Mammals consume more calories to maintain normal body temperature when exposed to cold. This increase in cold-activated energy consumption also triggers an increase in appetite. Even though the internal mechanism that controls this aspect has been unknown to specialists until now, neuroscientists from the Scripps Research Institute have identified the brain circuits that cause mammals to eat more when exposed to cold temperatures.
In the new study, published in the journal Nature, the researchers identified a group of neurons in mice that functions as a “switch” for this behavior related to cold and food.
The discovery could lead to the development of therapies for metabolic health and weight loss.
“This is a fundamental adaptation mechanism in mammals, and future treatments could increase the metabolic benefits of cold exposure or other forms of fat burning,” says the study’s lead author, Li Ye, associate professor and chair of the department. of chemistry and chemical biology at The Scripps Research Institute (TSRI), in California, United States.
Since cold exposure leads to burning more calories to maintain normal temperature, immersion in cold water and other forms of “cold therapy” have been explored as methods for weight loss and improving metabolic health, reports news.ro.
A disadvantage of cold therapies is that humans’ evolved responses to cold are not designed to cause weight loss (an effect that could have been fatal during frequent periods of food scarcity in the premodern era).
Cold, like diet and exercise, increases appetite to counteract any weight loss effect.
In the study, the team aimed to identify the brain circuits that mediate this cold-induced increase in appetite.
One of their first observations was that, with the onset of cold temperatures, mice increase their foraging activity after 6 hours of not consuming any food, suggesting that this behavioral change is not simply a direct result of exposure to cold.
Using “whole brain clearing” techniques, the researchers compared the activity of neurons in the brain during the cold with that during a normal temperature.
They observed that while most of the neural activity throughout the brain was much lower in cold conditions, portions of a region called the thalamus showed greater activation.
Finally, the team focused on a specific group of neurons, called the xiphoid nucleus of the medial thalamus, showing that the activity of these neurons increased under cold conditions even before the mice awoke from their cold-induced torpor to search for food.
When less food was available at the start of the cold condition, the increase in activity in the xiphoid nucleus was even greater, suggesting that these neurons are responding to a cold-induced energy deficit rather than to the cold itself.
When the researchers artificially activated these neurons, the mice increased their foraging, but not other activities.
Similarly, when the team inhibited the activity of these neurons, the mice decreased their foraging.
These effects occurred only under cold conditions, implying that cold temperatures provide a separate signal that must also be present for changes in appetite.
In a final set of experiments, the team showed that these neurons in the xiphoid nucleus project to a brain region called the nucleus accumbens—an area long known for its role in integrating reward and aversion signals to guide behavior. including eating behavior.
Ultimately, these results could have clinical relevance, the researchers say, because they suggest the possibility of blocking the usual cold-induced increase in appetite, allowing relatively simple regimens of cold exposure to induce weight loss much more effectively.
“One of our key goals now is to figure out how to decouple the increase in appetite from the increase in energy expenditure,” says Ye.
The researchers also set out to find out if this cold-induced increase in appetite is part of a more complex one that the body uses to compensate for additional energy expenditure, for example, after exercise.