A118G/A112G decreased or did not change MOPR mRNA levels depending on brain regions. In human postmortem tissues, A118G lowered levels of MOPR mRNA in the cortical lobes and pons (Zhang et al., 2005). In the mouse, A112G led to lower MOPR mRNA in the cortices, NAc, VTA, hypothalamus, and PAG, but not in the hippocampus (Mague et al., 2009) and thalamus (Mague and Blendy, unpublished data). In the thalamus of G/G mice, the protein level of the MOPR was lower with its mRNA unchanged, compared with A/A mice, indicating that the effects of A112G on MOPR protein levels are independent of changes in MOPR mRNA. On the other hand, A112G induced similar changes in mRNA and protein levels of MOPR in the hippocampus, NAc, VTA, hypothalamus, and PAG; however, no causal relationship was established between mRNA and protein changes. In general, there is no correlation between the expression level of a protein and its mRNA abundance (Gygi et al., 1999).
