EFFECTS OF NEUROTOXINS AND HINDPAW INFLAMMATION ON OPIOID RECEPTOR IMMUNOREACTIVITIES IN DORSAL-ROOT GANGLIA

Three types of opioid receptors mediate peripheral opioid antinocicept ion in inflammation. Recently, antisera that recognize unique epitopes of the cloned mu-, delta-, and kappa-opioid receptors have been devel oped. Using these antisera we examined the regulation of opioid recept ors in rat dorsal root ganglia after hindpaw inflammation and the infl uence of neurotoxins for primary afferent neurons and sympathetic neur ons thereon. Peripheral tissue inflammation was produced by injection of complete Freund's adjuvant into the right hindpaw. Capsaicin was in jected subcutaneously once a day for three days using a total dose of 150 mg/kg. 6-hydroxydopamine was injected intraperitoneally 75 mg/kg/d ay for three days. Freund's adjuvant induced a marked increase in the percentage of mu-, but a decrease in delta and kappa-opioid receptor-p ositive neurons. Capsaicin significantly decreased mu-, delta-and kapp a opioid receptor immunoreactivity in both Freund's adjuvant treated a nd non-treated rats. No significant changes on the mu-, delta-and kapp a-opioid receptor immunoreactivities were observed after 6-hydroxydopa mine treatment in either Freund's adjuvant-treated or non-treated rats . Our studies indicate: (1) Peripheral inflammation can differentially regulate the expression of the three opioid receptors in dorsal root ganglia neurons with an up-regulation of mu-and down-regulation of del ta-and kappa-opioid receptors. 2) A significant portion of mu-, delta- and kappa-opioid receptors are located on capsaicin-sensitive neurons in dorsal root ganglia of both non-inflamed and inflamed hindlimbs. 3) The expression of opioid receptors in dorsal root ganglia of either i nflamed or non-inflamed hindlimbs is not influenced by sympathetic pos tganglionic neurons. (C) 1998 IBRO. Published by Elsevier Science Ltd.