Compartmentation of alpha 1 and alpha 2 GABAA receptor subunits within rat extended amygdala: implications for benzodiazepine action

The extended amygdala, a morphological and functional entity within the basal forebrain, is a neuronal substrate for emotional states like fear and anxiety. Anxiety disorders are commonly treated by benzodiazepines that mediate their action via GABAA receptors. The binding properties and action of benzodiazepines depend on the alpha -subunit profile of the hetero-pentameric receptors: whereas the alpha 1 subunit is associated with benzodiazepine type I pharmacology and reportedly mediates sedative as well as amnesic actions of benzodiazepines, the alpha 2 subunit confers benzodiazepine type II pharmacology and mediates the anxiolytic actions of benzodiazepines. We determined the localization of alpha 1 and alpha 2 subunits within the extended amygdala, identified by secretoneurin immunostaining, to define the morphological substrates for the diverse benzodiazepine actions. A moderate expression of the alpha 1 subunit could be detected in compartments of the medial subdivision and a strong expression of the alpha 2 subunit throughout the central subdivision. It is concluded that the alpha 1 and alpha 2 subunits are differentially expressed within the extended amygdala, indicating that this structure is compartmentalized with respect to function and benzodiazepine action.