Role of cholecystokinin receptors in induction of an antinociception in hot-plate test

In the present study, the antinociceptive effect of cholecystokinin recepto r agonists in the hot-plate test in mice has been evaluated. Subcutaneous a dministration of cholecystokinin octapeptide (cholecystokinin-8; 0.001, 0.0 05, 0.01, 0.05, and 0.1 mg/kg), unsulfated cholecystokinin octapeptide (cho lecystokinin-8U; 0.1 mg/kg) or caerulein (0.25 mg/kg) produced antinocicept ion. Administration of the cholecystokinin tetrapeptide (cholecystokinin-4; 0.25, 0.5 and 1.0 mg/kg) had no effect in the hot-plate test. Subcutaneous injection of the selective cholecystokinin receptor antagonists, MK-329 (0 .125, 0.25 and 0.5 mg/kg) or L-365,260 (0.125, 0.25 and 0.5 mg/kg), produce d no antinociceptive response. When the animals were pretreated with the ch olecystokinin receptor antagonists or naloxone (0.5 and 1 mg/kg), a signifi cant decrease in the antinociceptive response induced by cholecystokinin-8 and caerulein was obtained. The results indicate that single administration of cholecystokinin receptor agonists could produce an antinociceptive effe ct which is probably mediated via cholecystokinin receptors. With respect t o the results obtained from morphine and naloxone administration, it is con cluded that there may be an interaction between cholecystokinin and opiate mechanisms.