The nucleus of the solitary tract and area postrema receive direct input from the vagus nerve, which relays gut information to the brain.

“so these are actually the neurons in that desate rat story I was telling earlier these are the brain regions that are preserved in the deser rat the deser rat still has these very coddle brain stem structures um they're two very special brain regions because they get direct input from the vagus nerve so the vagus nerve is the nerve that inates your stomach and intestines and heart and lungs and it's sort of the major pathway from gut to brain and provides most of the sensor of the neural input from gut the brain telling you about things like this your stomach distension how many nutrients are in your intestine breathing all that stuff and almost all of those vagal nerves terminate on these two structures in the brain stem”