Which of the following substance is not involved in Panic disorder?

Ans. D. GABAPanic-Inducing Substances* Panic-inducing substances (sometimes called pnicogens) induce panic attacks in most patients with panic disorder and in a much smaller proportion of persons without panic disorder or a history of panic attacks. (The use of panic- inducing substances is strictly limited to research settings; no clinically indicated reasons exist to stimulate panic attacks in patients.) So-called respiratory panic-inducing substances cause respiratory stimulation and a shift in the acid-base balance. These substances include carbon dioxide (5 to 35 percent mixtures), sodium lactate, and bicarbonate.* Neurochemical panic-inducing substances that act through specific neurotransmitter systems include yohimbine, an I^+-2-adrenergic receptor antagonist; m-chlorophenyl piperazine (mCPP), an agent with multiple serotonergic effects; m-Caroline drugs; GABAB receptor inverse agonists; flumazenil (Romazicon), a GABAB receptor antagonist; cholecystokinin; and caffeine. Isoproterenol (Isuprel) is also a panic-inducing substance, although its mechanism of action in inducing panic attacks is poorly understood.* The respiratory panic-inducing substances may act initially at the peripheral cardiovascular baroreceptors and relay their signal by vagal afferents to the nucleus tractus solitarii and then on to the nucleus paragigantocellularis of the medulla.* The hyperventilation in panic disorder patients may be caused by a hypersensitive suffocation alarm system whereby increasing PCO2 and brain lactate concentrations prematurely activate a physiological asphyxia monitor.* The neurochemical panic-inducing substances are presumed to primarily affect the noradrenergic, serotonergic, and GABA receptors of the CNS directly.