Cerebellotectal projection in the rat: anterograde and retrograde WGA-HRP study of individual cerebellar nuclei.

Cerebellotectal projections were studied in the rat by the anterograde and retrograde tracing methods using wheat-germ-agglutinin-conjugated horseradish peroxidase. The pathway arises from all four cerebellar nuclei on the contralateral side; mainly from the posterior interpositus nucleus and lateral nucleus and to a lesser extent from the medial nucleus and anterior interpositus nucleus. The fibers arising from the medial nucleus and the posterior interpositus nucleus terminate mainly in the deeper zone of layer IV and in layer VI throughout the entire rostrocaudal extent of the contralateral superior colliculus. Those arising from the anterior interpositus nucleus and the lateral nucleus terminate mainly in the superficial zone of layer IV in the rostral three-fourths of the contralateral superior colliculus. In addition, the fibers from the lateral nucleus terminate densely in a zone extending from the deep part of layer III through layer VII in the lateral portion of the rostral half of the superior colliculus. In comparison with data on other species the present findings are discussed with respect to the evolutional changes from monocular to binocular vision.