Neuronal localization of the 5-HT(2) receptor family in the amygdaloid complex

The amygdaloid complex (or amygdala), a heterogeneous structure located in the medial portion of the temporal lobe, is composed of deep, superficial, and “remaining” nuclei. This structure is involved in the generation of emotional behavior, in the formation of emotional memories and in the modulation of the consolidation of explicit memories for emotionally arousing events. The serotoninergic fibers originating in the dorsal and medial raphe nuclei are critically involved in amygdalar functions. Serotonin (5-hydroxytryptamine, 5-HT) regulates amygdalar activity through the activation of the 5-HT(2) receptor family, which includes three receptor subtypes: 5-HT(2A), 5-HT(2B), and 5-HT(2C.) The distribution and the functional activity of the 5-HT(2) receptor family has been studied more extensively than that of the 5-HT(2A) receptor subtypes, especially in the deep nuclei. In these nuclei, the 5-HT(2A) receptor is expressed on both pyramidal and non-pyramidal neurons, and could play a critical role in the formation of emotional memories. However, the exact role of the 5-HT(2A) receptor subtypes, as well as that of the 5-HT(2B) and 5-HT(2C) receptor subtypes, in the modulation of the amygdalar microcircuits requires additional study. The present review reports data concerning the distribution and the functional roles of the 5-HT(2) receptor family in the amygdala.