Brains from MOPR(-/-) mice or A/A112 and G/G112 littermate mice were collected. The striatum or thalamus tissues were dissected and homogenized in 8 volumes of 25 mM Tris-HCl buffer/pH 7.4 containing 1 mM EDTA and 0.1mM PMSF (pH 7.4) on ice and then centrifuged at 100,000 g for 30 min. Pellets were twice rinsed with 25 mM Tris-HCl buffer and resuspended in 0.32 M sucrose in 50 mM Tris-HCl/pH 7.0. Suspended membranes were passed through a 26.5 G needle 5 times and then frozen at - 80°C until use.
