Researchers show how to shut off hunger craving.

It is known that the brain regulates food intake by processing sensory cues and peripheral physiological signals, however, the neural basis of this integration remains unclear.  Now, a study from researchers at the University of Pennsylvania maps the biological mechanism behind the craving of hunger. The team state that while the mere sight or smell of food can temporarily turn off neurons responsible for the drive to eat, their data shows that the neurons only stay off if the brain receives a signal from the stomach that calories have been ingested.  The opensource study is published in the journal Cell Reports.

Previous studies show that the brain’s hypothalamus, which controls the sensation of hunger, is home to a population of neurons known as agouti-related protein-expressing neurons, or AgRP neurons. Recent studies from the lab showed that these neurons are highly active when an animal is hungry, their activity is suppressed upon eating and that merely smelling or seeing food can also lead to a rapid decline in their activity. Therefore, the group hyposthesized that these neurons functioned as a way for animals to avoid starvation.  The current study distinguishes between the effects of simply seeing or smelling food and actually consuming food on reducing the activity of the AgRP neurons.

The current study worked with mice which are genetically engineered to allow the tracking of AgRP neuronal activity as the animals were presented food and/or fed. Results show that nutrients are necessary and sufficient for sustained reductions in AgRP neuron activity and that activity reductions are proportional to the calories obtained. Data findings show that this change in activity is recapitulated by exogenous administration of gut-derived satiation signals.

The team state as they were confident that the nutrients are delivering a signal to the brain, they wanted to ascertain how they were doing it.  Results show that giving mice hormones, such as cholecystokinin, peptide tyrosine tyrosine and amylin, which are normally secreted during digestion, led to dramatic and dose-dependent decreases in AgRP neuronal activity. Data findings show that when low doses of these three peptides were combined, they acted synergistically, leading to a robust decrease in AgRP neuron activity.

The team surmise their data shows that the detection of nutrients by the central nervous system is critical for food intake control, controlling the hunger craving.  For the future, the researchers state that they plan to further explore the ways in which these hormones suppress AgRP neuronal activity, perhaps looking for a way to trigger their release by mimicking the presence of nutrients in the gut.

Source: University of Pennsylvania 


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