Three antagonists at the μ opiate receptor site: naloxone, naltrexone and diprenorphrine, and one agonist-antagonist compound: nalorphine, at doses usually not analgesic elicited analgesia in rats when administered after non-naloxone-reversible shock-induced analgesia had disappeared. The χ receptor antagonist, MR 2266, and the δ antagonist, ICI 154129, were all ineffective. This effect was no longer present when non-naloxone-reversible shock-induced analgesia was inhibited by the administration of the χ receptor antagonist, MR 2266. These results suggest that the μ opiate receptor may change its conformation under particular conditions such as continuous inescapable shock. © 1985.
Sacerdote, P., Mantegazza, P., & Panerai, A. E. (1985). Analgesic effects of μ antagonists after naloxone non-reversible stress-induced analgesia. Brain Research, 359(1–2), 34–38. https://doi.org/10.1016/0006-8993(85)91409-X