Intracranial self-stimulation and concomitant behaviors following systemic methamphetamine administration in Hnrnph1 mutant mice.

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).