Immunohistochemical study of neurons in the rat abducens nucleus that project to the flocculus.

The neurons of the rat abducens nucleus that project to the flocculus of the cerebellum were studied by double labelling using the retrograde transport of horseradish peroxidase (HRP) and choline acetyltransferase (ChAT) immunohistochemistry. Double-labelled cells were present bilaterally in the dorsal and dorsomedial zones of the cranial pole of the nucleus. They represented about half of the total number of HRP-positive neurons. These findings show the existence of a bilateral projection from the abducens nucleus to the flocculus which uses acetylcholine as a neurotransmitter. This projection could be part of the system of the nerve circuits through which the cerebellum modulates visual activities.