Parkinson's disease is a disorder caused by a loss of cells that produce dopamine, a neurotransmitter that plays a key role in the body's movement systems.
The discovery could immediately lead to new opportunities for drug development.
Researchers at Oregon Health & Science University have discovered that adenosine, a neurotransmitter, acts as a brake on dopamine, another neurotransmitter involved in motor control. The findings, which were published in the journal Nature, reveal that adenosine and dopamine operate in a push-pull dynamic in the brain.
"There are two neuronal circuits: one that helps promote action and the other that inhibits action," said senior author Haining Zhong, Ph.D., a scientist at the OHSU Vollum Institute. "Dopamine promotes the first circuit to enable movement and adenosine is the 'brake' that promotes the second circuit and brings balance to the system."
The discovery has the potential to immediately suggest new avenues for the development of drugs to treat the symptoms of Parkinson's disease.
Scientists have long suspected that dopamine is affected by an opposing dynamic of neuronal signalling in the striatum, a critical region of the brain that mediates movement along with motivation and learning. The striatum is also the main brain region affected in Parkinson's disease by the loss of dopamine-producing cells.
"People have long suspected that there must be this push-pull system," said co-author Tianyi Mao, Ph.D., a Vollum scientist who is married to Zhong.
In the new study, researchers for the first time clearly and definitively revealed that adenosine is the neurotransmitter that acts oppositively to dopamine. The study, which involved mice, used new genetically modified protein probes recently developed in Zhong and Mao laboratories. An example of such technology was highlighted last month in a study published in the journal Nature Methods.
In particular, adenosine is also well known as the receptor on which caffeine acts.
"Coffee acts in our brain through the same receptors," Mao said. "Drinking coffee lifts the brake imposed by adenosine."