Neuroglial relationships and structures of interneuronal communication of the white rat sensorimotor cortex layer v after the common carotid artery ligation

Abstract

The aim of research was to study changes in neurons, gliocytes and structures of the interneuronal communication system (dendrites, terminals) of the mature white rat sensorimotor cortex (SMC) layer V after the common carotid artery (CCA) bilateral ligation.Material and methods. Acute/chronic incomplete cerebral ischemia was simulated in white Wistar rats by the CCA bilateral ligation. The brain was fixed by perfusion. A comparative histological, immunohistochemical and morphometric evaluation of the related structures in the norm (n=6), and in 1, 3, 7, 14 and 30 days after the common carotid artery bilateral ligation (n=30) was carried out. Nissl and hematoxylin-eosin stains, immunohistochemical reactions for NSE, MAP-2, p38, GFAP and IBA1 were used. The numerical density of pyramidal neurons, astrocytes, oligodendrocytes, microgliocytes and the relative area of p38-positive material (synapse terminals) were determined. Statistical hypotheses were tested by nonparametric methods using Statistica 8.0 program.Results. CCA bilateral ligation led to the appearance of destructively altered dark, hypochromic, vacuolated neurons and shadow cells in layer V of the SMC. These changes were accompanied by a decreased overall numerical density of pyramidal neurons, hyperhydration of the neuropil (processes of dendrites, astrocytes, and synapses), and a pronounced reaction (hypertrophy, proliferation) of all neuroglial cell types. One day after the CCA bilateral ligation, the appearance of neurons with both reversible and irreversible changes was accompanied by an increase in the layer V relative area of edema-swelling zones in the neuropil of the rat SMC up to 14.5 (10.6– 16.4) %, in control – 7.2 (6.9–7.5) %. The maximum content of destructively altered neurons (25%) was found in the rat SMC layer V one day after ischemia. The total number density of neurons in layer V of the SMC decreased by 27.9% after 30 days (Mann–Whitney U Test; p=0.0001). In the areas of damaged neuron accumulation, the content of astrocytes, microgliocytes, and oligodendrocytes increased. The neuroglial index in the control group was 1.30; it was 1.37 in 3 days, it was 1.50 in 7 days, it was 1.63 in 14 days, and it was 1.30 in 30 days. The maximum increase in the number density of microgliocytes was noted after 1 day (Mann–Whitney U Test; p=0.001), oligodendrocytes – 7 days after CCA ligation (Mann–Whitney U Test; p=0.02). According to the data of immunohistochemical typing of p38, two peaks of the relative area of the terminals were revealed: in the acute period (days 1 and 3) and after 30 days. These quantitative changes were first associated with an increase (on the 1st and 3rd day) and then a decrease in the degree of the neuropil hydration. Negative statistically significant strong correlations were detected in 3 days (R=-0.90) and 7 days (R=-0.70) after CCA ligation. This can be explained by hydropic changes in the terminals (destruction of synapses according to the light type). The total numerical density of neuropil terminals decreased to 102300±19400 (by 35.0%) in 3 days after CCA ligation in layer V of white rats and partially recovered to 135000±27100 (24.4%) after 30 days, compared to the animals of the control (157500±20500 per 1 mm2).Conclusion. Thus, the CCA ligation resulted in destructive and compensatory-restorative changes in the structures of interneuronal communication associated with preservation of a significant part of pyramidal neurons and compensatory reorganization of neuroglial relationships in layer V of white rats.