It is known that the expression of 5-HT, a gastrointestinal hormone produced mainly in the SI, is significantly related to hepatic regeneration after injury (Lesurtel et al., 2006; Ebrahimkhani et al., 2011) and progression of fatty liver disease (Li et al., 2018; Choi et al., 2018; Wang et al., 2020), but it is inhibited by autonomic nerve signal blockade, especially that of afferent sympathetic fibers from the injured liver (Inoue et al., 2018). The gene discussed is HTR5A; the disease is fatty liver disease.