Motoneuron reinnervation of phasic uropod muscles in crayfish.

Motoneuron reinnervation of the lateral abductor and adductor muscles in the exopodite of the crayfish uropod was obtained by cross-tying the cut proximal ends of one set of uropod nerve roots to the cut distal ends of their contralateral homologues. In normal (nonsurgically treated) animals the abductor was innervated by two excitatory motoneurons and an inhibitor while two excitors innervated the adductor. For each muscle one of the excitors produced large excitatory junction potentials (EJPs) while the other evoked small EJPs. When stimulated repetitively only the smaller EJP in the adductor generated a facilitating response. Within less than 10 weeks postsurgery the muscles were each reinnervated by two excitatory motoneurons. While the abductor motoneurons generated synaptic potentials with similar amplitudes and time courses to those of normal animals, they differed from those in normal animals in that they facilitated when stimulated repetitively. In contrast to the large and small EJPs evoked in the normal animal, the two motoneurons that reinnervated the adductor muscle elicited similar amplitude EJPs, neither of which facilitated in response to repetitive stimulation.