Peer influences on drug self-administration: Social facilitation and social inhibition of cocaine intake in male rats

Abstract

Rationale One problem facing animal models of intravenous drug self-administration, particularly those examining social manipulations, is that subjects must be removed from the home environment and separated from cagemates during testing. This represents a limitation of animal models, because it fails to capture the complex social environments in which drug use often occurs. Objectives The aim of this study was to examine intravenous cocaine self-administration in isolated and socially housed rats, with the caveat that the socially housed subjects lived together 24 hr/day, including during daily self-administration sessions. As a secondary aim, the study examined the impact of a companion that also self-administered cocaine versus a companion without access to cocaine. Methods Male rats were obtained at weaning and reared in isolated or pair-housed conditions for 6 weeks. Rats were then implanted with intravenous catheters and transferred to custom-built operant conditioning chambers that served as home cages for the remainder of the study. For some socially housed subjects, both rats had simultaneous access to cocaine; for others, only one rat of the pair had access to cocaine. Results Cocaine self-administration was facilitated in socially housed rats if both members of the pair had access to cocaine; however, cocaine self-administration was inhibited if only one rat of the pair had access to cocaine. Conclusions These data indicate that the self-administration behavior of a peer, not merely the presence of a peer, determines whether cocaine self-administration is facilitated or inhibited by social contact.

The effects of social learning on the acquisition of cocaine self-administration

“…The present findings are consistent with our previous study reporting that cocaine selfadministration is enhanced in socially housed rats if both members of the pair have access to cocaine, but cocaine self-administration is inhibited if only one member of the pair has access to cocaine (Smith, 2012). In our previous study, all rats were trained to press a response lever prior to self-administration training, so there was no opportunity to examine the role of social learning on the acquisition of a novel drug-reinforced response (i.e., all rats responded on the first day in which cocaine was available and received the maximum number of infusions available).…”

“…Despite the popularity of these models, very few experimental studies have examined the role of social learning in drug use, possibly due to a lack of animal models that allow subjects to observe and mimic the drug use behavior of another subject. We recently described the use of custom-built, operant conditioning chambers that permit two rats to be tested simultaneously during periods of intravenous, drug self-administration (Smith, 2012). Using these chambers, we reported that cocaine selfadministration could either be increased or decreased based on the behavior of a partner.…”

Cocaine self-administration in social dyads using custom-built operant conditioning chambers

“…Rats had concurrent access to cocaine reinforcement, were in no danger of becoming entangled with the tethering system of their social partner, and were prevented from responding on the lever of a social partner. We recently demonstrated that these chambers could be used to show how one peer can influence the drug intake of another peer (Smith, 2012; Peitz et al, 2013), and how drug self-administration can influence a preference for one peer over another (Smith and Pitts, 2014). In this paper, we show that these chambers may also be used to compare individual patterns of responding between social partners, and how these patterns of responding become more similar over time.…”

“…For instance, we previously reported that drug self-administration could either be facilitated or inhibited in these chambers, depending on whether one rat or both rats had access to cocaine (Smith, 2012). Specifically, cocaine self-administration was facilitated if both rats had access to cocaine, but cocaine self-administration was inhibited if only rat of the pair had access to cocaine.…”

“…For instance,Gipson et al (2011) and Chen et al (2011) examined amphetamine and nicotine self-administration, respectively, in laboratory rats using customized chambers that permitted a social partner (without access to drugs) to be present during experimental sessions. Similarly, we recently developed custom-built chambers that permit two rats to be tested in a single experimental session, with the caveat that both rats have access to drugs and data can be collected from both rats simultaneously (Smith, 2012). One novel aspect of this arrangement is that it allows for comparison of individual response patterns from each subject within a social pair.…”