The effect of litter separation on methamphetamine-conditioned place preference in post-partum dams.

Methamphetamine (METH) abuse among women has recently increased to levels comparable to those observed in men. Although studies using animal models of addiction have begun to include more female subjects, examination of the effects of drugs of abuse on post-partum females is currently lacking. This is especially important in light of the significant hormonal and neurobiological changes that accompany pregnancy and rearing experiences. Furthermore, stress in a known factor in addiction vulnerability and the post-partum experience in the clinical population can be highly stressful. Here, we utilized the conditioned place preference paradigm to investigate the conditioned rewarding effects of METH either in virgin rats or in dams exposed to brief separation (15 min) or long separation (180 min) from the litter. We found that females in the brief separation group showed significantly greater METH conditioned place preference compared with both the long separation and virgin groups. No differences were found in locomotor activity during the conditioning sessions. These findings suggest that peripartum experience and brief litter separation may enhance the rewarding effects of METH.

Interactions between Early Life Stress, Nucleus Accumbens MeCP2 Expression, and Methamphetamine Self-Administration in Male Rats.

Early life stress (ELS) is highly related to the development of psychiatric illnesses in adulthood, including substance use disorders. A recent body of literature suggests that long-lasting changes in the epigenome may be a mechanism by which experiences early in life can alter neurobiological and behavioral phenotypes in adulthood. In this study, we replicate our previous findings that ELS, in the form of prolonged maternal separation, increases adult methamphetamine self-administration (SA) in male rats as compared with handled controls. In addition, we show new evidence that both ELS and methamphetamine SA alter the expression of the epigenetic regulator methyl CpG-binding protein 2 (MeCP2) in key brain reward regions, particularly in the nucleus accumbens (NAc) core. In turn, viral-mediated knockdown of MeCP2 expression in the NAc core reduces methamphetamine SA, as well as saccharin intake. Furthermore, NAc core MeCP2 knockdown reduces methamphetamine, but not saccharin, SA on a progressive ratio schedule of reinforcement. These data suggest that NAc core MeCP2 may be recruited by both ELS and methamphetamine SA and promote the development of certain aspects of drug abuse-related behavior. Taken together, functional interactions between ELS, methamphetamine SA, and the expression of MeCP2 in the NAc may represent novel mechanisms that can ultimately be targeted for intervention in individuals with adverse early life experiences who are at risk for developing substance use disorders.

mGluR5 positive allosteric modulation and its effects on MK-801 induced set-shifting impairments in a rat operant delayed matching/non-matching-to-sample task.

RATIONALE: Positive allosteric modulators (PAMs) of type 5 metabotropic glutamate receptors (mGluR5) exert pro-cognitive effects in animal models of various neuropsychiatric diseases. However, few studies to date have examined ability of mGluR5 PAMs to reverse cognitive deficits in operant delayed matching/non-matching-to-sample (DMS/DNMS) tasks. OBJECTIVES: This study aims to determine the ability of the mGluR5 PAM 3-cyano-N-(1,3-diphenyl-1H-pyrazol-5-yl)benzamide (CDPPB) to reverse set-shifting deficits induced by the N-methyl-D-aspartate (NMDA) receptor antagonist MK-801. METHODS: Male Sprague-Dawley rats were initially trained to lever press for sucrose reinforcement under either DMS or DNMS conditions. Following successful acquisition of the task, reinforcement conditions were reversed (DNMS → DMS or DMS → DNMS). In Experiment 1, rats were treated daily prior to each session with vehicle/vehicle, vehicle/MK-801 (0.06 mg/kg) simultaneously, CDPPB (20 mg/kg)/MK-801 simultaneously, or CDPPB 30 min prior to MK-801. In Experiment 2, rats were treated with either vehicle/vehicle, vehicle/MK-801, or CDPPB 30 min prior to MK-801 only prior to sessions that followed task reversal. RESULTS: In Experiment 1, no group differences in initial task acquisition were observed. Rats treated with vehicle/MK-801 showed significant set-shifting impairments following task reversal, which were partially attenuated by simultaneous administration of CDPPB/MK-801 and completely precluded by administration of CDPPB 30 min prior to MK-801. In Experiment 2, MK-801 did not impair reversal learning, and no other group differences were observed. CONCLUSIONS: MK-801-induced deficits in operant set-shifting ability were prevented by pretreatment with CDPPB. MK-801 did not produce deficits in task learning when treatment was initiated following task reversal.