In the central nervous system (CNS), the major mediators of the symptoms of anxiety disorders appear to be norepinephrine, serotonin, dopamine, and gamma-aminobutyric acid (GABA). Other neurotransmitters and peptides, such as corticotropin-releasing factor, may be involved. Peripherally, the autonomic nervous system, especially the sympathetic nervous system, mediates many of the symptoms.
Positron emission tomography (PET) scanning has demonstrated increased flow in the right parahippocampal region and reduced serotonin type 1A receptor binding in the anterior and posterior cingulate and raphe of patients with panic disorder. MRI has demonstrated smaller temporal lobe volume despite normal hippocampal volume in these patients. The CSF in studies in humans shows elevated levels of orexin, also known as hypocretin, which is thought to play an important role in the pathogenesis of panic in rat models.