The reticulocerebellar projection to the pyramis copula pyramidis in the rat: an experimental study using retrograde transport of horseradish peroxidase.

The organization of the lateral reticulocerebellar projection to the pyramis and copula pyramidis in the rat was studied with the use of microinjections of horseradish peroxidase (HRP). These injections were made in different mediolateral positions along the width of this lobule. The objective was to determine whether reticulocerebellar parasagittal zones (Chan-Palay et al., '77) receive differential inputs from the lateral reticular nucleus (LRN). This material has previously been used to analyze the olivo and pontocerebellar projection to this same cortical region of the rat cerebellum (Eisenman, '81a,b). The results do not support a clear-cut topographic organization in this projection system to the pyramis and copula pyramidis in the rat. There is some suggestion, however, of a difference in emphasis in the region of the LRN projecting to different mediolateral positions in this lobule. Injections in medial and lateral parts of this lobule result in the labeling of cells in the subtrigeminal and ventral parts of the parvicellular and magnocellular divisions. Injections in intermediate parts of this lobule result in the labeling of cells primarily in the subtrigeminal division. However, cells in each of the divisions (primarily the subtrigeminal and parvicellular) are labeled in each experiment. These results are discussed with reference to electrophysiological and other anatomical studies of the topography of the reticulocerebellar projection in the cat.