Parkinson’s disease is a movement disorder that develops when the loss of midbrain neurons substantially reduces brain levels of a signaling molecule called dopamine. However, the midbrain is composed of different types of dopamine-releasing neurons, suggesting that these cells might play distinct roles in normal motor behavior and in disease.

To address this possibility, researchers in the journal PNAS recorded the activity of dopaminergic neurons in three midbrain structures—the substantia nigra pars compacta (SNc), the ventral tegmental area (VTA), and the substantia nigra pars lateralis (SNL)—in mice that were placed on a running wheel.

The firing rate of most SNc neurons, but not VTA or SNL neurons, decreased when the mice began to move, compared with when the animals rested in place. By contrast, in a genetic mouse model of Parkinson’s disease, the firing rate of SNc neurons did not change during the onset of movements, suggesting that the pauses in the firing of SNc neurons may be important for maintaining movement precision.

Taken together, the findings suggest that distinct midbrain dopaminergic neurons play different roles in both normal movement and motor disorders such as Parkinson’s disease, according to the authors.

http://www.pnas.org/content/early/2016/03/16/1515941113