Heroin Self-Administration in Rats

The heroin self-administration training paradigm and conditions were adapted from our previous studies (Ye et al., 2017 (link)). Operant chambers (AniLab Software and Instruments, Ningbo, China) were equipped with two nosepoke operandi (AniLab Software and Instruments, Ningbo, China) located 5 cm above the floor and with light stimuli. Rats were trained to self-administer heroin intravenously (0.05 mg/kg/infusion) during three 1-h daily training sessions separated by 5 min for 10 days. We used a fixed-ratio 1 (FR1) schedule of reinforcement with a 40-s time-out employed after each infusion. Briefly, rats were connected to a drug line consisting of a metal tether covering a polyethylene tubing which, through a fluid swivel (Instech, Plymouth Meeting, PA), was connected to a syringe pump loaded with a 10 ml syringe. The session began with the illumination of a house light that remained on for the entire session. Nosepokes into the active operandum led to a delivery of intravenous heroin accompanied by presentation of a 5-s tone-light cue. Nosepokes into the inactive operandum were counted but had no consequences. The heroin self-administration procedure was used in all four experiments. We excluded a total of eight rats from the experiments: three rats due to catheter patency failure and five rats due to failure to acquire heroin self-administration.