Examining endogenous dopamine in treated schizophrenia using [11C]-(+)-PHNO positron emission tomography: A pilot study

Using positron emission tomography (PET) it is possible to estimate endogenous dopamine (DA) occupying D2/3 receptors (D2/3R) in the living human brain. Persons with schizophrenia (SZ) (previously medicated and naïve) have increased endogenous DA occupying D2/3R in the caudate. It is unknown whether currently medicated patients demonstrate increased DA levels at D2/3R. Moreover, DA levels have not been estimated in SZ using agonist radiotracers, which may offer a more sensitive quantification over antagonists. Using the agonist radiotracer [11C]-(+)-PHNO, DA levels were estimated at D2/3R (ΔBPND) in three patients with SZ (male, mean age=30±16). Patients were currently being treated long-term with Olanzapine (147±88nmol/L). Results were compared to ten healthy controls (HCs). Medicated persons with SZ had greater ΔBPND in the left caudate (U=2, Z=−2.20, p=.03) and right putamen (U=2, Z=−2.20, p=.03). No differences were observed in the ventral striatum or globus pallidus. It is possible to estimate endogenous DA at D2/3R in SZ patients currently taking antipsychotics. Despite medication, patients continue to have increased endogenous DA at D2/3R. This lends more biological support to the clinical observation that relapses in symptoms can occur in the face of complete antipsychotic discontinuation. Future studies with larger samples are warranted. •Dopamine levels were estimated in the brains of medicated schizophrenia patients.•Patients with schizophrenia had more dopamine in the left caudate and the right putamen.•Despite being medicated dopamine levels are still high in patients with schizophrenia.