Concurrent positive and negative goalbox events produce runway behaviors comparable to those of cocaine-reinforced rats.

Rats traversing a straight-alley for reinforcing stimuli typically exhibit faster running times as training proceeds. In previous work from this laboratory, animals running for a reinforcement consisting of intravenous infusions of cocaine, unexpectedly demonstrated a progressive increased time to enter the goalbox over trials. Closer observation revealed that the animals were exhibiting a unique retreat behavior (i.e., stopping their forward advance toward the goalbox and returning toward the startbox). It was hypothesized that the retreat behavior reflected an inherent conflict that originated from concurrent positive and negative associations with the goalbox. Such associations were attributed to cocaine's dual and well documented reinforcing and anxiogenic effects. To test this idea, the present study compared the runway behavior of animals that concurrently received food and mild foot shock in the goalbox to the behavior of the other animals running for cocaine. Results demonstrated that food + shock reinforced animals took longer to enter the goalbox and made more retreats than a control group that received only food in the goalbox. Both these effects were reversed by pretreatment with the anticonflict, anxiolytic drug, diazepam. The behavior pattern of animals that received the combination of food and footshock was found to strongly resemble that of IV cocaine-reinforced rats, a result consistent with the notion that chronic cocaine administration has both positive and negative consequences.