Dopamine D₂ receptor binding in drug-naïve patients with schizophrenia examined with raclopride-C11 and positron emission tomography☆

Abstract 

The aim was to test the dopamine hypothesis of schizophrenia in a further analysis of D₂-like dopamine binding using the radioligand [¹¹C]raclopride and high resolution 3-dimensional (3D) PET. Eighteen drug-naive patients with schizophrenia and seventeen control subjects were examined. The D₂ binding potential (BP) in the putamen, the caudate and the thalamus was calculated using the simplified reference tissue model. The volume of regions of interest was controlled for by MRI. Symptoms were rated with the Positive and Negative Syndrome Scale for Schizophrenia (PANSS). No significant group differences were found for D₂ BP in the putamen or in the caudate and there was no significant hemispheric difference for any region. In the right thalamus the D₂ BP was significantly lower in patients as compared to control subjects, whereas a numerical difference did not reach statistical significance for the left thalamus. There was no significant correlation between D₂ BP and total PANSS score in any region. There was a highly significant age effect in the caudate and in the putamen, but not in the thalamus. In this relatively large PET study of exclusively drug-naive schizophrenic patients, a lower D₂ BP in the right thalamus was found in the patient group. This finding is in agreement with two previous studies in Sweden and in Japan using the high-affinity radioligand [¹¹C]FLB 457 and provide further support for a role of dopamine in the thalamus related to the pathophysiology of schizophrenia.

Keywords: Thalamus, Caudate, Putamen, Striatum, Age, PANSS, Dopamine, Basal ganglia