The structural base for changes in the interneuronal communication of CA₃ neurons in the hippocampus of white rats after severe traumatic brain injury

Abstract

Aim. To study changes in hippocampal CA₃ pyramidal neurons of white rats after severe traumatic brain injury (STBI). Methods. STBI was modeled with a free-falling weight (200-250 g) impact. The hippocampus was studied in control rats (n=5) 1, 3, 5, 7, and 14 days after STBI (n=25). The CA₃ field neurons were examined on preparations stained with hematoxylin-eosin and the number of neurons was determined with Nissl staining. The neuronal cytoskeleton was studied by immunotyping of the neuron-specific structural protein MAP-2, and synaptic terminals were studied by immunotyping of synaptophysin (p38). Neuronal MAP-2 and p38 were visualized with a multimeric Novolink™ (DAB) Polymer Detection Systems kit (Leica Biosystems Newcastle Ltd, Great Britain). Morphometric analysis was performed on color raster and binary images using ImageJ 1.52s plugins to determine the relative area of edema and swelling zones, number density of pyramidal neurons, content of dystrophic and necrobiotically altered neurons, and total and relative areas of synaptic terminals. Results. On the next day after STBI, manifestations of edema and swelling and the content of dystrophic and necrobiotically altered neurons were increased whereas the total and relative areas of terminals were decreased. In 14 days, the total density of neurons decreased by 31%, which was in parallel with activation of mechanisms for neuro- and synaptic plasticity. As a result, the cytoskeleton of damaged neurons recovered, and the content of interneuronal synapses increased 1.32 times compared to the control. Conclusion. The structural recovery of interneuronal communication was associated with a decrease in the total number density of pyramidal neurons. These changes were regarded as a base for permanent compensatory and restorative reorganization of hippocampal interneuronal relations in secondary cerebral ischemia.