OLIVOCEREBELLAR PROJECTIONS IN THE CAT STUDIED BY MEANS OF ANTEROGRADE AXONAL-TRANSPORT OF LABELED AMINO-ACIDS AS TRACERS

Following injections of tritiated leucine and proline into the inferior olivary complex of the cat, labeled terminals of olivocerebellar fibers were found in the molecular layer of the contralateral cerebellar cortex. Fields of termination in the cortex form parasagittal zones, indicating a particular olivary area which sends fibers to a longitudinally oriented strip in the cerebellum. The findings in general are in Agreement with those obtained recently by means of anterograde and retrograde axonal transport techniques; the caudal half of the medial accessory olive projects to zone A (of Voogd), the rostral half to zone C2, the caudolateral and rostromedial parts of the dorsal accessory olive project to zone B and zones C1 plus C3, respectively, and the entire principal olive projects to zone D. New information derived from the present study is that the zone B extends to the medial part of the paramedian lobule, and that there is a projection to the flocculus from the most rostral part of the medial accessory olive. In addition, it was confirmed that projections to zone A in lobules VI-VIII and the anterior lobe arise from separate parts, with some overlapping among them, of the caudal part of the medial accessory olive. The width of the parasagittal zones varied according to their locations in the cerebellar cortex. Zone A has a width of 200-400 μm in the anterior lobe and lobule VIII, and 1.0-1.5 mm in lobule VII, while zone B has a relatively constant width of 400-600 μm throughout the lobules. Each subzone of C and D (C1, C2, C3, D1, D2) has a width of approx 200-400 μm. Between these olivocerebellar projection zones, there are gaps 400-600 μm wide which are not labeled by tritiated amino acids. Since the inferior olive receives afferents from many areas of the central nervous system and since probably the large majority of the climbing fibers take their origin from the inferior olive, it is hoped that precise topographical correlations between parts of the inferior olive and longitudinal zones of the cerebellum, as shown in the present study, may provide further understanding of the function of the inferior olivary complex. © 1979.