Lumbar dorsal root projections to spinocerebellar cell groups in the rat spinal cord: a double labeling study

The aim of this study has been to investigate projections to spinocerebellar cell groups from lumbar dorsal root ganglia (DRGs) in the rat. The binding subunit of cholera toxin conjugated to horseradish peroxidase (B-HRP) was used to label primary afferent fibers. Spinocerebellar neurons were labeled retrogradely by Fluoro-Gold (FG). To determine the orientation of dendrites, retrogradely labeled spinocerebellar neurons were studied, following injections of wheat germ agglutinin conjugated horseradish peroxidase (WGA-HRP) into cerebellum. FG or WGA-HRP labeled neurons were found mainly in laminae V and VII, in the lateral group of lamina IX, in Clarke's column (CC) and in the dorsal funiculus. B-HRP labeled primary afferent fibers overlapping with FG labeled cells were observed at all these locations after injections of B-HRP into different DRGs. The overlap in lamina V was found mainly medially and dorsolaterally. CC was found to receive dense projections from DRGs L1-6. In the lumbar part of CC, labeling from DRGs L4-5 overlapped and was distributed over the entire mediolateral extent of the CC, whereas labeling from DRGs L1-3 was somatotopically organized and projected to successively more dorsomedial areas. The central area of lamina VII showed moderate labeling from DRGs L3-5. The lateral group of lamina IX received only smaller amounts of labeled fibers from DRGs L3-5.