OXALIPLATIN-INDUCED HYPEREXCITATION OF RAT SCIATIC NERVE FIBERS: AN INTRA-AXONAL STUDY

Oxaliplatin is an agent that is used extensively in gastrointestinal cancer chemotherapy. The agent's major dose-limiting toxicity is peripheral neuropathy that can manifest as a chronic or an acute syndrome. Oxaliplatin-induced acute neuropathy is purportedly caused by an alteration of the biophysical properties of voltage-gated sodium channels. However, sodium channel blockers have not been successful at preventing acute neuropathy in the clinical setting. We report intra-axonal recordings from the isolated rat sciatic nerve preparation under the effect of oxaliplatin. The depolarization phase of single action potentials remains intact with a duration of 0.52 +/- 0.02 ms (n=68) before and 0.55 +/- 0.01 ms (n=68) after 1-5 h of exposure to 150 mu M oxaliplatin (unpaired t-test, P>0.05) whereas there is a significant broadening of the repolarization phase (2.16 + 0.10 ms, n=68, before and 5.90 + 0.32 ms after, n=68, unpaired t-test, P<0.05). Apart from changes in spike shape, oxaliplatin also had drastic concentration-and time-dependent effects on the firing responses of fibers to short stimuli. In the intra-axonal recordings, three groups of firing patterns were indentified. The first group shows bursting (internal frequency 90 - 130 Hz, n=88), the second shows a characteristic plateau (at -19.27+/-2.84 mV, n=31, with durations ranging from 45 - 140 ms depending on the exposure time), and the third combines a plateau and a bursting period. Our results implicate the voltage-gated potassium channels as additional oxaliplatin targets, opening up new perspectives for the pharmacological prevention of peripheral neuropathy.