Motor Nerve Terminal Morphology with Unloading and Reloading of Muscle in Procambarus Clarkii

Skeletal muscle shows dynamic changes in mass that correlate with activity and weight bearing loads. The electrical excitation of the muscle of Procambarus clarkii (Girard, 1952) used in this study is graded which requires refined nerve-muscle matching in synaptic efficacy. We used the anterior levator (a.l.) muscle in crayfish as a model to address matching of the extent of nerve terminal and muscle size. This muscle repetitively becomes loaded and unloaded for various lengths of time due to limb autotomy. When an adult P. clarkii loses a cheliped, by autotomy, the a.l. muscle will atrophy over time. The leg stump still moves suggesting functional innervation. During atrophy, the muscle is drastically reduced in mass as compared to the contralateral control with a functional intact cheliped. The a.l. muscle is innervated by multiple excitatory neurons and at least 1 inhibitory neuron. Since the innervation is less extensive and identifiable for the inhibitory neuron the focus was on the innervation profile based on anti-GABA immunocytochemistry. Preliminary findings based on electron microscopic images of a few samples suggest that terminals on atrophied muscles have fewer synapses than terminals on control muscles. In addition, the extent of terminals on atrophied muscle is much more extensive as compared to muscle per surface area for animals with intact chelipeds. The atrophied muscles appear to be hyperinnervated when considering terminal length per surface area of