The location of cerebellar-projecting neurons within the lumbosacral spinal cord in the cat. An anatomical study with HRP and retrograde chromatolysis.

The locations of lumbosacral spinocerebellar neurons were examined by two anatomical methods in kittens. In one group of animals chromatolytic changes were provoked by cerebellar lesions. In another group horseradish peroxidase (HRP) was injected into the cerebellum. Projection laterality was investigated by making unilateral spinal lesions prior to the cerebellar HRP injections. Diaminobenzidine (DAB) or tetramethylbenzidine (TMB) was used as substrate fo HRP. The morphological characteristics of HRP-labeled neurons in the TMB-processed material were examined. Neurons marked by the two methods were located within the same regions. A greater number of cells were marked with the HRP method, however, than with the retrograde chromatolysis method. Spinocerebellar neurons were found in laminae IV-IX with large differences with regard to specific locations depending on segmental level. Numerous marked neurons were found in the following areas: laminae IV-Vi in L3-L7, the column of Clarke in L3-L4, the medial part of lamina VII in L6-L7, the lateral part of lamina VII in L3-L4, the dorsolateral nucleus of lamina IX in L3-L6, the ventrolateral nucleus of lamina IX in L4-L5, and the ventromedial nucleus of lamina IX in S3 (and Ca1). Dorsally located neurons were in general more likely to project ipsilaterally than ventrally located neurons. Marked structural differences were frequently observed between spinocerebellar neurons in different locations. These results provide additional information on the anatomical complexity of the spinocerebellar pathways from the lumbosacral region in the cat. Together with results from some other recent anatomical studies on spinocerebellar tracts, they also form a basis for further anatomical and physiological investigations which could contribute to a better understanding of the organization of the spinocerebellar tracts.