The coding region of part of the cytoplasmic tail (FREFCIPTSSTIEQQNSARIRQNTREHPSTANTVDRTNHQ) within exon 3 was replaced with the sequence from the delta opioid peptide receptor (FRQLCRTPCGRQEPGSLRRPRQATTRERVTACTPSQ) and a floxed neo cassette. Expression of the receptor in homozygotes was similar to the endogenous receptor. (J:131412)