The origin of olivary afferents from the central grey and its surroundings in the cat.

The olivary afferents from the mesencephalic central grey and its surroundings have been studied in cats in which microinjections of horseradish peroxidase have been made into the inferior olive from a ventral approach. Retrogradely labelled cells are present in the ventral part of the central grey, the nucleus of Darkschewitsch (especially its ventral part), the Edinger-Westphal nucleus, the interstitial nucleus of Cajal and the reticular formation between the red nucleus and the central grey. The projection is ipsilateral and the heaviest contribution of afferents is derived from the interstitial nucleus of Cajal. The findings indicate that the afferents from the mesencephalic reticular formation to the inferior olive probably are collaterals of fibres terminating dorsally to the olive or passing to the spinal cord. The observations are discussed and related to previous experimental studies in the cat.