Abstract
The number of cells comprising biological structures represents fundamental information in basic anatomy, development, aging, drug tests, pathology and genetic manipulations. Obtaining unbiased estimates of cell numbers, however, was until recently possible only through stereological techniques, which require specific training, equipment, histological processing and appropriate sampling strategies applied to structures with a homogeneous distribution of cell bodies. An alternative, the isotropic fractionator (IF), became available in 2005 as a fast and inexpensive method that requires little training, no specific software and only a few materials before it can be used to quantify total numbers of neuronal and non-neuronal cells in a whole organ such as the brain or any dissectible regions thereof. This method entails transforming a highly anisotropic tissue into a homogeneous suspension of free-floating nuclei that can then be counted under the microscope or by flow cytometry and identified morphologically and immunocytochemically as neuronal or non-neuronal. We compare the advantages and disadvantages of each method and provide researchers with guidelines for choosing the best method for their particular needs. IF is as accurate as unbiased stereology and faster than stereological techniques, as it requires no elaborate histological processing or sampling paradigms, providing reliable estimates in a few days rather than many weeks. Tissue shrinkage is also not an issue, since the estimates provided are independent of tissue volume. The main disadvantage of IF, however, is that it necessarily destroys the tissue analyzed and thus provides no spatial information on the cellular composition of biological regions of interest.
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Acknowledgments
Thanks to Roberto Lent for supporting the creation of the isotropic fractionator, to Nicole Young and Christine Collins for establishing the automated variation and to Paul Manger for insights on tissue storage. Flow cytometry experiments were conducted in the Vanderbilt Medical Center Flow Cytometry Shared Resource and aided by the expertise of David K. Flaherty.
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The development and improvement of the isotropic fractionator was made possible by grants from CNPq and FAPERJ to Suzana Herculano-Houzel. Work comparing the isotropic fractionator with other methods was supported by NIH grants NS079884 and GM103554 (Center of Biomedical Research Excellence from the National Institute of General Medical Science) to Christopher von Bartheld and by a grant from the G. Harold and Leila Y. Mathers Foundation to Jon H. Kaas. Flow cytometry experiments were conducted in the Vanderbilt Medical Center Flow Cytometry Shared Resource, which is supported by the Vanderbilt Ingram Cancer Center (P30 CA68485) and the Vanderbilt Digestive Disease Research Center (DK058404).
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Herculano-Houzel, S., von Bartheld, C.S., Miller, D.J. et al. How to count cells: the advantages and disadvantages of the isotropic fractionator compared with stereology. Cell Tissue Res 360, 29–42 (2015). https://doi.org/10.1007/s00441-015-2127-6
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DOI: https://doi.org/10.1007/s00441-015-2127-6