Differential effects of morphine-6-glucuronide, an active metabolite of morphine, and morphine on locomotor activity in mice: involvement of the opioid receptor
Uchihashi, Y.; Kuribara, H.; Morita, T.; Kitani, Y.; Karasawa, F.; Sato, T.
Pharmacology and Toxicology 78(5): 322-326
1996
ISSN/ISBN: 0901-9928 PMID: 8737968 Document Number: 460696
Subcutaneous administration of morphine (2.5 to 20 mg/kg) or an active metabolite of morphine, morphine-6-glucuronide (2.5 to 20 mg/kg), increased the locomotor activity of mice in a dose-dependent manner. Fifteen mg/kg of morphine and 20 mg/kg of morphine-6-glucuronide were almost equipotent. Subcutaneous administration of the universal opioid antagonist, naloxone, but not the delta-selective antagonist, naltrindole, significantly suppressed the hyperlocomotion induced by morphine (15 mg/kg). On the other hand the subcutaneous administration of relatively higher doses of naloxone or naltrindole significantly reduced the hyperlocomotion induced by morphine-6-glucuronide (20 mg/kg). These findings suggest that agonistic actions at the opioid receptors, especially at the delta- and mu-receptors, contribute to the morphine6-glucuronide-induced hyperlocomotion.