5-HT Receptors and Temperature Homeostasis

The present review summarizes the data concerning the influence of serotonin (5-HT) receptors on body temperature in warm-blooded animals and on processes associated with its maintenance. This review includes the most important part of investigations from the first studies to the latest ones. The established results on the pharmacological activation of 5-HT1A, 5-HT3, 5-HT7 and 5-HT2 receptor types are discussed. Such activation of the first 3 type of receptors causes a decrease in body temperature, whereas the 5-HT2 activation causes its increase. Physiological mechanisms leading to changes in body temperature as a result of 5-HT receptors’ activation are discussed. In case of 5-HT1A receptor, they include an inhibition of shivering and non-shivering thermogenesis, as well simultaneous increase of peripheral blood flow, i.e., the processes of heat production and heat loss. The physiological processes mediated by 5-HT2 receptor are opposite to those of the 5-HT1A receptor. Mechanisms of 5-HT3 and 5-HT7 receptor participation in these processes are yet to be studied in more detail. Some facts indicating that in natural conditions, without pharmacological impact, these 5-HT receptors are important links in the system of temperature homeostasis, are also discussed.

Intracellular thermometry uncovers spontaneous thermogenesis and associated thermal signaling

Conventional thermal biology has elucidated the physiological function of temperature homeostasis through spontaneous thermogenesis and responses to variations in environmental temperature in organisms. In addition to research on individual physiological phenomena, the molecular mechanisms of fever and physiological events such as temperature-dependent sex determination have been intensively addressed. Thermosensitive biomacromolecules such as heat shock proteins (HSPs) and transient receptor potential (TRP) channels were systematically identified, and their sophisticated functions were clarified. Complementarily, recent progress in intracellular thermometry has opened new research fields in thermal biology. High-resolution intracellular temperature mapping has uncovered thermogenic organelles, and the thermogenic functions of brown adipocytes were ascertained by the combination of intracellular thermometry and classic molecular biology. In addition, intracellular thermometry has introduced a new concept, “thermal signaling”, in which temperature variation within biological cells acts as a signal in a cascade of intriguing biological events.

The effects of estrogens on neural circuits that control temperature

Declining and variable levels of estrogens around the time of menopause are associated with a suite of metabolic, vascular, and neuroendocrine changes. The archetypal adverse effects of peri-menopause are vasomotor symptoms, which include hot flashes and night sweats. Although vasomotor symptoms are routinely treated with hormone therapy, the risks associated with these treatments encourage us to seek alternative treatment avenues. Understanding the mechanisms underlying the effects of estrogens on temperature regulation is a first step toward identifying novel therapeutic targets. Here we outline findings in rodents that reveal neural and molecular targets of estrogens within brain regions that control distinct components of temperature homeostasis. These insights suggest that estrogens may alter the function of multiple specialized neural circuits to coordinate the suite of changes after menopause. Thus, defining the precise cells and neural circuits that mediate the effects of estrogens on temperature has promise to identify strategies that would selectively counteract hot flashes or other negative side effects without the health risks that accompany systemic hormone therapies.

Temperature management and its role in cardiac arrest patients—a review

Thermoregulation constitutes one of the most important homeostatic systems of the human body. The human thermoregulatory system is highly complex and intertwined with other regulatory homeostatic systems. Different evolutionary adaptations have evolved to ensure a well-regulated body temperature, encompassing simple behavioural (e.g., seeking shelter, going underground) as well as physiological changes (e.g., vasodilatation, sweating). However, when the heat, cold or other stimuli cause a disruption in the thermoregulatory state and our adaptations can no longer cope with the additional stress, the body enters a pathological state. In such instances other measures must be undertaken. In medicine there are several pathological states associated with disruptions in temperature homeostasis. Consequently, these patients have to be, in broad terms, thermoregulated. Speaking specifically, the most common application of thermoregulation is therapeutic temperature management. A prominent example is the utilisation of this technique in post-cardiac arrest patients, who remain comatose after resuscitation. This technique has been in use for almost 20 years since the first major reports on its benefits in improving out-of-hospital cardiac arrest and in-hospital cardiac arrest survival as well as improving neurological outcome. Recently, the findings from one of the biggest targeted temperature international and multicentre trials to date have been published (TTM2 trial; https://ttm2trial.org/). The study surprisingly showed no difference in mortality between patients after out of hospital cardiac arrest, who underwent normo- or hypothermia. Consequently, we might need to re-evaluate certain guidelines, recommendations, and perspectives. The aim of the current review is to present an overview of targeted temperature management in the field of intensive care medicine and cardiac arrest.

Synchronous and opponent thermosensors use flexible cross-inhibition to orchestrate thermal homeostasis

Body temperature homeostasis is an essential function that relies upon the integration of the outputs from multiple classes of cooling- and warming-responsive cells. The computations that integrate these diverse outputs to control body temperature are not understood. Here we discover a new set of Warming Cells (WCs), and show that the outputs of these WCs and previously described Cooling Cells (CCs1) are combined in a cross-inhibition computation to drive thermal homeostasis in larval Drosophila. We find that WCs and CCs are opponent sensors that operate in synchrony above, below, and near the homeostatic set-point, with WCs consistently activated by warming and inhibited by cooling, and CCs the converse. Molecularly, these opponent sensors rely on overlapping combinations of Ionotropic Receptors to detect temperature changes: Ir68a, Ir93a, and Ir25a for WCs; Ir21a, Ir93a, and Ir25a for CCs. Using a combination of optogenetics, sensory receptor mutants, and quantitative behavioral analysis, we find that the larva uses flexible cross-inhibition of WC and CC outputs to locate and stay near the homeostatic set-point. Balanced cross-inhibition near the set-point suppresses any directed movement along temperature gradients. Above the set-point, WCs mediate avoidance to warming while cross-inhibiting avoidance to cooling. Below the set-point, CCs mediate avoidance to cooling while cross-inhibiting avoidance to warming. Our results demonstrate how flexible cross-inhibition between warming and cooling pathways can orchestrate homeostatic thermoregulation.

Chronic High-Dose Neonicotinoid Exposure Decreases Overwinter Survival of Apis mellifera L.

Overwinter colony mortality is an ongoing challenge for North American beekeepers. During winter, honey bee colonies rely on stored honey and beebread, which is frequently contaminated with the neonicotinoid insecticides clothianidin and thiamethoxam. To determine whether neonicotinoid exposure affects overwinter survival of Apis mellifera L., we chronically exposed overwintering field colonies and winter workers in the laboratory to thiamethoxam or clothianidin at different concentrations and monitored survival and feed consumption. We also investigated the sublethal effects of chronic thiamethoxam exposure on colony pathogen load, queen quality, and colony temperature regulation. Under field conditions, high doses of thiamethoxam significantly increased overwinter mortality compared to controls, with field-realistic doses of thiamethoxam showing no significant effect on colony overwinter survival. Under laboratory conditions, chronic neonicotinoid exposure significantly decreased survival of winter workers relative to negative control at all doses tested. Chronic high-dose thiamethoxam exposure was not shown to impact pathogen load or queen quality, and field-realistic concentrations of thiamethoxam did not affect colony temperature homeostasis. Taken together, these results demonstrate that chronic environmental neonicotinoid exposure significantly decreases survival of winter workers in the laboratory, but only chronic high-dose thiamethoxam significantly decreases overwinter survival of colonies in the field.

Some age-related features of intrauterine infection in premature infants

Annotation. The protective forces of newborns born prematurely, with low body weight under conditions of infection, are not capable of an adequate response. The aim of our study was to study some of the features of premature infants with low birth weight at the background of intrauterine infection. The first group consisted of 67 stories of premature babies born with low birth weight (LBW) from 1500 to 2500 g and gestational age 32–35 weeks (average gestational age — 34±2 weeks). It was revealed that a feature of the temperature homeostasis of children of group I is the establishment and maintenance of a temperature gradient, that is, the difference between central and peripheral temperatures, which ranged from 1,100 C to 1,500 C at the age of 6–7 days. It was found that the dynamics of the temperature gradient in the neonatal period is very often depended on the presence of perinatal pathology, namely, hypoxic-ischemic damage to the central nervous system. The regularities of temperature homeostasis in children of the second group are characterized, which amounted to 27 newborns with gestational age 38–40 weeks of gestation, birth weight 2600–3200 g without a clinic of respiratory disorders and neurological symptoms. On the 4th–5th day after birth, these children were discharged home under the supervision of a family doctor. In group II children who, after 1.5–2.5 months, were admitted to the neonatal pathology department diagnosed with acute respiratory viral infections: acute rhinopharyngitis or bronchitis, the temperature gradient ranged from 2.100 С to 3.500 С. In children, an increase in central temperature or a decrease in peripheral temperature was observed. It was found that with effective treatment on days 4–6, the temperature gradient was always constant and amounted to 1.500 С to 1.700 С. To identify the cause of the disease in the I and II groups, studies of blood, mucus from the pharynx and nose, and secretions from the trachea were performed. For this, we used the method of polymerase chain reaction (PCR), enzyme-linked immunosorbent assay (ELISA) and bacteriological methods of research. The effect of intrauterine infection, the colonization of pathogenic intestinal microflora was evaluated, a low Apgar score of 1 and 5, the presence of respiratory disorders, hyporeflexia, a decrease in thymus, leukocytosis of more than 10 thousand, leukopenia of less than 4 thousand, neutrophilia with a shift to the left, which are very dangerous, were taken into account for premature babies and require respiratory support, colonization of the intestines with bifidobacterium and the use of immunocorrective therapy (venoimun at a dose of 0.4 ml / kg every other day for 3–5 days), which gives good results for nursing preterm infants.

Cell thermoregulation and origin of homeothermic animals

Temperature has a fundamental influence in all chemical and biochemical reactions. It influences reaction rates, equilibrium amounts, viscosity, solubility, molecular arrangements and numeric other parameters. Temperature is important for all physiological processes. Maintaining the relative constancy of the internal temperature (temperature homeostasis) is a necessary condition for normal life. Some living beings maintain temperature homeostasis in the body due to external sources of energy (poikilothermy), others due to the energy of food consumption (homeothermy). However, it is unknown the origin of homeothermic organisms. Despite the fundamental similarity of the mechanisms of the central organ-based physiological thermoregulation, even among the higher vertebrates exists poikilothermy and homeothermy animals. It is assumed that homeothermy is not the result of the evolution of physiological mechanisms of thermoregulation. Homeothermy is the result of the evolution of non-coding DNAs in the genome, some of which formed the so-called chromosomal heterochromatin regions (HRs). Chromosomal HRs constitutes the material basis of cell thermoregulation, which is responsible for the removal of excess thermal energy from the nucleus into the cytoplasm. Homeothermic organisms, unlike poikilotherms capable of faster and more efficient leveling of temperature difference between the nucleus and the cytoplasm with all the ensuing consequences.

B-chromosomes and cell thermoregulation

B-chromosomes have been studied for over a hundred years. Thousands of works are devoted to the study of morphology, distribution, inheritance and molecular structure of B-chromosomes. However, the biological role of these additional to the main set of chromosomes is still unknown. The main directions of researches aimed at elucidating the biology of B-chromosomes are related to the study of their molecular structure using the latest methods of molecular biology and genomics. Without disputing the importance of such researches, we suggest paying attention to the physiology of cells as well. We believe that B-chromosomes may be involved in maintaining the organism's temperature homeostasis under different environmental conditions by actively incorporating into the process of cell thermoregulation. Keywords: B-chromosomes; Cell Thermoregulation; Heterochromatin; Condensed Chromatin; Adaptation B-chromosomes and cell thermoregulation