Serotonin (5-hydroxytryptamine) has different types of receptors classified into 7 families. Some 90% of this indolamine is present in the gut, and the rest throughout the circulatory system in the platelet and the central nervous system. There are subtypes in the families of these receptors according to their pharmacological properties. Most are G-protein coupled metabotropics, the exception being the 5-HT3 receptors which are ionotropic. The discovery and study of these receptors employed pharmacological antagonists and agonists which allowed the different serotonin receptor subtypes to be distinguished. It is also possible to base the description of these receptors on their location in the brain because, while some are widely distributed, others are strictly confined to certain neuronal nuclei. This distribution reflects the cell physiology of the different receptors and the concomitant metabolic signaling for the cell and its functions. But we believe that their study would be even further facilitated by a classification based on their anatomical location. We therefore reviewed the literature to determine in which regions of the brain the 7 receptors and their subtypes have been reported as being present. To summarize the findings, the brain regions in which the presence of these receptors is greatest in mammals are: cortex, basal ganglia (neostriatum), amygdala (substantia nigra), hippocampal region, hypothalamus, the metencephalon (raphe nuclei and nucleus accumbens), and cerebellum.
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