It is good to read papers which look at mechanism rather than describe phenomena. This a good paper describing why anorexia is a feature of acute illness.
Anorexia is part of the body’s acute-phase response to illness. Microbial products such as lipopolysaccharides. which are also commonly used to model acute illness, trigger the acute-phase response and cause anorexia mainly through pro-inflammatory cytokine
Lipopolysaccharide stimulate cytokine production through the cell-surface structural molecule CD14 and toll-like receptor-4. Cytokines ultimately change neural activity in brain areas controlling food intake and energy balance. The blood-brain barrier endothelial cells (BBB EC) are an important site of cytokine action in this context. BBB EC and perivascular cells (microglia and macrophages) form a complex regulatory interface that modulates neuronal activity by the release of messengers (e.g. PG. NO) in response to peripheral challenges. Serotonergic neurons originating in the raphe nuclei and glucagon-like peptide-1-expressing neurons in the hindbrain may be among the targets of these messengers, because serotonin (5-HT). acting through the 5-HT2C receptor, and glucagon-like peptide-l have recently emerged as neurochemical mediators of lipopolysaccharides anorexia. The central melanocortin system, which is a downstream target of serotonergic neurons, also appears to be involved in mediation of lipopolysaccharide anorexia. Interestingly. Lipopolysaccharides also reduce orexin expression and the activity of orexin neurons in the lateral hypothalamic area of fasted mice. As the eating-stimulatory properties of orexin are apparently related to arousal, the inhibitory effect of lipopolysaccharides on orexin neurons might be involved in lipopolysaccharide-induced inactivity and anorexia.
In summary, the immune signalling pathways of lipopolysaccharides -induced. and presumably acute illness-induced, anorexia converge on central neural signalling systems that control food intake and energy balance in healthy individuals
Langhans 2007 Signals generating anorexia during acute illness Proceedings of the Nutrition Society vol 66 p 321-330
Lipopolysaccharid.es: food intake: Acute-phase response: Cytokines
- Martin Eastwood