The effects of repeated morphine exposure on mu opioid receptor number and affinity in C57BL/6J and DBA/2J mice

Rebecca Petruzzi, Thomas N. Ferraro, Veit C. Kürschner, Gregory T. Golden, Wade H. Berrettini

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30 Scopus citations


C57BL/6J (B6) mice self-administer substantial quantities of morphine compared to DBA/2J (D2) mice, and most of the genetic component of this strain difference has been attributed to a locus on chromosome 10 in the vicinity of the mu opioid receptor gene. To compare binding characteristics of mu opioid receptor populations between the two strains, mice were given single daily injections of a long-acting preparation of morphine sulfate (80 mg/kg, sc) or saline for a period of seven days, and euthanatized six hours after the last injection. Brains were removed and dissected into specific regions. Receptor binding studies were performed on frontal cortex and striatum. Data were analyzed using non-linear regression, and K(d) and B(max) comparisons made between strains and treatments. Specific [3H]DAMGO binding in striatum indicates that the density of mu opioid receptors in saline- treated B6 mice and saline-treated D2 mice does not differ significantly. After repeated morphine injection, B6 mice exhibited a decrease in striatal [3H]DAMGO binding, indicating a downregulation of receptor density by approximately 45% (p=.0003 vs saline-treated B6), a phenomenon not observed in D2 mice. In frontal cortex, no differences in [3H]DAMGO binding were observed between strains or treatment groups. These results demonstrate a significant difference between mu opioid receptor regulation in B6 and D2 mice, and may underlie well documented strain differences in specific opioid- related behaviors.

Original languageEnglish (US)
Pages (from-to)2057-2064
Number of pages8
JournalLife Sciences
Issue number20
StatePublished - Oct 10 1997
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • General Pharmacology, Toxicology and Pharmaceutics
  • General Biochemistry, Genetics and Molecular Biology


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