Abstract
Attention deficit hyperactivity disorder (ADHD) is a common behavioral disorder in childhood. Methylphenidate (MPH: Ritalin), a psychostimulant, is widely used drug for the treatment of ADHD as well as attention enhancer in normal adults. Pharmacological studies have shown that MPH blocks dopamine transporter (DAT) and thereby elevates extracellular dopamine (DA) level in mammalian brain. It is hypothesized that these pharmacological actions are relevant to its therapeutic effects whereas underlying mechanisms of the effects remain unclear.Neurochemical mechanisms of the effect of MPH have mostly been studied by using rodents that do not have enough higher cognitive abilities. Thus, we tried to investigate neurochemical mechanisms concerning how MPH elevates extracellular DA, in the prefrontal cortex and striatum of the primate that has much higher cognitive abilities. We first examined effects of MPH on monkeys' cognitive behavior. We trained monkeys on several kinds of cognitive tasks such as delayed response, go/no-go, stop signal and self-control tasks, and examined effects of MPH on monkeys' performance in these cognitive tasks.Oral administration of MPH significantly changed performance of the animal in those cognitive tasks in dose-dependent manner. Especially, clear improvements were observed in the performance of go/no-go and self-control tasks. The results indicate that monkeys could be appropriate models to examine changes in neurotransmitter in relation to MPH-induced cognitive behavior. [J Physiol Sci. 2008;58 Suppl:S147]
