Positron Emission Tomography Assessments of Phosphodiesterase 10A in Patients With Schizophrenia

Background and hypothesis: Phosphodiesterase 10A (PDE10A) is a highly expressed enzyme in the basal ganglia, where cortical glutamatergic and midbrain dopaminergic inputs are integrated. Therapeutic PDE10A inhibition effects on schizophrenia have been reported previously, but the status of this molecule in the living patients with schizophrenia remains elusive. Therefore, this study aimed to investigate the central PDE10A status in patients with schizophrenia and examine its relationship with psychopathology, cognition, and corticostriatal glutamate levels. Study design: This study included 27 patients with schizophrenia, with 5 antipsychotic-free cases, and 27 healthy controls. Positron emission tomography with [¹⁸F]MNI-659, a specific PDE10A radioligand, was employed to quantify PDE10A availability by measuring non-displaceable binding potential (BP_ND) of the ligand in the limbic, executive, and sensorimotor striatal functional subregions, and in the pallidum. BP_ND estimates were compared between patients and controls while controlling for age and gender. BP_ND correlations were examined with behavioral and clinical measures, along with regional glutamate levels quantified by the magnetic resonance spectroscopy. Study results: Multivariate analysis of covariance demonstrated a significant main effect of diagnosis on BP_ND (p = .03). A posthoc test showed a trend-level higher sensorimotor striatal BP_ND in patients, although it did not survive multiple comparison corrections. BP_ND in controls in this subregion was significantly and negatively correlated with the Tower of London scores, a cognitive subtest. Striatal or dorsolateral prefrontal glutamate levels did not correlate significantly with BP_ND in either group. Conclusions: The results suggest altered striatal PDE10A availability and associated local neural dysfunctions in patients with schizophrenia.