NICOTINIC CHOLINOCEPTOR-MEDIATED EXCITATORY POSTSYNAPTIC POTENTIALS IN RAT NUCLEUS AMBIGUUS

In rat brainstem slice preparations, intracellular recording from neur ons (n=39) in the compact formation of the nucleus ambiguus (AMB(c)) r evealed spontaneous and miniature excitatory postsynaptic potentials ( EPSPs; n=11) that, along with acetylcholine-induced depolarization, we re enhanced by physostigmine (10 muM; n=2) and blocked by dihydro-beta -erythroidine 15 pmol (n=4). Retrograde neuronal tracing combined with choline acetyltransferase immunocytochemistry demonstrated that the A MB(c) receives a projection from a subpopulation of cholinergic neuron s in the zona intermedialis reticularis parvicellularis. Electrical st imulation of this region in slices evoked fast EPSPs in AMB(c) neurons (n=23) that were inhibited by dihydro-beta-erythroidine 2 5 pmol (n=8 ), but not by methscopolamine 1 pmol (n=2). The present findings stron gly support the existence of a cholinergic nicotinic synapse mediating fast transmission in brainstem vagal motoneurons.