When you’re sick you also feel awful: no appetite, weak, sleepy, feverish, achy, and so on. This is called, appropriately so, the sickness syndrome.
Saper, Romanovsky & Scammell (2012) wrote a beautiful review of the neural circuits underlying this collection of symptoms. In a nutshell, the immune system releases cytokines to fight the inflammation, which in turn stimulate the release of prostaglandins. Prostaglandins bind to various areas in the brain to produce the sickness syndrome symptoms. Below are outlined four simplified brain circuits which the non-specialists can skip entirely.
- Prostaglandins in the median preoptic nucleus lead to a cascade involving dorsomedial hypothalamus, rostral medullary raphe and finally the spinal cord to produce fever by activating the brown adipose tissue.
- Prostaglandins in the preoptic area lead to the inhibition of the brain’s analgesic system involving the descending projections of the periaqueductal grey to spinal cord, thus promoting achiness.
- Prostaglandins in the meninges result in adenosine release in nucleus accumbens and ventrolateral preoptic nucleus which, downstream, end in inhibiting the arousal system to produce sleepiness.
- Prostaglandins in the arcuate nucleus lead to inhibition of several hypothalamic nuclei involved in promoting feeding, thereby producing anorexia.
The sickness syndrome and the role prostaglandins play in it has tremendous adaptive role, as it promotes rest and recuperation. So don’t blame them too much. And if you’re really done feeling sick, take some non-steroid anti-inflammatory drugs, like aspirin, which inhibit the prostaglandins’ synthesis very effectively. That’s how and why NSAIDs work.
Reference: Saper CB, Romanovsky AA & Scammell TE (26 Jul 2012). Neural Circuitry Engaged by Prostaglandins during the Sickness Syndrome. Nature Neuroscience, 15(8):1088-95. doi: 10.1038/nn.3159. Article | FREE Fulltext PDF
By Neuronicus, 21 December 2015