Schaal D.W., Branch M.N.
Department of Psychology, University of Florida, Gainesville, FL 32611, USA.
Behav Pharmacol. 1992 Feb;3(1):5-9. doi: 10.1097/00008877-199203010-00003.
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.
八只鸽子的反应在固定比率为30的食物强化程序下得以维持。当鸽子体重维持在自由进食体重的80%时，测定了会前注射一系列可卡因剂量（1.0或3.0毫克/千克至10.0或17.0毫克/千克）的效果。然后，一组鸽子的体重增加到自由进食体重的90%至100%之间，而另一组鸽子的体重则降至自由进食体重的70%。再次测定可卡因的效果。在此之后，将鸽子的体重调整到它们尚未接触过的自由进食体重的百分比，并第三次测定可卡因的效果。可卡因产生了剂量依赖性的反应率下降。当鸽子相对食物饱足时（即自由进食体重的90%至100%），在较小的可卡因剂量下就观察到了反应率下降；当鸽子维持在自由进食体重的70%时，需要更大的剂量才能降低反应。如果在可卡因自我给药时，当食物剥夺水平增加时对可卡因行为抑制作用的抵抗力也增加，这可能有助于解释在食物剥夺条件下可卡因强化行为量的增加。
