Social facilitation of d-amphetamine self-administration in rats

Abstract

The link between social influence and drug abuse has long been established in humans. However, preclinical animal models of drug abuse have only recently begun to consider the role of social influence. Since social factors influence the initiation and maintenance of drug use in humans, it is important to include these factors in preclinical animal models. The current study examined the effects of the presence of a social partner on responding for sucrose pellets under various motivational conditions, as well as on d-amphetamine (AMPH) self-administration. Rats were trained to lever press for either sucrose or AMPH (0.01 or 0.1 mg/kg/infusion unit dose). Following response stability, a novel same-sex conspecific was presented in an adjacent compartment separated by a clear divider, and responding for sucrose or AMPH reward was measured. Rats were allowed to restabilize, and subsequently given an additional partner presentation. Presence of the social partner increased responding only during the first pairing with the AMPH 0.1 mg/kg/infusion unit dose, whereas inhibition of responding was observed during the first pairing during access to the 0.01 mg/kg/infusion unit dose. Under free feed conditions, inhibition of sucrose pellet responding was observed in the presence of the social partner, but this effect was attenuated under food restriction. In contrast, the results demonstrate social facilitation of AMPH self-administration at a high unit dose, thus extending the influence of social factors to an operant conditioning task. This model of social facilitation may have important implications as a preclinical model of social influence on drug abuse.

Figure 1

(a) Image of social self-administration chamber. Rats are separated by a Plexiglas divider. The responder rat (rat A) is trained in one compartment to lever press for either food or drug, while the other compartment is vacant until a partner pairing occurs. During a partner pairing, a naïve conspecific (rat B) is placed into the adjacent compartment. (b) Schematic of the social self-administration chamber.

Figure 2

(a) Cumulative pellets earned under free feed conditions for the first baseline and partner pairing and (b) total active and inactive lever presses for the first baseline and partner pairing (n = 6). (c) Cumulative pellets earned for the second baseline and partner pairing and (d) total active and inactive lever presses for the second baseline and partner pairing. There was a significant main effect of lever. (*p < .01; **p < .001 baseline compared to partner pairing at each time point or active compared to inactive and baseline active compared to partner pairing active lever presses). Data expressed as mean ± SEM.

Figure 3

Cumulative pellets earned and total active and inactive lever presses under conditions of food restriction (n = 6). There was a significant main effect of lever. All details are as in Figure 2.

Figure 4

Cumulative infusions and total active and inactive lever presses for the AMPH 0.01 mg/kg/infusion unit dose (n = 5; *p < .01, **p < .001). There was a significant main effect of lever. All other details are as in Figure 2.

Figure 5

Cumulative infusions and total active and inactive lever presses for the AMPH 0.1 mg/kg/infusion unit dose(n = 5; *p < .01, **p < .001). All other details are as in Figure 2.