TIME-COURSE OF MOTONEURON DEATH AFTER NEONATAL SCIATIC-NERVE CRUSH INTHE RAT

Sciatic motoneurones were retrogradely labelled with long-lasting fluo rescent dyes prior to unilateral nerve crush in either 3-day-old or ad ult rats. The number of surviving labelled motoneurones at intervals a fter nerve injury were compared to the number in the contralateral con trol ventral horn and in unoperated animals. Following adult nerve cru sh there was no significant reduction in the number of labelled motone urones, but after neonatal nerve crush the count was reduced to about 35%. Most of the cell death occurred during the first 6 days after ner ve injury, mainly from the lower half of the motor column, but about o ne third died between 6 and 12 days, mainly from the upper part. These results suggest that less mature motoneurones tend to die earliest, b efore the muscle is reinnervated. Those in the upper, more mature part of the motor pool survive longer but may still die during reinnervati on. At least two types of glial cell were secondarily labelled by this method, distinguished by their response to nerve injury.