The document discusses the hippocampus and serotonin receptors. It covers characteristics of the raphe nuclei which are clusters of serotonin-containing neurons located in the brainstem. These nuclei, including the dorsal and median raphe nuclei, project to various brain regions including the hippocampus. The document then reviews serotonin receptor subtypes and their signal transduction pathways. It also discusses how malfunctions in hippocampal neurogenesis may contribute to depression, and how serotonin projections from the raphe nuclei innervate the hippocampus.