In the humanized knock-in mouse model of the OPRM1 A118G SNP generated by Ramchandani et al. (2011), there were no differences in [3H]DAMGO binding in the dorsal striatum, NAc, and VTA between homozygous G118 and A118 mice. The discrepancy between our results and those of Ramchandani et al. (2011) may be due to the replacement of the mouse exon 1 sequence with that of the human in the mouse, which may influence receptor expression.
