title: Partial antinociceptive cross-tolerance to intracerebroventricular beta-endorphin in mice tolerant to systemic morphine.
abstract: The effects of subcutaneous morphine pellet-implantation on antinociception induced by intracerebroventricular (i.c.v.) administration of beta-endorphin or morphine and intrathecal (i.t.) administration of morphine, [D-Pen2,D-Pen5]enkephalin (DPDPE), [D-Ala2,NMePhe4,Gly5-ol]enkephalin (DAMGO), serotonin or norepinephrine were studied in male ICR mice. The tail-flick and hot-plate responses were used for antinociceptive tests. The ED50 values for i.c.v. administered morphine for antinociception in morphine pellet-implanted mice were increased from 3.3- and 2.2-fold at 0 h to 14.2- and 19.0-fold at 4 h and declined to 4.8- and 3.0-fold at 8 h after pellet removal in the tail-flick and hot-plate tests, respectively. On the other hand, the ED50 values for i.c.v. administered beta-endorphin for antinociception were only slightly increased (1.7- to 5.1-fold increases) throughout the same time course. The inhibition of the tail-flick response induced by i.t. injection of morphine, DPDPE and serotonin, but not norepinephrine or DAMGO, was attenuated in morphine pellet-implanted mice. These findings are consistent with previous studies indicating that different neuronal mechanisms are involved in morphine- and beta-endorphin-induced antinociception.
authors.affiliation: Department of Pharmacology and Toxicology, Medical College of Wisconsin, Milwaukee 53226.
authors.forename: L F
authors.initials: LF
authors.lastname: Tseng
authors.forename: J J
authors.initials: JJ
authors.lastname: Lin
authors.forename: K A
authors.initials: KA
authors.lastname: Collins
mesh_terms: D000700:Analgesics / Q000494:pharmacology*; D000818:Animals; D004343:Drug Implants; D004361:Drug Tolerance; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D020881:Enkephalin, D-Penicillamine (2,5)-; D004745:Enkephalins / Q000494:pharmacology; D007276:Injections, Intraventricular; D007278:Injections, Spinal; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology*; D009638:Norepinephrine / Q000494:pharmacology; D010147:Pain Measurement / Q000187:drug effects; D012701:Serotonin / Q000494:pharmacology; D001615:beta-Endorphin / Q000008:administration & dosage / Q000494:pharmacology*
chemical_list: D000700:Analgesics; D004343:Drug Implants; D004745:Enkephalins; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D012701:Serotonin; D001615:beta-Endorphin; D009020:Morphine; D020881:Enkephalin, D-Penicillamine (2,5)-; D009638:Norepinephrine