The study found that the brains of rats bred to be lean are more sensitive to a chemical produced in the brain, orexin A, which stimulates appetite and spontaneous physical activity such as fidgeting and other unconscious movements. Compared to rats bred to be obese, the lean rats had a far greater expression of orexin receptors in the hypothalamus.
"The greater expression of orexin receptors suggests the lean rats' brains were more sensitive to the orexin the brain produces," said Catherine M. Kotz, the study's senior researcher. "The results point to a biological basis for being a couch potato."
This line of research suggests that frequent minor unconscious movements such as fidgeting and other behaviours associated with restlessness burn calories and help control weight, Kotz said. Further, it suggests a strategy to reduce weight gain and could lead to the development of a drug to stimulate minor activity.
"Many people focus on diet, but it may be more feasible for some people to stand or move more throughout the day" as a way to control their weight, Kotz said. Contrary to common belief, metabolism rates don not vary greatly from person to person and weight gain usually results from eating too much, burning too few calories, or both, she said.
The researchers drew their conclusions after performing a series of experiments with obesity-prone and obesity-resistant rats.
"We knew from previous studies that orexin stimulated physical activity, and so we wanted to find out whether it enhances activity more in lean rats than in obese rats, Kotz explained. The researchers injected orexin into the lateral hypothalamus area of the brains of both groups and found that the lean rats became even more active, while the obese rats didn't respond much at all.
MEDICA.de; Source: American Physiological Society