EFFECTS OF CCK RECEPTOR AGONISTS AND ANTAGONISTS ON MORPHINE-INDUCED ANTINOCICEPTION IN MICE

In the present study the effects of both CCK receptor agonists and antagonists on antinociception induced by morphine in the tail-flick test have been evaluated. M orphine induced dose-dependent antinociception in mice. The response of morphine was potentiated by sulfated cholecystokinin-8 (CCK-8S) but not by unsulfated cholecystokinin-8 (CCK-8U). The CCK receptor antagonists MK-329 and L-365, 260 decreased the potentiation of morphine antinociception induced by CCK-8S.•The antagonists even decreased the response induced by morphine in the pre5ence ofCCK-8U. High doses ofMK-329 and L-365, 260 also potentiated morphine's antinociception. Single administration of the CCK receptor agonists CCK-8 and CCK-8U or CCK receptor antagonists did not elicit any response in the tail-flick test. It is concluded that CCK receptor mechanisms are involved in the modulation of pain response and/or morphine antinociception.