Anxiogenic effect of naltrexone in social interaction test in rats

To study the anxiogenic effect of naltrexone (Nal) on the emotional state of rats.The duration of active interaction was measured in the social interaction test in rats.Without influence on the locomotor activity, Nal (0.1-50 mg.kg-1) dose- and time-dependently decreased the duration of active interaction, which was antagonized by morphine (5 mg.kg-1) or fenclonine (Fen, 150 mg.kg-1 x 3 d) and was enhanced by 5-hydroxytryptophan (5-HTP, 50 mg.kg-1).Nal produced anxiety via its blockade of opioid receptors; central opioidergic neurons were involved in the regulation of anxiety through their tonic inhibitions in serotonergic neurons.