Ghrelin, a hormone synthesized by endocrine cells of the stomach, is known as the ‘hunger hormone’ given its role in increasing appetite, meal initiation and food intake. A new study by researchers from the University of Southern California and University of Florida suggests that ghrelin may also be important for memory control.
“Ghrelin levels would be high if you were at a restaurant, looking forward to a delicious dinner that was going to be served shortly,” said study lead author Dr. Elizabeth Davis, a researcher at the University of Southern California.
“Once it is secreted, ghrelin binds to specialized receptors on the vagus nerve, a nerve that communicates a variety of signals from the gut to the brain.”
“We recently discovered that in addition to influencing the amount of food consumed during a meal, the vagus nerve also influences memory function,” added study senior author Dr. Scott Kanoski, also from the University of Southern California.
The scientists hypothesized that ghrelin is a key molecule that helps the vagus nerve promote memory.
Using an approach called RNA interference to reduce the amount of the ghrelin receptor, they blocked ghrelin signaling in the vagus nerve of lab rats.
When given a series of memory tasks, animals with reduced vagal ghrelin signaling were impaired in a test of episodic memory, a type of memory that involves remembering what, when, and where something occurred. For the rats, this required remembering a specific object in a specific location.
The study authors also investigated whether vagal ghrelin signaling influences feeding behavior.
They found that when the vagus nerve could not receive the ghrelin signal, the animals ate more frequently, yet consumed smaller amounts at each meal.
“Our results may be related to the episodic memory problems. Deciding to eat or not to eat is influenced by the memory of the previous meal,” Dr. Davis said.
“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.”
Elizabeth A. Davis et al. Vagal afferent ghrelin signaling promotes episodic memory and influences meal patterns in rats. SSIB 2019