Biogenic Amines as Circulating Hormones in Insects

The biogenic amines include the phenolamines such as octopamine, dopamine, and the trace amine tyramine, as well as the indolamine serotonin. They are ancient, evolutionarily conserved molecules that have been adapted for use in several physiological contexts, with critical and nonoverlapping functions in development beyond their roles as signaling molecules in the nervous system. These molecules interact with hormone-signaling pathways to elicit distinct behavioral and developmental responses. Both dopamine and serotonin are vital for life; insects lacking dopamine or serotonin die as embryonic lethals. Octopamine and tyramine, while not vital, play diverse critical roles in behavior and development. While the number of octopamine-, tyramine-, dopamine-, and serotonin-containing neurons is relatively small in most insect species (approximately 100 or fewer throughout the central nervous system), their processes extend throughout the body to target numerous peripheral organs, strong evidence for a neurohormonal role for these molecules. These numerous functions are key to maintaining the homeostasis of the organism, and current data suggest that several of these pathways have been conserved throughout evolution.