Striatal presynaptic dopamine in schizophrenia, Part I: meta-analysis of dopamine active transporter (DAT) density

Striatal dopaminergic neurotransmission has been postulated to be fundamental to the emergence of key symptoms of schizophrenia, such as psychotic symptoms, and is targeted by currently available dopaminergic drugs. A specific marker of the integrity of presynaptic dopamine neurons in the striatum, the density of striatal dopamine terminals, can be quantified through molecular neuroimaging of the dopamine active transporter (DAT). However, the currently available results using this approach in schizophrenia are inconsistent.

Thirteen Single Photon Emission Tomography or Positron Emission Tomography (PET) studies investigating DAT density in the striatum of schizophrenic patients and matched controls were included in a quantitative meta-analysis. Binding potentials in the striatum, caudate, and putamen, as well as demographic, clinical, and methodological variables, were extracted from each publication. Hedges' g was used as a measure of effect size.

The overall database contained 202 subjects with schizophrenia and 147 controls, well matched with respect to sociodemographic variables. Striatal DAT density was not significantly different between patients and controls. Similar negative findings were regionally confirmed in the putamen and caudate. There was no moderating effect for external factors.

Our meta-analysis uncovered no evidence indicating altered density of striatal dopamine terminals in schizophrenia. Moreover, striatal DAT density did not seem to be influenced by antipsychotic medication or illness duration. Our data suggest that altered integrity of striatal dopaminergic synapses is not critical for the emergence of schizophrenia or its treatment. These findings should be useful in further refining dopaminergic hypotheses of schizophrenia.