Nicotine stimulation of the medulla increases blood flow of the common carotid artery in cats

Microinjection of nicotine or glutamate into the dorsal facial area (DFA) of the medulla increases blood flow of common carotid artery (CCA). Whether there is a causal relationship between these two events is not known. Various agonists and antagonists for the nicotinic and glutamatergic receptors were microinjected through a four-barrel tubing into the DFA of anesthetized cats. Microinjections of nicotine [a non-selective nicotinic acetylcholine receptor (nAChR) agonist], choline (a selective α7-nAChR agonist), glutamate or KCl induced a modest increase in CCA blood flow. The nicotine- and choline-induced increases were reduced by α-bungarotoxin (an α7-nAChR antagonist) as well as MK-801 (a non-competitive NMDA receptor antagonist) or glutamate diethylester (a competitive AMPA/kainate receptor antagonist). The glutamate or KCl-induced increases were blocked by MK-801 and glutamate diethylester, but not by α-bungarotoxin. In conclusion, activation of nAChRs primarily via α7-nAChR caused a release of glutamate, which in turn activated NMDA and AMPA receptors, while cholinergic substance was not released into the DFA to activate the nicotinic receptor.