Journal Article

Reward‐enhancing effect of methylphenidate is abolished in dopamine transporter knockout mice: A model of attention‐deficit/hyperactivity disorder

Sora, Ichiro, Ikeda, Kazutaka, Uhl, George R., Ikekubo, Yuiko, Ide, Soichiro, Hua, Jennifer, Takamatsu, Yukio

2018

Overview

Aim Attention‐deficit/hyperactivity disorder is a heterogeneous neurobiological disorder that is characterized by inattention, impulsivity, and an increase in motor activity. Although methylphenidate has been used as a medication for decades, unknown is whether methylphenidate treatment can cause drug dependence in patients with attention‐deficit/hyperactivity disorder. This study investigated the reward‐enhancing effects of methylphenidate using intracranial self‐stimulation in an animal model of attention‐deficit/hyperactivity disorder, dopamine transporter knockout mice. Methods For the intracranial self‐stimulation procedures, the mice were trained to nosepoke to receive direct electrical stimulation via an electrode that was implanted in the lateral hypothalamus. After the acquisition of nosepoke responding for intracranial self‐stimulation, the effects of methylphenidate on intracranial self‐stimulation were investigated. Results In the progressive‐ratio procedure, dopamine transporter knockout mice exhibited an increase in intracranial self‐stimulation compared with wild‐type mice. Treatment with 5 and 10 mg/kg methylphenidate increased intracranial self‐stimulation responding in wild‐type mice. Methylphenidate at the same doses did not affect intracranial self‐stimulation responding in dopamine transporter knockout mice. We then investigated the effects of high‐dose methylphenidate (60 mg/kg) in a rate‐frequency procedure. High‐dose methylphenidate significantly decreased intracranial self‐stimulation responding in both wild‐type and dopamine transporter knockout mice. Conclusions These results suggest that low‐dose methylphenidate alters the reward system (ie, increases intracranial self‐stimulation responding) in wild‐type mice via dopamine transporter inhibition, whereas dopamine transporter knockout mice do not exhibit such alterations. High‐dose methylphenidate appears to suppress intracranial self‐stimulation responding not through dopamine transporter inhibition but rather through other mechanisms. These results support the possibility that methylphenidate treatment for attention‐deficit/hyperactivity disorder does not increase the risk of drug dependence, in attention‐deficit/hyperactivity disorder patients with dopamine transporter dysfunction. This study investigated the reward‐enhancing effects of methylphenidate (MPH) using intracranial self‐stimulation (ICSS) in an animal model of ADHD, dopamine transporter knockout (DAT‐KO) mice. Low‐dose MPH affects the reward system (ie, increased ICSS responding) in wild‐type mice via DAT inhibition, but not in DAT‐KO mice. MPH treatment for ADHD may not increase the risk of drug dependence, in ADHD patients with DAT dysfunction.

• Publisher: John Wiley & Sons, Inc,John Wiley and Sons Inc,Wiley
• Subject: Attention deficit hyperactivity disorder / Dopamine / dopamine transporter / Drug dosages / Experiments / Hyperactivity / intracranial self‐stimulation / methylphenidate / Micro Report / Micro Reports / reward / Rodents / Substance abuse treatment / Variance analysis