompanying lumbar nerve sympathoexcitation was converted to sympathoinhibition. In baroreceptor- denervated vagotomiz..