The impact of social reward on drug self-administration in different animal models of addiction
| Addiction Model | Behavioral Results |
|---|---|
| Escalation model | In the study introducing the social self-administration and choice model (Venniro et al., 2018), the authors first used the established extended-access (6 h/day) escalation model of addiction (Ahmed and Koob, 1998) to determine whether methamphetamine (0.05, 0.1, 0.2, 0.4 mg/kg/infusion) or heroin (0.05, 0.1, 0.1 mg/kg/infusion) self-administration would be prevented by operant access to social interaction. The authors then devalued the social reward by either increasing the delay after social-lever press or by punishment of 50% of social-lever presses with foot shock of increasing intensity (0.0 to 0.5 mA). Social reward prevented methamphetamine and heroin self-administration independent of drug unit dose. Methamphetamine or heroin self-administration resumed only if there was a long delay before social reward or if social-lever presses were punished. Rats preferred social interaction over methamphetamine even after either 15 or 30 days of forced abstinence. |
| Three-criteria DSM-IV–based model | Subsequently, the authors performed a more stringent test of the effect of social reward using rats identified as addicted in the three-criteria DSM-IV–based model (Deroche-Gamonet et al., 2004). In this experiment, they trained rats for methamphetamine self-administration in 50 daily sessions that included three 40-min drug periods separated by two 15-min nondrug periods (during which we measured nonreinforced active lever presses). The authors then determined the rats’ addiction score by measuring 1) total nonreinforced lever presses during two daily nondrug periods under the fixed-ratio reinforcement schedule, 2) number of drug rewards earned under a progressive-ratio reinforcement schedule, and 3) punishment responding. They classified rats as highly addicted, or High (≈19%); moderately addicted, or Medium (≈21%); and mildly addicted, or Low (≈60%). Finally, we trained some or all rats from each group (High, Medium, Low) for social self-administration (six sessions) and then determined drug versus social-reward preference in five discrete-choice sessions. The main finding was that the rats strongly preferred social interaction over methamphetamine and that this effect was independent of addiction-score group. |
| Intermittent-access drug self-administration model | Next, the authors determined whether rats with high addiction scores would be more vulnerable to reversal of their preference for social over drug reward. In this experiment, they trained rats to self-administer methamphetamine first using the escalation model (Ahmed and Koob, 1998) (9 days, 6 h/day) and then using the intermittent-access drug self-administration model (Zimmer et al., 2012). They determined the rats’ addiction score, which included the number of drug rewards earned under the progressive-ratio reinforcement schedule and punishment responding. The authors classified rats as High (≈22%), Medium (≈30%), and Low (≈48%). They trained some rats from each group (High, Medium, Low) for social self-administration (four sessions) and ran discrete-choice sessions using delay or punishment of social reward. As in the previous experiments, the rats strongly preferred social interaction over methamphetamine, and this effect was independent of the addiction-score group. Additionally, high addiction scores did not predict lower social preference. |