Decreased response to social defeat stress in μ-opioid-receptor knockout mice

Hiroshi Komatsu, Arihisa Ohara, Kazumasu Sasaki, Hiromi Abe, Hisaki Hattori, F. Scott Hall, George R. Uhl, Ichiro Sora

Research output: Contribution to journalArticlepeer-review

47 Citations (Scopus)


Substantial evidence exists that opioid systems are involved in stress response and that changes in opioid systems in response to stressors affect both reward and analgesia. Reportedly, mice suffering chronic social defeat stress subsequently show aversion to social contact with unfamiliar mice. To further examine the role of opioid systems in stress response, the behavioral and neurochemical effects of chronic social defeat stress (psychosocial stress) were evaluated in μ-opioid-receptor knockout (MOR-KO) mice. Aversion to social contact was induced by chronic social defeat stress in wild-type mice but was reduced in MOR-KO mice. Moreover, basal expression of brain-derived neurotrophic factor (BDNF) mRNA in MOR-KO mice hippocampi was significantly lower than in wild-type mice. Psychosocial stress significantly decreased BDNF mRNA expression in wild-type mice but did not affect BDNF expression in MOR-KO mice; no difference in basal levels of plasma corticosterone was observed. These results suggest that the μ-opioid receptor is involved in the behavioral sequelae of psychosocial stress and consequent regulation of BDNF expression in the hippocampus, and may play an important role in psychiatric disorders for which stress is an important predisposing or precipitating factor, such as depression, posttraumatic stress disorder, and social anxiety disorder.

Original languageEnglish
Pages (from-to)676-682
Number of pages7
JournalPharmacology Biochemistry and Behavior
Issue number4
Publication statusPublished - 2011 Oct


  • Behavior
  • Brain-derived neurotrophic factor
  • Chronic social defeat stress
  • Hippocampus
  • μ-opioid-receptor knockout


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