Regulation of the common carotid arterial blood flow by nicotinic receptors in the medulla of cats

Background and purpose: Actions of glutamate and serotonin on their respective receptors in the dorsal facial area (DFA) of the medulla are known to regulate common carotid arterial (CCA) blood flow in cats. Less is known about acetylcholine action on its nicotinic receptor (nAChR) subtypes in the DFA for regulation of CCA blood flow and this aspect was investigated. Experimental approach: Nicotinic and muscarinic agonists and antagonists were microinjected into the DFA through a three-barrel tubing in anesthetized cats. Results: CCA blood flow was dose-dependently increased by nicotine (a non-selective nAChR agonist) and choline (a selective alpha 7-nAChR agonist). These effects of nicotine were attenuated by alpha-bungarotoxin (an alpha 7-nAChR antagonist), methyllycaconitine (an alpha 7-nAChR antagonist), mecamylamine (a relatively selective alpha 3 beta 4-nAChR antagonist) and dihydro-beta-erythroidine (a relatively selective alpha 4 beta 2-nAChR antagonist). The choline-induced flow increase was attenuated by alpha-bungarotoxin and mecamylamine, but not by dihydro-beta-erythroidine. Muscarinic agonists (muscarine and methacholine) and antagonist (atropine) affected neither the basal nor the nicotine-induced increase in the CCA blood flow. Conclusions and implications: Functional alpha 7, alpha 4 beta 2, and alpha 3 beta 4 subunits of the nAChR appear to be present on the DFA neurons. Activations of these receptors increase the CCA blood flow. The present findings do not preclude the presence of other nAChRs subunits. Muscarinic receptors, if any, on the DFA are not involved in regulation of the CCA blood flow. Various subtypes of nAChRs in the DFA may mediate regulation of the CCA and cerebral blood flows.