In vivo conduction properties of regenerating giant nerve fibers in earthworms

Abstract

AbstractNon‐invasive electrophysiological techniques have been used to study spatial and temporal aspects of conduction properties in regenerating earthworm giant nerve fibers. The initial coupling of medial giant fiber (MGF) spikes across the lesion can occur as early as five (and usually within seven) days after severing the ventral nerve cord. In the case of the lateral giant fiber (LGF), the initial coupling of spikes across the lesion occurs as early as 12 days after severing the cord. During the first, few days after initial coupling across the lesion, properties of the recovering giant fibers included: a) intermittent and labile coupling of spikes across the lesion, b) long conduction times (up to 6 msec) across the lesion, c) frequent occurrence of, “rebound” spikes initiated in the lesion area, and d) similarity of conduction properties across the lesion for orthodromic and antidromic spikes. Three to four weeks after initial coupling, the following changes were observed: a) increased tendency for,1:1 coupling of spikes across the lesion, b) reduction in conduction time across the lesion, and c) decreased tendency for “rebound” spikes. The results are consistent with a model in which conduction across the lesion, during the first few days after initial coupling and thereafter, occurs by means of an electrical junction established between the severed giant fibers.