Biogenic amines and peptides can act both as circulating neurohormones and as classical central and peripheral neurotransmitters. This article reviews some of the variety of roles played by amines and peptides in crustacean nervous systems. Cardiac, stomatogastric and postural systems are used to illustrate: (1) the functional versatility of amines and peptides; (2) the molecular basis of their actions; (3) the coexistence of amines and peptides with other bioactive compounds; and (4) the developmental expression of amine and peptide phenotypes. We will deal in detail with the postural neuromuscular system of the lobster, Homarus americanus. Physiological and pharmacological experiments have shown that the biogenic amines serotonin and octopamine are capable of regulating posture by direct neurohormonal actions on the muscles and by central actions that alter motoneuronal output. We have localized serotonin to identified neurones in the lobster ventral nerve cord and have shown further that the pentapeptide proctolin coexists with the amine in these cells. Such neuronesprovide a convenient system in which to study the functional interactions between peptide and amine cotransmitters. In addition, the serotonin and proctolin phenotypes of these cells are first expressed at widely different times in development. This presents the possibility of studying the regulation of these two transmitter phenotypes in a system that is readily amenable to experimental manipulation.

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