Increased interstitial white matter neuron density in the dorsolateral prefrontal cortex of people with schizophrenia

Abstract

Background: Interstitial white matter neurons (IWMNs) may reflect immature neurons that migrate tangentially to the neocortex from the ganglionic eminence to form cortical interneurons. Alterations of interneuron markers have been detected in gray matter of dorsolateral prefrontal cortex in schizophrenia, and IWMNs are also reported to be altered in schizophrenia. In this study, we considered whether a potential link exists between these two pathological findings.

Methods: From a cohort of 29 schizophrenia subjects and 37 control subjects, IWMN densities were determined in the dorsolateral prefrontal cortex by counting neuronal nuclear antigen (NeuN) and somatostatin (SST)-positive cells. Double-label immunofluorescence was carried out to determine the overlap between SST+/NeuN+ and SST+/neuropeptide Y + neurons.

Results: We found that density of NeuN + IWMNs in superficial white matter is significantly increased in schizophrenia subjects compared with control subjects. There was a significant negative correlation between SST mRNA expression in gray matter and NeuN + IWMN density. In schizophrenic patients with increased NeuN IWMN density, the density of SST-expressing neurons in white matter was also higher compared with control subjects. A subpopulation of SST immunopositive cells also show coexpression of neuropeptide Y.

Conclusions: Our study confirmed previous results indicating that the density of NeuN + IWMNs is increased in superficial white matter in schizophrenia. We provide the first evidence that increased IWMN density correlates with a gray matter interneuron deficit, suggesting that migration of interneurons from white matter to the cortex may be deficient in some patients with schizophrenia, consistent with an interneuron deficit in schizophrenia.

Figure 1

Neuronal nuclear antigen (NeuN)-positive neurons (A) below grey matter (grey matter/white matter border represented by dotted line. In superficial white matter from (B) control and (C) schizophrenia subjects. Arrows show representative NeuN immunopositive interstitial white matter neurons that were quantified. Arrowheads indicate processes aligned parallel to the pial surface. Calibration bar (A) 200 μm, (B, C) 50 μm.

Figure 2

Density of NeuN+ IWMNs (neurons/mm²) in (A) superficial white matter and (B) deep white matter in controls (squares) and schizophrenics (triangles). Hemisphere (left: black, right: gray) dependant alterations of IWMNs density in (C) superficial white matter and (D) deep white matter. ** p<0.01.

Figure 3

Superficial NeuN+ IWMNs density (neurons/mm²) negatively correlates with gray matter SST expression in controls and schizophrenia (controls, squares; schizophrenia, triangles).

Figure 4

Representative in situ hybridization images showing SST mRNA signals in control (A, C) and schizophrenia (B, D) subjects. Autoradiographic film images (A, B) show the signal distribution in a single gyrus. Photomicrographs (C, D) show SST mRNA expression at the cellular level. SST mRNA positive cells could be distinctly determined with dense black silver grains over the nucleus (counterstained by cresyl violet). Calibration bar =25 μm.

Figure 5

SST and NeuN expression in IWMN cells. Double label immunohistochemistry for SST (red) and NeuN (green), with DAPI nuclear counterstaining (blue). A-D shows a neuron that is SST positive but NeuN negative; E-H shows a neuron that is SST positive and also NeuN positive. Calibration bar = 10 μm.

Figure 6

SST and NPY expression in IWMN cells. A-C Double label immunohistochemistry showing SST (red) and NPY (green), with DAPI nuclear counterstaining (blue). D shows a neuron that is SST positive and also NPY positive. Calibration bar = 10 μm.