Distribution of CB1 cannabinoid receptors and their relationship with mu-opioid receptors in the rat periaqueductal gray

A. R. Wilson-Poe, M. M. Morgan, Sue Aicher, D. M. Hegarty

Research output: Contribution to journalArticle

36 Scopus citations


The periaqueductal gray (PAG) is part of a descending pain modulatory system that, when activated, produces widespread and profound antinociception. Microinjection of either opioids or cannabinoids into the PAG elicits antinociception. Moreover, microinjection of the cannabinoid 1 (CB1) receptor agonist HU-210 into the PAG enhances the antinociceptive effect of subsequent morphine injections, indicating a direct relationship between these two systems. The objective of this study was to characterize the distribution of CB1 receptors in the dorsolateral and ventrolateral PAG in relationship to mu-opioid peptide (MOP) receptors. Immunocytochemical analysis revealed extensive and diffuse CB1 receptor labeling in the PAG, 60% of which was found in somatodendritic profiles. CB1 and MOP receptor immunolabeling were co-localized in 32% of fluorescent Nissl-stained cells that were analyzed. Eight percent (8%) of PAG neurons that were MOP receptor-immunoreactive (-ir) received CB1 receptor-ir appositions. Ultrastructural analysis confirmed the presence of CB1 receptor-ir somata, dendrites and axon terminals in the PAG. These results indicate that behavioral interactions between cannabinoids and opioids may be the result of cellular adaptations within PAG neurons co-expressing CB1 and MOP receptors.

Original languageEnglish (US)
Pages (from-to)191-200
Number of pages10
Publication statusPublished - Jun 28 2012



  • -Ir
  • Antinociception
  • Bsa
  • Camp
  • Cb1
  • Descending modulation
  • Dmso
  • Ems
  • Erk
  • Mapk
  • Mop
  • Nida
  • Nt
  • Pag
  • Pain
  • Pb
  • Periaqueductal gray
  • Roi
  • Thc
  • Ts

ASJC Scopus subject areas

  • Neuroscience(all)

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