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

Abstract

Background: Social learning models of substance use propose that drug-use behaviors are learned by observing and mimicking the behavior of others. The aim of this study was to examine the acquisition of cocaine self-administration in three groups of experimentally naïve rats: rats that were tested in isolation, rats that were tested in the presence of another rat that had access to cocaine and had previously been trained to self-administer cocaine, and rats that were tested in the presence of another rat that did not have access to cocaine.

Methods: Male rats were reared in isolated or pair-housed conditions and implanted with intravenous catheters. Pair-housed rats were then assigned to drug-experienced or drug-naïve conditions. In the drug-experienced condition, one rat of each pair was trained to self-administer cocaine in isolation before the reintroduction of its partner. In the drug-naïve condition, one rat of each pair did not have access to cocaine for the duration of the study. For each group, the acquisition of cocaine self-administration was measured over 15 days in rats with access to cocaine but no prior operant training.

Results: Rats tested with a drug-experienced partner were faster to acquire cocaine self-administration and emitted more active lever presses than rats tested with a cocaine-naïve partner. Data for the isolated control group fell between the other two groups on these measures.

Conclusion: These data indicate that the acquisition of cocaine self-administration can either be facilitated or inhibited by social contact. Collectively, these results support a social learning model of substance use.

Keywords: Cocaine; Rat; Self-administration; Social; Social learning.

Figure 1

A. Percent of experimentally naïve rats reaching the acquisition criterion over 15 days of testing in each of the three groups. B. Number of days to reach the acquisition criterion. C. Number of active lever presses per session over 15 days of testing. D. Total number of active lever presses over 15 days of testing. E. Number of inactive lever presses per session over 15 days of testing. F. Total number of inactive lever presses over 15 days of testing. Asterisks (*) indicate significant difference between groups. For panels A, C, and E, vertical reference lines represent transitions between different experimental events: self-administration testing with 0.25 mg/kg/infusion cocaine (days 1–5); self-administration testing with 0.75 mg/kg/infusion cocaine (days 6–10); self-administration testing with 1.5 mg/kg/infusion cocaine (days 11–15). For all panels, vertical lines surrounding data points represent the SEM; where not indicated, the SEM fell within the data point.

Figure 2

Cocaine self-administration during the 15^th session in only those rats meeting the acquisition criterion. Vertical axis indicates number of infusions during 2-hr test session. Data are shown from 8 experimentally naïve rats from the cocaine-experienced group, 19 experimentally naïve rats from the isolated group, and 5 experimentally naïve rats from the cocaine-naïve group.

Figure 3

A. Number of active lever presses per session over 15 days of testing for the cocaine-experienced group. B. Total number of active lever presses over 15 days of testing. Asterisks (*) indicate significant difference between groups. See Figure 1 for additional details.

Figure 4

A. Number of active lever presses per session over 15 days of testing for the cocaine-naïve group. B. Total number of active lever presses over 15 days of testing. See Figure 1 for additional details.