Cloning, expression and classification of a kappa₃-related opioid receptor using antisense oligodeoxynucleotides

Using degenerate oligodeoxynucleotide primers based upon the predicted amino acid sequence of the cloned delta receptor in RT-PCR we isolated a cDNA of approximately 500 bases with high homology to the cloned delta, mu and kappa₁ receptors. Before proceeding to clone the full length coding region, we designed an antisense oligodeoxynucleotide (ODN) and examined its actions in vivo. Administered intracerebroventricularly, the antisense ODN effectively blocks the analgesic actions of the kappa₃ agent naloxone benzoylhydrazone (NalBzoH) without affecting morphine (mu) analgesia. A mismatch ODN identical in base composition to the antisense but with four bases out of sequence is inactive. Having established the relevance of the sequence, we proceeded to clone the full length cDNA from a mouse brain library and characterize the expressed protein.