Descending connections from the mesencephalon to the inferior olive: An experimental study in the cat

Summary

The descending connections to the inferior olive from the central grey and adjacent reticular formation in the cat have been re-studied. Only a very limited area of the periaquaductal substance gives origin to afferent olivary fibers. This area lies latero-ventrally in the central grey rostral to the rostral pole of the red nucleus. The findings indicate that the aquaducto-olivary fibers emerge from the nucleus of Darkschewitsch and possibly from the central grey ventral to this nucleus. The fibers terminate within the rostral half of the ipsilateral principal and rostral half of the medial accessory olive including the dorso-medial cell column. The fibers from the adjacent reticular formation terminate within the caudal half of the medial accessory olive including nucleus β, and probably also within the principal olive and rostral half of the medial accessory olive. The findings made in the present study are at variance with those made previously (Walberg, 1956, 1960). The observations support the findings made by Maekawa and Simpson (1972, 1973). Their physiological studies indicate that certain areas send impulses to the parts of the inferior olive mediating climbing fiber responses to the flocculus. The present study has not clarified whether all parts of the reticular formation indicated in Figs. 4 and 5 project to the same areas of the inferior olive. Double operations or studies with injection of isotopes will be necessary for a further study of these projections.