henry copeland:

Body movements just need a 'puff' of dopamine to get started: A new study in mice suggests that a burst of dopamine levels at the beginning of a movement only, as opposed to all the time, is what gets us going; this may have important implications for treating Parkinson's disease -- ScienceDaily

Experts have long worked to understand why the absence of these so-called dopaminergic neurons (and therefore, the lack of dopamine) leads to the motor dysfunctions that are the hallmarks Parkinson's, such as stiffness, slow movements and tremors. The more widely accepted explanation has been that, in order to move normally, our brain constantly needs a certain level of dopamine -- something that Parkinson's patients progressively lose. However, as psychiatrist and neuroscientist Joaquim Alves da Silva, first author of the new study, explains, people with Parkinson's disease actually "do not have a global motor problem." As incredible as it may seem, they can even ride a bicycle -- a rather complex motor task -- if pushed at the right time. The motor problems that Parkinson's patients experience are more specific, and this was the observation that motivated the new study. "The patients' problem is in the difficulty to initiate movement and in the slowness of movement," adds Alves da Silva. In fact, as these authors now showed in mice not afflicted by Parkinson's disease, for a movement to unfold correctly it only takes a "puff" of dopamine -- or more precisely, a peak of dopaminergic cell activity -- right before the movements starts. In other words, dopamine (or, in this case, the activity of the cells that produce it) is just a "trigger" for voluntary movements. "Our most important result is that we showed, for the first time, that the change in neural activity is necessary to promote movement," says Alves da Silva. "And also for the first time, we showed that the dopamine peak that precedes movement initiation does not only regulate initiation, but also regulates movement vigor."
- www.sciencedaily.com