Adenosine A_2A receptor in schizophrenia: an in vivo brain PET imaging study

Adenosine A_2A receptors are highly enriched in the basal ganglia system, a region that is functionally implicated in schizophrenia. Preclinical evidence suggests a cross-regulation between adenosine A_2A and dopamine D₂ receptors in this region and that it is linked to the sensitization of the dopamine system. However, the relationship between A_2A receptor availability and schizophrenia has not been directly examined in vivo in patients with this disorder. To investigate, using positron emission tomography (PET), the availability of A_2A receptors in patients diagnosed with schizophrenia in comparison to matched healthy controls. A_2A receptor availability was measured using the PET tracer [¹¹C]SCH442416. Twelve male patients with chronic schizophrenia were compared to 13 matched healthy subjects. All patients were medicated with antipsychotics and none presented with any motor or extrapyramidal symptoms. Binding potential (BP_ND), a ratio measure between specific and non-specific tracer uptake, were compared between the groups for the caudate, putamen, accumbens and globus pallidum. There was no differences between A_2A receptor binding potential (BP_ND) of schizophrenia patients in the caudate (p = 0.16), putamen (p = 0.86), accumbens (p = 0.44) and globus pallidum (p = 0.09) to that of matched healthy subjects. There was also no significant correlation between [11C]SCH442416 binding and severity of psychotic symptoms (p = 0.2 to 0.82) or antipsychotic dosage (p = 0.13 to 0.34). By showing that A2A receptor availability in medicated patients with chronic male schizophrenia is not different than in healthy controls, this study does not support the primary role of this receptor in the pathogenesis of schizophrenia.