STRESS-INDUCED CHANGES IN THE MORPHO-FUNCTIONAL STATE OF NEURONS IN SUPRAOPTIC NUCLEUS OF RAT HYPOTHALAMUS

Abstract

SUMMARY. Motor activity is an important feature of animals and humans, this is one of the conditions for their normal existence and development, which depends on the level of illumination. Restriction of motor activity (hypokinesia, or immobilization) is a powerful stress factor that can cause various pathological processes.

The hypothalamus, as the highest subcortical center of the autonomic nervous system, exerts a powerful regulating effect on all vital functions of the body, including maintaining the homeostatic balance of the living system, which is disturbed as a result of stressors, in particular immobilization. In connection with the important role of the large neurosecretory cells of the hypothalamic supraoptic nucleus (SON) in the realization of the adaptive capabilities of the organism, it is urgent to study the nature of their response when the organism of experimental animals is exposed to immobilization stress.

The aim – to learn the effect of immobilization stress on the morpho-functional state of the SON of the rat hypothalamus.

Material and Methods. The experiments were carried out on nonlinear male white rats weighing 200–220 g; immobilization stress was modeled by keeping the rats in special plastic cage-cases for 6 hours daily during 7 days.

 The animals were divided into 2 series of studies, in each of which the sampling of biomaterial was carried out at 2 p.m. and 2 a.m. using morpho-functional and statistical research methods.

Results and Discussion. The study of the morphometric characteristics of the neurons of the SON of the hypothalamus revealed the diurnal dynamics of the indices. Under the standard light regime in rats, the circadian rhythm of the morpho-functional activity of the neurons of the SON was recorded with a maximum activity at night (2 a.m.). When the animals were kept under immobilization stress at 2 p.m., the area of the neuron of the SON of the hypothalamus reached (305.67±7.939) μm² and was significantly higher (by 9.97 %) relative to the same value in intact rats. At the same time, there was an increase in the size of its cytoplasm by 17.0 %, and the nuclear-cytoplasmic ratio, which reached (3.69±0.019) units. Immobilization stress led at 2 p.m. to a significant decrease in the RNA concentration in the nucleus by 33.1 %, in the nucleolus and cytoplasm of neurons of the SON of the hypothalamus relative to these values ​in intact animals.

Keeping animals under conditions of immobilization stress caused more pronounced changes in the morpho-functional state of the neurons of the SON of the hypothalamus at 2 a.m. rather than at 2 p.m. Thus, the area of the neuron nucleus was (261.94±6.240) μm² and was significantly less (by 14.3 %) than that in intact animals. These changes were accompanied by a decrease in the area of the nucleolus and cytoplasm of the neuron, which was (165.33±4.642) μm² and was significantly less (by 24.2 %) than that in animals kept under standard illumination. It was noted that the stay of animals under immobilization stress disturbed the circadian rhythm of the morpho-functional activity of the neurons of the SON of the hypothalamus. Their greater activity, in contrast to the rats under normal lighting conditions, was recorded during the daytime observation period.

Conclusions. 1. Under the standard light regime, the daily rhythm of the morpho-functional activity of the neurons of the SON with the maximum activity at night was recorded in rats. 2. Immobilization stress causes a disturbance in the rhythm of the morpho-functional activity of the studied neurons. 3. Keeping animals under conditions of immobilization stress caused more pronounced changes in the morpho-functional state of neurons in the SON of the hypothalamus at 2 a.m. than at 2 p.m., which was accompanied by a decrease in the area of ​​the nucleus, nucleolus and cytoplasm of the neuron, which were significantly less than those in intact animals.