Association between Rhythmic Variations of Mouse Body Temperature with 4-16-Minute Periods and Geomagnetic Undulations in Corresponding Frequency Range Pc5/Pi3.

The rhythmic variations of body temperature in two groups of mice located in Moscow and Novosibirsk were compared with geomagnetic undulations within Pc5/Pi3 (1-5 mHz) range measured in Borok and Novosibirsk middle-latitude geophysical observatories located at the same longitudes as the examined mice. The spectral maxima of geomagnetic undulations and body temperature variations were observed with greatest probability at the frequencies of 1.6, 2.3, and 3.1 mHz. At this, the mean square of the distance between the frequencies of spectral maxima of simultaneous oscillations was smaller than that of random intervals favoring the hypothesis on geomagnetic undulations as the synchronizer of biorhythms. In both groups of mice, the share of intervals with a high spectral coherency between geomagnetic undulations and body temperature variations had common maximum in the pre-midnight sector of local time and it was higher for the large-scale geomagnetic undulations. Dependence of geomagnetic undulations on spatial scale suggests that body temperature is affected by electrotelluric field.

[Interpopulation variability of endocrine-metabolic reaction to cold stress in northern red-backed vole (Myodes rutilus)].

In natural environment, stresses, when animals happen to be exposed to them, influence the functional activity of adrenal cortex. It can be expected that in animals, living under unfavorable conditions, basal concentration of glucocorticoid hormones would be increased while adrenocortical response to acute stress would be weakened. Since the main function of stress-reaction is resources mobilization meant to compensate an environmental impact, its weakening should lead to reduction of reserve metabolic capacities. To test this hypothesis, we compared energy metabolism, body temperature, and corticosterone concentration in blood plasma measured in northern red-back voles (Myodes rutilus) before and after acute cooling in helium-oxygen mixture. Voles belonged to two populations that deffered in relative abundance. It is found out that voles from a population of low relative abundance inhabiting the recreational forest of Novosibirsk Scientific Center, despite their being more stress-prone and having weakened stress-reaction, have higher maximum metabolic rate than voles from the mountain taiga polulation with high relative abundance. The results obtained suggest that living under unfavorable conditions leads to physiological adaptations which enhance resistance to acute stress, yet increase the risk of chronic stresses that have negative effect on fitness.