The Comprehensive Neural Mechanism of Oxytocin in Analgesia

: Oxytocin (OXT) is a nine amino acid neuropeptide hormone that has become one of the most intensively studied molecules in the past few decades. The vast majority of OXT is synthesized in the periventricular nucleus and supraoptic nucleus of the hypothalamus, and a few are synthesized in some peripheral organs (such as the uterus, ovaries, adrenal glands, thymus, pancreas, etc.) OXT modulates a series of physiological processes, including lactation, parturition, as well as some social behaviors. In addition, more and more attention has recently been focused on the analgesic effects of oxytocin. It has been reported that OXT can relieve tension and pain without other adverse effects. However, the critical role and detailed mechanism of OXT in analgesia remain unclear. Here, this review aims to summarize the mechanism of OXT in analgesia and some ideas about the mechanism.

LIGHT DEPREVATION INFLUENCE ON MORPHOFUNCTIONAL STATE OF NEURONS OF THE HYPOTHALAMUS SUPRAOPTIC NUCLEI IN RATS

The supraoptic nucleus (SON) of the hypothalamus is one of the key neurosecretorylinks that ensure the joining of the nervous and endocrine regulation mechanismsinto the general neuroendocrine system, thereby participating in the realization of thebody’s response to experimental influences. Despite deep and comprehensive studies ofthe hypothalamus, until now there are no unified ideas about its individual reactivityand the degree of involvement of these structures in the stress response, caused by prolonged exposure to constant darkness (light deprivation).The aim of this work is to study the effect of light deprivation on the morphofunctionalstate of the supraoptic nucleus of the hypothalamus in rats.Material and methods. The experiments were carried out on nonlinear male white rats,which were divided into 2 series of studies, biomaterial sampling of which was taken at14.00 and 02.00 h using morphofunctional and statistical research methods.Results. The study of the morphometric characteristics of the neurons of thehypothalamus SON revealed the diurnal dynamics of indices. Under the light regime12.00C:12.00T, a daily rhythm of the morpho-functional activity of SON neurons witha maximum activity is registered in rats in the daytime.When the animals were kept under conditions of constant darkness (00C:24.00T), anincrease in the size of its nucleus 21.1±2.4% (r=0.73), caused by an increase in thearea of the neuron nucleolus (r=0.89), which constituted 61.94±7.07 µm2, was revealedat 14.00. Attention was also drawn to a significant decrease in the nuclear-cytoplasmicratio (NCR) relative to intact animals, which constituted 2.07±0.041 units. Lightdeprivation led at 14.00 to a significant RNA concentration decrease in the nucleus35.3±2.1%, and in the nucleolus 26.6±1.9%.The studies, carried out at 02.00 h, revealed that the area of the neuron nucleuswas 98.33±5.40µm2and significantly larger than that in the intact animals. Thesechanges were accompanied by an increase in the area of the nucleolus, which was48.90±6.892µm2(r=0.87) and the area of the neuron cytoplasm, which was within217.61±7.19 µm2(r=0.91). The NCR of a neuron in the SON of the hypothalamus at02:00 was lower than that in the intact animals 2.67±0.17%. A significant increasein RNA concentration in the nucleus, nucleolus and cytoplasm of neurons in thehypothalamic SON was noted relative to the indices of animals of the previous timeinterval, which were under conditions of constant darkness.Compared to the daytime period (14.00 h), up to 02.90 h, NCR increase was revealedin the nighttime observation period in the neurons under study, which constituted2.55±0.022 units.Conclusions. 1. Photoperiod duration significantly affects the daily activity of thehypothalamus SON. 2. Permanent darkness (light deprivation) does not lead to aninversion of the rhythm of the morphofunctional activity of the neurons under study,the maximum values, as in intact animals, are registered in the daytime interval. 3.Light deprivation causes a significant increase in the area of the neuron, its nucleus,nucleolus in the night and day intervals of observation. At the same time, a decrease inthe nuclear-cytoplasmic ratio, a decrease in the concentration of RNA in the nucleusand nucleolus of the neuron of SON of the hypothalamus of rats in the daytime isobserved.