The effect of schedule removal on the maintenance of heroin self-injection.

The present study investigated the effect of schedule removal on the maintenance of heroin self-injection in 80% reduced body weight Wistar rats. During the acquisition phase, 42 animals were subjected to a fixed time 1 min food delivery schedule and were allowed to self-inject either heroin or saline for 10 days. During the maintenance phase (Days 11-15), animals in both the heroin and saline conditions were randomly allocated to schedule, no schedule, and no schedule plus food groups. Infusion rates, hot plate response latencies, and food intake were used as dependent measures to monitor differences between groups. The results revealed that schedule removal disrupted, but did not extinguish, heroin-seeking behaviour.