Experiment
200 (C57BL/6J x DBA/2J)F2 intercross animals and 24 BXD (B = C57BL/6J, D = DBA/2J) recombinant inbred (RI) strains were used to screen provisional loci associated with morphine induced pain reduction (antinociception). Provisional loci were confirmed using high and low antinociception lines and incipient or completed congenic strains derived from C57BL/6J and DBA/2J progenitors. Progenitor strain C57BL/6J is insensitive to morphine antinociception whereas progenitor strain DBA/2J is sensitive to morphineantinociception. Four QTLs mapped to mouse Chromosomes 1, 4, 9, and 11. Morph1 maps to mouse Chromosome 1 at 9 cM with a LOD score of 4.7 at D1Mit67. On mouse Chromosome 9, Morph2 maps to 20 cM with a LOD score of 5.2 at D9Mit91, and Morph3 maps to 42 cM with a LOD score of 4.5 at Myo5a. On mouse Chromosome 10, Morph4 maps to 9 cM with a LOD score of 7.5 at D10Mit51. A suggestive locus mapped to mouse Chromosome 9 at 71 cM with a LOD score of 3.8 at D9Mit18. DBA/2J-derived alleles conferred higher morphine antinociception with mostly additive inheritance at all loci. Oprk1 on Chromosome 1 (5.5 cM) is a possible candidate gene for Morph1, and Oprm on Chromosome 10 (9 cM) is a possible candidate gene for Morph4.
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