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Jarmo Hietala, MD; Erkka Syvälahti; Klaus Vuorio, MD; Kjell Nägren, PhD; Pertti Lehikoinen, PhD; Ulla Ruotsalainen, MSc; Viljo RäkkÖläinen, MD; Ville Lehtinen, MD; Uno Wegelius, MD

Arch Gen Psychiatry. 1994;51(2):116-123.

Abstract
Background
According to the D₂ dopamine receptor hypothesis of schizophrenia, there is an increased number of D₂ receptors in the brains of schizophrenic patients than in those of healthy controls. We tested this hypothesis in 13 newly admitted neuroleptic-naive schizophrenic patients and 10 healthy volunteers using positron emission tomography.

Method
The quantification of striatal D₂ dopamine receptor density (B_max) and affinity (K_d) was done using an equilibrium model described for raclopride labeled with carbon 11.

Results
No statistically significant alterations were found in D₂ receptor densities or affinities between the patient and control groups. However, a subgroup of four patients with a relatively high striatal D₂ dopamine density was identified. Two patients, especially, had D₂ dopamine densities almost twice as high as the mean control B_max value. The K_d values also tended to be higher in this subset of patients than in the controls. No consistent striatal D₂ dopamine receptor laterality was observed in schizophrenic patients or controls. However, an association of high D₂ dopamine density in the left striatum and the mass of raclopride injected in the scan with low-specific radioactivity was observed in patients but not in controls.

Conclusion
There are no general changes in D₂ dopamine receptor B_max or K_d values in neuroleptic-naive schizophrenics, but there may be a subgroup of patients with aberrant striatal D₂ dopamine receptor characteristics in vivo.

Author Affiliations
From the Department of Pharmacology, University of Turku, Finland (Drs Hietala and Syvälahti); Turku Medical Cyclotron/Positron Emission Tomography Project (Drs Hietala, Syvälahti, Någren, Lehikoinen, and Wegelius and Ms Ruotsalainen); Psychiatric Clinic, Turku City Hospital (Dr Vuorio and RäkkÔäinen); and Psychiatric Clinic, Turku University Hospital (Dr Lehtinen).

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