Afferent projections from the brainstem to the three floccular zones in cats. II. Mossy fiber projections

Abstract

Mossy fiber projections from the brainstem to the flocculus were studied following injections of horseradish peroxidase (HRP) into the flocculus and following microinjections of HRP into each of the three zones of the flocculus. It has been found that the flocculus receives mossy fiber projections from 4 main sources. (1) Perihypoglossal nucleus--dense projections originate from discrete areas of the rostral pole of the intercalated nucleus, the ventral part of the prepositus hypoglossal nucleus and the adjacent reticular formation. (2) Vestibular nuclear complex--secondary vestibular fibers come from discrete areas in the vestibular nuclei: the ventromedial and dorsomedial parts of the medial and inferior nucleus, the central area of the superior nucleus, the ventromedial part of the lateral nucleus, the group y and the interstitial nucleus of the vestibular nerve. (3) Medullary reticular formation--the strongest projection of mossy fibers arises from the accessory group of the paramedian reticular nucleus. (4) Pontine reticular formation and raphe nucleus--dense projections originate from a narrow zone which involves the caudal part of the dorsal nucleus of the raphe, the inferior and superior central nucleus of the raphe and the medial part of the nucleus reticularis tegmenti pontis. No clear indication of a different mossy fiber projection from the nuclei in the brainstem to the 3 zones of the flocculus was found.