Localization of substance P, acetylcholinesterase, muscarinic receptors and alpha-bungarotoxin binding sites in the rat interpeduncular nucleus.

On the basis of acetylcholinesterase (AChE) staining, the rat interpeduncular nucleus was subdivided into five distinct zones. Intense AChE staining was observed in the dorsal cap and the lateral zones. Moderate staining was seen in the median zone and the dorsoventral column. The perivascular zones were unlabeled. Adjacent sections were stained for AChE and for substance P immunofluorescence. Substance P like immunoreactivity was found to coincide with the localization of AChE in the dorsal cap and the lateral zones. Both muscarinic receptors and alpha-bungarotoxin binding sites had distributions resembling that of AChE. Neither unilateral nor bilateral lesions of the habenulae changed the number or distribution pattern of the receptors. It was concluded that cholinergic receptors are localized postsynaptically. Our study suggests AChE and substance P containing fibers terminate in well defined zones of the interpeduncular nucleus which also contain muscarinic and nicotinic receptors.