ABSTRACT
In recent years, the use of invertebrates as models in biomedical research has gained considerable attention. 1 In particular, the relevance of information gained from the study of insects has been established by the demonstration of remarkable structural, functional, and biochemical parallels between their neuroendocrine control mechanism and that of vertebrates. 2 The presence of biologically active neuropeptides, known to play a central role in these integrative systems and in neurobiology in general, has been reported in a variety of invertebrates, including insects 3 5 (see also Chapter 13 of this work). However, detailed information on a specific class of these peptides, the endogenous opioids, is largely confined to the mammalian nervous system. 6 The recent upsurge of interest in the diverse roles and modes of operation of these active principles has sparked a search for their evolutionary history. Whereas several reports on the occurrence of endogenous opioids in submammalian vertebrates have become available, 7 comparable data in invertebrates are still scarce. They pertain to the demonstration, in certain ganglia, either of opioid peptides comparable to those of vertebrates or of specific receptor sites for such active principles. 8
