A. I. Anufriev

Ecological Mechanisms of the Formation of Biological Rhythms in Hibernators of the Family Sciuridae in Northeastern Siberia

A mechanism of the formation of biological rhythms in hibernators at cold temperatures is proposed. Certain ecophysiological characteristics have been studied in three hibernating species: the ground squirrels Citellus undulatus Pallas, 1778 and C. parryi Richardson, 1825 and the chipmunk Tamias sibiricus Laxmann, 1769. The changes in body temperature and the temperature of litter in wintering nests during hibernation seasons have been studied. The dependences of metabolic rate on ambient temperature and the size and species of animals have been studied.

Changes in the body temperature of hibernating animals of the Sciuridae family in the year life cycle.

370 Body temperature is an integral characteristic of mammalian metabolism. Measurement of body temperature of animals in practice, especially under nearnatural conditions, is not sufficiently accurate owing to the characteristics of measurement instruments, on the one hand, and changes in animal bodies during forced measurement of their temperature, on the other hand. Implantation of a DS 1922 L-F5 temperature logger under the skin or into the body cavity makes it possible to partially overcome these disadvantages. A homoiothermal core and a heterogeneous envelope can be distinguished in the body of animals, between which there is a temperature gradient whose value depends on the living conditions and the ambient temperature. Under normal conditions, reactions in the envelope maintain the optimal temperature in the core tissues of the body [4]. The body temperature of hibernating mammals varies in a wider range. During hibernation, fluctuations in the body temperature vary from several degrees in large hibernators (such as bears) to tens of degrees in small hibernators (rodents and chiropterans) [2, 3, 8, 11, 12]. In summer, the body temperature of hibernating mammals fluctuates in a narrow range of values and is maintained nearly constant by the same mechanisms of heat production and emission that the temperature of nonhibernating animals. Even a decrease in temperature during entering hibernation does not seem a manifestation of insufficiency of temperature homeostasis resulting in a dramatic drop in body temperature [6].

Bat (Vespertilionidae) hibernation in the northeasternmost part of their geographic range.

In November 2002, we found 16 live and one dead (a northern bat) Vespertilionidae in a spent area of the Olekminskii gypsum mine, in adits along a 1.5-km route. Among these 16 live animals, 10, 5, and 1 were brown, northern, and Ikonnikov’s bats, respectively. The latter species ( Myotis ikonnikovi Ognev, 1912) was previously found only in the vicinity of the Tommot settlement [4] southwest of our finding and had never been found to winter in Yakutia before.

Store-operated Ca2+ entry supports contractile function in hearts of hibernators

Hibernators have a distinctive ability to adapt to seasonal changes of body temperature in a range between 37°C and near freezing, exhibiting, among other features, a unique reversibility of cardiac contractility. The adaptation of myocardial contractility in hibernation state relies on alterations of excitation contraction coupling, which becomes less-dependent from extracellular Ca2+ entry and is predominantly controlled by Ca2+ release from sarcoplasmic reticulum, replenished by the Ca2+-ATPase (SERCA). We found that the specific SERCA inhibitor cyclopiazonic acid (CPA), in contrast to its effect in papillary muscles (PM) from rat hearts, did not reduce but rather potentiated contractility of PM from hibernating ground squirrels (GS). In GS ventricles we identified drastically elevated, compared to rats, expression of Orai1, Stim1 and Trpc1/3/4/5/6/7 mRNAs, putative components of store operated Ca2+ channels (SOC). Trpc3 protein levels were found increased in winter compared to summer GS, yet levels of Trpc5, Trpc6 or Trpc7 remained unchanged. Under suppressed voltage-dependent K+, Na+ and Ca2+ currents, the SOC inhibitor 2-aminoethyl diphenylborinate (2-APB) diminished whole-cell membrane currents in isolated cardiomyocytes from hibernating GS, but not from rats. During cooling-reheating cycles (30°C–7°C–30°C) of ground squirrel PM, 2-APB did not affect typical CPA-sensitive elevation of contractile force at low temperatures, but precluded the contractility at 30°C before and after the cooling. Wash-out of 2-APB reversed PM contractility to control values. Thus, we suggest that SOC play a pivotal role in governing the ability of hibernator hearts to maintain their function during the transition in and out of hibernating states.

Ecological and physiological characteristics of the mountain hare (Lepus timidus) cold resistance in the northeastern Siberia.

139 A series of ecological, physiological, and morphological adaptations to the conditions of cold climate is inherent in the mountain hare ( Lepus timidus ) inhabiting central Yakutia and Verkhoyansk Range (northeastern Siberia) [7–9]. Earlier, the authors of the monograph Mlekopitayushchie Yakutii (Mammals of Yakutia) emphasized the small size of this animal [7]. As early as in the 1970s, one of us noted that this species does not comply with Bergmann’s rule and tried to explain the small body size of Yakut hares and extremely wide range of the population density by lowcalorie food [8]. Analysis of the geographical variation of the mountain hare skull in Russia has shown that the Yakutia subspecies complies with neither Bergmann’s rule nor the rule of optimum or rule of latitude [9]. Mountain hares inhabiting Yakutia are capable of consuming and metabolizing large quantity of low-calorie food during the eight-month winter period; low mobility resulting from accessible food and few enemies is another specific feature of this species. Due to the low mobility, stable metabolism that increases insignificantly with a decrease in ambient temperature to –40 ° C is characteristic of the mountain hare [1]. In homoiothermal animals, the body temperature is one of the major indicators of the metabolic rate. However, no measurements of the mountain hare body temperature for a long period of time have been available so far. Here, we report data on changes in the body temperaGENERAL BIOLOGY

The effect of insulin on the heart rate and temperature of the ground squirrel Spermofilus undulatus during arousal from hibernation

The effect of insulin on the heart rate and body temperature, measured per rectum, of ground squirrels (Spermophilus undulatus) during triggered arousal from winter hibernation was studied. We found that the outcomes of insulin injection to hibernating ground squirrels varied in the course of arousal. During the first stage, while body temperatures were less than 10°C, the heart rates and rectal temperatures in both control and insulin-treated groups changed in the same manner. During the next stage of arousal, when the body temperature rose above 12°C, elevation of the heart rate and rectal temperature in the insulin-treated animals was significantly retarded and lasted 110 min compared to 80 min in the control group. Conversely, in the final stage of arousal at body temperatures above 20°C, the heart rate and body temperature increased more rapidly in the insulin-treated animals that reached normal body temperature within 40 min compared to 60 min in the control group. Suggested mechanisms of bidirectional effects of insulin on the heart rates and body temperatures in ground squirrels at the particular stages of arousal, with regard to the progression of endogenous insulin and glucose levels in the blood serum, are discussed.

Possible reasons for the variability of the inotropic insulin effect in papillary muscles of ground squirrel myocardium

The effects of insulin (0.1–50 nM) on isometric twitch force (0.1 to 1.0 Hz; 30 ± 1°C; 1.8 mM Ca2+) were studied in right ventricular papillary muscles from active ground squirrels of different seasons (summer, n = 14; autumn, n = 16 and winter interbout, n = 16) in control conditions and after one-hour pretreatment of PM with 2 μM nifedipine (an L-type Ca2+-channel inhibitor) and 1.0 mM orthovanadate (a tyrosine phosphatase inhibitor). In active animals of different seasonal periods insulin causes both positive and negative inotropic effects. At low frequencies (0.1–0.5 Hz), insulin of low concentrations (0.1–1.0 nM) induces a transient (within the first 20 min after application) positive effect (about 15–25%). Application of high hormone concentration (10 nM) in a low range of stimulation frequencies causes a biphasic effect (a small initial positive inotropic effect followed by a marked negative one). At frequencies above 0.5-Hz stimulation, insulin of 10 nM concentration causes presumably a negative inotropic effect. It was proposed that ICaL is possibly involved in the insulin-induced negative inotropy in ground squirrels hearts. Alteration of protein phosphorylation in tyrosine residues is known to be a major link in the mechanism of insulin action. We performed a study on sodium orthovanadate action (a known inhibitor of tyrosine phosphatase) on the inotropic insulin effect. In the group of summer animals the pretreatment of papillary muscles with sodium orthovanadate (100 μM) does not change the negative inotropic effect of insulin in a low range of stimulation frequencies but almost completely removes this effect at stimulation frequencies above 0.3 Hz (n = 4). Nifedipine (1–1.5 h pretreatment), a blocker of L-type calcium channel, reduces the inhibitory effect of insulin in autumn and winter animals, and on the contrary intensifies it in summer animals. This fact indicates that different mechanisms must be involved in insulin actions in animals of summer and winter periods. The main findings of the present study are that insulin induces positive, negative or no inotropic effects in papillary muscles of ground squirrels myocardium. The character of the effects of insulin depends on the physiological state of animals; time and concentrations of the hormone applied; affected by conditions that alter cellular Ca2+ loading and the ratio of protein-tyrosine kinases/phosphatases activity.

Annual dynamics of the body temperature in musk oxen (Ovibos moschatus) under the conditions of Yakutia

Republic of Sakha (Yakutia), situated in northeast ern Siberia, is one of the coldest regions of Russia [2]. The adaptive potential of species living here is expressed, in particular, in their ecology and energy metabolism. The body temperature is an integrated indicator of the thermal condition of animals and humans. In the body, we distinguish the homeother mal core and the heterothermal envelope. Under favorable conditions, the reactions in the envelope maintain an optimal temperature in the core of the body [4]. By changes in the temperature of the body envelope, we may estimate the influence of the ambi ent temperature on the body and the ability of the body to resist this effect [8, 9].

Frequency-dependent effect of insulin on myocardial contractility in active ground squirrel Citellus undulatus in different seasons.

Insulin plays a key role in the regulation of myocardial contractility in normal and pathological states. However, the mechanisms of its inotropic effect are still unknown, and the published data are contradictory [1–4]. It is known that insulin increases the contractility of the myocardium in different animal species [1, 2]. However, in some cases, insulin and insulin-like agents either have no effect on the contractility [1, 3, 4] or suppress it [5, 6]. It was shown that the pattern of insulin effects may change in pathologies [4] and depends on the age of the animals [3, 5] and the experimental conditions [6]. Earlier, we demonstrated a pronounced multidirectional effect of insulin in the myocardium of the Yakutian ground squirrel [7, 8]. The discovered seasonal variability of the sensitivity of the myocardium to insulin and a pronounced dependence of its effects on the animal’s state (active, hibernating, or awakening) make the myocardium of hibernators a convenient model for studying the mechanisms of the insulin effects on the myocardium.