The contribution of drug history and time since termination of drug taking to footshock stress-induced cocaine seeking in rats.

RATIONALE

There is reason to think that footshock stress-induced reinstatement of cocaine may be affected by the history of drug use and time since termination of drug taking.

OBJECTIVES

Here, we assessed the contribution of daily access (hours per day) and duration (number of days) of cocaine self-administration to propensity to reinstate drug seeking following footshock stress at three time points following cocaine self-administration.

METHODS

Rats were trained to self-administer cocaine (0.5 mg kg(-1) infusion(-1)) on a fixed ratio 1 schedule in one of four training combinations of hours per day and number of days [2/7, 2/21, 12/7, and 12/21 (h/day)]. Rats were then tested for the first time under extinction conditions at either day 1, 10, or 60 after termination of cocaine availability. Once extinction criterion was met (<15 lever presses in 1 h), rats were then tested for stress-induced reinstatement after 15 min of intermittent, inescapable footshock (0.8 mA, 0.5 s/shock, mean off period of 40 s).

RESULTS

Rats that were given 12-h access to cocaine during training responded less in tests of extinction than those rats given 2-h access. Rats in all groups tested in extinction at days 10 and 60 showed higher responding than at day 1, suggesting an incubation of responding. In footshock stress-induced reinstatement tests, rats with greater exposure to cocaine showed a similar suppression of responding at day 1 and enhanced responding at day 60. As expected, rats that were given 12-h/21-day access to cocaine had the greatest intake of cocaine across the training phase with a slow escalation of hourly intake.

CONCLUSION

Greater access to cocaine results in suppression of cocaine seeking following footshock stress at early time points and a progressive increase over time.