Physiological properties of regenerated rat sciatic nerve following lesions at different postnatal ages

Electrophysiological properties of regenerated sciatic nerves were examined in vitro following sciatic crush lesions performed on rats at 1 week to 4 months of age. Pharmacological blockade of potassium channels with 4-aminopyridine (4-AP) in control nerves resulted in only minimal changes in the waveform of whole nerve responses, but was associated with slight prolongation of relative refractory periods and compromised frequency-following abilities at all ages examined. A more marked sensitivity to application of 4-AP was observed in all regenerated nerves compared to control nerves. This sensitivity was characterized by the development of a prominent delayed negativity of the compound action potential. Specific features of the waveform alterations differed for nerves crushed before age 3 weeks compared to those injured at the older postnatal ages. Alteration of refractory properties and frequency-following abilities of regenerated nerves following 4-AP were also more pronounced than in control nerves with the most marked disruption being observed in nerves from animals lesioned at the older ages. These data suggest that the process of regeneration is modified by ongoing maturation at the time of crush.