Background
Convergent findings indicate that cortical gamma-aminobutyric acid (GABA)ergic circuitry is altered in schizophrenia. Postmortem studies have consistently found lower levels of glutamic acid decarboxylase 67 (GAD67) messenger RNA (mRNA) in the prefrontal cortex (PFC) of subjects with schizophrenia. At the cellular level, the density of GABA neurons with detectable levels of GAD67 mRNA is ~30% lower across cortical layers. Knowing how this transcript deficit translates to GAD67 protein levels in axonal boutons is important for understanding the impact it might have on GABA synthesis. In addition, because reductions in GAD67 expression before, but not after, the maturation of GABAergic boutons
Conclusions
Our findings suggest that GABA production is markedly reduced in a subset of boutons in the PFC of schizophrenia subjects and that this reduction likely occurs after the maturation of GABAergic boutons.
Methods
PFC tissue sections from 20 matched pairs of schizophrenia and comparison subjects were immunolabeled for the vesicular GABA transporter (vGAT) and GAD67.
Results
vGAT+ bouton density did not differ between subject groups, consistent with findings that vGAT mRNA levels are unaltered in the illness and confirming that the number of cortical GABAergic boutons is not lower in schizophrenia. In contrast, in schizophrenia subjects, the proportion of vGAT+ boutons with detectable GAD67 levels (vGAT+/GAD67+ boutons) was 16% lower and mean GAD67 levels were 14% lower in the remaining vGAT+/GAD67+ boutons. Conclusions: Our findings suggest that GABA production is markedly reduced in a subset of boutons in the PFC of schizophrenia subjects and that this reduction likely occurs after the maturation of GABAergic boutons.