Ischemic neurophysiological changes of rat sciatic nerve in vitro

PURPOSE: Patients with ischemic neuropathy always have a progressive reduction in nerve conduction resulting in a transient increase in sensation, such as pain or hyperesthesia. We examined the effect of acute complete ischemia on neurophysiological functions in rat and related electrophysiological changes in ischemic nerve with adenosine 5'-triphosphate (ATP) administration. METHODS: The sciatic nerve of rat was placed directly on 16 parallel 0.5 mm diameter platinum electrodes (5 mm interelectrode distance) in a Perspex chamber bathed in Ringer's solution. The stimulus was applied through the electrode at the rostral end of the nerve, and the action potential recorded along different recording electrodes towards the caudal end of the nerve. Measurements were recorded immediately upon initial nerve placing and then 5, 10, 15, 30, 60, 90 and 120 min after nerve placing. RESULTS: We observed two major components in the monophasic compound action potential of the sciatic nerve of rats (A and B waves). Nerve conduction and amplitude of A and B waves underwent an initial increase followed by a reduction and after ATP administration, the transient augmentation of conduction velocity and amplitude in A and B waves disappeared. The median survival time of peripheral nerve was 60 min. CONCLUSION: At the onset of ischemia, the membrane Na-K pump does not work resulting in an increase of threshold potential in nerve membrane. When ATP levels further decrease, nerve function progressively fails.