Ghrelin, the hormone that induces hunger, also seems to play a role in memory control.

Image credits Christine Sponchia.

If you’re sitting in a restaurant keenly anticipating a delicious meal that will be served shortly, chances are you’ll feel hungry. That sensation is created by ghrelin, a hormone secreted in the stomach as you anticipate food. Ghrelin has been linked with the mediation of hunger signals between our gut and our brain, but new research at the Society for the Study of Ingestive Behavior suggests that the molecule might also play an important part in memory control.

Food for memory

“We recently discovered that in addition to influencing the amount of food consumed during a meal, the vagus nerve also influences memory function,” said Dr. Scott Kanoski, senior author of the study.

After its secreted, ghrelin binds to specialized receptors on the vagus nerve, which transmits signals between the gut and the brain. The team’s hypothesis was that ghrelin might also help the vagus nerve support memory formation.

Using a method called RNA interference, the team artificially reduced the amount of ghrelin receptor in the vagus nerve for a group of lab rats. The animals were then put through a series of memory tasks. The rats with reduced ghrelin signaling in the vagus nerve showed impaired performance in an episodic memory test compared to the control group. Episodic memory is the type of memory involved in remembering what, when, and where something occurred. For the rats, the test required remembering a specific object in a specific location.

A second part of the study looked at whether ghrelin signaling in the vagal nerve influences feeding behavior. They report that mice whose vagus nerve can’t receive signals from ghrelin ate more frequently than unaltered mice but consumed less food at each meal. The team says this might come down to deficits in episodic memory associated with impaired ghrelin signaling rather than feelings of hunger.

“Deciding to eat or not to eat is influenced by the memory of the previous meal,” says Dr. Elizabeth Davis, lead author on the study. “Ghrelin signaling to the vagus nerve may be a shared molecular link between remembering a past meal and the hunger signals that are generated in anticipation of the next meal.”

The team plans to expand their research to see if they can improve memory capacity in humans by manipulating ghrelin signaling between the gut and the brain.

The findings, “Vagal afferent ghrelin signaling promotes episodic memory and influences meal patterns in rats” have been presented at the 2019 Annual Meeting of the Society for the Study of Ingestive Behavior in Utrecht, Netherlands, in July.