The Journal of Neuroscience, February 15, 2001, 21(4):1334-1339
The Untranslated Region of µ-Opioid Receptor mRNA Contributes
to Reduced Opioid Sensitivity in CXBK Mice
Kazutaka
Ikeda1, 2,
Toru
Kobayashi3,
Tomio
Ichikawa3,
Toshiro
Kumanishi3,
Hiroaki
Niki1, and
Ryoji
Yano2
Laboratories for 1 Neurobiology of Emotion and
2 Cellular Information Processing, Brain Science Institute,
RIKEN, Wako, Saitama 351-0198, Japan, and 3 Department of
Molecular Neuropathology, Brain Research Institute, Niigata University,
Asahimachi, Niigata 951-8585, Japan
It is well known that there are individual differences in a
sensitivity to analgesics. Several lines of evidence have suggested that the level of opioid-induced analgesia is dependent on the level of
expression of the µ-opioid receptor (µ-OR). However, the molecular
mechanisms underlying the diversity of the level of the opioid receptor
and the opioid sensitivity among individuals remain to be elucidated.
In the present study, we analyzed the opioid-receptor genes of CXBK
recombinant-inbred mice, which show reduced sensitivity to opioids.
Northern blotting, nucleotide sequencing, and in situ
hybridization histochemical analyses demonstrated that CXBK mice
possessed µ-OR mRNA with a normal coding region but an abnormally
long untranslated region (UTR). In addition, the µ-OR mRNA level in
CXBK mice was less than in the control mice. Next, we produced
littermate mice that had inherited two copies of the wild-type µ-OR
gene, had inherited two copies of the CXBK µ-OR gene, and had
inherited both copies of the µ-OR genes. In these mice, inheritance
of the CXBK µ-OR gene was well correlated with less µ-OR mRNA and
reduced opioid effects on nociception and locomotor activity. We
conclude that the CXBK µ-OR gene is responsible for the CXBK
phenotypes. Because UTR differences are known to affect the level of
the corresponding mRNA and protein and because UTRs are more divergent
among individuals than coding regions, the present findings suggest
that opioid sensitivity may vary, depending on different µ-OR levels
attributable to divergent UTR of µ-OR mRNA.
Key words:
CXBK mouse; µ-opioid receptor; UTR; individual
difference; analgesia; morphine
Copyright © 2001 Society for Neuroscience 0270-6474/01/2141334-06$05.00/0