Neurobiological mechanisms of the reinstatement of drug-conditioned place preference

Genetically correlated effects of selective breeding for high and low methamphetamine consumption

Improved prevention and treatment of drug addiction will require deeper understanding of genetic factors contributing to susceptibility to excessive drug use. Intravenous operant self-administration methods have greatly advanced understanding of behavioral traits related to addiction. However, these methods are not suitable for large-scale genetic experiments in mice. Selective breeding of mice can aggregate 'addiction alleles' in a model that has the potential to identify coordinated effects of multiple genes. We produced mouse lines that orally self-administer high (MAHDR) or low (MALDR) amounts of methamphetamine, representing the first demonstration of selective breeding for self-administration of any psychostimulant drug. Conditioned place preference and taste aversion results indicate that MAHDR mice are relatively more sensitive to the rewarding effects and less sensitive to the aversive effects of methamphetamine, compared to MALDR mice. These results validate the oral route of self-administration for investigation of the motivational effects of methamphetamine and provide a viable alternative to intravenous self-administration procedures. Gene expression results for a subset of genes relevant to addiction-related processes suggest differential regulation by methamphetamine of apoptosis and immune pathways in the nucleus accumbens of MAHDR and MALDR mice. In each line, methamphetamine reduced an allostatic state by bringing gene expression back toward 'normal' levels. Genes differentially expressed in the drug-naï ve state, including Slc6a4 (serotonin transporter), Htr3a (serotonin receptor 3A), Rela [nuclear factor kappaB (NFkappaB)] and Fos (cFos), represent candidates whose expression levels may predict methamphetamine consumption and susceptibility to methamphetamine reward and aversion.

18-Methoxycoronaridine blocks acquisition but enhances reinstatement of a cocaine place preference

The iboga alkaloid congener, 18-methoxycoronaridine (18-MC), decreases self-administration of multiple drugs of abuse. Here, in a biased procedure, we investigated whether 18-MC would have a similar effect on the acquisition, expression and reinstatement of a cocaine conditioned place preference (CPP) in male Sprague-Dawley rats. While 18-MC attenuated acquisition of a cocaine CPP, it had no effect on CPP expression, and enhanced the reinstatement of cocaine CPP following extinction. Our results are consistent with those obtained using ibogaine, but reinforce the notion that acquisition, expression and reinstatement of a CPP likely involve separate mechanisms.

Relapse to drug seeking following prolonged abstinence: the role of environmental stimuli

Successful treatment of drug addiction must involve relapse prevention informed by our understanding of the neurobiological bases of drug relapse. In humans, exposure to drug-associated environmental stimuli can elicit drug craving and relapse. Because exposure to drug-paired stimuli similarly induces drug-seeking behavior in laboratory animals, several animal models of drug relapse have been developed. Here, we review animal models of cue-induced drug relapse and critically evaluate their validity and utility in addressing human relapse behaviors.