Interaction of cocaine with positive GABA sub(A) modulators on the repeated acquisition and performance of response sequences in rats

Rationale: Although positive GABA sub(A) modulators can attenuate several cocaine-induced behavioral effects, there is a paucity of data on their interaction with cocaine on transition behavior or learning. Objectives: The current study examined the effects of cocaine (3.2-32 mg/kg), pregnanolone (3.2-24 mg/kg), and lorazepam (0.1-10 mg/kg) alone and in combination in rats responding under a multiple schedule of repeated acquisition and performance. Methods: In the acquisition component, subjects acquired a different three-response sequence each session, whereas in the performance component, they responded on the same three-response sequence each session. Results: All three drugs produced dose-dependent rate-decreasing and error-increasing effects. Cocaine was the least effective in decreasing rates and the most effective in increasing the percentage of errors. In combination with pregnanolone (3.2 or 10 mg/kg), the rate-decreasing effects of cocaine were relatively unchanged in both components, but 3.2 mg/kg of pregnanolone enhanced its error-increasing effects and the 10-mg/kg dose produced a significant dose-dependent interaction on errors. The combination of cocaine with lorazepam (0.32 mg/kg, 70-min pretreatment) produced significantly greater rate-decreasing and error-increasing effects than cocaine alone. A 15-min pretreatment with the same dose of lorazepam enhanced the error-increasing effects of small doses and attenuated the effects of larger doses of cocaine. Combinations of pregnanolone and lorazepam produced greater rate-decreasing and error-increasing effects in both components than either drug alone. Conclusions: The present data show that cocaine is more disruptive to learning in rats than pregnanolone or lorazepam, and that the disruptive effects of cocaine can be enhanced by CNS depressants.