CHOLINERGIC MECHANISMS RESPONSIBLE FOR BLOOD-PRESSURE REGULATION ON SYMPATHOEXCITATORY NEURONS IN THE ROSTRAL VENTROLATERAL MEDULLA OF THE RAT

We examined whether reticulospinal sympathoexcitatory neurons in the r ostral ventrolateral medulla (RVLM) have muscarinic receptors and ACh inputs, and whether these cholinergic mechanisms on RVLM neurons are i nvolved in the presser response induced by peripheral administration o f physostigmine. Microiontophoretic application of ACh and carbachol e nhanced the firing rate of RVLM sympathoexcitatory neurons and the enh ancement of RVLM neurons by these cholinoceptor agonists was abolished by the nonselective muscarinic receptor antagonist scopolamine and/or by the M(2) muscarinic receptor antagonist methoctramine. Physostigmi ne and the ACh releaser 3,4-diaminopyridine also enhanced the firing r ate of RVLM neurons. Intravenous administration of physostigmine enhan ced RVLM sympathoexcitatory neuronal activity and the physostigmine-in duced response was reversed by iontophoretic application of scopolamin e onto the neurons. These results are consistent with the hypothesis t hat M(2) muscarinic receptors responsible for blood pressure regulatio n are present on RVLM sympathoexcitatory neurons and these receptors r eceive ACh inputs. Physostigmine injected systemically may exert a por tion of its hypertensive effect through a direct enhancement of cholin ergic mechanisms on RVLM sympathoexcitatory neurons. Copyright (C) 199 7 Elsevier Science Inc.