Transcriptional profiles of psychostimulant reinforcement in rats

Drug-induced alterations in transcriptional regulation play a central role in establishing the persistent neuroplasticities that occur during drug addiction. Additionally, changes in gene expression associated with drug administration provide valuable insight into the molecular basis of drug abuse. The molecular mechanisms that underlie susceptibility to psychostimulant addiction remain unknown. Identifying the common gene transcriptional responses to psychostimulants can provide a mechanistic insight to elucidate the molecular nature of drug dependence. Male Wistar rats (4 weeks old) were acclimatized for a week to their housing conditions prior to experiments. Thereafter, they were divided into two groups: (cohort 1) 4 groups of rats (n=12 rats per group) given saline only (i.p., "drug-naive" rats); and (cohort 2): 3 groups of rats given either methamphetamine, amphetamine or methylphenidate (5 mg/kg,i.p., “drug-pretreated") for 7 days (2x daily) prior to behavioral assays. Conditioned place preference (CPP) tests were conducted a day after the final drug administration. Rats which showed CPP were evaluated for self-administration of the psychostimulants. [Cohort 1] A day after the final self-administration test, brains of 2-3 rats from each subgroups (i.e. those which showed the most robust self-administration), as well as 5 rats from the control group were removed for microarray analysis. The striatum (rostral part of the caudate putamen and the nucleus accumbens [NAc]) and the prefrontal cortex were dissected and immediately frozen at -70°C. Total RNA was isolated and gene expression profiling was conducted on independent pools of total RNA from 2-5 animals per group. [Cohort 2] A day after the final self-administration test, brains of 3 rats from each subgroups (i.e. those which showed the most robust self-administration), as well as 3 rats from the control group were removed for microarray analysis. The striatum (rostral part of the caudate putamen and the nucleus accumbens [NAc]) and the prefrontal cortex were dissected and immediately frozen at -70°C. Total RNA was isolated and gene expression profiling was conducted on independent pools of total RNA from three animals per group.