Vol 111, No 3 (2025)

It is known that the pineal gland hormone melatonin, synthesized during hours of darkness, regulates daily and seasonal changes in metabolism, reproduction and behavior. To date, many experimental studies have been conducted investigating the effects of exogenous melatonin administration on behavior in various tests in rats. The aim of this work is to use meta-analysis to investigate melatonin effects on the behavior of rats kept under standard conditions. We selected 57 publications for meta-analysis that studied melatonin monotherapy: 35 papers with the open field (OF) test, 23 papers with the elevated plus maze (EPM), 12 publications with the forced swim (FS) test, and 21 papers with the Morris pool (MP). The meta-analysis showed that a single peripheral administration of melatonin in low doses (≤ 1 mg/kg/day) increases the locomotor activity of rats in the OF test. Long-term administration of melatonin also contributed to an increase in the locomotor activity of rats. Melatonin has an anxiolytic effect, which is confirmed by an increase in the time spent by rats in the center of the OF test and in the open arms of EPM. A reduction in the immobilization period in the FS test indicates an antidepressant effect of the hormone. The anxiolytic and antidepressant effects were more pronounced in females than in males. No convincing evidence of a dose effect on the anxiolytic and antidepressant effects of melatonin was obtained. With melatonin therapy, there was a tendency to increase the time for rats to search for a platform in MP. In most studies, the hormone was administered intraperitoneally, and researchers usually used young animals. For these reasons, we were unable to correctly assess dependence of melatonin effects on the route of administration and the age of rats.

The study was devoted to the assessment of postural stability in female athletes involved in rhythmic (n = 17), artistic (n = 20) gymnastics and non-athletes (n = 19). The main objective was to identify the features of the center of pressure (CoP) oscillations in female and non-athletes under various conditions of activation of visual and somatosensory inputs. The method of computer stabilometry was used on the automated complex “Stabilan-01-5”. To assess postural stability, the parameters of the stabilographic test were analyzed: linear velocity of CoP movement (ALV, mm/sec), angular velocity of CoP movement (AAV, deg/sec) and ellipse area (EIIS, sq. mm), the Romberg coefficient was calculated. Spectral analysis of stabilographic signals was conducted. The participants performed tests in a normal stance on a hard and soft surface with their eyes closed and open.

The results showed that CoP oscillations in female and non-gymnasts in a calm stance were comparable, but differences were observed on a soft surface. Rhythmic and artistic gymnasts demonstrated better postural stability indicators, which is explained by their ability to integrate proprioceptive and visual signals. Spectral analysis showed smaller fluctuations in the high-frequency range in both rhythmic and artistic gymnasts, which indicates the formation of specific motor and neuromuscular strategies in them. It was also found that rhythmic gymnasts were more dependent on visual control to maintain postural stability, which is probably due to the need to accurately assess the distance and body position when performing elements specific to this sport. The results obtained can serve as a basis for developing individual training programs taking into account sensory integration and movement control in different groups of athletes.

Recently, highly specialized mechano-activated (MA) channels of the Piezo family have aroused increased interest among researchers in connection with their participation in the processes of mechanotransduction in mammals. However, until now nothing has been known about the role of these channels in the regulation of muscles’ passive stiffness and contraction. We assumed that both passive deformation of an isolated muscle and induced twitch and tetanic muscle contraction would lead to activation of Piezo1 channels, which increases passive stiffness and amplitude of muscle contraction. The purpose of the study: using Dooku1, a specific inhibitor of Piezo1 channels, and gadolinium chloride, a non-specific inhibitor of MA channels, to evaluate the possible contribution of Piezo1 channels to the mechanical response of an isolated slow muscle to passive deformation and induced twitch and tetanic contractions. The experimental results showed that the use of gadolinium led to a significant decrease in the parameters of passive muscle stiffness. Interestingly, the specific blocking of the Piezo1 MA channels using Dooku1 did not affect these parameters. At the same time, when the isolated muscle was treated with Dooku1 solution, the maximum tension of the induced twitch and tetanic contractions decreased by 21 and 25% respectively. Also, incubation of muscles in Gd³⁺ solution did not lead to significant changes in the parameters of induced contraction. Thus, we have shown that the MA channels, which can be blocked by Gd³⁺, are stimulated by passive muscle stretching and are involved in the regulation of muscle stiffness. At the same time, the Piezo1 MA channels are activated during muscle contraction and are involved in its regulation. It can be assumed that the participation of calcium channels in maintaining muscle stiffness and in the realization of muscle contraction can be carried out by additional activation of myofibrils with calcium ions, the concentration of which in muscle fiber increases as a result of the activity of these channels.

Severe sepsis (endotoxicosis), similar to cytokine storm, is aggravated by acute respiratory failure, hypotension, hypoxemia and hypercapnia, which is the main cause of high mortality. The aim of the work is to study the effectiveness of hypercapnic-hypoxic training for the relief of cardiorespiratory disorders and increased tolerance to acute hypoxia in rats with LPS-induced endotoxicosis. The experiments were conducted on anesthetized male Wistar rats. Endotoxicosis was simulated by administration of LPS (Escherchia coli) 7 mg/kg. The assessment of resistance to hypoxia was carried out by the rebreathing method (RM) with a gradual decrease in oxygen in the rebreather from 21% to the onset of apnea. 3 groups of animals were studied: I – control – NaCl, II – LPS, III – LPS+HHT. The following parameters were recorded: external respiration, mean blood pressure (APm.), saturation (SpO₂), fraction of inhaled O₂ (FiO₂) and CO₂ (FiCO₂), time of onset of apnea, the amount of spontaneous respiratory recovery (autoresuscitation) in the posthypoxic period. The LPS+HHT group was previously subjected to hypercapnic-hypoxic training. For this purpose, the rebreather was filled with room air, the volume of which was selected in such a way that during the breathing of the animal into / out of the rebreather, FiO₂ decreased to 11 ± 0.5% for 3 minutes, and FiCO₂ increased to 5.0 ± 0.5%, after which the rat was switched to breathing air. The training regime consisted of 3 cycles: 3 min – HHT, 5 min – normoxia. It was found that the maximum decrease in resistance to acute hypoxia was observed in rats with LPS, respiratory recovery after apnea was carried out in 10%, HHT prevented a fatal decrease in SpO₂ and APm, autoresuscitation occurred in 100% of cases. Based on the data obtained, it can be concluded that the combined effects of hypercapnia and hypoxia effectively contribute to increased tolerance to acute hypoxia in rats with LPS-induced endotoxemia.

Heterometric regulation of myocardial contractility is the most important property regulating the pumping function of the heart. Calcium ions play a key role in the activation and regulation of muscle contraction. In addition to changes in the degree of actin-myosin filament overlap, one consequence of myocardial stretch is a length-dependent change in the shape and duration of the intracellular calcium transient (CaT). As the degree of myocardial stretch increases, the duration of the CaT decreases in the upper half of the CaT decline and increases in the lower half. To determine the contribution of myosin bridge kinetics to CaT changes, length-dependent changes in CaT were assessed in three states of myosin bridge kinetics; (1) intact, (2) slowed under the influence of omecamtiv mecarbil 1 µM (OM), and (3) blocked under the influence of blebbistatin 10 µM (BB). It was found that length-dependent multidirectional changes in CaT decay (CaT crossover phenomenon) were pronounced in the right ventricular (RV) myocardium and weak in the right atrial (RA) myocardium of intact male nine-week-old Wistar rats. OM significantly slows the rate of tension development and decline in myocardium of RA and RV rats; enhances length-dependent changes in CaT duration; OM decreases the duration of CaT at 80% of its amplitude and increases the duration of CaT at 20% of its amplitude in both RA and RV. BB almost completely abolishes the ability of the myocardium to develop tension; length-dependent changes in CaT duration are monotonous, CaT crossover in RV myocardium disappears. The phenomenon of CaT crossover in the myocardium of the RV is a consequence of the attachment and detachment of myosin bridges to the thin filament. The absence of length-dependent changes in CaT in rat RA myocardium seems to be associated with a more developed calcium sequestering system in RA, in comparison with the calcium sequestering system in RV.