Stimulation of either cholecystokinin receptor subtype reduces while antagonists potentiate or sensitize a morphine-induced excitatory response.

Cholecystokinin peptides (CCK) have been shown to antagonize many opioid-mediated effects. The present study was undertaken to determine whether peripheral injections of cholecystokinin sulphated octapeptide (CCK8), cholecystokinin tetrapeptide (CCK4), the CCK(1) (lorglumide) and the CCK(2) (PD-135,158 and LY-225910) receptor antagonists can influence a classic morphine excitatory effect, i.e.