Periaqueductal gray matter involvement in the muscimol-induced decrease of morphine antinociception

Abstract
Microinjections of muscimol, a GABA receptor agonist, into the periaqueductal gray matter (PAG) counteracted the antinociceptive effect of morphine in rats, as measured by the “tail-flick” method. Muscimol's effect was partially reversed by bicuculline.