[Study of expression of slit2 mRNA in rats of different age after sciatic nerve injury]

To determine the age-related expression features of slit2 mRNA at various intervals at the proximal and distal parts of sciatic nerve during re-innervation after severance injury, and to investigate the molecular biological reason why co-contraction occurs more commonly in the young rats than in the adults after peripheral nerve injury.

The right sciatic nerve was transected sharply at the midthigh in the young and adult rats, 28 in each group. The proximal and distal stumps were inserted into a medical silicone tube with a gap of 3 mm. Before the injury, and 1, 3 and 7 days (6 rats at each interval) after sciatic nerve severance injury, both stumps of the sciatic nerve were harvested. Reverse transcription polymerase chain reaction (RT-PCR) was use to examine the expression of slit2 mRNA in the young and adult group rats. In situ hybridization was done to detect the cell location of slit2 mRNA expression in young and adult rats, 4 rats in each group, 2 rats used before the injury and 2 rats used on the postoperative third day.

RT-PCR results suggested that slit2 mRNA at both stumps was significantly lower in the young group of rats than in the adult except that at the proximal part on the postoperative 7th day. There was statistically significant difference (P < 0.01). In situ hybridization studies indicated that the slit2 mRNA was specifically expressed in the cytoplasm of Schwann cells both in the young and adult rats before injury and 3 days after injury.

The expression of slit2 mRNA by Schwann cells in the young rats is lower than that in the adult rats after peripheral nerve injury. These findings suggests the lower expression of chemotactic factor (slit2) by Schwann cells in the young group is likely to be the molecular biological reason for the higher incidence of co-contraction between agonists and antagonists in the younger rats.