DIFFERENT EFFECTS OF 4-AMINOPYRIDINE ON REGENERATED CUTANEOUS AND MUSCULAR RAT SCIATIC-NERVE BRANCHES

Developing and regenerated myelinated rat dorsal and ventral root fibe rs respond differently to the fast potassium channel blocking agent 4- aminopyridine (4-AP). To pursue this issue further, we made unilateral sciatic nerve crushes in adult rats. Sural (SN) and lateral gastrocne mius (LGN) nerve branches were collected 4-6 months later, for physiol ogical and morphological examination. Regenerated and control nerves i n Ringers solution showed generally similar compound action potential (CAP) waveforms, but CAPs of regenerated SNs and LGNs in 4-AP were mar kedly different. While regenerated SNs showed a prominent late CAP neg ativity with a ''rippled'' appearance and markedly compromised recover y properties, the CAP and recovery properties of regenerated LGNs were minimally changed. Light and electron microscopic examination of SN a nd LGN fibers failed to reveal any features obviously related to the o bserved physiological differences. We conclude, that the effect of 4-A P on regenerated cutaneous afferents differs from its action on regene rated muscular afferents and efferents. This physiological diversity l acks obvious structural correlates.