Topical application of colchicine, vinblastine and vincristine prevents strychnine-enhanced transsynaptic degeneration in the medullary dorsal horn following transection of the inferior alveolar nerve in adult rats

The effect of topical application of axonal transport blockers to the transected peripheral nerve was assessed by quantitating the strychnine-enhanced transsynaptic degeneration following transection of the inferior alveolar nerve in adult rats. Systemic administration of strychnine (1 mg/kg/day) for 7 days at the postoperational interval of 23 days proved to be suitable for quantitating the transsynaptic degeneration at the light microscopic level. When the proximal stump of transected nerve was treated with 2% colchicine immediately after transection, 5.8 ± 6.8 dark neurons in a single section of the medullary dorsal horn, ipsilateral to the nerve transection, were observed. Following similar treatment with 0.4% vinblastine and 0.2% vincristine, 24.4 ± 10.5 and 9.4 ± 7.0 dark neurons were seen, respectively. When compared with 43.0 ± 9.4 dark neurons, which were seen in animals without alkaloid treatment, colchicine, vinblastine and vincristine significantly reduced the transsynaptic degeneration by 86, 43, and 78%, respectively. Possible mechanisms involved in prevention of transsynaptic degeneration by the alkaloids are discussed.