BackgroundThe importance of the neurotransmitter serotonin (5-HT) in the pathophysiology of anxiety is well known. A key role for postsynaptic 5-HT_1A receptors has recently been suggested in studies of genetic knockout mice.AimsTo measure 5-HT_1A receptor binding in patients with panic disorder in the untreated state and after recovery on treatment with selective serotonin reuptake inhibitors (SSRIs).MethodNine symptomatic untreated patients with panic disorder, seven patients recovered on SSRI medication and nineteen healthy volunteers underwent a single positron emission tomography (PET) scan using the 5-HT_1A tracer [¹¹C]WAY-100635.ResultsIn comparison with controls, both presynaptic and postsynaptic 5-HT_1A receptor binding was reduced in untreated patients, with the most significant reductions being in the raphe, orbitofrontal cortex, temporal cortex and amygdala. In recovered patients presynaptic binding was reduced, but there was no significant reduction in postsynaptic binding.ConclusionsPanic disorder is associated with reduced 5-HT_1A receptor availability, which is also known to have a key role in depression.