Pretectal projections to the inferior olive in the rabbit

Direct pretectal projections to limited regions of the inferior olivary nucleus were found in the rabbit by means of the Nauta-Gygax and Fink-Heimer methods. The lesions were produced stereotaxically in the pretectal region of five rabbits. They encroached commonly upon the nucleus tractus opticus, the rostral half of the nucleus olivaris pretectalis, and involved some of the nucleus pretectalis posterior and anterior. Degeneration in the inferior olivary nucleus was found ipsilaterally in the dorsal cap and in the medial and dorsal aspects of the β-nucleus. Degeneration in the dorsal cap was marked and that in the β-nucleus was slight. Degenerated fibers terminating within these regions of the inferior olivary nucleus appeared to descend the brain stem ipsilaterally, mainly through the medial portions of the tegmentum, with no tendency to form compact fascicles. Based on the present and previous findings, it is presumed that the pretecto-olivary fibers provide a link of the pathways for the visual inputs to the vestibular nuclei and cerebellum.