Substance P and serotonin immunoreactivity in the rat inferior olive.

The present study analyzes in detail the distribution of substance P and serotonin immunoreactivity in the inferior olivary complex of the rat using the indirect antibody peroxidase-antiperoxidase technique. The entire dorsal accessory olive contains an abundance of substance P fibers and varicosities. In addition, the dorsal cap of Kooy, nucleus Beta, parts b and c of the medial accessory olive, and the dorsomedial cell column contain numerous substance P immunoreactive elements. Fibers and varicosities positive for serotonin are present throughout the entire dorsal accessory olive. In addition, the rostral medial accessory olive contains an abundance of serotonin immunostaining. Scattered serotonin immunoreactive elements are present in the principal olive in particular in the area immediately subjacent to the lateral aspect of the dorsal accessory olive. Only scant serotonin immunolabeling is present in the dorsal cap of Kooy, nucleus Beta and the dorsomedial cell column. Speculations on possible functional roles of these two putative neurotransmitters are presented.