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Pharmacol Biochem Behav. 1993 Sep;46(1):145-8.

Naloxone-induced analgesia: involvement of kappa-opiate receptors.

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Department of Pharmacology, School of Medicine, University of Milano, Italy.


Rats treated with an acute high dose (30 mg/kg) or 4 days with a lower dose (5 mg/kg) of naloxone or naltrexone show an analgesic response at the hot-plate test. This paradoxical analgesic effect of the two mu-opiate receptor antagonists is blocked by the kappa opiate receptor antagonist MR 1452, and is modulated by the kappa opiate receptor agonist U 50-488. Our results suggest that kappa opiate receptors are involved in naloxone-induced analgesia and are consistent with a high degree of plasticity of the opiatergic system.

[Indexed for MEDLINE]

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