title: Development of opiate tolerance in the chick embryo.
abstract: Tolerance to morphine was produced in the chick embryo. Eggs were injected with morphine sulfate (MS) (20 mg/kg egg) or H2O daily starting on incubation day 12. On day 16, embryo activities were recorded and eggs were injected with either MS or naloxone. Activity of H2O-pretreated controls decreased after both MS and naloxone. Embryos treated with MS from incubation days 12-15 showed no activity change after morphine and responded to naloxone with increases in activity. Baseline rates of distress vocalizations (DV) of 1-2 day old chicks were not affected by MS pretreatment during incubation days 12-19. However, 1 mg/kg MS decreased the rate of DV of control chicks by 90% whereas MS-pretreated chicks were unaffected. At age 4-5 days, the baseline rate of DV and rate after MS were higher in MS-pretreated chicks. However, all chicks showed significant decreases in rate of DV after MS injection. Naloxone increased the rate of DV of paired 1-2 day old chicks, but response of MS-pretreated chicks was significantly greater than controls.
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D002642:Chick Embryo; D002645:Chickens; D004361:Drug Tolerance; D009020:Morphine / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects; D009270:Naloxone / Q000494:pharmacology; D009294:Narcotics / Q000494:pharmacology*; D014828:Vocalization, Animal / Q000187:drug effects
chemical_list: D009294:Narcotics; D009270:Naloxone; D009020:Morphine