RESUMEN
In the rat, tail nerves are the longest peripheral nerves in their body. We suggest that ventral caudal nerve (VCN) may serve as a model for studying nerve injury and long distance regeneration. For this purpose, we have studied the anatomy and morphometry of the VCN in control animals. 10â¯cm long segment of the VCN was removed, and transversal sections were collected at 10â¯mm distances. The myelinated axons were counted, and the series of data were used to characterize the craniocaudal tapering of the nerve. In a separate group of animals, retrograde tracing with Fluorogold was used to localize and quantitate the spinal neurons projecting their axons into the VCN. After complete nerve transection, the time course of histopathological changes in the distal segment was studied. The primary goal was to define the time needed for axonal disintegration. In later periods, axonal debris removal and rearrangement of tissue elements was documented. After compression injury (axonotmesis), Wallerian degeneration was followed by spontaneous regeneration of axons. We show that the growing axons will span the 10â¯cm distance within 4-8 weeks. After different survival periods, the numbers of regenerating axons were counted at 10â¯mm distances. These data were used to characterize the dynamics of axonal regeneration during 4 months' survival period. In the present study we show that axonal regeneration across 10â¯cm distance can be studied and quantitatively analyzed in a small laboratory animal.