Similarly, A1 18G/A112G decreased or did not change MOPR mRNA levels depending on brain regions. In humans, A118G lowers levels of MOPR mRNA in the cortical lobes and pons [39]. Decreased MOPR mRNA was also found in G/G mice, compared with A/A mice, in the periaqueductal gray, hypothalamus, ventral tegmental area, nucleus accumbens and cortex [18], while no difference was found in the hippocampus [18] and thalamus (our unpublished data). Although MOPR protein levels in most of these brain regions have not been compared between wildtype and the A118G (A112G) variants, it is clear that lower protein expression of the MOPR is not due to lower mRNA level since in the thalamus of G/G mice, the protein level of the MOPR is lower, but its mRNA is unchanged, compared with that of A/A mice.
