Nicotinic and Muscarinic Receptors of Renshaw Cells

Abstract

THE method of electrophoretic ejection from multibarrel micropipettes, in conjunction with the recording of electrical responses from single neurones¹, provides a unique opportunity for classifying central acetylcholine receptors according to their pharmacological properties. It has been usual to subdivide these receptors into nicotinic and muscarinic types, a classification based on the original use of these terms by Dale² to describe the peripheral actions of certain derivatives of choline. The following evidence has suggested that the receptors of Betz cells are muscarinic₃: nicotine is a weak excitant; acetyl-β-methylcholine and dl-muscarine are almost as active as acetylcholine; the excitation by acetylcholine is slow in onset and is readily blocked by atropine but not by dihydro-β-erythroidine. In contrast the acetylcholine receptors of Renshaw cells exhibit nicotinic properties⁴: nicotine is a more powerful excitant than acetylcholine; acetyl-β-methylcholine and dl-muscarine are very weak; the excitation by acetylcholine is rapid in action and is readily blocked by dihydro-β-erythroidine but not by atropine. The acetylcholine sensitivities of ventrobasal thalamic neurones, and of cerebellar neurones, are of intermediate types⁵.