Effect of different conditions of hyperbaric oxygenation on morphology and transcription of cortical neurons of rats with experimental stroke

Abstract

The protective action of hyperbaric oxygenation (I-IBO) in stroke has been described by many research workers [3, 7, 8], but its clinical use in the treatment of acute cerebral ischemia still rests on an inadequate basis. The aim of this investigation was to study the trend of the morphological changes and transcription activity of pyramidal neurons in the frontal cortex of rats with acute ischemia, depending on the conditions of HBO. METHODS Experiments were carried out on 120 noninbred albino rats weighing 200 g. Two models of ischemia were used: moderately severe -- after fight-sided ligation (group I), and severe, with bilateral ligation of the common carotid arteries (group II) [1, 2, 6]. The operation was performed under pentobarbital anesthesia. The state of the animals in group I immediately after the operation was satisfactory, and their behavior and general appearance were not visibly different from those of intact animals, yet a few hours later these rats were found to have mild mono- and hemipareses. The animals of group II were in a severe state after the operation. With the passage of time the state of the animals worsened and their mortality increased, so that after 24 h it was 100%. The effect of a single application of HBO on the morphologic and functional state of the frontal cortical neurons of the rats was investigated on these models, when three different conditions of HBO were used: exposure for 1 h to 2.0 atm (absolute atmospheres) with oxygen, and in group II, the same but with air, and exposure for 30 rain to 1.2 atm with oxygen, which is the situation closest to that observed clinically [3]. The sessions were given 2 h after the operation. The use ofHBO, whatever the conditions, was accompanied after 10-15 min by appreciable improvement of the animals' state. In the animals of group II the cyanosis disappeared, behavior and external appearance returned to normal, and their general state remained good for several hours after HBO. The survival rate of the rats after the operation in this group, following the use of HBO toward the end of the 1st day, amounted to 50% after exposure to 1.2 atm and 30% after exposure to 2.0 atm with oxygen. The animals' state 24 h after HBO at 1.2 arm was rather better than after exposure to 2.0 arm. S~uctural changes and transcription activity of the large and medium-sized pyramidal neurons in the frontal cortex of the ligated rats was assessed 15 rain after a session of HBO and 24 h later. The material was taken from 3-5 animals (except in group II after 24 h, when it was only from 2-3 survivors). Intact rats, rats undergoing a mock operation, and rats undergoing ligation but not treated with HBO, and killed 2.5 h after the operation, served as the control. The number of large and medium-sized preserved pyramidal neurons was counted in several fields of vision and the results averaged. To determine transcription (template) activity of the chromatin of the neurons studied, the histoautoradiographic method of detecting activity of endogenous RNA-polymerases in fixed neurons in sections was used [ 10]. The RNA