Immunohistochemical Characteristics of Glial Cells Reorganization in Neocortex as a Result of Severe Traumatic Brain Injury
Authors: Stepanov S. S. , Shoronova A. Yu. , Akulinin V. A. , Korzhuk M. S. , Makarieva L. M. , Avdeev D. B. , Stepanova L. V. , Tsuskman I. G. 
Published: October 2023

The aim was to study the reorganization of gliocytes and GFAP expression of the rat neocortex  using  histological,  immunomorphological  and  morphometric  methods  (in  particular  fractal  analysis)  after severe traumatic brain injury (STBI).

Material and methods. Modeling of STBI was performed using a patented device with a shock mechanism based on the principle of transferring kinetic energy of a falling cylindrical load. During the experiment, the rats were divided into 2 groups: main (n=30) and control (intact, n=6). The brain of rats was extracted after 1, 3, 7, 14 and 30 days after heavy traumatic brain injury. The assessment of the glia of layers III and V of the sensorimotor cortex (SMC) was carried out by analyzing histological preparations of the rat brain (stained with hematoxylin-eosin and thionin) using light microscopy, immunohistochemical reaction  to  glial  fibrillary  acid  protein  (GFAP)  and  morphometric  processing  in  the  Image  1.53  program.  Fractal analysis was performed using the FracLac 2.5 plugin to evaluate the astrocyte network. Statistical processing of the  data  obtained was  carried  out  using  nonparametric  methods  of  information  processing  of  the  application package Statistica 10.0 programs.

Results. Throughout the post-traumatic period, changes in the SMC neurons were accompanied by an increase in the numerical density of gliocytes. The maximum peak of the microglyocyte content was higher already 1 day after HTBI: by 13.4% in layer III of the SMC and by 24.2% in layer V of the SMC. The minimum indicator of the numerical density of oligodendrocytes was observed 30 days after HTBI: in layer III of the SMC by 32.2%, and in layer V of the SMC – 43.9%. 1 day after the injury, there was a statistically significant increase in the numerical density of astrocytes in layers III and V of the SMC above the control values. During 30 days, the content of gliocytes decreased: in layer III of the SMC – 23%, and in layer V of the SMC – 26.8%.  When  GFAP  was  expressed,  protoplasmic  and  fibrous  astrocytes  differing  in  body  size  and  length  of processes were found in layer III and V of the SMC. The indicators characterizing the appendages as a spatial object changed statistically significantly in comparison with the control and in the post-traumatic period between terms. The fractal dimension changed the most and a high lacunarity was observed in layer III of the SMC. For 14 days, the indicator was less than the reference value, and by this time it was already recovering in layer V of the SMC. Taken together, all this indicated a higher reactive reorganization of the processes of astrocytes of the small cell layer of the III SMC.

Conclusion. After a heavy traumatic brain injury, a heterogeneous reorganization of the neuroglial complex was observed in the sensorimotor cortex (SMC). The detected changes in the numerical density of gliocytes in layers III and V of the SMC throughout the post-traumatic period were heterochronous. Morphometric analysis data confirmed the spatial reorganization of astrocytes, active proliferation of microglyocytes and oligodendrocytes – changes that contribute to the compensatory protection of the structures of the nervous tissue of the SMC in the post-traumatic period.