From the article:
Cells in the NST [nucleus of the solitary tract] are a critical part of the neural circuitry that regulates digestive functions, including vomiting.
The researchers conducted a study in rats to determine how these brainstem neurons responded to TNF. Rats were injected with levels of TNF comparable to concentrations present during a chronic infection. This TNF concentration activated NST neurons and caused digestion to stop - a condition called stasis. This leads to nausea, loss of appetite, and vomiting.
In this research, many NST neurons exposed to TNF did not return to a normal level of function during the course of the study. Furthermore, these neurons became overly sensitive to normal gastrointestinal events for a prolonged time.