Morgan M M, Gold M S, Liebeskind J C, Stein C
Department of Psychology, University of California, Los Angeles 90024-1563.
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.
