ACTIVITY-DEPENDENT CONDUCTION-VELOCITY CHANGES OF A-DELTA FIBERS IN ARAT MODEL OF NEUROPATHY

ACTIVITY-DEPENDENT changes of conduction velocity (CV) and conduction block in single A delta fibers of primary afferent neurons were charac terized in a rat model of neuropathy (NP). Injured dorsal root (DR) fi ber in NP rats exhibited profoundly greater decreases of CV following impulse activity than did DR fiber in normal rats. Activity-dependent conduction block was absent up to 100 Hz of activity rate in DR fiber of NP rats, but was present above 25 Hz in normal rats. Profiles of ac tivity dependence in sciatic fibers were similar in both NP and normal rats. These results suggest that nerve injury may alter activity-depe ndent hypoexcitability of A delta DR fibers. Furthermore, this excitab ility change may be responsible for the elevated pain perception in ne uropathy.