Interaction of GABA and Serotonin in the Anxiolytic Action of Diazepam and Serotonergic Anxiolytics

The general purpose of the present study was to analyze the possible interactions between the GABA-benzodiazepine and the serotonergic (5-HT) systems in the anxiolytic action of diazepam and the 5-HT1A agonists, ipsapirone, indorenate, and 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT). The effect of the benzodiazepine receptor antagonist, flumazenil (10.0 mg/kg), on the anxiolytic action of ipsapirone (5.0 mg/kg), indorenate (5.0 mg/kg), and 8-OH-DPAT (0.125 mg/kg) was examined on the avoidance exploratory behavior paradigm in mice. The effect of the 5-HT1 blockers, methiotepin (0.31 mg/kg), pindolol (3.1 mg/kg), and alprenolol (5.0 mg/kg), on the anxiolytic action of diazepam (0.5 mg/kg) was also studied. In the last part of this work, the putative potentiation between diazepam (0.25 mg/kg) and each of the serotonergic anxiolytics was investigated. The antianxiety effect of diazepam, ipsapirone, indorenate, and 8-OH-DPAT was prevented by flumazenil. The serotonergic/beta-blocker, alprenolol, partially antagonized the diazepam effect. Finally, a potentiation of suboptimal doses of diazepam and ipsapirone, but not with indorenate or 8-OH-DPAT, was observed. The findings suggest an interaction between both systems on the anxiolytic action of diazepam and the 5-HT1A agonists.