title: The periaqueductal gray: site of morphine analgesia and tolerance as shown by 2-way cross tolerance between systemic and intracerebral injections.
abstract: The periaqueductal gray was shown to be an important component of morphine analgesia and tolerance. Two-way analgesic cross tolerance was obtained between systemic and intracerebral morphine administrations when the intracerebral site was the periaqueductal gray. Rats were pretreated with intraperitoneal morphine and tested with intracerebral morphine in the periaqueductal gray. A dose-dependent reduction in analgesia as a function of morphine pretreatment level was obtained. Conversely, when rats were pretreated with intracerebral morphine in the periaqueductal gray and tested with intraperitoneal morphine, significant reductions in analgesia were obtained.
mesh_terms: D000698:Analgesia; D000818:Animals; D002535:Cerebral Aqueduct / Q000187:drug effects*; D002540:Cerebral Cortex / Q000187:drug effects*; D004361:Drug Tolerance; D007267:Injections; D007274:Injections, Intraperitoneal; D008297:Male; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology*; D051381:Rats
chemical_list: D009020:Morphine