123I-β-CIT SPECT demonstrates increased presynaptic dopamine transporter binding sites in basal ganglia in vivo in schizophrenia
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The dopamine hypothesis for schizophrenia postulates overactivity of dopamine transmission in the basal ganglia. Most effective antipsychotic drugs block postsynaptic dopamine receptors, but in-vivo imaging studies have not been able to show changes in these receptors in drug-naive schizophrenics.
The presynaptic dopamine transporter (DAT) is thought to be an important regulator of synaptic dopamine concentration. We have used SPECT with 123I-β-CIT, which has a high affinity for DAT, in order to further examine the dopamine hypothesis for schizophrenia.
Six patients with chronic schizophrenia treated with classic dopamine D2-receptor blocking neuroleptics were investigated. The number of DAT binding sites in the basal ganglia was calculated and compared with five healthy volunteers and ten parkinsonian patients.
The schizophrenic patients showed a 36–63% increase in DAT binding sites compared with the volunteers, whereas the parkinsonian patients showed a 57–96% decrease. The differences between the groups were highly significant (even after correction for different age composition within the groups).
There was an increased number of DAT binding sites in the schizophrenic patients treated with dopamine D2-receptor blocking neuroleptics. This fits well with several recent reports that have shown increased volumes of basal ganglia in this patient category. It thus appears that there is an increased number of presynaptic dopamine releasing nerve terminals in the basal ganglia, possibly as a biological adaptation to counteract the postsynaptic dopamine D2-receptor blockade.
KeywordsSPECT β-CIT Schizophrenia Dopamine Dopamine transporter
The skillful technical support from engineer Torbjørn Jacobsen is gratefully acknowledged. The project was supported by a grant from the Norwegian Research Council.
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