Cycloheximide enhances maintenance of methamphetamine-induced conditioned place preference

Accrued evidence demonstrated the necessity of protein synthesis at acquisition, consolidation and expression stages in conditioning/learning tasks, while the underlying mechanisms of the maintenance of memory remained less explored. This study was designed to characterize the maintenance of methamphetamine-induced conditioned place preference, a drug-induced learning and memory. In addition, cycloheximide, a protein synthesis inhibitor, was used to examine the involvement of protein synthesis in the maintenance of such place preference memory. We found that the maintenance of the rapidly-established methamphetamine (2 mg/kg, i.p.) -induced conditioned place preference could be long-lasting and even over fifty days under the present protocol of extinction. Moreover, it was of interest to note the undulating expression of this conditioned place preference throughout the extinction protocol. Most importantly, as the methamphetamine-induced conditioned place preference was acquired and expressed by mice, the saline-pretreated control mice underwent numbers of intermittent extinction across a long-term retention test period, while cycloheximide-pretreated mice exhibited unaltered methamphetamine-induced conditioned place preference throughout the same retention test period. Taken together, we conclude that [1] methamphetamine-induced conditioned place preference could last for a long period of time, and such place preference memory is reluctant to extinguish even animals' repeated exposure to the previous conditioned environment at a drug-free status, and [2] blockade of protein synthesis may enhance the maintenance of the methamphetamine-induced conditioned place preference.