Cerebellar corticonuclear projection in the cat. Crus II. An experimental study with silver methods

Abstract

Small differently placed, bilateral lesions were made by transdural coagulation of the cerebellar cortex in the crus II of the cerebellum in 18 cats. In 10 cerebellar halves the lesions were confined to the crus II. The present study is based on these and on 5 halves with some concomitant injury to the dorsal paraflocculus. The ensuing course of the degenerating efferent fibres and the distribution of degeneration in the intracerebellar nuclei were studied with the Nauta 31 method and mapped, in most cases in sagittally cut, approximately serial, sections. This facilitated comparisons between cases. The crus II projects onto the nucleus lateralis (NL) as well as the nuclei interpositus anterior (NIA) and posterior (NIP; subdivisions according to Flood and Jansen 17). One band of degeneration extends from the dorsocaudal part of the NL, medially and slightly ventrally, through the transition region between NL and NIA into the caudal medial part of the latter. Another band extends from lateral to medial in the rostral part of the lateral half of the NIP. Within both projections there is a topical pattern, less marked in the NIP than in the other band: lateral parts of the crus II project more laterally and ventrally than do medial parts (Fig. 8). The findings demonstrate that the corticonuclear projection of crus II is precisely organized, but there is no strict correlation between lateral and medial parts of the crus II and lateral and medial regions of the lateralis-interpositus complex, respectively, as suggested by Jansen and Brodal 21, 22. Even lesions situated most laterally in crus II result in degeneration in the NIP. The pattern of longitudinal subdivisions of the cerebellum which can be recognized during cerebellar corticogenesis 24, 25 appears to be considerably distorted during later development. Since there appears to be a somatotopical pattern in the crus II 20, 35, it is possible to indicate approximately regions ‘representing’ hindlimb, forelimb and face in the lateralis-interpositus complex.