Effect of neonatal treatment with capsaicin on carrageenan-induced paw oedema in the rat.

The time course of the paw oedema induced by the subplantar injection of carrageenan was studied in rats treated neonatally with capsaicin and in their vehicle-treated controls. In the capsaicin-treated rats, which show a permanent deficit of unmyelinated primary sensory neurones, carrageenan produced an oedema which was larger and lasted longer than in the vehicle-treated rats. Pretreatment with the histamine liberator compound 48/80 reduced the carrageenan-induced paw oedema only in the capsaicin-treated rats whereas pretreatment with indomethacin reduced it in both groups of rats. The increased and prolonged inflammatory response to carrageenan in capsaicin-treated rats may be explained by an enhanced release of histamine from mast cells and may also reflect a 'trophic disorder of the denervated skin'.