Electrophysiological actions of nicotine on substantia nigra single units

Abstract

1 Extracellular recordings of single unit activity were made in the substantia nigra (SN) of chloral hydrate-anaesthetized rats. 2 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. 3 Nicotine, when administered intravenously (2–128 μg kg⁻¹ cumulative dose), also stimulated dopamine cells and this action was dose-related. 4 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. 5 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.