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

The response to tissue injury includes sensitization of peripheral nocicept ors and central neuronal pathways leading to acute clinical and inflammator y pain. A further response is sprouting of sensory nerve terminals in the r egion of skin damage. This hyperinnervation response is particularly intens e in neonates compared with adults. In this study, we tested the effect of regional nerve block at the time of injury on skin hyperinnervation. Anaest hetized newborn rat pups were treated with percutaneous sciatic nerve block injections of 0.25% bupivacaine 25 mu l followed by a localized hindpaw sk in wound. Cutaneous innervation was studied by image analysis of immunostai ned skin sections, 7 days after wounding. and sensory thresholds were asses sed using von prey hairs. The results showed that both hyperinnervation and hypersensitivity were not significantly altered by the application of a re gional nerve block at the time of injury. This suggests that regional analg esia, used commonly in clinical practice, is unlikely to prevent the hyperi nnervation that follows skin wounding.