Lumbosacral dorsal root terminations in the nucleus gracilis of the cat. Some observations on terminal degeneration in other medullary sensory nuclei

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Abstract
Following lumbosacral dorsal rhizotomies (L1, L5, L6 and S1), fiber degeneration could be traced throughout three rostro‐caudal regions of nucleus gracilis by utilizing the Nauta method. In rostral region, fiber degeneration was less dense and localized with greater intersegmental overlap than in middle region, where roots terminated in fairly specific cell clusters. Little could be stated about the caudal region because of sparsity of terminal degeneration. Fiber degeneration in rostral region appeared to be distributed primarily in the dendritic fields while that in the middle region terminated on both cell somata and dendrites. Overlap of dermatomes in periphery and centrally in nucleus parallel each other. Throughout the nucleus, greatest overlap of root distribution was encountered in more ventral regions. A root supplying a more distal dermatome (e.g. L6) compared to a more proximal one (e.g. L1), terminates more densely and dorsally in the nucleus. An occasional degenerated fiber passed into the contralateral gracile nucleus at obex level. Root degeneration proceeded, ipsilaterally, into rostro‐dorsal regions of lateral cuneate, cuneate, and caudo‐lateral regions of 2 nuclei. Bilateral degeneration from all roots, excepting S1, was noted in rostral pole of subnucleus caudalis and the subnucleus interpolaris of spinal trigeminal complex and nucleus reticularis parvicellularis. The pathway to the spinal trigeminal and parvicellular nuclei was undetermined. The concept of the non‐homogenous organization of the gracile nucleus was supported.

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