Sensory hyperinnervation after neonatal skin wounding: effect of bupivacaine sciatic nerve block.

The response to tissue injury includes sensitization of peripheral nociceptors and central neuronal pathways leading to acute clinical and inflammatory pain. A further response is sprouting of sensory nerve terminals in the region of skin damage. This hyperinnervation response is particularly intense in neonates compared with adults. In this study, we tested the effect of regional nerve block at the time of injury on skin hyperinnervation. Anaesthetized newborn rat pups were treated with percutaneous sciatic nerve block injections of 0.25% bupivacaine 25 microliters followed by a localized hindpaw skin wound. Cutaneous innervation was studied by image analysis of immunostained skin sections, 7 days after wounding, and sensory thresholds were assessed using von Frey hairs. The results showed that both hyperinnervation and hypersensitivity were not significantly altered by the application of a regional nerve block at the time of injury. This suggests that regional analgesia, used commonly in clinical practice, is unlikely to prevent the hyperinnervation that follows skin wounding.