The effect of naloxone on cerebellar cGMP content. A possible GABA-antagonistic action?

Naloxone in high doses (60--240 mg/kg i.p.) produced a dose-dependent increase in cerebellar cGMP content of mice. The rise in cGMP content reached its maximum within 5 min and was of short duration. Short-lasting episodes of clonic seizures were noted after 240 mg/kg naloxone. Low doses of naloxone (5--10 mg/kg) had no effect on cerebellar cGMP content, but markedly potentiated the increase in cGMP induced by isoniazid. On the other hand, naloxone (5 mg/kg) partially antagonized the fall in cGMP elicited by diazepam, but had only a slight effect on the action of pentobarbital (30 mg/kg i.p.). These results support the assumption proposed by other authors that naloxone exerts GABA antagonistic effects aside from the potent opiate receptor antagonistic activity.