title: Periaqueductal gray stimulation produces a spinally mediated, opioid antinociception for the inflamed hindpaw of the rat.
abstract: The objective of the present study was to characterize stimulation-produced antinociception from the periaqueductal gray matter (PAG) in rats with unilateral hindlimb inflammation induced by an intraplantar injection of Freund's complete adjuvant. Rats were chronically implanted with a bipolar stimulating electrode in the PAG. Nociception was assessed using a paw pressure test. Prior to inflammation, PAG stimulation significantly increased paw pressure threshold in both paws compared to non-stimulated controls. Following inflammation, PAG stimulation inhibited nociception in the inflamed, but not the non-inflamed paw. Systemic administration of naloxone blocked antinociception from ventral, but not dorsal PAG stimulation sites. Intrathecal, but not subcutaneous, administration of quaternary naltrexone completely blocked stimulation-produced antinociception from the PAG. The known increased levels of endogenous opioids occurring in the spinal cord ipsilateral to the site of inflammation suggest a mechanism for the selective antinociceptive effect of ventral PAG stimulation seen for the inflamed paw.
authors.affiliation: Department of Psychology, University of California, Los Angeles 90024-1563.
authors.forename: M M
authors.initials: MM
authors.lastname: Morgan
authors.forename: M S
authors.initials: MS
authors.lastname: Gold
authors.forename: J C
authors.initials: JC
authors.lastname: Liebeskind
authors.forename: C
authors.initials: C
authors.lastname: Stein
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D004558:Electric Stimulation; D005620:Freund's Adjuvant; D006614:Hindlimb / Q000294:innervation; D007249:Inflammation; D008297:Male; D009161:Mycobacterium; D009270:Naloxone / Q000494:pharmacology; D009271:Naltrexone / Q000494:pharmacology; D010146:Pain / Q000503:physiopathology*; D010487:Periaqueductal Gray / Q000502:physiology / Q000503:physiopathology*; D051381:Rats; D011919:Rats, Inbred Strains; D013116:Spinal Cord / Q000187:drug effects / Q000502:physiology / Q000503:physiopathology*
chemical_list: D009270:Naloxone; D009271:Naltrexone; D005620:Freund's Adjuvant