Hydropic degeneration of the sensorimotor cortex of white rats in the context of the formation of dark neurons and changes in neuroglial relationships following short-term common carotid arteries occlusion

Introduction. Neurodegenerative processes are key in the development of a number of diseases — strokes, Parkinson’s and Alzheimer’s diseases, epilepsy, and traumatic brain injury. They include primary and secondary structural and functional changes in the nervous tissue, as well as the death of neurons and complete loss of functions.

Aim. To study the manifestations of hydropic degeneration and reorganization of glio-cytoarchitectonics during the formation of dark neurons in the sensorimotor cortex (SMC) of the cerebrum of mature white rats in 40 min after the common carotid arteries occlusion (CCAO).

Materials and methods. A 40-minute CCAO was simulated in white Wistar rats. The brain was fixed by perfusion method. Morphometric assessment of manifestations of edema — swelling, cyto- and glio-cyto-architectonics of SMC was performed normally (n = 6, control group), on the 1st (n = 6), 3rd (n = 6) and 7th days (n = 6) after CCAO. The Nissl staining, hematoxylin and eosin, immunohistochemical typing NSE, MAP-2, GFAP and AIF1 were applied. The relative area of edema-swelling zones, the numerical density of normochromic and dark pyramidal neurons, oligodendrocytes (OD), m icrogliocytes (MG) were determined.

Results. The high content (20–50%) of dark neurons after CCAO was accompanied by a 3.3-fold increase in the relative area of edema-swelling zones (r = 0.82, p = 0.01). Specific proteins (NSE, MAP-2) of most dark neurons were preserved. The total numerical density of SMC neurons decreased by 26.4% (layer III, p = 0.001) and 18.5% (layer V, p = 0.01) after 7 days of CCAO. The content of astrocytes, MG and OD increased. The peak in the number density of MG was observed in the 1st day, and OD — in the 7th day after acute subtotal ischemia (p ≤ 0.001). The revealed changes were of a diffuse-focal nature.

Conclusion. After a 40-minute CCAO, the content of dark neurons in SMC increased and, as a result, signs of hydropic degeneration appeared. Against this background, the number of satellite OD, astrocytes and MG increased. Probably, edema-swelling, active MG and astrocytes previously (on the 1st – 3rd day) sanitate the nerve tissue, ensuring its subsequent (on the 7th day) structural and functional recovery with the participation of OD.

1. Rami A. (2009). Review: autophagy in neurodegeneration: fi refi ghter and/or incendiarist? Neuropathol. Appl. Neurobiol., 35 (5), 449–461.

2. Zille M., Farr T.D., Przesdzing I. et al. (2012). Visualizing cell death in experimental focal cerebral ischemia: promises, problems, and perspectives. J. Cereb. Blood Flow Metabol., 32 (2), 213–231.

3. Harris T.C., de Rooij R., Kuhl E. (2019). The shrinking brain: cerebral atrophy following traumatic brain injury. Ann. Biomed. Eng., 47 (9), 1941–1959.

4. Cole J.H., Jolly A., de Simoni S. et al. (2018). Spatial patterns of progressive brain volume loss after moderate- severe traumatic brain injury. Brain, 141 (3), 822–836.

5. Stepanov S.S., Akulinin V.A., Avdeev D.B., Stepanov A.S., Gorbunova A.V. (2018). Reorganization of the nucleolar apparatus of neurons of the neocortex, archicortex and basal ganglia of the brain of white rats after a 20-minute occlusion of the common carotid arteries. Journal of Anatomy and Hystopathology, 7 (4), 67–74. In Russ.

6. Bon E.I., Maksimovich N.E., Zimatkin S.M. (2020). Morphological disorders in the neurons of the rats hippocampus with subtotal and total ischemia. Orenburg Medical Bulletin, 8, 2 (30), 41–46.

7. Ahmadpour S., Behrad A., Fernández-Vega I. (2019). Dark neurons: A protective mechanism or a mode of death. J. Med. Histolog., 3 (2), 125–131.

8. Bolon B., Garman R., Jensen K. et al. (2006). A “best practices” approach to neuropathologic assessment in developmental neurotoxicity testing. Toxicol. Pathol., 34 (3), 296–313.

9. Gallyas F., Pál J., Bukovics P. (2009). Supravital microwave experiments support that the formation of “dark” neurons is propelled by phase transition in an intracellular gel system. Brain Res., 1270, 152–156.

10. Kövesdi E., Pál J., Gallyas F. (2007). The fate of “dark” neurons produced by transient focal cerebral ischemia in a non-necrotic and non-excitotoxic environment: Neurobiological aspects. Brain Res., 1147, 272–283.

11. Garman R.H. (2011). Histology of the central nervous system. Toxicol. Pathol., 39, 22–35.

12. Lychko V.S., Malakhov V.A., Potapov A.A. (2015). Morphological changes of the brain tissue in rats with experimental model of ischemic stroke in the dynamics of treatment by immunobiological preparation Cryocell-Cryocord. СТМ, 7 (4), 58–62.

13. Yakovlev A.A., Gulyaeva N.V. (2015). Possible role of proteases in preconditioning of brain cells to pathological conditions. Biokhimia, 80, 2, 204–213.

14. Stepanov A.S., Akulinin V.A., Stepanov S.S., Avdeev D.B. (2017). Cellular systems for the recovery and recycling of damaged brain neurons in white rats after a 20-minute occlusion of common carotid arteries. Russ. Journal of Physiology, 103 (10), 1135–1147.

15. Stepanov A.S., Akulinin V.A., Mysik A.V., Stepanov S.S., Avdeev D.B. (2017). Neuro-glio-vascular complexes of the brain after acute ischemia. General Reanimatology, 13, 6, 6–17. In Russ.

16. Chen Z., Trapp B.D. (2016). Microglia and neuroprotection. J. Neurochem., 136 (1), 10–17.

17. Paxinos G., Watson C. (2005). The Rat Brain in Stereotaxic Coordinates. 5th ed. San Diego: Elsevier Academic Press.

18. Ooigawa H., Nawashiro H., Fukui S. et al. (2006). The fate of Nissl-stained dark neurons following traumatic brain injury in rats: difference between neocortex and hippocampus regarding survival rate. Acta Neuropathol., 112, 471–481.

19. Borovikov V. (2003). Statistica. The Art of Data Analysis Using Computer: for Professionals. Saint Petersburg. In Russ.

20. Eyo U.B., Dailey M.E. (2013). Microglia: key elements in neural development, plasticity, and pathology. J. Neuroimmune Pharm. 8, 494–509.

21. Stepanov S.S., Akulinin V.A., Avdeev D.B., Stepanov A.S., Gorbunova A.V. (2019). Reorganization of the rat neocortical astrocytes after 20-min occlusion of the common carotid arteries. Russ. Journal of Physiology, 105, 5, 578–590.

22. Alekseeva O.S., Kirik O.V., Gilerovich E.G., Korzhevskii D.E. (2019). Microglia of the brain: origin, structure and functions. Journal of Evolutionary Biochemistry and Physiology, 55, 4, 231–241.

23. Wagner D.-C., Scheibe J., Glocke I. et al. (2013). Object- based analysis of astroglial reaction and astrocyte subtype morphology after ischemic brain injury. Acta Neurobiol. Exper., 73 (1), 79–87.