Putative stimulants for functional recovery after neural trauma: only spermine was effective

The motor functional recovery after sciatic nerve crush was measured in rats treated with daily injections of (a) thyrotropin-releasing hormone (2.0 mg/kg, (b) alpha-melanocyte-stimulating hormone (0.07 mg/kg/48 h), or (c) testosterone propionate (4.4 mg/kg). The recovery of the motor function of the sciatic nerve was indicated by using the return of the toe-spreading response. None of the treatments differed significantly from saline controls in the time needed for recovery. The same procedure (without injections) was carried out with castrated and noncastrated male rats in order to test the effect of the lack of testosterone on recovery time after sciatic crush. The groups did not differ significantly as to their recovery times. The same method was used to study the effect of spermine (10.0 mg/kg/day) on the recovery of motor function. Spermine seemed to reduce the time needed for recovery from a mean value of 15.7 to 11.0 days (P less than 0.01). We also studied the effect of daily injections of spermine (13.0 mg/kg) on the sensory division of the peripheral nerve using the foot-flick test. The time needed for recovery after crush in the sciatic notch was reduced from 13.7 to 7.7 days (P less than 0.005). These results do not support the hypothesis that alpha-melantocyte-stimulating hormone, thyrotropin-releasing hormone, or testosterone enhance functional recovery of severed motor axons. Our results confirm a previous observation that spermine reduces the time needed for recovery after trauma in peripheral motor neurons. The result of the foot-flick test suggests that spermine enhances both motor and sensory recovery.