Axotomy increases excitability in crayfish fast flexor motoneuron somata

Somata of crayfish fast flexor motoneurons whose axons had been cut several days previously were found to display much greater electrical excitability than intact contralateral controls. This increased excitability was evidenced by the consistent appearance in intracellular (soma) recordings of overshooting action potentials during antidromic stimulation, in contrast to the decremented passive antidromic potentials usually seen in control cells. The excitability increase was apparently shared by all fast flexor motoneurons whose axons pass out through the severed (main third) root (arising from three major clusters of somata in two ganglia); it also occurred when only one of the first two major branches of the root was cut. These findings corroborate and extend similar results from crayfish and other arthropods, and may find application in the study of central motoneuron circuitry.