title: Single-dose tolerance to morphine-induced analgesic and hypoactive effects in infant rats.
abstract: A single injection of morphine or isotonic saline was administered to rats at either 1, 5, 9, ro 13 days of age. At 26-29 days of age, animals were tested for pain responsivity and activity following either morphine (5 mg/kg) or saline. Animals which received morphine at 1 day of age displayed tolerance at 26 days of age, whereas animals which received morphine at either 5, 9, or 13 days of age failed to display tolerance. This age-dependent change in susceptibility to single-dose morphine tolerance may involve alterations in opiate receptor ontogeny.
mesh_terms: D000367:Age Factors; D000818:Animals; D004361:Drug Tolerance; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology*; D009043:Motor Activity / Q000187:drug effects; D051381:Rats; D011957:Receptors, Opioid / Q000187:drug effects*
chemical_list: D011957:Receptors, Opioid; D009020:Morphine