[Effect of acetylcholine on the discharge of presympathetic neurons of the rostral ventrolateral medulla of rats].

Effect of acetylcholine (ACh) on presympathetic neurons of the rostral ventrolateral medulla (RVLM) was studied by extracellular recording technique and microiontophoresis in urethane-anaesthetized rats. Spontaneous discharges of 35 presympathetic neurons of RVLM were recorded. All the neurons showed increased discharge by microiontophoresis of ACh dose- dependently with the increase of iontophoretic current. In 22 units microiontophoresis of atropine decreased the baseline discharge rate and completely blocked the excitatory effect of ACh on these neurons, while in the remaining 7 and 6 neurons microiontophoresis of d-tubocurarine (d-TC) and hexamethonium (C(6)) respectively had no effect and did not block the action of ACh. The above finding suggests that presympathetic neurons of RVLM receive a tonic excitatory cholinergic input mediated by M receptors.