Periaqueductal gray stimulation produces a spinally mediated, opioid antinociception for the inflamed hindpaw of the rat

Brain Res. 1991 Apr 5;545(1-2):17-23. doi: 10.1016/0006-8993(91)91264-2.


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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Analysis of Variance
  • Animals
  • Electric Stimulation
  • Freund's Adjuvant
  • Hindlimb / innervation
  • Inflammation
  • Male
  • Mycobacterium
  • Naloxone / pharmacology
  • Naltrexone / pharmacology
  • Pain / physiopathology*
  • Periaqueductal Gray / physiology
  • Periaqueductal Gray / physiopathology*
  • Rats
  • Rats, Inbred Strains
  • Spinal Cord / drug effects
  • Spinal Cord / physiology
  • Spinal Cord / physiopathology*


  • Naloxone
  • Naltrexone
  • Freund's Adjuvant