Earlier this year, an article was published in the January 15th issue of the Journal of Neuroscience, in which the authors demonstrated for the first time how Methylphenidate (commercially known as Ritalin) acts in the human brain and why it is so effective.

Although Ritalin has been used therapeutically for the last 50 years, little is known about the drug's mechanism(s) of action. This latest study, indicates that Ritalin works by significantly increasing levels of the neurotransmitter, dopamine, in the brain, thereby stimulating attention and motivational circuits - enhancing one's ability to focus and complete tasks.

Previously, animal and human studies have suggested that Ritalin interferes with the recycling (or "reuptake") of dopamine within the brain by blocking dopamine transporters (Solanto, 1998). However, since these earlier studies involved injection of much higher doses of Ritalin, it was unclear whether the drug would increase extracellular dopamine at doses used therapeutically for children.

Using a PET scan (Positron Emission Tomography scan), researchers at at U.S. Department of Energy's Brookhaven National Laboratory's Center for Imaging and Neurosciences studied dopamine levels in 11 normal male subjects. Over two sessions, the volunteers were each given a dose of Ritalin (calculated using their body weight to correspond to the doses given to children with ADHD) or a placebo. Next, while their brains were scanned to record dopamine levels, the subjects rated their feeling of restlessness and "high".

The results showed that brain dopamine levels increased significantly approximately 60 minutes after ingestion of the drug as compared to the placebo.

Psychiatrist Nora Volkow, head of the research team and associate laboratory director for life sciences, suggested that Ritalin also suppresses "background" firing of neurons not associated with task performance, allowing the brain to transmit a clearer signal.

Volkow is now planning a follow-up study of subjects suffering from ADHD. "We hypothesize that we will find that ADHD sufferers have decreased function of dopamine circuits and are therefore easily distracted," she said. "The effect of Ritalin should be to normalize these levels, allowing them to focus and pay attention."

Reference

Volkow, N.D., Wang, G.J., Fowler, J.S., Logan, J., Gerasimov, M., Maynard, L., Ding, Y.S., Gatley, S.J., Gifford, A., & Franceschi, D.(2001).
Therapeutic Doses of Oral Methylphenidate Significantly Increase Extracellular Dopamine in the Human Brain. Journal of Neuroscience, 21 (2), RC121, 1 - 5.

Solanto, M.V.(1998)
Neuropsychopharmacological mechanisms of stimulant drug action in attention-deficit hyperactivity disorder: a review and integration. Behavioral Brain Research, 94 (1), 127 - 152.

For more information, contact Peter Genzer or Mona S. Rowe, from the Brookhaven National Laboratory, USA.