Differential effects of morphine- and cocaine-induced nNOS immunoreactivity in the dentate gyrus of hippocampus of mice lacking μ-opioid receptors

Ji Hoon Yoo, Jae Han Cho, Seok Yong Lee, Sanggeol Lee, Horace H. Loh, Ing K. Ho, Choon Gon Jang

Research output: Contribution to journalArticle

12 Scopus citations

Abstract

This study investigated the expression of nNOS after repeated morphine or cocaine administration in order to determine if nNOS (neuronal nitric oxide synthase) is involved in the morphine- or cocaine-induced behavioral sensitization in μ-opioid receptor knockout (MOR-/-) mice. Higher numbers of nNOS-positive cells were observed in the dentate gyrus of the hippocampus (DG) of the wild-type (MOR+/+) mice repeatedly treated with either morphine or cocaine than in the saline treated MOR+/+ mice (morphine, +122%; cocaine, +82%). Moreover, the MOR-/- mice also showed significantly higher morphine- or cocaine-induced nNOS expression levels in the DG than in the saline treated MOR+/+ mice (morphine, +234%; cocaine, +54%). The MOR-/- mice showed a significantly higher morphine-induced nNOS expression level (+103%) or a lower cocaine-induced nNOS expression level (+38%) in the DG than in the morphine- or cocaine-treated MOR+/+ mice. These results suggest that morphine and cocaine sensitization is differentially regulated by the μ-opioid receptors in MOR-/- mice via the nNOS systems in the DG.

Original languageEnglish (US)
Pages (from-to)98-102
Number of pages5
JournalNeuroscience Letters
Volume395
Issue number2
DOIs
StatePublished - Mar 6 2006

Keywords

  • Cocaine
  • Immunohistochemistry
  • Knockout mice
  • Morphine
  • nNOS
  • μ-Opioid receptors

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