Sex differences in anxiety and threat avoidance in GAD65 knock-out mice

Abstract

Anxiety disorders have been linked to a disbalance of excitation and inhibition in a network of brain structures comprising frontal cortical regions, the amygdala and the hippocampus, among others. While recent imaging studies in humans suggest sex differences in the activation of such anxiety network structures in processing emotional information, the neuronal basis of activation shifts and their relation to anxiety endophenotypes is less well studied. Rodent models with genetically altered ϒ-amino butyric acid (GABA) neurotransmission may provide a targeted approach for addressing such questions, but to date sex effects have rarely been addressed in such models. Using mice with a null mutation of the GABA synthetizing enzyme glutamate decarboxylase 65 (GAD65-/-), we started to compare anxiety-like behavior, discrimination and avoidance learning in male vs. female GAD65-/- mice and their wildtype littermates. Our behavioral test battery revealed increased activity on GAD65-/- mice in the open field and an adaptation of anxiety-like behavior especially in male GAD65-/- mice. Male GAD65-/- mice further displayed a deficit in avoidance learning, while Female GAD65 -/- mice performed well in this task. To gain insights into interneuron function in anxiety and threat perception network structures, fast oscillations (10-45 Hz) were measured in ex vivo slice preparations of the ACC. GAD65-/- mice of both sexes displayed increased gamma power in the ACC that was further accompanied by higher densities of PV-positive interneurons, which are crucial for generating such rhythmic activity. In addition, male GAD65-/- mice had lower numbers of somatostatin-positive interneurons in the basolateral amygdala and dorsal dentate gyrus, two key regions important for anxiety and active avoidance responses. Together, male mice appeared more challenged by GAD65 deficiency in avoidance learning tasks and adapted their anxiety-like response differently, which was associated with an altered interneuron composition and function in an ACC-amygdala-hippocampal network.