INFUSIONS OF ALPHA-2 NORADRENERGIC AGONISTS AND ANTAGONISTS INTO THE AMYGDALA - EFFECTS ON KINDLING

We reported previously that activation of alpha-2 adrenoceptors with i nfusions of clonidine into the amygdala/pyriform region is sufficient to retard kindling. To characterize further the involvement in kindlin g of alpha-2 receptors in the amygdala/pyriform, we exposed rats to un ilateral intraamygdaloid infusions of a variety of noradrenergic drugs followed by either low-frequency stimulation of the amygdala, to indu ce rapid kindling, or conventional high-frequency stimulation. Infusio ns and electrical stimulation were administered once every 48 h. The p rophylactic effects of clonidine were blocked by simultaneous infusion of idazoxan, an alpha-2 adrenergic antagonist, which suggests strongl y that these effects were produced at an alpha-2 receptor. Intraamygda loid infusions of xylazine, another alpha-2 agonist, also significantl y retarded low-frequency kindling. Unexpectedly, intraamygdaloid infus ions of the alpha-2 antagonists idazoxan, yohimbine, and SK&F 104856 f ailed to accelerate kindling. Infusion of the alpha-1 antagonist coryn anthine also failed to affect kindling. We propose that the alpha-2 ad renoceptors in the amygdala/pyriform region contribute to the prophyla ctic effects of systemically administered clonidine and that the facil itation of kindling observed after systemic administration of alpha-2 antagonists may be due to blockade of alpha-2 adrenoceptors outside of the amygdala/pyriform region.