Animals: A112G-MOPR knock-in mice (A/A and G/G mice) were generated on a C57BL/6 genetic background in Dr. Blendy's laboratory [18]. MOPR-knockout (-/-) mice were originally developed in the lab of Dr. John Pintar (University of Medicine and Dentistry of New Jersey) by disruption of exon-1 of the MOPR-1 gene through homologous recombination [28]. The MOPR knockout (-/-) mice used in this study were derived following at least 10 generations of successive backcrossing of 129S6×C57BL/6J heterozygotes to C57BL/6J mice.
