Striatal D2 dopamine receptor characteristics in neuroleptic-naive schizophrenic patients studied with positron emission tomography.
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.


METHODS
The quantification of striatal D2 dopamine receptor density (Bmax) and affinity (Kd) 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 Bmax value. The Kd 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.


CONCLUSIONS
There are no general changes in D2 dopamine receptor Bmax or Kd values in neuroleptic-naive schizophrenics, but there may be a subgroup of patients with aberrant striatal D2 dopamine receptor characteristics in vivo.
Hietala
J
J
Department of Pharmacology, University of Turku, Finland.
Syvälahti
E
E
Vuorio
K
K
Någren
K
K
Lehikoinen
P
P
Ruotsalainen
U
U
Räkköläinen
V
V
Lehtinen
V
V
Wegelius
U
U
D000328:Adult; D000367:Age Factors; D014150:Antipsychotic Agents / Q000008:administration & dosage* / Q000494:pharmacology; D002250:Carbon Radioisotopes / Q000378:metabolism; D002531:Cerebellum / Q000000981:diagnostic imaging / Q000378:metabolism; D003342:Corpus Striatum / Q000000981:diagnostic imaging / Q000378:metabolism*; D065127:Dopamine D2 Receptor Antagonists; D005260:Female; D006801:Humans; D008297:Male; D011569:Psychiatric Status Rating Scales; D020891:Raclopride; D017448:Receptors, Dopamine D2 / Q000187:drug effects / Q000378:metabolism*; D012457:Salicylamides / Q000378:metabolism; D012559:Schizophrenia / Q000175:diagnosis / Q000000981:diagnostic imaging / Q000378:metabolism*; D014055:Tomography, Emission-Computed; D015854:Up-Regulation
D014150:Antipsychotic Agents; D002250:Carbon Radioisotopes; D065127:Dopamine D2 Receptor Antagonists; D017448:Receptors, Dopamine D2; D012457:Salicylamides; D020891:Raclopride