Projection from the dorsal column nuclei to the carebellar caudal vermis: comparison of collateral and non-collateral connection
The study was performed to determine projection from the dorsal column nuclei (DCN), both independent and by way of axonal collaterals, to the pyramis and uvula. Two different fl uorescent tracers were unilaterally injected into the two vermal targets. Single and double retrogradely labeled neurons, parent for non-collateral and collateral projections, were found in defi ned regions of DCN. Non-collateral bilateral projections directed to the pyramis and uvula are stronger to the latter, and originate from neurons in the lateral cuneate nucleus (CuL; n= 5 040 vs. 6 637), the complex of gracile and medial cuneate nucleus (Gr+CuM; n=820 vs. 2 190) and CuM (n=32 vs. 92). Weak projection from the dorsal Gr (n=57) is destined for the pyramis. Neurons in the rostral and middle CuL, projecting to the pyramis and uvula occupy ventrolateral and ventromedial positions, respectively, and a narrow region between them is common. More caudally, small areas in CuL, Gr+CuM and CuM supply the uvula, but in majority, areas of projection from these subnuclei to both lobules overlap. Weaker ipsilateral projections by way of axonal collaterals (n=175) arise from neurons in common projection areas in CuL and Gr+CuM. To sum up, neurons for the DCN-pyramis and DCN-uvula projections vary in number and distribution, and there is a small population of neurons participating in divergent projection to both lobules. Different extent of DCN infl uences may be due to disparate function of the pyramis and uvula.