Effect of intracerebroventricular and systemic injections of caerulein, a CCK analogue, on electrical self-stimulation and its interaction with the CCK_A receptor antagonist, L-364,718 (MK-329)

Abstract

Systemic administration of caerulein (10–100 µg/kg SC), a potent analogue of cholecystokinin, caused a profound dose-related depression of variable-interval self-stimulation, followed by progressive recovery within 60 min. Intracerebroventricular injection of caerulein (3–1000 ng) was not more effective than systemic injection, while injections into the nucleus accumbens (3–100 ng bilaterally) were without detectable effect. Systemic injections of L-364,718 (70–700 µg/kg IP), a specific competitive antagonist of CCK_A (“peripheral-type”) receptors, had no effect on self-stimulation when given alone. When given in combination with caerulein, L-364,718 (200 µg/kg IP) significantly reduced the inhibitory effect of caerulein (30 µg/kg SC); however, this dose, and higher doses of L-364,718, failed to confer complete protection. It is concluded that self-stimulation performance may be subject to modulation by CCK receptors distributed predominantly in the peripheral nervous system and that some but not all of these receptors are CCK_A receptors.