Introductory paragraph Panic disorder is a severe anxiety disorder with recurrent, debilitating panic attacks. In subjects with panic disorder there is evidence of decreased central GABAergic activity as well as marked increases in autonomic and respiratory responses following intravenous infusions of 0.5M sodium lactate1–3. In an animal model of panic disorder, chronic inhibition of GABA synthesis in the dorsomedial/perifornical hypothalamus of rats produces anxiety-like states and a similar vulnerability to sodium lactate-induced cardioexcitatory responses4–9. The dorsomedial/perifornical hypothalamus is enriched in orexin (ORX, also known as hypocretin)-containing neurons10 that play a critical role in arousal10,11, vigilance10 and central autonomic mobilization12, all of which are key components of panic. Here, we demonstrate that activation of the ORX neurons is necessary for developing a panic-prone state in the animal model, and either silencing the hypothalamic ORX gene (Hcrt) product with RNA interference or systemic ORX1 antagonists blocks the panic responses. Moreover, we show that subjects with panic anxiety have elevated levels of ORX in the cerebrospinal fluid compared to subjects without panic anxiety. Taken together our results suggest that the ORX system may be involved in the pathophysiology of panic anxiety, and that ORX antagonists constitute a potential novel treatment strategy for panic disorder.

Glutamate and ␥-amino butyric acid (GABA) systems are emerging as targets for development of medications for mood disorders. There is increasing preclinical and clinical evidence that antidepressant drugs directly or indirectly reduce N-methyl-D-aspartate glutamate receptor function. Drugs that reduce glutamatergic activity or glutamate receptor-related signal transduction may also have antimanic effects. Recent studies employing magnetic resonance spectroscopy also suggest that unipolar, but not bipolar, depression is associated with reductions in cortical GABA levels. Antidepressant and mood-stabilizing treatments also appear to raise cortical GABA levels and to ameliorate GABA deficits in patients with mood disorders. The preponderance of available evidence suggests that glutamatergic and GABAergic modulation may be an important property of available antidepressant and mood-stabilizing agents. Future research will be needed to develop and evaluate new agents with specific glutamate and GABA receptor targets in the treatment of mood disorders. Molecular Psychiatry (2002) 7, S71-S80.

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Norepinephrine (NE) is a major monoamine neurotransmitter that has widespread effects across multiple brain areas to regulate arousal and stress responses. The underlying function of the NE cortical system is to balance vigilance/scanning behavior with focused attention on novel environmental stimuli and the state of arousal. The central NE system is involved intrinsically with the stress response system, and dysregulation within the NE system has been implicated in the pathogenesis of anxiety and depressive disorders. Central NE activity paradoxically has either anxiogenic or anxiolytic effects, depending on whether the time course of the stress is acute or chronic, whether the stress is predictable or unpredictable, and which underlying brain regions are affected. Under conditions of chronic stress, NE system activity dysregulation of the hypothalamic-pituitary-adrenal system may turn a homeostatic stress response into a pathological stress response. Data suggest that the NE interplay with the serotonin system may exert neurobiological normalization of the pathophysiological state of anxious depression. Accordingly, pharmacological interventions targeting the NE system can result in anxiolytic, rather than anxiogenic, outcomes when used to treat patients with anxiety and depression. Depression and Anxiety 27:339-350, 2010. r r