Opiate peptide modulation of amino acid responses suggests novel form of neuronal communication

Mouse spinal neurons grown in tissue culture were used to study the electrophysiological pharmacology of the opiate peptide leucine-enkephalin. Enkephalin depressed glutamate-evoked responses in a noncompetitive manner independent of any other effects on membrane properties. The results demonstrate a neuromodulatory action of opiate peptide functionally distinct from the conventional neurotransmitter class of operation.