Coexistence of choline acetyltransferase and GABA in axon terminals in the dorsal cap of the rat inferior olive.

The dorsal cap of Kooy of the inferior olive (DC) is involved in compensatory eye movements. The rat DC receives a prominent input from the nucleus prepositus hypoglossi (NPH); part of these axon terminals are immunoreactive for choline acetyltransferase (ChAT) and part of them are GABAergic. In the present study we investigated the fine distribution of cholinergic terminals in the rat DC, and the possible coexistence of ChAT and GABA. ChAT-positive terminals were observed throughout the entire neuropil of the rat DC contacting both extraglomerular and intraglomerular dendrites. Twenty nine percent of these terminals also contained GABA. The ChAT/GABA double-labelled terminals showed the same morphological characteristics as terminals traced from the NPH. The present data demonstrate colocalization of ChAT and GABA in axon terminals of the rat DC and strongly suggest that neurons in the NPH are the source of these profiles.