PTK7 and panic disorder: Panic attacks can be induced in PD individuals by a variety of agents such as CO2,36, 37 sodium lactate,38 doxapram,39 isoproterenol,40 caffeine,41 yohimbine,42 cholecystokinin (CCK-4 and agonists),43 the benzodiazepine receptor antagonist, flumazenil,44 serotonin receptor agonists45 and opioid receptor antagonists.46 It is important to note, however, that homeostatic perturbations such as CO2, lactate and doxapram that cause direct or compensatory pH shifts reliably evoke panic attacks that closely resemble spontaneous panic attacks.