Role of Organic Cation Transporter 3 in the Locomotor Sensitizing Effects and Rewarding Properties of Amphetamine in Male and Female Mice

Abstract

Strategies targeting the dopamine (DA) transporter have yielded little benefit in treating addiction to amphetamine or amphetamine-like psychostimulants, possibly due to significant action of these stimulants elsewhere to modulate dopaminergic transmission. Our recent studies support organic cation transporter 3 (OCT3) as a previously unsuspected player in the actions of amphetamine. (Mayer et al., 2018, PMID: 29773909). Here, we investigated the role of OCT3 in the rewarding effects of amphetamine, in sensitization to the locomotor stimulant effects of amphetamine, and in the sex-dependency of these effects. We used genetic (constitutive OCT3 knockout (-/-) mice), and pharmacological (decynium-22 (D22, 0.1 mg/kg), a blocker of OCTs and the plasma membrane monoamine transporter (PMAT)) approaches to test the hypothesis that sensitization and conditioned place preference (CPP) for amphetamine (1 mg/kg) would be attenuated in OCT3-/- mice compared with wild-type (OCT3+/+) mice, and that D22 would attenuate the behavioral effects of amphetamine in OCT3+/+ mice, but not in OCT3-/- mice. Supporting our hypothesis, D22 prevented amphetamine CPP in male and female OCT3+/+ mice. In partial support of our hypothesis, OCT3-/- male mice did not develop CPP for amphetamine, however CPP for amphetamine persisted in OCT3-/- female mice, though not as robustly as in OCT3+/+ counterparts. Saline-pretreated female OCT3+/+, but not OCT3-/-, mice given an acute injection of amphetamine showed a robust increase in locomotor activity, whereas male OCT3+/+ and OCT3-/- mice displayed only a modest increase in locomotor activity. Sensitization to the locomotor stimulant effects of amphetamine occurred in females regardless of pretreatment or genotype. Male mice did not develop sensitization, regardless of pretreatment or genotype. D22 pretreatment did not affect the locomotor response to amphetamine in either sex or genotype. The main findings from this study are that 1) OCT3 is a key, and necessary player in the rewarding properties of amphetamine in males, but not females; 2) CPP for amphetamine persisted in female OCT3-/- mice, and was blocked by D22, suggesting that another D22-sensitive transporter, putatively PMAT (which avidly transports DA), is critical for the rewarding properties of amphetamine in females; 3) Consistent with literature, OCT3+/+ females are more sensitive to the locomotor stimulant effects of amphetamine than males; 4) OCT3 is important for the locomotor stimulant effect of amphetamine, and 5) Sensitization to the locomotor stimulant effects of amphetamine does not appear to be dependent on OCT3, and is not affected by D22. These data support OCT3 as a novel mechanism contributing to sex-dependent variation in the rewarding effects of amphetamine-like stimulants, and introduce a role for other D22 sensitive transporters, putatively PMAT, in the actions of amphetamine in females. These results have important implications for OCT3 and PMAT as sex-specific targets for therapeutic intervention in the treatment of amphetamine addiction.