Changes due to food deprivation in the effects of cocaine on the responding of pigeons.

The responding of eight pigeons was maintained under a fixed-ratio 30 schedule of food reinforcement. While the pigeons were maintained at 80% of their free-feeding body weights the effects of presession injection of a range of cocaine doses (1.0 or 3.0mg/kg to 10.0 or 17.0mg/kg) were determined. The weights of one group of pigeons were then increased to between 90 and 100% of their free-feeding weights, while the other group's weights were reduced to 70% of their free-feeding weights. The effects of cocaine were determined again. Following this, pigeons' weights were adjusted to the percentage of free-feeding weight to which they had not yet been exposed, and the effects of cocaine determined a third time. Cocaine produced dose-dependent decreases in response rates. Decreases were observed at smaller cocaine doses when pigeons were relatively food-satiated (i.e. 90-100% of free-feeding weight); larger doses were required to decrease responding when pigeons were maintained at 70% free-feeding weight. If increased resistance to the behaviorally suppressive effects of cocaine when food deprivation levels are increased occurs also when cocaine is self-administered, this could help account for increases in amounts of cocaine-reinforced behavior under conditions of food deprivation.