Mytilus edulis pedal ganglia express μ opiate receptor transcripts exhibiting high sequence identity with human neuronal μ1

Previous pharmacological and biochemical evidence suggests that μ-subtype opiate receptors are expressed in the mollusk Mytilus edulis (Bivalve), including the organism's ganglia. In this study, we present molecular evidence of μ opiate receptor expression. Using primers derived from the human neuronal μ1 opiate receptor, we used reverse transcription-polymerase chain reaction (RT-PCR) to detect expression of μ transcripts from Mytilus pedal ganglia. Sequence analysis of the RT-PCR products revealed 95% identity with the neuronal human μ1 receptor. Furthermore, interleukin-1 and morphine exposure to excised pedal ganglia resulted in up- and down-regulation of the μ receptor transcripts, respectively. This study provides molecular evidence that μ-type opiate receptors are expressed in molluscan ganglia, suggesting that they first appear in invertebrate organisms and are retained during evolution. Copyright (C) 1999 Elsevier Science B.V.