Previous research has shown that exercise can actually affect the structure of the brain by triggering the creation of new brain cells. A new study has now found that inactivity also has an effect on the brain — by significantly affecting the shape of certain neurons.

We already know that a sedentary lifestyle isn’t good for us. More and more research is surfacing about how sitting all day is harmful and can shorten your lifespan. Being sedentary increases the risk for heart disease, diabetes, and various other chronic disorders. And even though the new research was done on rats, the authors hope the study will offer further insight into why being sedentary is indeed so detrimental.

Researchers at Wayne State University School of Medicine studied a dozen rats in the study, which was published in The Journal of Comparative Neurology. Half of the rats were placed in cages with running wheels, where they were able to run at will. The other rats were put in cages lacking wheels, and thus remained sedentary. During the course of three months, the rats with wheels ran about 3 miles per day, while the others remained inactive.

After three months, the scientists injected the rats with a dye that colors certain neurons. They wanted to identify neurons in the rostral ventrolateral medulla, which is a part of the brain controlling breathing and various other unconscious systems that contribute to exercise. This part of the brain also controls blood pressure and what is called the sympathetic nervous system — which is essential in monitoring blood vessels to contract and widen to allow blood to flow through. If this sympathetic nervous system is hindered in any way — or overactive — the person may be more likely to develop cardiovascular disease.

The researchers found that there were significant differences between the neurons of the rats who had exercised for three months, and those that didn’t. The neurons in the rostral ventrolateral medulla of sedentary rats had actually changed shape, and had sprouted more branches than normal neurons. These branches made the neurons easily over-stimulated, and able to send confusing messages to the nervous system, ultimately impacting blood pressure. Though this has not yet been studied in humans, the researchers point out that this section of the brain in rats is similar to the area in our brains that controls the same systems. 

"We suggest that these structural changes provide an anatomical underpinning for the functional differences observed in our in vivo studies," the study authors write in the abstract. "These inactivity-related structural and functional changes may enhance the overall sensitivity of RVLM neurons to excitatory stimuli and contribute to an increased risk of cardiovascular disease in sedentary individuals."