Impaired memory and reduced sensitivity to the circadian period lengthening effects of methamphetamine in mice selected for high methamphetamine consumption.

Drug abuse runs in families suggesting the involvement of genetic risk factors. Differences in addiction-related neurobiological systems, including learning and memory and circadian rhythms, may exist prior to developing addiction. We characterized the cognitive phenotypes and the free-running circadian period of mouse lines selectively bred for high methamphetamine (MA) drinking (MA high drinking or MAHDR) and low MA drinking (MA low drinking or MALDR). MA-naïve MALDR mice showed spatial memory retention while MAHDR mice did not. MA-naïve MAHDR mice had elevated hippocampal levels of the AMPA receptor subunits GluA2 (old terminology: GluR2), but not GluA1 (old terminology: GluR1). There were no line differences in the free running period (τ) when only water was available. During a 25 mg/L MA solution access period (vs water), there was an increase in τ in MALDR but not MAHDR mice, although MAHDR mice consumed significantly more MA. During a 50 mg/L MA solution access period (vs water), both lines showed an increased τ. There was a positive correlation between MA consumption and τ from baseline in MALDR, but not MAHDR, mice. Thus, a heritable proclivity for elevated MA self-administration may be associated with impairments in hippocampus-dependent memory and reduced sensitivity to effects of MA on lengthening of the circadian period.