Análise estereológica do córtex visual primário de Dasyprocta leporina: Estimação de volume e densidade celular

Abstract

Theoretical studies hypothesized that the emergence of a columnar functional organization in the primary visual cortex (Area 17 or V1) could be related to the cortical volume, total cortical neurons or cell density in this region. It is very likely that the Dasyprocta species does not present large columns in their visual cortex. Several studies have used the Cavalieri method to estimate cortical volume and the Optical Fractionator to estimate cell density, but there are no published studies which have calculated primary visual cortex’s volume and cell density for Dasyprocta with these methods. Especially, for Dasyprocta leporina there are no data on volume, neuronal density or cellular density of V1 at all. In this study we aimed to estimate the volume and the cell density for Area 17 for the Dasyprocta leporina, an animal whose neuronal properties are also studied with electrophysiological methods in the lab of the Brain Institute. Our methods included area 17 volume and cell density estimation using Nissl stained and DAPI marked 50 μm thick sequential coronal sections, Stereo Zeiss Imager M.2 microscope and Stereo Investigator 10.0 software using Cavalieri stereological method and the Optical Fractionator. Our results are that Dasyprocta leporina’s primary visual cortex has a volume of 545 mm³ ± 42 mm³, 25% ± 10% higher than described in a previous study for the Dasyprocta azarae and total cell density of 82,516 cells/mm², a smaller number than compared to previous data. Because these are different species, there may be also differences in the size of area 17. Furthermore, the previously described animals had smaller visual cortex lengths in the macroscopic view and thinner cortices than ours. Our results indicate that the Dasyprocta leporina can have a considerable V1 volume but a smaller cellular density compared to other species such as cats and monkeys, which present columnar organization. That strengthens the hypothesis that these parameters could be related to the emergence of columnar organization in area 17.