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Is frozen sections an advantage for unbiased stereological methods?

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Author(s): Akdogan I

Journal: Neuroanatomy
ISSN 1303-1783

Volume: 3;
Issue: 1;
Start page: 61;
Date: 2004;
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Keywords: anatomy | neuroanatomy | frozen | section | stereology

ABSTRACT
The optical fractionator is one of the most used unbiased stereologicalmethods. It involves counting of neurons with optical dissectors ina uniform systematic sample that constitutes a known fraction of thevolume of the region being analyzed. In order to practice optical dissectorfor counting cell/neuron, both embedding (including, methacrylate resin,paraffin, paraplast and etc.) and unembedding (vibratome, frozen and etc.)methods can be utilized with thick sections after fixation and staining [1].However, possible problems have to be considered for both tissue preparationmethods. These common problems may include neuronal distributiondifferences between the core and margin, z-axis distortion and problemsat providing thick sections. Here, I want to debate some issues regardingthese problems. According to the optical dissector counting rules, it shouldbe let guard zone at the top and bottom surface of the sections. It has beenshown in a previous study that the number of the counting neurons at coreis 25% lower than accurate neuron numbers at paraffin and plastic sections[2]. This may be due to the fact that neurons are accumulated at the marginin paraffin and plastic embedded sections, while this is not true in frozensection, because there is no significant neuron number difference betweenthe core and margins of section [2, 3]. Furthermore, z-axis distortion isan important problem in optical dissector application. Vibratome sectionsshowed a pronounced z-axis distortion, while cryostat sections wereminimally distorted [4]. In another study, it has been found that cryostatsections of snap-frozen nervous tissue are reliably and successfully usedfor counting neuron numbers using optical dissector [5]. Tissue shrinkageproblem has been overcome in frozen section since it is possible to get thicksections in spite of tissue shrinkage. As a result, I emphasize that frozensectioning is more advantageous than paraffin, vibratome and methacrylatesectioning for counting of neurons using an unbiased stereological method/optical dissector. The disadvantageous of this method is that researcherneeds an expensive apparatus for an application of stereological countingmethod. So, if someone plan to constructs a new laboratory, this pointshould be taken into account. In conclusion, during the planning of aneurostereological study in nervous system, investigators have to considerthe proper method, i.e., embedding or unembedding methods, and theiradvantageous or disadvantageous.
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