Ineffectiveness of cholecystokinin in impairing runway performance

We compared changes in runway performance by rats for sucrose reward following injections of the synthetic C-terminal octapeptide of cholecystokinin (CCK-8) with those seen after variations in food deprivation and injections of lithium chloride. No effects on running for either 10% or 30% sucrose were found following 0.5 to 4.0 micrograms/kg of CCK-8, though such doses suppressed 30-min sucrose intake up to 53%. Statistically reliable slowing of running for 10% sucrose was observed on two series of tests after 8.0 micrograms/kg of CCK-8. Running for 30% sucrose was not significantly affected by this dose. The general ineffectiveness of CCK-8 for producing decrements in running spread contrasts with significantly reduced performance after either reductions in food deprivation (21 h vs 12 and 3 h) or injections of 75 mg/kg lithium chloride. These results suggest that the mode of action of CCK-8 in reducing food intake is different than that produced by changes in hunger or by non-specific interference with motivation by malaise. The finding that CCK-8 can substantially reduce consumption with no apparent changes in appetitive motivation is consistent with the hypothesis that this substance acts only late in the meal to prematurely trigger satiety.