BACKGROUND: Sciatic nerve injury in neonatal rats impairs muscle recovery and significantly reduces the number of surviving motoneurons. We examined the rate of motoneuron death after sciatic nerve crush in neonatal rats, as well as the neuroprotective effect of systemic MgSO4 administration, by assessing the number of horseradish peroxidase -labelled motoneurons in the spinal cord ventral horn, after injecting EDL and TA muscles.MATERIAL/METHODS: Left sciatic nerve crush was performed on the 2nd postnatal day. MgSO4 (0.05 ml of 1 M solution/10 g body weight) was administered subcutaneously, daily for twelve days. Animals were examined for the number of motoneurons of EDL and TA muscles, in the spinal cord ventral horns at 14, 21, and 28 days postnatally (P) and adulthood. 24 h to 48 h after intramuscular HRP injection, the animals were perfused transcardially with a fixative containing glutaraldehyde. Serial sections of the spinal cords were cut and processed for Hanker-Yates staining, and the number of labeled motoneurons was measured under a camera lucida.RESULTS: Nerve crush resulted in 37% motoneuron survival at P14, 33% at P21, 28% at P28 and 21% in adult rats. Following MgSO4 administration motoneuron survival rates of 51%, 47%, 44% and 39% were observed respectively, for the different age groups. The values obtained in magnesium-treated rats proved to be significantly different (p<0.05), compared to non-treated rats of the same age group.CONCLUSIONS: Nerve crush after birth resulted in significant motoneuron death, established already at P14. MgSO4 administration induced significant motoneuron survival.