Serotonin Pathway in Neuroimmune Network

Abstract

Once considered merely as a neurotransmitter, serotonin (5-HT) now enjoys a renewed reputation as an interlocutor in the dense and continuous dialogue between neuroendocrine and immune systems. In the last decades, a role has been depicted for serotonin and its derivatives as modulators of several immunological events, due to the expression of specific receptors or enzymes controlling 5-HT metabolism in diverse immune cell types. A growing body of evidence suggests that the effects of molecules belonging to the 5-HT pathways on the neuroimmune communication may be relevant in the clinical outcome of autoimmune/inflammatory pathologies of the central nervous system (CNS), such as multiple sclerosis, but also in Alzheimer’s disease, or in mood disorders and major depression. Moreover, since the predominance of 5-HT is produced by enterochromaffin cells of the gastrointestinal tract, where 5-HT and its derivatives are important mucosal signalling molecules giving rise to the so-called “brain-gut axis”, alterations in brain-gut communication are also involved in the pathogenesis and pathophysiology of several psychiatric and neurologic disorders. Here we illustrate how functional interactions between immune and neuronal cells are crucial to orchestrate tissue homeostasis and integrity, and the role of serotonin pathway components as pillars of the neuroimmune system.