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 microg/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 microg/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 microg/rat) decreased %OAT and %OAE at the doses of 0.1 and 0.5 microg/rat showing an anxiogenic-like effect. Intra-BLA administration of histamine (0.05, 0.1 and 0.5 microg/rat) also showed anxiogenic-like effects at the doses of 0.1 and 0.5 microg/rat while intra-BLA administration of pyrilamine (an H1 receptor selective antagonist; 5, 10 and 20 microg/rat) induced anxiolytic effects at the dose of 20 microg/rat. Coadministration of histamine (0.1 microg/rat) with muscimol reversed the anxiolytic effect of muscimol at the dose of 0.1 microg/rat while coadministration of histamine (0.1 microg/rat) with bicuculline increased the anxiogenic effect of bicuculline at the dose of 0.05 microg/rat. On the other hand, coadministration of pyrilamine (10 microg/rat) with bicuculline decreased anxiety-like behaviors of bicuculline at the dose of 0.5 microg/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.
Copyright 2008 S. Karger AG, Basel.