Fig. 2.

Microglia cells play a role in eradication of invading microorganisms and in removal of debris. During these processes, the cells adapt specialized phenotypes (M1 and M2-like, respectively). During the respiratory burst, labile oxygen products are formed that oxidize microbial proteins and nucleic acids, but also oxidize the essential cofactor for monoamine synthesis, tetrahydrobiopterin. Sterile neuroinflammation is a common observation in neurological and psychiatric disorders. Acetylcholine, acting via α7 nAChRs, promotes M2-polarization. As such, it reduces neuroinflammation, while promoting phagocytosis. M2-polarized microglia cells not only produce neurotrophins and anti-inflammatory cytokines, they also effectively phagocytose and catabolize Aβ. α7 nAChR agonists are expected to improve neurological and psychiatric disorders via inhibition of neuroinflammation, to restore tetrahydrobiopterin levels (improve mood symptoms) and to provide neuroprotection