Altered vesicular glutamate transporter expression in the anterior cingulate cortex in schizophrenia

Abstract

Background: Schizophrenia is a chronic, severe mental illness with profound emotional and economic burdens for those afflicted and their families. An increasing number of studies have found that schizophrenia is marked by dysregulation of glutamatergic neurotransmission. While numerous studies have found alterations of postsynaptic molecules in schizophrenia, a growing body of evidence implicates presynaptic factors. Vesicular glutamate transporters (VGLUTs) have been identified and are known to package glutamate into vesicles in the presynaptic terminal for subsequent release into the synaptic cleft. Recent studies have shown that VGLUTs regulate synaptic activity via the amount of glutamate released. Accordingly, we hypothesized that VGLUTs are altered in schizophrenia, contributing to dysfunction of presynaptic activity.

Methods: Using in situ hybridization and Western blot analysis, we investigated alterations in VGLUT1 and VGLUT2 transcript and protein expression in the anterior cingulate cortex (ACC) and dorsolateral prefrontal cortex (DLPFC) of subjects with schizophrenia and a comparison group.

Results: We found increased VGLUT1 transcript and reduced VGLUT1 protein expression in the ACC, but not DLPFC, in schizophrenia. Vesicular glutamate transporter 2 was unchanged at both levels of gene expression. We did not find changes in VGLUT1 messenger RNA (mRNA) or protein levels following 28-day treatment of rats with haloperidol (2 mg/kg/day), suggesting that our findings in schizophrenia are not due to an effect of antipsychotic treatment.

Conclusions: Overall, our data suggest decreased glutamate release in the ACC, as well as discordant regulation of VGLUT1 expression at different levels of gene expression.

Figure 1

In situ hybridization analysis of VGLUT1 and VGLUT2 mRNA expression in the dorsolateral prefrontal cortex (DLPFC) and the anterior cingulate cortex (ACC) in subjects with schizophrenia and a comparison group. The inset panels on the right side of the VGLUT1 images are from nissl stained tissue sections. Isodense bands (1–4 for VGLUT1 and 1–3 for VGLUT2) are shown on the left side of each image and corresponding cortical lamina (I–VI) and white matter (wm) on the right. VGLUT1 mRNA is increased in ACC in schizophrenia. Data are expressed as mean ± SEM optical density values.

Figure 2

VGLUT 1 and VGLUT2 mRNA (n = 10) and protein (n = 8) expression in rat cortex following 28 days treatment with haloperidol 2/mg/kg/day or vehicle. Haloperidol decreased VGLUT2 protein in FC but had no other effects. Abbreviations: frontal cortex (FC), parietal cortex (PC), cingulate cortex (CC). mRNA data are expressed as mean ± SEM optical density values. Protein data are expressed as the mean ± SEM of VGLUT optical density/tubulin optical density.

Figure 3

Western blot analysis of VGLUT 1 and VGLUT2 protein expression in the dorsolateral prefrontal cortex (DLPFC) and the anterior cingulate cortex (ACC) in subjects with schizophrenia and a comparison group. VGLUT1 protein is decreased in ACC in schizophrenia. Data are expressed as the mean ± SEM of VGLUT optical density/tubulin optical density.

Figure 4

Summary of changes and schematic of VGLUT1 (red) and VGLUT2 (green) expression in the anterior cingulate cortex in schizophrenia, based on data from the present study and earlier reports. In a previous study, increased VGLUT2 mRNA was found in the thalamus in schizophrenia. Question marked statements in the boxes labeled Other Cortical Areas, Subcortical Structures, and Thalamus are putative explanations to account for the observed changes in the ACC in schizophrenia.