Wednesday, October 22, 2008

Autism and Schizophrenia: a minicolumnar deficit?

It has been my long standing thesis that Autism and Schizophrenia are opposite poles on a continuum; and the most recent evidence I would like to allude to is the mini columnar structure and abnormalities associetd with it in both the diseases. 

Let me at the outset, say that I am not an expert on mini-columns and hardly understand them, so would be glad if somebody corrected me or pointed out errors in the analysis.

First let me report on Schizophrenia from an abstract of a paper titled Mean cell spacing abnormalities in the neocortex of patients with schizophrenia by M Casanova et al

It has been postulated that the prefrontal cortices of schizophrenic patients have significant alterations in their interneuronal (neuropil) space. The present study re-examines this finding based on measurements of mean cell spacing within the cell minicolumn. The population studied consisted of 13 male schizophrenic patients (DSM-IV criteria) and 13 age-matched controls. Photomicrographs of Brodmann's areas 9, 4 (M1), 3b (S1), and 17 (V1) were analyzed with computerized image analysis to measure parameters of minicolumnar morphometry, i.e., columnarity index (CI), minicolumnar width (CW), dispersion of minicolumnar width (VCW), and mean interneuronal distance (MCS). The results indicate alterations in the mean cell spacing of schizophrenic patients according to both the lamina and cortical area examined. The lack of variation in the columnarity index argues in favor of a defect postdating the formation of the cell minicolumn.

To simplify the terms, I assume that CI relates to number of minicolumns in the neocortical broadmann area under consideration; CW is generally refered to as the width of the minicolumns i.e how big a particular minicolumn is , VCW I presume is related to how widely are the minicolumns themselves spaced from each other ie. the distance between two mini-columns and the last MCS is related to how densely neurons are packed within a mini-column.

Now for Schizophrenia, what I could find on the net, seems to suggest that they have reduced MCS as compared to controls i.e the neurons of schizophrenics are more densely packed within a mini-column as compared to controls .  Also, it was found that the density was greatest in core region and lesser so in the outer neuropil region of the mini-column.

An  opposite pattern is observed in Autism. Here is the abstract of article titled: Disruption in the inhibitory architecture of the cell minicolumn: implications for Autisim. by M Casanova et al again: 

The modular arrangement of the neocortex is based on the cell minicolumn: a self-contained ecosystem of neurons and their afferent, efferent, and interneuronal connections. The authors' preliminary studies indicate that minicolumns in the brains of autistic patients are narrower, with an altered internal organization. More specifically, their minicolumns reveal less peripheral neuropil space and increased spacing among their constituent cells. The peripheral neuropil space of the minicolumn is the conduit, among other things, for inhibitory local circuit projections. A defect in these GABAergic fibers may correlate with the increased prevalence of seizures among autistic patients. This article expands on our initial findings by arguing for the specificity of GABAergic inhibition in the neocortex as being focused around its mini- and macrocolumnar organization. The authors conclude that GABAergic interneurons are vital to proper minicolumnar differentiation and signal processing (e.g., filtering capacity of the neocortex), thus providing a putative correlate to autistic symptomatology.

Now the above clearly shows that the Autistics have an increased interneuronal space in mini-columns as opposed to normals and thus have lesser density of neurons within a minicolumn. However, they have more number of minicolumns to make up for this so that overall the number of neurons in the Broadmann area remains the same or the overall neuronal density does not differ. 

We can extend the results in other directions and hypothesize that 
1) Autistics will have increased no. of mini-columns, narrower mini-columns, narrowly spaced minicolumns and decreased neuronal density within a mini0-column as compared to controls.
2) Scchizophrenics will have lesser no. of minicolumns, wider mini-columns, widely spaced minicolumns and increased neuronal density within a mini-column as compared to controls.

Some of the above hypothesis is already supported and the rest may be in press/ under lab trials. 

What this means for in cognitive terms and how this translates to autistic and schizophrenic behaviour is another issue that I may address later (once I understand more of this minicolumn stuff!!)
D Buxhoeveden (2000). Reduced interneuronal space in schizophrenia Biological Psychiatry, 47 (7), 681-682 DOI: 10.1016/S0006-3223(99)00275-9

M CASANOVA, L DEZEEUW, A SWITALA, P KRECZMANSKI, H KORR, N ULFIG, H HEINSEN, H STEINBUSCH, C SCHMITZ (2005). Mean cell spacing abnormalities in the neocortex of patients with schizophrenia Psychiatry Research, 133 (1), 1-12 DOI: 10.1016/j.psychres.2004.11.004

Manuel F. Casanova, Daniel Buxhoeveden, Juan Gomez (2003). Disruption in the Inhibitory Architecture of the Cell Minicolumn: Implications for Autisim The Neuroscientist, 9 (6), 496-507 DOI: 10.1177/1073858403253552

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