Multiple opioid receptor-like genes are identified in diverse vertebrate phyla

Polymerase chain reaction was used to determine whether opioid receptor-like sequences are present in species from the protostome and deuterostome branches of the metazoan kingdom. Multiple opioid receptor-like sequences were found in all vertebrates, but no specific fragments were obtained from any invertebrates. Delta, mu, kappa and ORL-1 receptors were identified from bovine DNA, and three different opioid receptor-like fragments were identified from the other vertebrates analyzed. The data suggest that the opioid receptor gene family has been highly conserved during vertebrate evolution and that, even in the primitive jawless fish, multiple members of the opioid receptor family appear to be present.