Absence of cross-tolerance to heroin in morphine-tolerant mice.
Mice implanted with morphine pellets demonstrated a 30-fold increase in tolerance to subcutaneously administered morphine but showed no cross-tolerance to subcutaneously administered heroin. When given morphine intracerebroventricularly, the mice showed no tolerance to morphine or cross-tolerance to heroin. These observations depended on the presence of the morphine pellet. If the pellets were removed prior to determinations of potency, the expected responses--tolerance to morphine and cross-tolerance to heroin--were obtained. The blood-brain barrier may be a prime site for the expression of morphine tolerance in mice.
D000818:Animals; D001812:Blood-Brain Barrier / Q000187:drug effects; D004347:Drug Interactions; D004361:Drug Tolerance; D003932:Heroin / Q000008:administration & dosage / Q000494:pharmacology*; D051379:Mice; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology*
D003932:Heroin; D009020:Morphine