Contribution of the sensory and sympathetic nervous system to scalding-induced edema in the rat paw

It has recently been hypothesized that both the sensory and sympathetic nervous system contribute to the inflammatory reaction. A scalding model was developed in anaesthetized rats to investigate the contribution of neuropeptides in heat-induced edema localized to the hindpaw. After immersing the paw in water at 60°C for 10, 20, 30 and 60 s, edemic reactions were registered as change of paw volume in a plethysmograph and hindpaw perfusates collected to measure the content of neuropeptides by radioimmunoassay. A scalding period of 30 s induced the most prominent edemic reaction. There was a marked increase of the sensory neuropeptide neurokinin A and the sympathetic related transmitter neuropeptide Y in hindpaw perfusates after scalding. The effect of peripheral nerve ligation on edemic reaction and on the release of neuropeptides was investigated in rats scalded for 30 s at 60°C. There was a significant decrease of edema formation in the scalded nerve ligated paw as compared with the scalded paw on the non-ligated side. Neurokinin A was not detected in nerve ligated rats before or after scalding, whereas mononeuropathic rats showed increased concentrations of neuropeptide Y. The present results indicate that the sensory as well as the sympathetic nervous system, possibly through the release of neuropeptides, may contribute to scald-induced edema.