The GABA B -receptor antagonist, CGP 35348, antagonises ?-hydroxybutyrate- and baclofen-induced alterations in locomotor activity and forebrain dopamine levels in mice

Previous studies have shown that administration of γ-hydroxybutyric acid (GHBA) or baclofen is associated with a decrease in locomotor activity as well as an increase of dopamine (DA) in brain. In the present study we analyse whether these actions are related to activation of GABA B -receptors utilising a GABA B -receptor antagonist, CGP 35348. Administration of GHBA (200 or 800 mg/kg, i.p.) or baclofen (4 or 16 mg/kg, i.p.) induced a marked and dose-dependent decrease in locomotor activity in mice, that was antagonised by pretreatment with CGP 35348 (400 mg/kg, i.p.). Treatment with the highest doses of GHBA and baclofen produced clear-cut increases in forebrain DA concentration. Also these effects were effectively antagonised by pretreatment with CGP 35348. Treatment with the GABA B -receptor antagonist alone did not influence the locomotor activity or brain DA concentration. These results indicate that the behaviourally depressive and DA increasing effects of GHBA and baclofen are mediated by activation of GABA B -receptors.