Neural attrition following limb loss and regeneration in juvenile lobsters

Lobsters have considerable regenerative capacity, being able to regrow an entire, albeit smaller, limb in one intermolt. Whether there is a corresponding downscaling in the hemiganglion and its nerves to the regenerate side compared with its contralateral intact side was examined in juvenile lobsters which had undergone single or multiple (2, 4, and 6) cycles of limb loss and regeneration on the one side. The limbs studied were the enlarged thoracic chelipeds or claws which appeared as paired symmetrical cutter-type claws. The size of the regenerate limb, as indicated by its propus length, was approximately 30% smaller than its intact counterpart. Correspondingly, the total number of axons in the nerves to the regenerate side was smaller than on the intact, contralateral side. Such attrition was also by about 30% in lobsters experiencing a single cycle of limb loss and regeneration, but was considerably greater with multiple cycles. Tissue degeneration was occasionally seen in the nerves to the regenerate side but not in the ganglion. The paired hemiganglia were equivalent in all respects except in the size of the neuropil, which was smaller on the regenerate side compared with the contralateral intact side. Neuropil attrition was most marked with multiple cycles of limb loss and regeneration. Such attrition in nerve and neuropil are most likely due to the reduced number of sensory elements in the newly regenerated, but smaller, limb.