INHIBITION OF SEROTONIN SYNTHESIS ATTENUATES INHIBITION OF INGESTIVE BEHAVIOR BY CCK-8

Ingestive behavior was activated in male rats by intraoral infusion of a 1-M solution of sucrose. Injection of cholecystokinin octapeptide ( CCK-8; 1.6 or 5.0 mu g) inhibited ingestion of the sucrose solution an d increased the concentration of 5-hydroxytryptamine (5-HT) in the par aventricular hypothalamic nuclei. The inhibitory effect of the low, bu t not the high, dose of CCK-8 was attenuated by depleting 5-HT in the brain with p-chlorophenylalanine (PCPA; 100 mg/kg for 3 days). Treatme nt with 5-hydroxytryptophan (20 mg/kg) increased the concentration of 5-HT in the brain of rats pretreated with either NaCl or PCPA and enha nced the inhibitory effect of CCK-8 on ingestive behavior in the PCPA- , but not NaCl-, treated rats. 5-HT may play a role in the mechanism o f action of CCK-8 but additional factors must be involved.