A new Yale University study with scientists from Germany has shown that the liver plays an important role in regulating eating behavior in mice.
One of the implications of this work is that the classical way of trying to understand brain function by looking only at the brain itself doesn't tell the whole story, said authorы of the study the results of which were published in the journal Nature Metabolism.
Through a series of experiments, the research team discovered the circuit by which the brain and liver communicate with each other and control each other. Two key players in this conversation are a group of cells known as agouti-related protein (AgRP) neurons that reside in the brain's hypothalamus, and a type of lipid secreted by the liver called lysophosphatidylcholine (LPC).
AgRP neurons, which interact with the cerebral cortex associated with complex behaviors and abilities, are required for the development of hunger. But they also interact with other parts of the body such as the liver and pancreas; when a person is hungry, these neurons play an important role in releasing lipids from fat stores in the body.
When LPC is released by the liver, an enzyme in the blood quickly converts it to lysophosphatidic acid, or LPA. Other researchers have shown that LPA can change the activity of neurons in the brain.
In this study, the researchers noticed that after fasting, the mice had increased levels of LPA in both their blood and cerebrospinal fluid, a special fluid found in the central nervous system. The increase in LPA levels caused an increase in neuronal activity in the cerebral cortex, which caused increased appetite after fasting. And all these effects depended on the function of AgRP neurons.
These results suggest a circuit in which AgRP neurons regulate liver function and lipid release, and then these lipids are returned to the brain, where they affect the cerebral cortex and its functions.