Vol 53, No 1 (2017)

The concept of the hypothalamus as a brain structure responsible for metabolic and thermal homeostasis of an organism emerged in the 60s and 70s of the XX century (hypothalamus as a homeostatic or thermal homeostat). In the following decades, studies of molecular mechanisms behind the genesis of circadian and circannual rhythms sinificantly expanded our knowledge of hypothalamic functions. According to current ideas, hypothalamic nuclei function as pacemakers for other structures and trigger various processes that have different temporal parameters (latency, velocity, duration, periodicity, sequentiality, density) and form together the organism’s endogenous time. In this review, the authors analyze some features of local networks in the hypothalamic nuclei and formulate the principles of neuropeptide action underlying the homeostatic regulation of the endogenous time by the hypothalamus.

The phospholipid and fatty acid composition of rat erythrocytes was studied after stress exposure—swimming until drowning. This kind of stress was found to increase the content of phospholipids typical for the outer membrane layer (phosphatidylcholine by 13% and sphingomyelin by 23%). In contrast, the content of acid phospholipids, referring to the inner membrane layer, decreased (phosphatidylethanolamine by 16%, phosphatidylserine by 14% and monophosphoinositide by 23%). Our data indicate that under stress conditions the erythrocyte membrane undergoes certain structural changes, which appear to affect its functional properties. At the same time, the content of saturated and unsaturated fatty acids, as well as their “unsaturation index”, remain basically intact under the above stress conditions, probably, preserving functional properties of the erythrocyte membrane by compensating its impaired phospholipid structure. Based on the analysis of absorption spectra of lipid extracts, stress was established to induce a 2-fold spectrum enhancement in the heme-specific range of 390–410 nm. The appearance of heme in the extract indicates hemoglobin saponification induced by changes in pH of the erythrocyte internal environment. Indeed, during lipid extraction hemoglobin converts into a disordered state due to the effect not only of temperature and pH of the medium, but also of organic solvents, having a lower capacity to form hydrogen bonds than water. Probably, a small portion of phospholipids undergoes trans-esterification during their extraction from erythrocytes by the chloroform–methanol mixture.

In the recent years, an identification of regulatory mechanisms underlying the general adaptation syndrome as an organism’s response to drastic emotional stress-evoking environmental changes is gaining in its importance. The ability to control over visceral functions plays a crucial role in stress reactions due to a threat of neurodynamic imbalance in sympathetic-parasympathetic relationships with the heart as their most vulnerable element. Fast stress adaptation promotes restoration not only of the sympathetic-parasympathetic balance, but also of energy metabolism. Taurine is one of the major regulatory molecules that activate metabolic processes. The present work addresses the following issues: (1) the descending influence of the paraventricular nucleus (PVN) on neural reaction of the solitary tract nucleus (STN), which is the first link in the visceral sensitivity pathway, (2) the mechanisms of central control over visceral reactions as investigated by mathematical modelling and analysis of the heart rate variability (HRV), and (3) morphofunctional changes in brain structures, integrating and regulating the visceral sphere (hypothalamic PVN, amygdala), under psycho-emotional stress with and without intraperitoneal injection of taurine (50 mg/kg). Acute and semichronic experiments were conducted on white nonlinear rats under 5-h immobilization stress. An extremely strong centralization of the vegetative HRV parameters (HR, VBI, SSTI) was revealed, with these parameters normalized on days 7 and 14 post taurine injection. An interaction and interdependence of the central regulatory mechanisms of cardiovascular reactions as well as a considerable protective role of taurine, promoting fast restoration of adaptive properties of the central and peripheral visceral sensitivity components under the development of long-term psycho-emotional stress, were shown.

The long-term effects of perinatal hypoxic exposure followed by the administration of salifen, a GABA derivative, on morphological characteristics of the vascular wall elements in the neocortical microvasculature were studied in rats. Salifen, when applied at therapeutic doses, was established to exert an endothelial protective effect. It prevents such typical pathomorphological consequences of perinatal hypoxia as endothelial hypertrophy, the appearance of multiple intravascular endothelial outgrowths, narrowing of the capillary lumen, malformation of the lamina densa, swelling of perivascular astrocytes, and reactive changes in pericytes. In all neocortical layers, a density of blood vessel distribution across microvasculature as well as their cross-sectional area were found to be approximately the same in adult animals both in control and after hypoxic exposure followed by salifen administration. Changes and rearrangements in the capillary bed after hypoxic exposure and salifen administration were shown to occur at earlier developmental stages, while by the maturity period the structural parameters of microvasculature become stabilized. The endothelial protective effect of salifen promises high clinical efficiency of this preparation and serves as a basis for further studies in this direction.

The spectral parameters of heart rate variability are a measure of activation of the sympathetic and parasympathetic branches of the mammalian autonomic nervous system. In this study, spectral analysis was used for the first time to evaluate the impact of acoustic noise (one of the major anthropogenic factors) on a cetacean. We analyzed cardiac intervals in a captive beluga (a member of the Odontoceti whales) in response to a 10-min band-pass acoustic noise at an intensity of 150–165 dB and frequency of 19–38 kHz. The beluga’s response to acoustic noise, when examined shortly after the animal’s capture, was characterized by a sharp tachycardia (the first phase) followed by a decrease in the heart rate (the second phase). Based on spectral analysis, the frequency range of heart rate oscillations in the beluga decreased during the period of tachycardia while shifting to a lower frequency range (below 0.01 Hz) as compared with the control conditions. Accordingly, the spectral power of low-frequency components was reduced. During the second phase, the range of heart rate variability oscillations expanded and fully recovered only after the noise had been turned off. After one year in captivity, no significant changes in the heart rate parameters (both in time and frequency domain) were recorded in response to a similar noise exposure. Therefore, the changes in the heart rate spectral components in the studied beluga exposed to acoustic noise were comparable to those recorded in terrestrial mammals and in humans in stressful and emotionally negative situations. The spectral characteristics of heart rate oscillations can be used as a quantitative measure of beluga whales’ response to acoustic noise as a stress factor.

The review addresses varied aspects of physiological and biochemical mechanisms aimed at creating special rheological conditions for blood flow termed non-Newtonian blood properties. We conducted a comparative analysis of structural features and phospholipid repertoire of the erythrocyte plasma membranes and cytoskeleton, extracellular ATP pool, and ecto-ATPase enzymatic activity in nucleated and non-nucleated erythrocytes in vertebrates, as well as a study of thermal effects in nucleated red blood cells. Based on data from the literature and our own research, we hypothesize that the phenomenon of non-Newtonian blood properties is underlain by a decrease in the relative blood viscosity due to thermal hydrolysis of extracellular ATP that erythrocytes release onto their surface most actively under capillary deformation stress. We believe that in fishes an important role in this process may belong to erythrocyte plasma membrane ecto-ATPases. Due to a heat released during hydrolysis of extracellular ATP, the marginal blood plasma layer, adjoining the capillary wall, appears to warm up. This may modify the structure of the membrane bilayer and deform the cytoskeleton, thus providing special rheological conditions for blood flow. The heat-producing ability, that we found in fish nucleated erythrocytes, may serve an additional evidence for the existence of this mechanism.