by [3H]DAMGO binding and/or immunoblotting, but did not change protein expression of the hMOPR in transiently transfected COS [40], HEK293 and AV-12 cells [38]. Thus, the A118G/A112G SNP either decreases or does not change expression of MOPR in different brain regions or cell lines. The variations in the impact of the SNP on the MOPR expression in different cell lines and brain regions may be due to differences in glycosylation machinery. The MOPR has been shown to have brain region-specific N-glycosylation patterns [27], which is confirmed in this studies (Fig. 2, thalamus vs striatum) and is likely the result of differential expression of various enzymes involved in glycosylation across brain regions. Indeed, Matsuhashi et al.[41] observed region-specific expression of glycotransferases in adult mouse brain. It is noteworthy that no RNA editing of the MOPR occurs in either the striatum or thalamus [27]. Nevertheless, it remains unknown whether the varied N-glycosylation patterns of the MOPR in the two brain areas resulted from the brain region-specific glycosylation of Asn residues and/or different N-glycan compositions attached to the Asn residues. Thus, a likely explanation for our observation is that the A118G/A112G mutation leads to brain area-specific changes in N-glycan contents and thereby differentially
