Scientists have discovered a tiny region of the brain that controls a mouse’s desire to run and join in on other rewarding activities. Called the dorsal medial habenula, the structure is similar in mice and men, and its ability to regulate mood and motivation should be the same across the two species.
“Changes in physical activity and the inability to enjoy rewarding or pleasurable experiences are two hallmarks of major depression,” says Eric Turner of the Seattle Children’s Research Institute. “But the brain pathways responsible for exercise motivation have not been well understood.” With new ways of manipulating activity within specific brain areas -- without impacting the rest of the brain’s activity -- researchers hope to develop more targeted, effective treatments for depression.
Turner and colleagues turned to mice genetically engineered to block signals from the dorsal medial habenula. Compared to normal mice who love to run on wheels (even in the wild), these mouse models were lethargic and ran far less. “Without a functioning dorsal medial habenula, the mice became couch potatoes,” Turner explains in a news release. “They were physically capable of running but appeared unmotivated to do it.”
These mice also didn’t prefer sweetened drinking water over regular water. The lack of motivation to exercise or even seek pleasure is a mouse model for depression -- and in this case, they just didn’t care, KPLU explains.
In another experiment, the team used light to precisely target the dorsal medial habenula: By turning one of two wheels with their paws, the mice could basically “choose” to activate this specific brain area. The team found that the mice “strongly preferred” turning the wheel that stimulates their dorsal medial habenula, indicating how the area is linked to rewarding behavior.
Depression probably doesn’t originate from just one brain area, Turner explains, but likely emerges from multiple centers and systems. Their new findings point to a new “node in the depression pathway” and helps fine-tune our understanding of depression.
The work was published in the Journal of Neuroscience last week.
Image: Lali Masriera via Flickr CC BY 2.0