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.

The title and the penultimate paragraph of the Discussion section incorrectly referred to the "medial prefrontal cortex." The word "medial" should not have appeared. This has been corrected in the article online.

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.

An association between maternal IgG antibodies reactive against proteins in fetal brain and an outcome of autism in the child has been identified. Using a mouse model of prenatal intraventricular administration of autism-specific maternal IgG, we demonstrated that these antibodies produce behavioral alterations similar to those in children with ASD. We previously demonstrated that these antibodies bind to radial glial stem cells (RG) and observed an increase in the number of divisions of translocating RG in the developing cortex. We also showed an alteration in brain size and as well as a generalized increased of neuronal volume in adult mice. Here, we used our intraventricular mouse model of antibody administration, followed by Golgi and Neurolucida analysis to demonstrate that during midstages of neurogenesis these maternal autism-specific antibodies produced a consistent decrease in the number of spines in the infragranular layers in the adult cortical areas analyzed. Specifically, in the frontal cortex basal dendrites of layer V neurons were decreased in length and volume, and both the total number of spines—mature and immature—and the spine density were lower than in the control neurons from the same region. Further, in the occipital cortex layer VI neurons presented with a decrease in the total number of spines and in the spine density in the apical dendrite, as well as decrease in the number of mature spines in the apical and basal dendrites. Interestingly, the time of exposure to these antibodies (E14.5) coincides with the generation of pyramidal neurons in layer V in the frontal cortex and in layer VI in the occipital cortex, following the normal rostro-caudal pattern of cortical cell generation. We recently demonstrated that one of the primary antigens recognized by these antibodies corresponds to stress-induced phosphoprotein 1 (STIP1). Here we hypothesize that the reduction in the access of newborn cells to STIP1 in the developing cortex may be responsible for the reduced dendritic arborization and number of spines we noted in the adult cortex.