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Just before the New Year celebrations, a team of researchers found that many people would have a hard time sticking to an exercise regime - and it's not just about having excess weight or being obese. A new study on mice provides some clues that physical inactivity results from altered dopamine receptors rather than being obese.

A new study by a team of researchers at the National Institutes of Health show that chronically inactive mice who are obese show very little motivation to move their bodies. They believe that the lack of motivation to exercise or move is linked to alterations in D2-type (D2R) dopamine binding receptors. Thus, it does not simply stem out from being overweight, obese or lack of will power.

"We know that physical activity is linked to overall good health, but not much is known about why people or animals with obesity are less active," Alexxai V. Kravitz, co-author of the study, said as reported by Science Daily.

"There's a common belief that obese animals don't move as much because carrying extra body weight is physically disabling. But our findings suggest that assumption doesn't explain the whole story," he added.

What They Found

In the study published in the journal Cell Metabolism, the researchers fed mice with a high-fat diet for 18 weeks. On the second week, the mice gained weight and by the fourth week, their movements decreased and got around much more slowly.

However, the mice on a high-fat diet moved less before they gained a majority of the weight, hinting that gaining excess weight was not responsible for the decreased movements. What could be causing this lack of motivation to move?

Dopamine's Role On Activity

The researchers studied the dopamine signaling pathway and discovered that the inactive and obese mice had problems in the D2 dopamine receptor. When analyzing the association between inactivity and weight gain, they found that the mice did not gain weight on a high-fat diet immediately. Instead, the weight gain started once the mice start moving less.

"In many cases, willpower is invoked as a way to modify behavior," Kravitz said. "But if we don't understand the underlying physical basis for that behavior, it's difficult to say that willpower alone can solve it," he added.

According to Psychology Today, dopamine receptors found in the striatum of the basal ganglia stimulate feelings of reward for the brain to become motivated and say "do it more". This helps boost positive lifestyle behaviors or even harmful addictions that eventually become habits.

Alterations in these receptors and malfunctions in the basal ganglia have been linked to certain conditions such as Parkinson's disease, Huntington's disease, obsessive-compulsive disorder (OCD), Tourette's syndrome, autism spectrum disorders (ASD) and other neuropsychiatric disorders.