![]() However, when closely examined, some genera exhibit significant variation in the extent of SB, which to date remains unexplained. Īlthough the specificities may vary, SB is widespread with respect to both pathogens and hosts: diverse pathogens, including viruses, bacteria, and protozoa, can trigger it, and equivalent behavioral responses characterize several vertebrate classes as well as arthropods. ![]() More recent data indicate that such ligands can also activate the epithelium in areas with an intact blood–brain barrier, causing it to synthetize various prostaglandins and release them into nuclei involved in specific behaviors. In the circulatory route, microbial ligands and cytokines travel through the blood to reach the meninges, choroid plexus, and circumventricular organs (pink) where they can enter the brain. These in turn relay the signal to various nuclei in the hypothalamus, thalamus, and amygdala. In the neural route, cytokines trigger activity in vagal afferents that innervate nuclei in the brain stem such at the nucleus of the solitary tract (NTS). ![]() Leukocytes, such as dendritic cells (DCs) and macrophages, sense microbes through pathogen-recognition receptors such as toll-like receptors (TLRs) and NOD-like receptors (NLRs) and then release inflammatory cytokines such as interleukin–1 beta (IL–1β), IL–6, and tumor necrosis factor alpha (TNF-α). Information regarding inflammation is communicated to the brain through parallel neural and circulatory routes.
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