title: Distribution of CB1 cannabinoid receptors and their relationship with mu-opioid receptors in the rat periaqueductal gray.
abstract: 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.
authors.affiliation: Department of Neuroscience, Washington State University, 14204 NE Salmon Creek Avenue, Vancouver, WA 98686, USA. adie.wilson@gmail.com
authors.forename: A R
authors.initials: AR
authors.lastname: Wilson-Poe
authors.forename: M M
authors.initials: MM
authors.lastname: Morgan
authors.forename: S A
authors.initials: SA
authors.lastname: Aicher
authors.forename: D M
authors.initials: DM
authors.lastname: Hegarty
mesh_terms: D000818:Animals; D007150:Immunohistochemistry; D008297:Male; D018613:Microscopy, Confocal; D046529:Microscopy, Electron, Transmission; D009474:Neurons / Q000378:metabolism* / Q000648:ultrastructure*; D010487:Periaqueductal Gray / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D043884:Receptor, Cannabinoid, CB1 / Q000096:biosynthesis*; D017450:Receptors, Opioid, mu / Q000096:biosynthesis*
chemical_list: D043884:Receptor, Cannabinoid, CB1; D017450:Receptors, Opioid, mu