Neuropathic pain in neonatal rats.

The aim of this study was to determine if peripheral nerve injury in neonatal rats triggers neuropathic pain behaviors as it does in adults. The injury was produced in three groups of neonatal rats (1, 2, and 3 weeks old) by tightly ligating the left L5 and L6 spinal nerves. Behavioral tests for mechanical allodynia were conducted from the 15th day after birth for the 1- and 2-week groups, and 1 day after surgery for the 3-week group. Rats in the 3-week group developed behaviors representing mechanical allodynia as is seen in adults. For the younger animals, however, the signs of mechanical allodynia lasted for a shorter period of time. These data suggest that a factor which is critically important for the maintenance of neuropathic pain develops between the 2nd and 3rd postnatal weeks.