Rationale: Methamphetamine (MA) addiction is a major public health issue in the USA, with a poorly understood genetic component. We previously identified heterogeneous nuclear ribonucleoprotein H1 (Hnrnph1; H1) as a quantitative trait gene underlying sensitivity to MA-induced behavioral sensitivity. Mice heterozygous for a frameshift deletion in the first coding exon of H1 (H1+/-) showed reduced MA phenotypes including oral self-administration, locomotor activity, dopamine release, and dose-dependent differences in MA conditioned place preference. However, the effects of H1+/- on innate and MA-modulated reward sensitivity are not known.
Objectives: We examined innate reward sensitivity and facilitation by MA in H1+/- mice via intracranial self-stimulation (ICSS).
Methods: We used intracranial self-stimulation (ICSS) of the medial forebrain bundle to assess shifts in reward sensitivity following acute, ascending doses of MA (0.5-4.0 mg/kg, i.p.) using a within-subjects design. We also assessed video-recorded behaviors during ICSS testing sessions.
Results: H1+/- mice displayed reduced normalized maximum response rates in response to MA. H1+/- females had lower normalized M50 values compared to wild-type females, suggesting enhanced reward facilitation by MA. Finally, regardless of genotype, there was a dose-dependent reduction in distance to the response wheel following MA administration, providing an additional measure of MA-induced reward-driven behavior.
Conclusions: H1+/- mice displayed a complex ICSS phenotype following MA, displaying indications of both blunted reward magnitude (lower normalized maximum response rates) and enhanced reward sensitivity specific to H1+/- females (lower normalized M50 values).
Keywords: Addiction; Behavioral genetics; Forward genetics; Genetics; Intracranial self-stimulation (ICSS); Methamphetamine; Mouse; Psychostimulants; QTL; Sensitization.