Immunohistochemical localization of opioid peptides in the brain of the leech Theromyzon tessulatum.

By use of antisera directed against met-enkephalin, leu-enkephalin, dynorphin or α-neoendorphin, immunoreactive structures were visualized in the central nervous system and proboscis of the leech Theromyzon tessulatum. Their distribution in the various compartments of the supra- and subesophageal ganglia was mapped. No correspondence could be established between the neurons containing met- or leu-enkephalin-like substances and the different types of neurosecretory cells classically described in Hirudinea. Successive localization of leu- and met-enkephalin on the same section revealed that these two peptides occur in different neurons. Only one cell located in compartment 6 of the supraesophageal ganglion was both dynorphin- and leu-enkephalin-positive. The other dynorphinimmunoreactive cells were not stained with the anti-leuenkephalin serum. The α-neoendorphin-immunopositive cells were leu-enkephalin immunonegative and vice versa.