By autoradiography, we found that the A112G substitution resulted in reduced MOPR expression in the cortices, NAc, hypothalamus, amygdala, PAG, SuG, and VTA, but not in the hippocampus and CPu. By receptor binding using brain membranes, we found that compared with A/A mice, G/G mice had lower levels of [3H]DAMGO binding to the MOPR in the cortex and thalamus but had similar levels in the hippocampus and CPu+NAc. When brain regions were dissected for membrane binding, CPu and NAc were dissected together to get sufficient tissues. It is likely that the lack of effects of A112G in the CPu masked the reduction in the NAc because the CPu is much larger. Thus, in general autoradiographic data are consistent with MOPR membrane binding results. In addition, the higher MOPR binding in the thalamus in A/A mice than in G/G mice is also in accord with our previous findings obtained by immunoblotting of the MOPR (Mague et al., 2009).
