Degeneration and Regeneration in Crustacean Neuromuscular Systems

Abstract

Crayfish motor neurons seem to repair damage to peripheral axons by selective fusion of outgrowing proximal stumps with severed distal processes that can survive morphologically and physiologically intact for over 200 days. Survival of isolated motor and CNS giant axons is associated with much hypertrophy of their glial sheath. The severed stumps of peripheral sensory neurons often degenerate within 21 days and their glial sheath does not hypertrophy. Denervation and immobilization produce relatively little change in the morphology and physiology of the opener muscle, whereas tenotomy produces much atrophy within 30-60 days. Crayfish motor and CNS giant neurons show no capability for regenerating ablated cell bodies, whereas peripheral sensory somata regenerate after limb autotomy. An entire opener muscle can be replaced after limb autotomy but the organism shows little or no ability to redifferentiate an entire muscle in the absence of body part regeneration. However, a few opener muscle fibers can be regenerated if the bulk of the muscle mass remains intact. The significance of all these findings are interpreted with respect to the developmental capabilities and environmental adaptations of the crayfish together with the evolution of regenerative abilities in anthropods and vertebrates.