THE OPIATE SYSTEM IN INVERTEBRATES

The presence in diverse species of a similar mode of communication, th at of a soluble messenger binding to a receptor, raises the question a s to whether the specific components of this system are equally widesp read. Do invertebrates use the same hormones and receptors as vertebra tes do? Invertebrates ranging from unicellular organisms to insects ha ve been shown to contain opiate-like peptides and binding sites, and t hey exhibit biological responses to opiates. However, critical genetic data are lacking. It is not known how signal systems arise phylogenet ically, but it is conceivable that signal molecules that are already p resent cause the formation of their own receptors from membrane protei ns.