BDNF-MEDIATED MECHANISM OF ANTI-STRESS EFFECT OF MELANOCORTINS
Authors: Yasenyavskaya A. L. , Andreeva L. A. , Myasoedov N. F. , Bashkina O. A. , Samotrueva M. A. 
Published: April 2022

In recent years studies devoted to the study of the mechanisms of regulation of physiological and pathophysiological processes are of particular interest in connection with the active development of molecular medicine. Stress caused by various biological, social and technogenic factors is an integral part of modern human life and is a non-specific reaction of the body to various extreme influences. Despite the formation of adaptive mechanisms under stress in the form of generalized activation of the body, focusing of attention and memory, stress-induced analgesia, under conditions of intense and prolonged influence of a negative factor, the central nervous system loses its ability to adapt and the processes of neurogenesis are often disturbed as a result of distress. This fact explains the development of stress-induced pathological processes in the central nervous system, which emphasizes the relevance of the search and study of the mechanisms of action of pharmacological agents exhibiting stress-protective and neurotropic properties.
Melanocortins (N-terminal fragments of adrenocorticotropic hormone, fragments of proopiomelanocortin and their synthetic analogs) are characterized by pronounced neurometabolic, neuroregenerative and antistress activity. One of the possible mechanisms of action of melanocortins is the influence on the levels of expression in the central nervous system of neurotrophic factors that provide the main processes of regulation of homeostasis of the body. Brain Derived Neurotrophic Factor (BDNF) which is able to reduce the negative effects of hypoxic, toxic and stressful damage to brain cells, which is due to binding to tyrosine kinase B receptor and activation of the main metabolic cascades, is one of the effective regulatory proteins. Taking into account the fact that the question of the mechanisms of the stress-protective action of substances capable of protecting brain cells from the damaging effect of stress factors is relevant, the study of the effect of melanocortins on the level of neurotrophic factors is of scientific interest.
The study was carried out on 70 male white rats of 6 months of age. Sensory contact in the absence of physical contact with the subsequent formation of aggressive and submissive types of behavior was used as an experimental model of «social» stress. Laboratory animals, taking into account the gradation by types of behavior, were divided into groups: a group of control / intact animals; a group of rats exposed to «social» stress for 20 days; a group of individuals who received Semax (ACTH(4-7)-Pro-Gly-Pro) at a dose of 100 μg / kg / day intraperitoneally from the 1st day of stress exposure for a course of 20 days; a group of animals that received ACTH(6-9)-Pro-Gly-Pro at a dose of 100 μg/kg/day intraperitoneally from day 1 of stress exposure for a course of 20 days. The BDNF level in the blood serum of white rats was assessed by the enzyme-linked immunosorbent assay using ELISA Kit for Brain Derived Neurotrophic Factor (BDNF) (USA).
It was found that under conditions of «social» stress, a decrease in the level of BDNF was observed. The introduction of the studied melanocortins (ACTH(4-7)-Pro-Gly-Pro (Semax) and ACTH(6-9)-Pro-Gly-Pro) under conditions of induced «social» stress increases the concentration of BDNF in the blood serum of experimental animals. The study of the mechanisms of disturbances induced by experimental stress in various models showed that stress provokes the development of a depression-like state in rodents, which is accompanied by neuroplastic changes, including inhibition of neurogenesis in the hippocampus.
Currently a large amount of experimental data has been accumulated, indicating that a pathological stress response contributes to a decrease in the level of BDNF. Deficiency of BDNF plays an important role in the pathophysiology of stress, inducing impairments of neurogenesis associated with impaired neuroplasticity, as well as dysfunction of the hypothalamic-pituitary-adrenal and neurotransmitter serotonergic systems. The effectiveness of therapy with stress protectors and antidepressants is due to their effect on neurogenesis and neuronal plasticity.
Thus the fact of a decrease of BDNF under conditions of «social» stress established in the work and the positive effect of melanocortins (ACTH(4-7)-Pro-Gly-Pro (Semax) and ACTH(6-9)-Pro-Gly-Pro), contributing to the restoration of these parameters, indicates the effect of neuropeptides on the expression of BDNF and allows us to suggest a possible mechanism of the antistress effect. It should be noted that the serum level of brain neurotrophic factor can be considered as a biomarker of stress-induced disorders and affective disorders, as well as an indicator of the effectiveness of therapy with stress protectors. In addition, the level of BDNF in the blood serum can be considered as indicators of prognosis and evaluation of the effectiveness of therapy.