Effect on the peripheral nervous system of the short-term intravenous administration of paclitaxel in the rat.

The effectiveness of paclitaxel (Taxol) in the treatment of different tumors is well-known but, on the other hand, there is little information regarding its neurotoxicity and the mechanism(s) underlying this potentially severe side effect. In this study, using behavioral, neurophysiological, morphological and morphometric methods, we evaluated the effect of intravenous administration of paclitaxel on the rat nervous system. After 2 pilot studies, 40 female Wistar rats were treated with intravenous paclitaxel via a catheter placed in the jugular vein, while 20 animals were used as controls. Paclitaxel dissolved in ethanol/Tween 80/saline (5/5/90%) was administered 5 times over a period of 10 days. At the end of the experiment half the surviving animals in each group were evaluated and sacrificed (day 11), while the rest of the rats were evaluated and sacrificed on day 25. On day 11 the treated animals had significant impairment in pain perception (tail-flick test), coordination (rota-rod test) and nerve conduction velocity in the tail nerve. At the light microscope minimal axonal damage and Schwann cell activation were observed in the sciatic nerve. At the electron microscope microtubular accumulation was present within the axon in dorsal and ventral spinal roots and in the sciatic nerve. On day 25 the behavioral tests were normal in treated rats, while the nerve conduction velocity was still moderately reduced in comparison with the controls. At the electron microscope a morphological examination evidenced that microtubular accumulation was less severe, but still evident, especially in the sciatic nerve. Morphometric determinations performed on days 11 and 25 did not evidence differences between paclitaxel-treated rats and controls. The results of this study, the first in which an extended examination of the nervous system of animals treated intravenously with paclitaxel has been carried out, suggest that short-term administration of the drug induces mainly reversible changes in the peripheral nerves and spinal roots. Microtubules seem to be the main target of paclitaxel neurotoxicity, in much the same way as has been described for its antineoplastic activity. Finally, no pathological changes were seen in the neuronal bodies of the spinal cord and dorsal root ganglia. This model may be used for further studies with combination treatments with other antineoplastic or neuroprotective agents.