IRRADIATION OF THE RAT SCIATIC-NERVE LEADS TO DELAYED RECOVERY FROM FUNCTION LOSS AFTER HEAT-TREATMENT OR MECHANICAL DAMAGE

The influence of irradiation on recovery of the rat sciatic nerve from motor function loss induced by localized heat treatment or crushing w as investigated. Heat treatment as well as crushing resulted in an acu te and complete loss of motor function. This function loss was transie nt and complete recovery took place in about 4 weeks. Radiation alone did not lead to detectable damage for at least 90 weeks. A 20 mm long segment of the nerve was irradiated intraoperatively using 50 kV X-ray s. Heat, 30 min at 45 degrees C was applied to the irradiated part (ov er a length of 5 mm) of the nerve using a brass thermode. Crushing the nerve was performed with a haemostat by keeping the nerve between the jaws for 30 s. Functional damage to the nerve was assessed using the toe-spreading test, which mainly assesses motor function. Irradiation (25 Gy) of a nerve segment, which included the part that was heated or crushed before, resulted in a delayed recovery from the heat or crush treatment compared to controls. X-ray induced delay was considerably longer after heating than after a 5 mm crush: 13.0 +/- 2.0 or 4.3 +/- 1.0 days respectively. This suggests that after heating considerably m ore cells in the nerve are forced to start proliferation (which leads to expression of X-ray damage) than after crushing. The site of the cr ush or heat application in relation to the irradiated part of the nerv e proved to be very important. The delay in recovery was maximal when crushing or heating was in the middle part of the irradiated segment. This further supports the hypothesis that migration of cells from outs ide the irradiated segment is required for recovery, moreover these ex periments show that recruitment of cells for recovery can take place f rom both sides: distally, where many cells are stimulated into prolife ration as a result of Wallerian degeneration, as well as proximally.