Afferent sources to the inferior olive and distribution of the olivocerebellar climbing fibers in cyprinids.

The inferior olive in teleosts is a major afferent origin to the cerebellum. However, inputs to the inferior olive remain largely unknown. The present study examined fiber connections of the inferior olive by tract-tracing methods in cyprinids. After tracer injections into the inferior olive, labeled somata were observed bilaterally in the pretectum, nucleus ruber, principal sensory trigeminal nucleus, descending trigeminal nucleus, inferior reticular formation, and cerebellar valvula. Principal sensory trigeminal and valvular afferents exhibited a clear contralateral preponderance, while afferents from the nucleus ruber were predominantly ipsilateral. Labeled somata were also seen ipsilaterally in the descending octaval nucleus, and contralaterally in the optic tectum, lateral funicular nucleus, cerebellar corpus, and inferior olive. A few somata were labeled in the inferior raphe. Climbing fibers terminated contralaterally in the ganglionic and molecular layers of the cerebellum, showing peculiar glomerular appearances. Labeled climbing fiber terminals were mainly distributed in the ventral region of cerebellar corpus, the medioventral region of lateral lobe of rostral cerebellar valvula, and the lateroventral region of medial lobe of cerebellar valvula in the present injection materials. Fiber connections of the inferior olive in teleosts thus appear quite similar to those in mammals.