Images: Distinct distribution patterns of DORs in subsets of DRG neurons of mice. Immunostaining with antibodies against DOR13-17 [A: 1:30,000, antibody 1 (ab #1); DiaSorin and C: antibody 2 (ab #2); Neuromics] shows DORs in small DRG neurons and afferent fibers in spinal laminae I-II. This immunostaining pattern is abolished by the antiserum preabsorption or the deletion of Oprd1 exon 1. Reduction in immunostaining is quantitatively assayed by determining the percentage of positive DRG neurons (B; n = 6) and fluorescence intensity (Ifluo.) in the laminae I-II (D; n = 5). **P < 0.01; ***P < 0.001. (Scale bars: A and C, 40 μm.). DOR labeling (anti-DOR13-17, 1:30,000; DiaSorin) associated with vesicles in peptidergic small DRG neurons (E and F) is absent in Oprd1 exon 1-deleted mice (G). Colocalization of DORs and neuropeptides is shown by correlated peaks of Ifluo. measured along lines. (Scale bar: 8 μm.) (H) Immunostaining with antibodies against DOR12-18 (1:60,000; Alomone) shows the presence of DORs on the cell surface of large DRG neurons of mice. (Scale bar: 25 μm.) This staining pattern is abolished by preabsorption and is absent in Oprd1 exon 1-deleted mice. (Scale bar: 80 μm.) (I) Triple-immunostaining shows that DOR+ large DRG neurons contain neither SP nor CGRP. (Scale bar: 80 μm.). www.pnas.org/cgi/doi/10.1073/pnas.1008382107