Quantitative analysis of the topographical organization of olivocerebellar projections in the rat.

The inferior olivary projection to anterior and posterior regions of the cerebellar vermis was studied in the rat using the retrograde fluorescent double-labelling technique in combination with a computerized data collection system. A technique for quantifying and statistically analysing the point-to-point (or nucleotopic) organization of the projection is presented. It was found that one group of neurones in the medial accessory olivary nucleus projected to cerebellar lobules 6 or 7, and second group projected to lobules 4 or 5, while a third sent collaterals to both areas. In the rostral part of the nucleus these three groups were spatially separated (P less than 0.05), whereas caudally they were intermingled. It is concluded that a double-labelling method has distinct advantages over a single-tracer technique (such as horseradish peroxidase) in the investigation of the topographic organization of neuronal projections. Quantitative analysis is used here to overcome the problems presented by collateralization, inter-animal variation and the accurate representation of results from a series of animals.