Publisher Summary The chapter focuses on sympathetic nervous activity and epinephrine secretion rates and epinephrine cotransmission in sympathetic nerves. Multiunit sympathetic nerve firing rates measured directly by microneurography, in the sympathetic outflow to the skeletal muscle vasculature, and rates of norepinephrine spillover from the sympathetic nerves of the whole body are normal in untreated, resting patients with panic disorder, as is the spillover of norepinephrine measured selectively for the sympathetic nerves of the heart. Release of epinephrine from the sympathetic nerves of the heart, as an accessory neurotransmitter, has been demonstrated in patients with panic disorder. Heart rate and blood pressure increase during a panic attack, primarily due to sympathetic nervous system activation and adrenal medullary secretion of epinephrine. When recorded directly by microneurography, the size of sympathetic bursts increases remarkably during a panic attack, without any increase in firing rate. With the pronounced activation of the cardiac sympathetic outflow occurring during a panic attack, neuropeptide Y (NPY) is coreleased from the cardiac sympathetic nerves and appears in measurable quantities in coronary sinus venous blood.