Association of morphine-induced antinociception with variations in the 5' flanking and 3' untranslated regions of the mu opioid receptor gene in 10 inbred mouse strains.
OBJECTIVE
Genetic factors are hypothesized to be involved in interindividual differences in opioid sensitivity. Inbred mouse strains that are genetically different and isogenic within each strain are useful for elucidating the genetic mechanisms underlying the interindividual differences in opioid-induced analgesia.


METHODS
We examined the effects of morphine in 10 inbred mouse strains, including wild-derived strains that have a wide range of genetic diversity, including BLG2, CHD, KJR, MSM, NJL, PGN2, and SWN. We also performed full sequencing of the 5' flanking region and exons of the mouse mu opioid receptor gene Oprm1 and analyzed the association between genotypes and phenotypes in these mice.


RESULTS
The effects of morphine on locomotor activation and antinociception varied among the inbred strains. The nucleotide differences that cause amino acid substitutions were not found in the Oprm1 gene in the inbred strains analyzed in this study. In the 5' flanking region and 3' untranslated region of the Oprm1 gene, four highly variable regions containing novel short tandem repeat polymorphisms (GA, T, TA, and CA/CT) were identified. The GA, T, and TA repeat numbers were significantly associated with morphine-induced antinociception.


CONCLUSIONS
These results suggest that the short tandem repeats in the 5' flanking and 3' untranslated regions of the mu opioid receptor gene are involved in interstrain differences in opioid sensitivity in mice. Wild-derived inbred mouse strains with different numbers of these repeats may be useful models for examining interindividual differences in opioid sensitivity.
Division of Psychobiology, Tokyo Institute of Psychiatry, Japan.
Yoshihiro
Y
Shigeta
Shinya
S
Kasai
Wenhua
W
Han
Harumi
H
Hata
Akinori
A
Nishi
Yukio
Y
Takamatsu
Yoko
Y
Hagino
Hideko
H
Yamamoto
Tsuyoshi
T
Koide
Toshihiko
T
Shiroishi
Kiyoto
K
Kasai
Koichi
K
Tsunashima
Nobumasa
N
Kato
Kazutaka
K
Ikeda
D020413:3' Untranslated Regions / Q000235:genetics*; D020121:5' Untranslated Regions / Q000235:genetics*; D019943:Amino Acid Substitution; D000818:Animals; D001483:Base Sequence; D014644:Genetic Variation / Q000187:drug effects; D006239:Haplotypes; D051379:Mice; D008815:Mice, Inbred Strains; D018895:Microsatellite Repeats / Q000235:genetics; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology*; D016366:Open Reading Frames / Q000235:genetics; D010146:Pain / Q000235:genetics*; D017450:Receptors, Opioid, mu / Q000235:genetics*
D020413:3' Untranslated Regions; D020121:5' Untranslated Regions; D017450:Receptors, Opioid, mu; D009020:Morphine