Cholinergic mechanisms in the nucleus tractus solitarii and cardiovascular regulation in the rat.

To determine the role played by cholinergic neurons in cardiovascular regulation by the nucleus tractus solitarii (NTS), microinjections (0.1 microliter) of acetylcholine (ACh) or carbachol (C) were made into the NTS of rats, and the changes in arterial pressure and heart rate were recorded. The dose-dependent hypotension and bradycardia which resulted were mediated by the activation of muscarinic, but not nicotinic, receptors confined to the NTS. Blockade of muscarinic receptors bilaterally in the NTS resulted in mild hypertension and attenuated, but did not abolish, the baroreceptor reflex. Eserine, injected into the NTS, augmented and prolonged the action of acetylcholine and slightly increased the maximal baroreceptor reflex response. Thus, cholinergic mechanisms in the NTS tend tonically to lower arterial pressure and may modulate the baroreceptor reflex, without being an integral part of the reflex arc.