The results of numerous studies have demonstrated that changes in fast glutamatergic tr ansmission in the amygdala play a major role in neural processes involved in the acquisition and extinction of conditioned fear. However, there are converging lines of evidence suggesting that changes in gamma-aminobutyric acid (GABA) may also be involved in these processes. In humans, involvement of GABAergic transmission in the regulation of fear and anxiety is highlighted by the fact that patients suffering from anxiety disorders are commonly treated by the administration of benzodiazepines (BZs), which mediate their actions via GABAA receptors (GABAARs).The amygdala is particularly rich in GABAARs which are known to be involved in the anxiolytic and anxiogenic effects of GABA agonists and antagonists, respectively. At present, there is a void in research designed to investigate how the changes in amygdala GABAergic transmission influences emotional memories and behaviors associated with anxiety and fear. Recently, our lab reported learningrelated changes in GABA-related genes and GABAAR levels in the amygdala after the acquisition and extinction of Pavlovian fear , a commonly used animal model of fear and anxiety disorders. Our findings showed that the acquisition of fear induced a down regulation of genetic markers related to decreased amygdala GABAergic function;whereas the acquisition of fear extinction produced an up regulation of GABAergic markers related to enhanced GABAergic transmission. This research proposal will employ a novel and powerful approach to investigating the role of amygdala GABAergic transmission in fear and behavioral responses to pharmacological agents. Specifically, in Aim 1 of this proposal, we propose to examine the acquisition and extinction of conditioned fear in mice with knocked down expression of 2-GABAARs or GAD67 in the amygdala using a vector-based RNA interference (RNAi) strategy to locally induce loss-of-function. We hypothesize that associated changes in GABAergic function will decrease the level of phasic inhibition, resulting in facilitated acquisition of fear and blunted extinction of fear.
In Aim 2 of this proposal, we plan to examine the behavioral effects of BZ administration in mice with knocked down expression of 2-GABAARs or GAD67 in the amygdala. We hypothesize that associated changes in amygdala GABAergic function will result in blunted anxiety-like behavioral effects to BZ.
The Role of Amygdala GABAergic Transmission in Fear and Anxiety According to the National Institute of Mental Health, the excessive fear of specific objects or in the absence of external threat are hallmarks of a variety of disabling anxiety disorders that affect approximately 40 million American adults during the course of any given year. There is considerable evidence suggesting that alterations in GABAergic transmission might actually form the basis of vulnerability for some anxiety disorders. While GABAAR agonists exert anxiolytic effects by acting at a number of limbic areas, there is converging lines of evidence indicating that that the amygdala is a major site of action. Given effectiveness of GABAAR -acting agents and their current widespread use in the treatment of anxiety-related disorders, a fuller understanding of how GABAergic mechanisms control anxiety and fear circuits will advance our understanding of anxiety-related disorders. This grant proposes to use a novel and powerful genetic method to functionally dissect region-specific GABA(A) subtype function. This research proposal will employ a novel and powerful approach to investigating the role of amygdala GABAergic transmission in conditioned fear and behavioral responses to pharmacological agents. This model system of inducing focal knocked down gene expression will provide a sizeable advantage over traditional transgenic and knockout approaches in determining the region-specific function genes in the amydala. The results of the current proposal will provide a better understanding of the role of GABAergic transmission in the amygdala may provide a better understanding of the mechanisms that influence emotional memories and behaviors associated with anxiety and fear.
