Figure 1.

Schematic representation of CPP procedure. On day 6, all animals were allowed free access to the CPP apparatus to test for initial chamber preference. Drug treatment and order of environment in which animals are confined are represented by the individual squares on days 7-15. On day 17, all animals were again allowed free access to the CPP apparatus to test for final chamber preference. Drug-paired (n = 10) and unpaired (n = 10) groups were each divided into two subgroups to counterbalance the environmental conditioning order. For additional details, see Materials and Methods (“Behavioral conditioning”).