E.V. Loseva - Dr.Sci. (Biol.), Chief Research Scientist, Laboratory of Functional Neurocytology, Institute of Higher Nervous Activity and Neurophysiology RAS, Moscow, Russia. E-mail: losvnd@mail.ru N.A. Loginova - Ph.D. (Biol.), Research Scientist, Laboratory of Functional Neurocytology, Institute of Higher Nervous Activity and Neurophysiology RAS, Moscow, Russia. E-mail: nadezhda.loginova1982@gmail.com N.V. Panov - Senior Assistant, Laboratory of Functional Neurocytology, Institute of Higher Nervous Activity and Neurophysiology RAS, Moscow, Russia. E-mail: nikolay.panov1966@yandex.ru V.V. Gavrilov - Ph.D. (Psychol.), Senior Research Scientist, Laboratory of Psychophysiology, Institute of Psychology RAS, Moscow, Russia. E-mail: nvvgav@mail.ru

We have previously revealed that the thickness of visual, retrosplenial posterior and motor cortex decreased in rats grown up in the darkness (Loseva, Loginova, Gavrilov, 2015). Futher morphological analysis of changes in these cortical areas in rats undergoing to visual deprivation for 3 monthes could help to understand the importance of these brain regions for development of vision. The aim of present work was a comparative analysis of cortical thickness and neuronal and glial relationships in layer V of neocortical areas mentioned above in rats grown up in the absolute darkness (experiment) or in daylight conditions (control). Newborn Wistar rats were separated into two groups and reared in different light conditions until 3-4 months old: experimental group (n = 9) and control group (n = 8). Their brains have been frozen in the vapor of liquid nitrogen. We have made frontal slices (thickness 18-20 µm) using cryostat on the level of motor cortex (Br. 3.20 mm), posterior retrosplenial cortex (Br. - 4.52 mm) and primary visual cortex (Br. - 7.30 mm) (Paxinos, Watson «The rat brain in stereotaxic coordinates», 2005). The slices were stained by Nissle method. For each rat we selected 3-5 slices from each level. In each rat the measurement was carried out in 15 random field of view (square=0,01 mm2) of the layer V of each area. The number of neurons, free glial cells, satellite glial cells, total number of glial cells, the ratio of free, satellite and total glial cells to neurons (glia-neuronal indices) were calculated. The statistical comparison of groups was carried out by nonparametric Kolmogorov-Smirnov two-sample test in STATISTICA 6.0. It was found a significant decreasing of thickness both in visual and in retrosplenial and motor areas of the neocortex (p < 0.001, p < 0.001 and p < 0.05, respectively). The number of free and total glia cells, and their ratio to neurons were increased in rats grown up in darkness compared to control rats (p < 0.001) in primary visual cortex. The density of neurons and satellite glia indices weren-t changed significantly. In the retrosplenial cortex the density of neurons, the number of free and total glia, and their ratio to neurons were increased (p < 0.001). Apparently, the increasing of density of neurons was linked with decreasing of thickness of layer V of this area, that was shown earlier. The number of satellite glia and their ratio to neurons also were decreased. (p < 0.001). The density of neurons was increased in the motor cortex (p < 0.001). The numbers of free and total glia were increased (p<0.001) and their ratio to neurons was increased (p < 0.001 and p < 0.05, respectively). The parameters of satellite glia change compared to control. Thus, in rats grown up in darkness the number of free and total glia and glia-neuronal indices were increased in layer V of all studied cortical areas that indicated the reactive gliosis. In the retrosplenial cortex, the density of sa-tellite glia and its - ratio to neurons were decreased that means a decline of supply of neurons. The most pro-nounced changes of all parameters were found in the retrosplenial cortex. It is known that reactive gliosis related to neuroinflamation and neurodegeneration. We suppose that pathological changes in different brain areas of rats grown up in darkness influence on the development of vision and its role in learning. Supported by RFBR grant № 15-06-06925.

 

1. Loseva E.V., Loginova N.A., Gavrilov V.V. Tolshhina slojov raznykh oblastejj neokorteksa u krys, vyrosshikh v temnote // Biomedicinskaja radioehlektronika. 2015. № 4. S. 51-53. http://www.radiotec.ru/catalog.php-cat =jr6&art=16400
2. KHonicheva N.M., Loseva E.V., CHabak-Garbach R., Lorija M.V., Ajjrapetjanc M.G. CHastnyjj sluchajj narushenija obuchenija u krys-izoljantov kak model dezintegracii // ZHurnal vysshejj nervnojj dejatelnosti. 2005. T. 55. № 3. S. 393-399.
3. Paxinos G., Watson C. The rat brain in stereotaxic coordinates, 5th edition. Elsevir Academic Press. 2005.