The cognitive phenotype of autism has been correlated with an altered balance of excitation to inhibition in the cerebral cortex, which could result from a change in the number, function, or morphology of GABA-expressing interneurons. The number of GABAergic interneuron subtypes has not been quantified in the autistic cerebral cortex. We classified interneurons into 3 subpopulations based on expression of the calcium-binding proteins parvalbumin, calbindin, or calretinin. We quantified the number of each interneuron subtype in postmortem neocortical tissue from 11 autistic cases and 10 control cases. Prefrontal Brodmann Areas (BA) BA46, BA47, and BA9 in autism and age-matched controls were analyzed by blinded researchers. We show that the number of parvalbumin+ interneurons in these 3 cortical areas-BA46, BA47, and BA9-is significantly reduced in autism compared with controls. The number of calbindin+ and calretinin+ interneurons did not differ in the cortical areas examined. Parvalbumin+ interneurons are fast-spiking cells that synchronize the activity of pyramidal cells through perisomatic and axo-axonic inhibition. The reduced number of parvalbumin+ interneurons could disrupt the balance of excitation/inhibition and alter gamma wave oscillations in the cerebral cortex of autistic subjects. These data will allow development of novel treatments specifically targeting parvalbumin interneurons.

An interneuron alteration has been proposed as a source for the modified balance of excitation / inhibition in the cerebral cortex in autism. We previously demonstrated a decreased number of parvalbumin (PV)-expressing interneurons in prefrontal cortex in autism. PV-expressing interneurons include chandelier (Ch) and basket (Bsk) cells. We asked whether the decreased PV+ interneurons affected both Ch cells and Bsk cells in autism. The lack of single markers to specifically label Ch cells or Bsk cells presented an obstacle for addressing this question. We devised a method to discern between PV-Ch and PV-Bsk cells based on the differential expression of Vicia villosa lectin (VVA). VVA binds to N-acetylgalactosamine, that is present in the perineuronal net surrounding some cell types where it plays a role in intercellular communication. N-acetylgalactosamine is present in the perineuronal net surrounding Bsk but not Ch cells. We found that the number of Ch cells is consistently decreased in the prefrontal cortex of autistic (n = 10) when compared with control (n = 10) cases, while the number of Bsk cells is not as severely affected. This finding expand our understanding of GABAergic system functioning in the human cerebral cortex in autism, which will impact translational research directed towards providing better treatment paradigms for individuals with autism.

Background

Autism is not correlated with any neuropathological hallmark as the brain of autistic individuals lack defined lesions. However, previous investigations have reported cortical heterotopias and local distortion of the cytoarchitecture of the neocortex in some cases of autism.

Case presentation

Our patient was a 40-year-old white woman diagnosed at an early age with autism and mental retardation. Pencil fibers were present within the prefrontal cortex (Brodmann area 47) and its composition resembled that of the underlying white matter region. Pencil fibers encompassed most of the extent of the cortical grey matter and were populated by oligodendrocytes, astrocytes, and microglial cells, but not by neurons.

Conclusions

Here we report a new cytoarchitectural abnormality that has not been previously described in autism. Future pathological examinations should keep in mind the potential presence of pencil fibers within the prefrontal cortex of cases with autism.

The dry mass and the orientation of biomolecules can be imaged without a label by measuring their permittivity tensor (PT), which describes how biomolecules affect the phase and polarization of light. Three-dimensional (3D) imaging of PT has been challenging. We present a label-free computational microscopy technique, PT imaging (PTI), for the 3D measurement of PT. PTI encodes the invisible PT into images using oblique illumination, polarization-sensitive detection and volumetric sampling. PT is decoded from the data with a vectorial imaging model and a multi-channel inverse algorithm, assuming uniaxial symmetry in each voxel. We demonstrate high-resolution imaging of PT of isotropic beads, anisotropic glass targets, mouse brain tissue, infected cells and histology slides. PTI outperforms previous label-free imaging techniques such as vector tomography, ptychography and light-field imaging in resolving the 3D orientation and symmetry of organelles, cells and tissue. We provide open-source software and modular hardware to enable the adoption of the method.