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Ghrelin, the hormone that causes hunger, also seems to play a role in controlling memory.
If you sit in a restaurant and look forward to a delicious meal that will be served soon, there is a good chance that you are hungry. This sensation is created by ghrelin, a hormone secreted in the stomach when you plan to eat. Ghrelin has been badociated with the mediation of hunger signals between our intestines and our brain, but new research from the Society for the study of ingested behavior suggests that the molecule could also play an important role in controlling the memory.
From memory
"We have recently discovered that in addition to influencing the amount of food consumed during a meal, the vagus nerve also influences the function of memory," said Dr. Scott Kanoski, lead author of the study.
After secretion, ghrelin binds to specialized receptors of the vagus nerve, which transmits signals between the intestine and the brain. The team's hypothesis was that ghrelin could also help the vagus nerve to support memory formation.
Using a method called RNA interference, the team artificially reduced the amount of ghrelin receptors in the vagus nerve of a group of laboratory rats. The animals were then subjected to a series of memory tasks. Rats with reduced ghrelin signaling in the vagus nerve showed impaired performance during an episodic memory test compared to the control group. Episodic memory is the type of memory involved in remembering what, when and where something happened. For rats, the test required the recall of a specific object to a specific location.
A second part of the study aimed to determine whether the signaling of ghrelin in the vagal nerve influences the feeding behavior. They reported that mice whose vagus nerve could not receive signals from ghrelin ate more frequently than unmodified mice but consumed less food at each meal. The team believes that this may be due to episodic memory deficits badociated with impaired ghrelin signaling rather than feelings of hunger.
"The decision to eat or not to eat is influenced by the memory of the previous meal," says Dr. Elizabeth Davis, lead author of the study. "Ghrelin signaling to the vagus nerve may be a molecular link shared between the memory of a past meal and the hunger signals generated in anticipation of the next meal."
The team plans to expand its research to see if they can improve memory capacity in humans by manipulating ghrelin signaling between the intestines and the brain.
The findings, "Signaling by afferent vagal ghrelin, promotes episodic memory and influences dietary habits in the rat" were presented at the Society's annual meeting for the study of ingestive behavior, held in Utrecht ( Netherlands) in July.
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