Electrophysiological actions of nicotine on substantia nigra single units

Abstract

Extracellular recordings of single unit activity were made in the substantia nigra (SN) of chloral hydrate‐anaesthetized rats. Dopaminergic neurones of the pars compacta (SNC) were stimulated by (—)‐nicotine bitartrate (1.0 mg k−1) given subcutaneously (s.c.). This action was prevented by the secondary amine mecamylamine HCl (2.0 mg kg−1 i.v.) but not by a ganglion‐blocking dose of the bisquaternary compound chlorisondamine Cl (0.1 mg kg−1 i.v.). Mecamylamine reduced the spontaneous activity of dopaminergic neurones. Nicotine, when administered intravenously (2–128 μg kg−1 cumulative dose), also stimulated dopamine cells and this action was dose‐related. Nicotine, administered intravenously, (2–128 μg kg−1 cumulative dose) markedly excited non‐dopamine cells in the pars reticulata (SNR) in a dose‐related manner. In rats pretreated with chlorisondamine (0.1 mg kg−1 i.v.), nicotine induced a small excitatory or depressant action, but the marked excitation was not seen. Mecamylamine (2 mg kg−1 i.v.) completely prevented the actions of nicotine. The results are consistent with a direct excitatory action of nicotine on dopaminergic neurones of the substantia nigra pars compacta. The pronounced excitatory action of systemically administered nicotine on non‐dopamine cells of the pars reticulata appears to be of peripheral origin. 1985 British Pharmacological Society