The Effects of Methylphenidate on Knockin Mice with a Methylphenidate-Resistant Dopamine Transporter

Abstract

Methylphenidate (Ritalin) is one of the most commonly abused prescription drugs. It is a psychostimulant that inhibits the dopamine and norepinephrine transporters with high affinity. In mice, methylphenidate stimulates locomotor activity, is selfadministered, and produces conditioned place preference, typical properties of an addictive drug. We have generated a knockin mouse line bearing a mutant dopamine transporter that is approximately 80-fold less sensitive to cocaine inhibition than wild type. It is interesting to note that this mutant is also almost 50-fold less sensitive to methylphenidate inhibition, suggesting similarities in the binding site for cocaine and methylphenidate. Because methylphenidate is not effective at inhibiting the mutant dopamine transporter, we hypothesized that it would not stimulate locomotor activity or produce reward in the knockin mice. In these knockin mice, doses up to 40 mg/kg methylphenidate either inhibit or fail to stimulate locomotor activity and do not produce conditioned place preference. Doses up to 40 mg/kg methylphenidate also fail to produce stereotypy in the knockin mice. Nisoxetine and desipramine, selective norepinephrine transporter inhibitors, also reduce locomotor activity in wild-type and knockin mice. These results indicate that enhanced dopaminergic neurotransmission is required for methylphenidate's stimulating and rewarding effects. In addition, we observed that drugs enhancing noradrenergic neurotransmission inhibit locomotor activity in mice, which is consistent with the notion that methylphenidate's ability to inhibit the norepinephrine transporter may contribute to its efficacy in treating attention deficit hyperactivity disorder.

Role of Aberrant Striatal Dopamine D1Receptor/cAMP/Protein Kinase A/DARPP32 Signaling in the Paradoxical Calming Effect of Amphetamine

“…We also observed that pharmacological enhancement of 5HT transmission did not alter P-Thr202/ Tyr204-ERK42/44 levels in DAT-CI striata. Consistent with previous data (Tilley and Gu, 2008b), we also found that a selective NET blocker, nisoxetine, through enhancement of NA transmission, attenuated the motor hyperactivity of DAT-CI mice. However, this effect results to be moderate, if compared with the strong motor sedation induced by amphetamine, nomifensine, and bupropion.…”

“…Consistently, DAT-KO mice have been considered a reliable animal model for this psychiatric disorder (Giros et al, 1996;Gainetdinov et al, 1999a;Gainetdinov, 2008). Recent studies have revealed that DAT-CI mutants with three point mutations in the cocaine binding site of the DAT gene show increased basal motor activity, absence of cocaineinduced extracellular DA elevation, and loss of cocaine-and methylphenidate-induced conditioned place preference (Chen et al, 2006;Tilley and Gu, 2008b). In this work, we further confirm that DAT-CI mutants show basal horizontal and vertical hyperactivity, accompanied by a mild reduction of cognitive ability, whereas no alterations were observed in motor coordination.…”

“…DAT-CI mice bear a triple point mutation (L104V/F105C/A109V) within DAT protein that is ϳ90-fold more insensitive to cocaine inhibition than wild type (WT) (Chen et al, 2006). The mutant mice have been backcrossed to C57BL/6J mice for 10 or more generations; thus, they are generally considered to be in the C57BL/6J background (Tilley and Gu, 2008b). Animals were housed in a maximum of five per cage, at a constant temperature (22 Ϯ 1°C) and maintained on a 12 h light/dark cycle, with food and water ad libitum.…”

Evaluation of anti-psychotic effect of nimodipine using methylphenidate as a model to induce psychosis in albino mice

“…It has also been shown that stereotypy was not seen with methylphenidate in dopamine depleted animals or knocked in mice. 22 Hence, on the above grounds, we recommend that methylphenidate can be used and further established as an alternative model for inducing psychosis in animals for evaluation of newer typical antipsychotics which work mainly through dopamine pathways.…”

The Membrane-Raft Protein Flotillin-1 is Essential in Dopamine Neurons for Amphetamine-Induced Behavior in Drosophila

“…14 Perhaps the most clear-cut data without such a developmental confound come from a knock-in mouse expressing a functional DAT mutant that transports DA at wild-type levels but has a greatly reduced affinity for cocaine 17 and MPH. 18 This mouse shows significantly reduced hyperlocomotion in response to cocaine and MPH, as well as impaired cocaine selfadministration 19 and conditioned place preference 17,18 , measures of drug-induced reward. These studies indicate that DAT is indeed the essential target for the rewarding properties of cocaine and MPH.…”