Harvard Mouse Study May Help Explain Parkinson’s Puzzle

By Rick Nauert PhD Senior News Editor Reviewed by John M. Grohol, Psy.D. on October 26, 2012

Researchers at Harvard Medical School may have solved the mystery of why the standard treatment for Parkinsons disease is often effective for only a limited period of time.

Experts say their findings could lead to a better understanding of many brain disorders, from drug addiction to depression.

Investigators used mouse models to study dopamine neurons in the striatum, a region of the brain involved in both movement and learning.

In people, these neurons release dopamine, a neurotransmitter that allows us to perform tasks such as walking, speaking and even typing on a keyboard.

When a person has Parkinsons the dopamine cells die and the ability to easily initiate movement is lost. Current Parkinsons drugs are precursors of dopamine that are then converted into dopamine by cells in the brain.

On the other hand, dopamine hyperactivity is associated with drug-seeking behaviors as heroin, cocaine and amphetamines rev up or mimic dopamine neurons, ultimately reinforcing the learned reward of drug-taking. Conditions such as obsessive-compulsive disorder, Tourette syndrome and even schizophrenia may also be related to the misregulation of dopamine.

In a current issue of Nature, Bernardo Sabatini and co-authors Nicolas Tritsch and Jun Ding report that midbrain dopamine neurons release not only dopamine but also another neurotransmitter called GABA, which lowers neuronal activity.

This unsuspected presence of GABA could explain why restoring only dopamine could cause initial improvements in Parkinsons patients to eventually wane, say the researchers. And if GABA is made by the same cells that produce other neurotransmitters, such as depression-linked serotonin, similar single-focus treatments could be less successful for the same reason.

If what we found in the mouse applies to the human, then dopamines only half the story, said Sabatini.

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Harvard Mouse Study May Help Explain Parkinson’s Puzzle