Methamphetamine Conditioned Place Preference in Adolescent Mice: Interaction Between Sex and Strain.

Background: Methamphetamine (METH) use is higher in adolescent women than men. While rodent studies support a sex difference in the reinforcing effects of METH, few have investigated sex differences in the underlying neural circuits, none of which tested rodents during adolescence. Aims: Investigate whether there are sex differences in the rewarding effects of METH in two strains of adolescent mice that are commonly used to generate transgenic lines. Identify changes in associated neural circuits. Methods: We tested METH-induced conditioned place preference (CPP) in male and female 129Sv/Ev and C57Bl/6 mice during middle adolescence using 1mg/kg of METH. Behaviorally-induced upregulation of c-Fos protein expression was quantified in the nucleus accumbens (NAc) and area CA1 of the hippocampus following the post-conditioning test. Results: In C57Bl/6 mice, METH induced CPP in females, but not males. Conversely, METH-induced CPP in 129Sv/Ev males, but not females. In both strains, groups that exhibited CPP had more c-Fos+ cells in the NAc and CA1 when compared to saline-treated control groups. The number of c-Fos+ cells in these two brain regions correlated in groups exhibiting CPP, indicating increased NAc-CA1 communication during retrieval of the conditioned memory. Finally, we found evidence of behavioral sensitization in 129Sv/Ev males only. Conclusions: Our study reveals that the rewarding effects of the METH in adolescent mice are both sex- and strain-dependent, indicating that METH response may result from an interaction between sex-specific and genetic mechanisms. Our findings will be informative when selecting an appropriate background strain in future studies using genetically modified mice.