ABSTRACT
Melatonin (MLT) is a neurohormone involved in numerous physiological processes, including circadian rhythms, mood regulation, anxiety, sleep, appetite, immune responses, and cardiac functions (Arendt, 1988; Reiter, 2003). Most of the effects of MLT in the brain result from the activation of two high-afnity G-protein coupled receptors (GPCRs), MT1 and MT2 (Dubocovich et al., 2010). A great number of ligands for the MLT receptors have been developed, but these advances have been met with difculty obtaining compounds with selectivity toward only one of the two MLT receptor subtypes, especially the MT1 receptor (Rivara et al., 2012). Since structure-activity relationships for the binding at the MT2 receptor are quite consolidated (Rivara et al., 2007), several MT2 receptor ligands belonging to different chemical classes have been synthesized (Mor et al., 2010). Despite this large number of selective MT2 receptor ligands, only four have been tested and employed in neurobiological/neuropharmacological studies.
