Enteric nervous system (ENS) & Enteroendocrine Cells (EEC)

The brain and gut are connected. Enteroendocrine Cells (EEC) play a role similar to the gut's role with the brain. They manage GI tract functions. Vagal afferent fibers reach the GI tract wall. They contact the intestinal lining. EECs secrete products that act on these fibers. This activates the fibers.
Raybould 2010 Auton Neurosci 153: 41-46

The release of basal 5-HT can activate vagal afferent fibers, which induces intestinal motility. Additionally, through gut-brain axis signaling, it promotes gastric emptying.
Rezzani et al. 2022 Int. J. Mol. Sci. 23: 3758

Activated fibers interact with the brainstem. They reach the nucleus tractus solitarii and nodose ganglion. Then, they connect to the brain. This process regulates many functions. These include motility, inflammation, immunity, and blood flow.
Raybould 2010 Auton Neurosci 153: 41-46

EECs communicate nutritional information to the nervous system
Ye et al. 2021 Cell Host & Microbe 29: 179–196

To guide some of these processes, the ENS is assisted by different types of enteroendocrine cells
Gribble & Reimann 2016 Annu Rev Physiol 78: 277-299
Fothergill & Furness 2018 Histochem Cell Biol 150(6): 693-702

EECs form synapses with sensory neurons
Bohorquez et al. 2015 J Clin Invest 125: 782-6
Bellono et al. 2017 Cell 170(1): 185-198
Kaelberer et al. 2018 Science 361: eaat5236

The synapse between EECs and neurons forms a direct pathway, the axis, for the gut epithelium to transmit sensory nutrient information to the brain
Kaelberer et al. 2018 Science 361: eaat5236

see also:
Enteric nervous system (ENS) & Intestinal Motility / Gastrointestinal physiology
Enterochromaffin Cells (EC)
Enteroendocrine Cells (EEC) & Food / Diets / Nutrients