. Interaction between amyloid-β pathology and cortical functional columnar organization. J Neurosci. 2012 Aug 15;32(33):11241-9. PubMed.

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  1. I think the results raise several questions and have some implications for the disease in humans, but I think it is also exciting that some of the implications and hypotheses arising from the finding can be tested in the transgenic mouse model used.

    For human AD, there have been quite a few published studies where investigators have been trying to make sense out of the often intricate patterns formed by amyloid plaques as well as neurofibrillary tangles. The most well known of these, by Powell and colleagues (Pearson et al., 1985), suggested that the distribution of neurofibrillary tangles predominantly to layers III and V of the cerebral neocortex was consistent with a hypothetical "spread" of the disease along cortico-cortical pathways. The authors of the current paper also cite work done by myself with Edith McGeer (Beach and McGeer, 1992), in which we suggested that the laminar pattern of amyloid plaque formation in human AD primary visual cortex might be due to excessive Aβ release as a result of loss of cholinergic, anti-amyloidogenic synaptic input.

    One of the basic issues has been whether patterns of degeneration in AD (and other neurodegenerative diseases) represent a neuroanatomical, perhaps trans-synaptic "spread" of disease, or whether the patterns are simply due to selective vulnerability. What remains tantalizing is the promise that such patterns of degeneration hold for understanding disease. As plaques are clearly distributed in a non-random manner, most often corresponding to neuronally defined cyto-architectonic compartments, it would seem that neurons are the cell types responsible, although the possibility remains that vascular cells may also produce the amyloid found in amyloid angiopathy.

    The authors' suggestion that the extracellular matrix composition might be responsible for the septal deposition within barrel cortex is also quite plausible, as in human AD it has long been considered that differences and changes in the avidity of amyloid binding to extracellular matrix molecules might underlie the varying distribution of amyloid to blood vessel walls (amyloid angiopathy) and neuropil (plaques), since such distributions are known to vary with, for example, apolipoprotein E genotypes.

    I have not read any of the cited papers showing that amyloid might preferentially depress the activity of inhibitory neurons, but it is an interesting hypothesis that should be testable in the mouse model.

    Many AD subjects develop seizures at a late stage of disease, and this could be due to decreased inhibitory activity, or also to the known loss of synaptic complexity and/or synaptic remodeling that occurs, also.

    References:

    . Anatomical correlates of the distribution of the pathological changes in the neocortex in Alzheimer disease. Proc Natl Acad Sci U S A. 1985 Jul;82(13):4531-4. PubMed.

    . Senile plaques, amyloid beta-protein, and acetylcholinesterase fibres: laminar distributions in Alzheimer's disease striate cortex. Acta Neuropathol. 1992;83(3):292-9. PubMed.

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