Collateral projections of neurons from the lower part of the spinal cord to anterior and posterior cerebellar termination areas. A retrograde fluorescent double labeling study in the cat.

The collateral projections of spinocerebellar neurons located in the L 2 to Ca 1 spinal segments in the cat were investigated by retrograde fluorescent double labeling technique. Rhodamine labeled latex microspheres (Rm) and Fast Blue (FB) were used for injections into the cerebellum in 8 cats. Two additional cats, with injections of Fluoro-Gold (FG) combined with Rm were excluded because lipofuchsin autofluorescence obscured the labeling. After injections with one tracer unilaterally in the paramedian lobule and another tracer bilaterally in the anterior lobe, double labeled neurons were found on the side of the paramedian lobule injection in the column of Clarke at L 2-L 4, laminae IV-VI at L 2-L 5 and the dorsolateral nucleus at L 2-L 6. After bilateral injections of one tracer in lobule VIII B and another in the anterior lobe, double labeled neurons were found bilaterally in the column of Clarke at L 2-L 4, laminae IV-VI at L 2-L 5, the medial part of lamina VII at L 6-L 7 and in certain cell groups at sacro-coccygeal levels. Neurons in the lateral part of lamina VII at L 3-L 5 and the ventrolateral nucleus of L 4-L 5 were labeled exclusively from injections in the anterior lobe. The findings indicate that spinocerebellar neurons at lumbar and more caudal levels of the cat spinal cord have different projection patterns in the cerebellum. A certain number of neurons which project to the anterior lobe have divergent axon collaterals supplying also the posterior vermis and/or the paramedian lobule. Other neurons project to the anterior or to the posterior lobe only.