Life Sciences Commons^™

Lack Of Antinociceptive Cross-Tolerance With Co-Administration Of Morphine And Fentanyl Into The Periaqueductal Gray Of Male Sprague-Dawley Rats, Erin N. Bobeck, Shauna M. Schoo, Susan L. Ingram, Michael M. Morgan

Biology Faculty Publications

Tolerance to the antinociceptive effect of mu-opioid receptor (MOPr) agonists, such as morphine and fentanyl, greatly limits their effectiveness for long-term use to treat pain. Clinical studies have shown that combination therapy and opioid rotation can be used to enhance opioid-induced antinociception once tolerance has developed. The mechanism and brain regions involved in these processes are unknown. The purpose of this study was to evaluate the contribution of the ventrolateral periaqueductal gray (vlPAG) to antinociceptive tolerance and cross-tolerance between administration and co- administration of morphine and fentanyl. Tolerance was induced by pretreating rats with morphine or fentanyl or low-dose combination …