Washington, Feb 6: Obesity isn't just about unhealthy eating habits; it may also have genetic roots in the brain, according to a new study conducted on rats.
Scientists at the University of Southern California suggest that a predisposition for obesity might be wired into the brain from the birth. The study showed that obese rats had faulty brain wiring that impaired their response to the hunger-suppressing hormone leptin. "The neurodevelopmental differences in these animals can be seen as early as the first week," said lead author of the study Sebastien Bouret, an assistant professor of neuroscience at the University of Southern California.
"The results show that obesity can be wired into the brain from early life. The three-million-dollar question now is how to get around this problem," he added.
It is commonly accepted that obesity results from a combination of genetic and environmental factors, the researchers said.
They added that rodent models of obesity could provide valuable insights into the biological processes underlying the development of obesity in humans.
Bouret explained that the "diet-induced obese" (DIO) rats used in the current study are particularly suited to the task, because their tendency to become overweight shares several features with human obesity, including the contribution of many genes.
Previous studies had suggested that the brains of DIO rats are insensitive to leptin, the researchers added.
Circulating leptin, produced by fat tissue, acts as a signal to the brain about the body's energy status. Leptin is also critical for the initial development of ARH neurons.
In the new study, the researchers examined the obesity-prone rats for signs of abnormal brain development. They found that the animals' brains had fewer neural projections from the ARH, a deficiency that persisted into adulthood. Those projections are needed to relay the leptin signal received by the ARH to other parts of the hypothalamus, Bouret said.
The researchers found further evidence that those changes in brain wiring stem from a reduced responsiveness of the brain to leptin's action during development.
"It seems [in the case of these rats] that appetite and obesity are built into the brain," Bouret said.
While their condition might be ameliorated by exercising and eating right, he added, the findings suggest that the propensity to gain weight can't be reversed.
The study appears in the February issue of Cell Metabolism.