In the second study (see previous post), published in Cell, the scientists discovered that the go and stop pathways from the BG control locomotion by regulating a group of nerve cells in the brainstem that connects the brain to the spinal cord. The researchers revealed that the go pathway selectively activates a type of neuron in the brainstem that releases the neurochemical glutamate, and these neurons are responsible for triggering locomotion.
The scientists used optogenetics–an innovative research tool that uses light to activate or inhibit select cells in the brain–to stimulate either the go or the stop pathway in mice that were running on a tiny treadmill, while recording neural activity in the brainstem. They discovered that the go pathway selectively activated glutamate neurons, causing the mice to move, whereas the stop pathway inhibited these neurons and made the mice stop.
“This is the first time we have been able to demonstrate how the go and stop pathways regulate locomotion,” says Tom Roseberry, a graduate student in the lab of Dr. Kreitzer. “We show a very precise connection from the basal ganglia to the brainstem that controls movement.”
Remarkably, the researchers discovered that the brainstem neurons can overpower the signals from the BG–that is, if glutamate neurons were turned on, the animal moved even if the stop pathway is activated.
“In order to understand why walking is particularly disrupted in Parkinson’s disease, we need to map out the circuitry that controls locomotion,” says Dr. Kreitzer. “Our study shows that a specific set of neurons in the brainstem are both necessary and sufficient to initiate locomotion. This finding could open the door for new treatment targets to help Parkinson’s patients walk more easily.”
Philip R.l. Parker, Arnaud L. Lalive, Anatol C. Kreitzer. Pathway-Specific Remodeling of Thalamostriatal Synapses in Parkinsonian Mice.Neuron, January 2016 DOI: 10.1016/j.neuron.2015.12.038
Gladstone Institutes. “Treating Parkinson’s disease by solving the mysteries of movement: Scientists discover a brain circuit that controls walking and identify a new target for treating Parkinson’s disease.”
Source; ScienceDaily. ScienceDaily, 28 January 2016. <www.sciencedaily.com/releases/2016/01/160128155004.htm>.