Influence of Cold-TRP Receptors on Cold-Influenced Behaviour

The transient receptor potential (TRP) channels, TRPA1 and TRPM8, are thermo-receptors that detect cold and cool temperatures and play pivotal roles in mediating the cold-induced vascular response. In this study, we investigated the role of TRPA1 and TRPM8 in the thermoregulatory behavioural responses to environmental cold exposure by measuring core body temperature and locomotor activity using a telemetry device that was surgically implanted in mice. The core body temperature of mice that were cooled at 4 °C over 3 h was increased and this was accompanied by an increase in UCP-1 and TRPM8 level as detected by Western blot. We then established an effective route, by which the TRP antagonists could be administered orally with palatable food. This avoids the physical restraint of mice, which is crucial as that could influence the behavioural results. Using selective pharmacological antagonists A967079 and AMTB for TRPA1 and TRPM8 receptors, respectively, we show that TRPM8, but not TRPA1, plays a direct role in thermoregulation response to whole body cold exposure in the mouse. Additionally, we provide evidence of increased TRPM8 levels after cold exposure which could be a protective response to increase core body temperature to counter cold.

Cold Exposure during the Active Phase Affects the Short-Chain Fatty Acid Production of Mice in a Time-Specific Manner

Chronic or acute ambient temperature change alter the gut microbiota and the metabolites, regulating metabolic functions. Short-chain fatty acids (SCFAs) produced by gut bacteria reduce the risk of disease. Feeding patterns and gut microbiota that are involved in SCFAs production are controlled by the circadian clock. Hence, the effect of environmental temperature change on SCFAs production is expected depending on the exposure timing. In addition, there is limited research on effects of habitual cold exposure on the gut microbiota and SCFAs production compared to chronic or acute exposure. Therefore, the aim was to examine the effect of cold or heat exposure timing on SCFAs production. After exposing mice to 7 or 37 °C for 3 h a day at each point for 10 days, samples were collected, and cecal pH, SCFA concentration, and BAT weight was measured. As a result, cold exposure at ZT18 increased cecal pH and decreased SCFAs. Intestinal peristalsis was suppressed due to the cold exposure at ZT18. The results reveal differing effects of intermittent cold exposure on the gut environment depending on exposure timing. In particular, ZT18 (active phase) is the timing to be the most detrimental to the gut environment of mice.

Adipose Lipolysis Regulates Cardiac Glucose Uptake and Function in Mice under Cold Stress

The heart primarily uses fatty acids as energy substrates. Adipose lipolysis is a major source of fatty acids, particularly under stress conditions. In this study, we showed that mice with selective inactivation of the lipolytic coactivator comparative gene identification-58 (CGI-58) in adipose tissue (FAT-KO mice), relative to their littermate controls, had lower circulating FA levels in the fed and fasted states due to impaired adipose lipolysis. They preferentially utilized carbohydrates as energy fuels and were more insulin sensitive and glucose tolerant. Under cold stress, FAT-KO versus control mice had >10-fold increases in glucose uptake in the hearts but no increases in other tissues examined. Plasma concentrations of atrial natriuretic peptide and cardiac mRNAs for atrial and brain-type natriuretic peptides, two sensitive markers of cardiac remodeling, were also elevated. After one week of cold exposure, FAT-KO mice showed reduced cardiac expression of several mitochondrial oxidative phosphorylation proteins. After one month of cold exposure, hearts of these animals showed depressed functions, reduced SERCA2 protein, and increased proteins for MHC-β, collagen I proteins, Glut1, Glut4 and phospho-AMPK. Thus, CGI-58-dependent adipose lipolysis critically regulates cardiac metabolism and function, especially during cold adaptation. The adipose-heart axis may be targeted for the management of cardiac dysfunction.

Tranilast treats cold-related hypertension by reducing the expression of NLRP3 inflammasome

Objective Cold exposure is associated with increased prevalence of hypertension and the related severe cardiovascular events. Aberrant activation of the nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3) inflammasome plays an important role in the development of hypertension. Tranilast (TR), an inhibitor of NLRP3, provides a useful pharmacological probe for exploring the role of NLRP3 in pathogenesis associated with inflammation and its potential application as a therapeutic agent. This study was designed to examine the effects of TR on NLRP3 and hypertension in rats exposed to cold environment to simulate the frigid-zone conditions. Methods and results Sprague Dawley (SD) rats were exposed to moderate cold temperature (4±1°C), and then were randomized to receive TR or vehicle for 3 weeks, while the control group was raised under rat room temperature (RT, 23±1°C). We found that cold exposure substantially increased blood pressure, NLRP3 inflammasome level, and fibrosis in aorta, which were reversed by TR. Conclusion TR has an anti-hypertensive property in cold environment, and this beneficial action is likely conferred by its inhibitory effects on inflammation and fibrosis. These findings suggest TR as a potential drug for the treatment of cold-induced hypertension.

Myocardial Contractility in Young People During Cold Exposure of the Foot

This paper studied the physiological response of the human circulatory system to local cooling of the feet. The research involved young men (n = 27) and women (n = 30) aged between 17 and 20 years, born and permanently living in the Arctic zone of the Russian Federation (Arkhangelsk). SIMONA 111 integrated monitoring system was used. We found that stimulation of peripheral temperature-sensitive receptors of the foot skin at local cooling causes a decrease in heart contractility in both sexes, while young women demonstrate greater sensitivity to the cold factor than young men. For citation: Korobitsyna E.V., Gudkov A.B., Popova O.N., Shcherbina Yu.F. Myocardial Contractility in Young People During Cold Exposure of the Foot. Journal of Medical and Biological Research, 2021, vol. 9, no. 4, pp. 459–462. DOI: 10.37482/2687-1491-Z084