Reduction of the reinforcing effectiveness of cocaine by continuous d-amphetamine treatment in rats: importance of active self-administration during treatment period
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- Zimmer, B.A., Chiodo, K.A. & Roberts, D.C.S. Psychopharmacology (2014) 231: 949. doi:10.1007/s00213-013-3305-4
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Continuous administration of d-amphetamine has shown promise as a treatment for psychostimulant addiction. In rodent studies, constant infusion of d-amphetamine (5 mg/kg/day) has been shown to reduce cocaine-reinforced responding in the dose range of 0.19–0.75 mg/kg/inf.
The present study tested whether these effects were a reflection of pharmacological interactions between d-amphetamine and cocaine or if they resulted from associative learning mechanisms
After stable progressive ratio (PR) baselines were established, rats were implanted with subcutaneous osmotic minipumps filled with either d-amphetamine (5 mg/kg/day—groups 1 and 2) or saline (group 3). During the treatment period, groups 1 and 3 self-administered cocaine at a dose that was previously shown to produce the most robust effects in combination with d-amphetamine treatment (0.19 mg/kg/inf), while group 2 received passive cocaine infusions.
In replication of previous studies, d-amphetamine treatment resulted in a significant (35 %) decrease in breakpoints relative to saline controls. By contrast, no reductions in breakpoints were observed in animals that received passive cocaine infusions during the treatment period (group 2).
Active self-administration of cocaine during the treatment period appears to be an important factor in reducing cocaine-reinforced breakpoints. These findings suggest learning mechanisms are involved in the therapeutic effects of continuous d-amphetamine, and pharmacological interaction mechanisms such as cross-tolerance cannot completely account for the observed decreases in cocaine seeking.