Apomorphine separates the antinociceptive effects of cholecystokinin octapeptide and ceruletide from those of morphine.

The antinociceptive effects of ceruletide (CER, 0.03 mg/kg s.c.), cholecystokinin octapeptide (CCK-8, 0.12 mg/kg s.c.) and morphine (0.33 mg/kg s.c.) were determined in mice with the hot plate test using paw licking and jumping up as endpoints. Licking was more resistant to antinociceptive effects than was jumping. Apomorphine 0.25 mg/kg, per se, produced more antinociception with licking than with jumping. With the jumping reaction, but not the licking response, apomorphine 0.063 and 0.125 mg/kg abolished the effect of morphine but did not modify that of CER and CCK-8.