Muscimol antagonizes morphine hypermotility without potentiation of analgesia.

Muscimol, a very potent and specific GABA agonist, strongly depressed characteristic morphine-induced locomotor activity. Muscimol induced only a very weak increase in the morphine analgesia measured in the hot plate test which perhaps could be a result of a freezing reaction. No effect on morphine analgesia was observed in the wire grid test. These results indicate that GABA differentially influences morphine stimulation and analgesia.