GABA and Histamine Interaction in the Basolateral Amygdala of Rats in the Plus-Maze Test of Anxiety-Like Behaviors

Abstract

In the present study, we have investigated the effects and the interaction of the GABAergic and histaminergic systems in the basolateral amygdala (BLA) of rats using the plus-maze test of anxiety-like behaviors. Unilateral injection of different doses of muscimol (GABA_A receptor selective agonist; 0.01, 0.05 and 0.1 µg/rat) into the BLA (intra-BLA) increased the percentage of open arm time (%OAT) and open arm entries (%OAE) at the doses of 0.05 and 0.1 µg/rat that are representative of an anxiolytic response. Intra-BLA injection of bicuculline (GABA_A receptor selective antagonist; 0.05, 0.1 and 0.5 µg/rat) decreased %OAT and %OAE at the doses of 0.1 and 0.5 µg/rat showing an anxiogenic-like effect. Intra-BLA administration of histamine (0.05, 0.1 and 0.5 µg/rat) also showed anxiogenic-like effects at the doses of 0.1 and 0.5 µg/rat while intra-BLA administration of pyrilamine (an H₁ receptor selective antagonist; 5, 10 and 20 µg/rat) induced anxiolytic effects at the dose of 20 µg/rat. Coadministration of histamine (0.1 µg/rat) with muscimol reversed the anxiolytic effect of muscimol at the dose of 0.1 µg/rat while coadministration of histamine (0.1 µg/rat) with bicuculline increased the anxiogenic effect of bicuculline at the dose of 0.05 µg/rat. On the other hand, coadministration of pyrilamine (10 µg/rat) with bicuculline decreased anxiety-like behaviors of bicuculline at the dose of 0.5 µg/rat while pyrilamine could not affect the anxiolytic effect of muscimol. In conclusion, it seems that both GABAergic and histaminergic systems not only play a part in the modulation of anxiety-like behaviors in the BLA of rats but may also have opposite effects in this brain region.