Pharmacological properties of cholinoceptive neurones in the medulla and pons of the cat

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Abstract
Iontophoretic application of acetylcholine to neurones in the medulla and pons of the unanesthetized decerebrate cat excited 35.5% and inhibited 22%. This was not a representative sample of lower brain stem neurones, since most penetrations were made medially. Some cholinoceptive neurones were in the medial reticular formation. The time course of the response to different doses was described. Nicotine and nicotinic agents 1,1-dimethyl-4-phenylpiperazinium iodide (DMPP) and choline phenyl ether (TM 1) excited neurones excited by acetylcholine but, with one exception, did not inhibit neurones inhibited by acetylcholine. Muscarinic agents mimicked both the excitatory and inhibitory responses to acetylcholine. ([plus or minus])-Muscarine and bethanechol [beta]-methylcholine carbamate) had a prolonged and powerful inhibitory action. Oxotremorine [l-(2-oxo-pyrrolidino)-4-pyrrolidino-butyne-2] had a long-lasting excitatory action on neurones excited by acetylcholine. Eserlne [physostigmine] and neostigmine potentiated the action of acetylcholine but in addition they had a strong excitatory effect on many brain stem neurones, independently of the action of acetylcholine. Excitatory and inhibitory responses to acetylcholine could be antagonized by gallamine, hexa-metnonium and atropine. Dihydro-[beta]-erythroidine (DH[beta]E) antagonized only excitatory responses. (+)-Tubocurarine was a weak antagonist. The excitatory responses have both nicotinic and muscarinic properties but the inhibitory responses are only muscarinic. Since the pharmacology of these 2 types of response is different, the inhibitory action is not due to an indirect effect from excitation of a neighboring inhibitory neurone.