Serotonin release measured in the human brain: a PET study with [ 11 C]CIMBI-36 and d-amphetamine challenge

Positron emission tomography (PET) enables non-invasive estimation of neurotransmitter fluctuations in the living human brain. While these methods have been applied to dopamine and some other transmitters, estimation of 5-hydroxytryptamine (5-HT; Serotonin) release has proved to be challenging. Here we demonstrate the utility of the novel 5-HT2A receptor agonist radioligand, [ 11 C]CIMBI-36, and a d-amphetamine challenge to evaluate synaptic 5-HT changes in the living human brain. Seventeen healthy male volunteers received [ 11 C]CIMBI-36 PET scans before and 3 h after an oral dose of d-amphetamine (0.5 mg/kg). Dynamic PET data were acquired over 90 min, and the total volume of distribution ( V T ) in the frontal cortex and the cerebellum derived from a kinetic analysis using MA1. The frontal cortex binding potential (BP ND frontal ) was calculated as ( V T frontal / V T cerebellum ) − 1. ∆BP ND frontal = 1 − (BP ND frontal post-dose/BP ND frontal baseline) was used as an index of 5-HT release. Statistical inference was tested by means of a paired Students t -test evaluating a reduction in post-amphetamine [ 11 C]CIMBI-36 BP ND frontal . Following d-amphetamine administration, [ 11 C]CIMBI-36 BP ND frontal was reduced by 14 ± 13% ( p = 0.002). Similar effects were observed in other cortical regions examined in an exploratory analysis. [ 11 C]CIMBI-36 binding is sensitive to synaptic serotonin release in the human brain, and when combined with a d-amphetamine challenge, the evaluation of the human brain serotonin system in neuropsychiatric disorders, such as major depression and Parkinson’s disease is enabled.