Rationale: Acute cocaine administration produces an initial rewarding state followed by a dysphoric/anxiogenic "crash."
Objective: The objective of this study was to determine whether individual differences in the relative value of cocaine's positive and negative effects would account for variations in subsequent drug self-administration.
Methods: The dual actions of cocaine were assessed using a conditioned place test (where animals formed preferences for environments paired with the immediate rewarding effects of 1.0mg/kg i.v. cocaine or aversions of environments associated with the anxiogenic effects present 15-min postinjection) and a runway test (where animals developed approach-avoidance "retreat" behaviors about entering a goal box associated with cocaine delivery). Ranked scores from these two tests were then correlated with each other and with the escalation in the operant responding of the same subjects observed over 10 days of 1- or 6-h/day access to i.v. (0.4 mg/inj) cocaine self-administration.
Results: Larger place preferences were associated with faster runway start latencies (r s = -0.64), but not with retreat frequency or run times; larger place aversions predicted slower runway start times (r s = 0.62), increased run times (r s = 0.65), and increased retreats (r s = 0.62); response escalation was observed in both the 1- and 6-h self-administration groups and was associated with increased CPPs (r s = 0.58) but not CPAs, as well as with faster run times (r s = -0.60).
Conclusions: Together, these data suggest that animals exhibiting a greater positive than negative response to acute (single daily injections of) cocaine are at the greatest risk for subsequent escalated cocaine self-administration, a presumed indicator of cocaine addiction.
Keywords: Cocaine; Cocaine addiction; Conditioned place test; Drug abuse; Drug aversion; Drug reward; Drug self-administration; Extended access; Operant runway; Opponent processes.