In vivo binding of naloxone to opioid receptors in morphine-dependent mice.
In vivo binding assay of opioid receptors for naloxone was tested in morphine-dependent mice. The content of naloxone in the brain (whole brain minus cerebellum) and cerebellum was determined as the total binding and non-specific binding, respectively, 20 min after the intravenous injection of [3H]-naloxone. Acute treatment with 8 mg/kg of morphine sulfate markedly enhanced the non-specific binding of naloxone. In contrast, withdrawal for 6 hr after 72 hr of implantation of morphine decreased the non-specific binding of naloxone. The Scatchard analysis of the specific binding revealed two binding sites. The apparent low affinity Kd values of both morphine-tolerant and morphine-withdrawn mice were significantly decreased when compared to their respective controls. The apparent high affinity Kd and the high and low Bmax values were not altered by the morphine dependent-tolerant state.
D000818:Animals; D001921:Brain / Q000378:metabolism*; D004361:Drug Tolerance; D006801:Humans; D007700:Kinetics; D008297:Male; D009021:Morphine Dependence / Q000378:metabolism*; D009115:Muridae; D009270:Naloxone / Q000378:metabolism*; D011957:Receptors, Opioid / Q000187:drug effects* / Q000378:metabolism; D013375:Substance Withdrawal Syndrome / Q000378:metabolism
D011957:Receptors, Opioid; D009270:Naloxone