Most previous studies of dopamine levels in the brain of schizophrenic patients have shown that they have the same average level of striatal dopamine receptors as the normal population, but that the levels in schizophrenics exhibit greater variation. Robert M. Kessler, MD and colleagues from the Radiology and Radiological Sciences Department at Vanderbilt University School of Medicine in Nashville, Tennessee, conducted a study to investigate changes in the striatal and extrastriatal D2R of schizophrenics.
The study involved four male and four female schizophrenics with a mean age of 31.9 who were off medication or had never been treated, and eight control subjects with matching ages and genders. All of the subjects underwent high resolution MRI scans as well as PET scans using the radiopharmaceutical [18F]fallypride.
The results of the study, which were presented at the Society of Nuclear Medicine's 50th Annual Meeting, demonstrated that schizophrenics had significantly elevated dopamine receptor levels in both the basal forebrain and substantia nigra/ventral tegemental (SN/VTA) areas of the brain. For both structures, the elevations were larger on the right side of the brain than on the left side. The study also revealed differences in cortical dopamine levels in certain parts of the brain.
Because SN/VTA dopamine D2 receptors regulate dopamine cell firing, the results of the study are, "consistent with the hypothesis of dysregulated cortical dopaminergic neurotransmission leading to abnormal regulation of SN/VTA neurons." As summarized by the researchers, "this abnormal regulation of SN/VTA DA neurons is believed to be responsible for the previously reported increased striatal DA release in schizophrenics."