THE EFFECT OF INTERNEURON LOSS ON MINICOLUMN STRUCTURE

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The correct balance between excitation and inhibition is pivotal to the fundamental operation of the brain, whether primary, unimodal or heteromodal neocortex. Studies have suggested that minicolumns in the brains of patients with autism are narrower than those of controls, with an altered internal configuration. (1) More specifically, their minicolumns reveal less peripheral neuropil space and increased spacing among their constituent cells. The peripheral neuropil space is the conduit for, among other things, inhibitory local circuit projections. A defect in these GABAergic fibers may correlate with the increased prevalence of seizures among autistic patients. Unsurprisingly, it has been argued that some of the behavior exhibited by autistic patients may be rooted in an imbalance between excitation and inhibition. A recent study shows that ?a single gene mutation can selectively alter the development of cortical interneurons in a region-and cell subtype-specific manner, with deficits leading to long-lasting changes in circuit organization and behavior.? The mi(uPAR) were targeted with a mutation that affects interneuron migration. Anterior cingulate and parietal cortical areas contained 50 % fewer GABAergic interneurons compared with Wild Type (WT) littermates. No differences were found in visual or piriform cortex. There was a complete loss of parvalbumin (PV) subtypes, with other classes remaining intact. GABAergic type cells known to be immunoreactive for PV include the basket and chandelier cells. The ability of a single gene mutation to cause a major loss in certain populations of specific GABAergic interneurons is especially significant in regards to genetic defects related to autism. The most prevalent genetic or environmental factor found among the first 100 cases in the South Carolina autism project is an abnormality of chromosome 15q that has three GABA receptor subunit genes. Furthermore, mice of the uPAR strain demonstrated certain behaviors associated with autism which included a propensity for seizure disorders and both increased anxiety and timidity or recluse-like behavior. Thus, we seek to determine whether the cortical minicolumn, as represented by cell soma and apical dendrite bundles, is narrower in the uPAR mouse than the WT. Secondly, we will identify the distribution of GABAergic interneurons in the uPAR mice. Positive results would show that the loss of GABAergic interneurons can cause a narrowing of minicolumns similar to that found in the minicolumns of patients withautism. The manifestations of autistic like behavior in the uPAR mouse, in conjunction with positive results from this study, could promote its use as an animal model for autism. Specific Aim 1: To determine whether a reduction in GABAergic inhibitory interneurons is associated with the narrowing of pyramidal cell arrays. Specific Aim 2: To determine whether a reduction in GABAergic cells is associated with a narrowing between layer V apical dendrite bundles. Specific Aim 3: To determine the extent of GABAergic cell loss in barrel cortex in the uPAR mouse.