Functional and Morphological Changes in the Pyramidal Layer of the Hippocampus in Rats with Encephalopathy Induced by Prolonged Exposure to Gravitational Overloading

Abstract

Studies of morphofunctional changes in the hippocampus using a model of impaired cerebral hemodynamics are needed for understanding the mechanisms of formation of psychoneurological deficits. The aim of the present work was to assess CNS damage and the characteristics of the expression of one of the main regulators of apoptosis – Bcl-2 – in the hippocampus of rats with impaired cerebral hemodynamics induced by repeated gravitational overloading. The study was carried out on Wistar rats which were subjected to gravitational overloading (9 g) in the caudocranial direction for two 5-min periods each day for 28 days. Psychoneurological impairments in the animals were assessed using the McGraw scale and the open field, adhesion, conditioned passive avoidance reaction (CPAR), and escape extrapolation (EET) tests. Brain sections were stained by the Nissl method and the specific numbers of neurons with signs of damage were counted. Immunohistochemical studies of the level of Bcl-2 expression assessed the relative areas of immunoreactive material in the pyramidal layer in all hippocampal fields. Gravitational overloading induced impairments to the animals’ behavior, which was expressed as low movement activity and signs of retrograde amnesia, decreased fi ne motor function, and increases in psychoneurological deficit. Histological studies identified destructive changes to vessels and increases in the specific number of pyramidal neurons with damage in all fields of the hippocampus. Fields CA2 and CA4 showed the greatest increases in the numbers of damaged neurons, along with marked Bcl-2 expression.