Identification of specific leech neurones immunoreactive to enkephalin.

The small endogenous peptides, Met- and Leu-enkephalin, bind to the same specific receptors as opiate analgesics. They, and the larger endorphin peptides, have been widely found in mammals, where they seem to have a significant role in neuronal pathways mediating pain and emotional behaviour. Only recently has enkephalin-like activity been identified in an invertebrate, the earthworm, although there is some preliminary evidence for opiate receptors in a marine mollusc. Here I report the detection, by an immunocytochemical technique, of an enkephalin-like moiety which is localised in one of the 400 cells of each posterior midbody ganglion of the leech. The presence of enkephalin-like activity in an identifiable easily accessible neurone of a well characterised nervous system such as that of the leech could greatly facilitate elucidation of its mechanism of action.