Accordingly, the central hypothesis of this translational human pilot project, and a more definitive project based on it, is as follows: PD is a human anxiety disorder associated with specific cortical and subcortical GABA deficits that result in disruption of normal inhibitory regulation of pro-arousal ORX neurons. This disruption promotes excessive ORX release, sympathetic activation, and vulnerability to spontaneous or chemically induced panic. Pretreatment with an ORX1 receptor antagonist prior to chemical challenge is therefore expected to block the evoked panic response.