The hypometabolic effect of the blood plasma from a hibernating suslik Citellus undulatus. Neokyotorphin activates cardiac and respiratory activities in the suslik during arousal from hibernation]

The effect of intraabdominal injection of the blood serum from ground squirrels Citellus undulatus obtained at various stages of the baut has been studied on the level of oxygen consumption in albino mice. The strongest hypometabolic effect exhibited the blood plasma from animals at the beginning of the baut. The onset of baut was used in further experiments on C. undulatus for investigation of activating effects of neokiotorphin (Thr-Ser-Lys-Tyr-Arg) which was earlier found in the brain of the ground squirrel. It was shown that intraabdominal injection of this peptide to hibernating animals facilitates their arousal stimulating both the cardiac activity and respiration. The strongest effect was noted with neokiotorphin of [D-Ser] 2-modification which is more stable to proteolysis.     

Protein synthesis in the organs of the long-tailed suslik (Citellus undulatus) in various functional states

Protein synthesis has been observed in brain and liver of susliks during hibernation using specific radioactivity assay and cycloheximide inhibitor analysis. The data on cycloheximide sensitivity and radioactivity of total protein fractions after differential centrifugation suggest that protein synthesis during hibernation is mostly carried out on microsomes. Experiments on protein synthesis in cell-free extracts from liver of suslik at various functional states indicated that the pool of polyribosomes during hibernation is similar to that during wakening period and waking state. This may ensure high intensity of protein biosynthesis at increase in body temperature during wakening.     

Hypothermic effect on mice of a 1-10 kD fraction of the small intestine of the hibernating suslik Citellus undulatus during hypoxia and hypercapnia

Studies have been made on a possibility of inducing a prolonged hypothermia by injections to albino mice of a fraction with a molecular mass 1-10 KD isolated from the small intestine of hibernating ground squirrels. Specific conditions for the onset of hibernation (hypoxia, hypercapnia, temperature) were simulated. Exposure of mice to hypoxia and hypercapnia for 2 hours in combination with injection of the mentioned fraction extended hypothermic condition in animals up to 24-36 hours as compared to 2-3 hours after sole injection of the fraction. After the injection of 5-OT under the same conditions, the prolonged hypothermia was less stable.     

Analysis of changes in heart rate and temperature of the ground squirrel Citellus undulatus in various physiological states

Heart rate (HR) of ground squirrel C. undulatus was studied in dependence of season, level of activity, physiological state and air temperature (T). In summer HR varies from 110-130 beat/min in sleep up to 420 beat/min at flight from danger. During winter hibernation HP was minimal (3-5 beat/min) at T 1-4 degrees C, the increase in T induced the growth of HP in correspondence to the Arrenius van't Hoff law. The temperature of the body in hibernation exceeded T on 1.5-3 degrees C. The time of getting off the hibernation increased with the decrease in T (6-7 hours at -1 degree C and 2.5-3 hours at +18 degrees C). At phase of increased thermogenesis during arousal heart temperature exceeded rectal one on 10-12 degrees C and heart rate run up to 360-420 beat/min i.e. 2-3 time higher than in active state. The decrease in T stimulated the increase in HP up to 3.8 in winter and 5.3 beat/min/degree C in summer. The highest values of Q10 for HP were revealed at the beginning of hibernation (15-20) and at the beginning of arousal (6-7), in other periods Q10 was similar to the normal biological values (2-2.5). Thus, at the beginning of transitional periods changes of HP were determined mainly by endogenic mechanisms that inhibited myocardium at the beginning of hibernation and activated in arousal. Some mechanisms of coordination between activities of heart and other systems of organism are considered. The features of hit exchange providing the hibernation in wide range of T are discussed.     

The thyroid status and lipid metabolism of the suslik Citellus parryi during hibernation

Thyroid hormone concentrations in blood were elevated all through the hibernating season while thyroid gland showed morphological signs of high activity. The specificities of lipid metabolism, increased fatty acid unsaturation and reduced cholesterol/phospholipids molar ratio in plasma membranes were attributed to high thyroid activity.     

Seasonal rhythms in the functioning of the hypophyseo-thyroid system of the suslik Citellus parryi

In experiments on the Arctic ground squirrel Citellus parryi, radioimmune assay of the content of thyrotropin of the hypophysis and thyroxine and triiodothyronine of the thyroid in the peripheral blood has been made at monthly intervals from July until May. It was found that during hibernation period, thyroxine and triiodothyronine concentrations in the blood of sleeping animals are high as compared with those during pre-hibernation period in autumn and active period in May. Thyrotropin content of the blood increases from October to May, being the lowest however during the season of the deepest hibernation from December to February. It is suggested that activation of the hypophysial--thyroid system after resting period in summer and autumn begins in October. During deep sleeping, it is depressed, being recovered in March. High levels of the thyroid hormones during hibernation period may be explained by metabolic strategy of the organism in hibernating animals which is directed to optimization of energy supply of hibernation.     

Seasonal characteristics of the functioning of the hypophysis-gonad system in the suslik Citellus parryi

In experiments on the arctic ground squirrel C. parryi, studies have been made on seasonal changes in the weight of testes, follicular diameter in the ovaries and the content of sex and gonadotropic hormones in the peripheral blood. Testicular involution and arrest of follicular development were observed in prehibernation period. During hibernation, follicular growth and the increase in the weight of testes take place. The level of LH decreases during hibernation. In sleeping animals, its level is higher as compared to that in active animals during short periods of arousal. The increase in LH level takes place both in males and females in April. FSH can not be detected in males during the first half of hibernation, appearing in the peripheral blood only in March and April. In females, FSH was found in the blood in October, being absent from November to January; beginning from February, it may be found both in sleeping and active animals. Testosterone was found in hibernating males and females, its level significantly increased in March in males, being approximately constant in hibernating females. Estradiol secretion was noted in hibernating females, whereas progesterone was found in the blood only in May.     

Characteristics of force-frequency relations in the myocardium of the squirrel Citellus undulatus

The force-frequency relationship (FFR) in papillary muscles of the heart of active ground squirrel in different seasons was studied. For comparison, similar preparations from rat and rabbit were used. It was shown that the FFR of papillary muscles of active ground squirrel undergo significant seasonal changes. In summer and a part of autumn squirrels, a negative staircase (a decrease in the isometric force with increasing stimulation frequency) similar to that in adult rat was revealed. The FFR of the majority of autumn, winter and spring squirrels were polyphasic and contained both positive and negative components. Changes in the force in response to the introduction of pauses at a constant stimulation frequency were recorded. Two types of the post-rest recovery pattern were revealed in the myocardium of ground squirrels. For frequencies range with the negative direction of FFR, a typical pattern of rest-potentiation similar to that in rat papillary muscles was observed. The amplitude of the first post-rest contraction (F1) was usually higher than that of the preceding steady-state contraction. In papillary muscles of autumn animals the F1 value was greater that in summer, which suggests an enhanced release of Ca2+ from the sarcoplasmic reticulum. There was no post-rest potentiation in the range of frequencies with positive direction of FFR, and the post-rest recovery pattern in these cases was principally different from those of rat and rabbit preparations. It was proposed that seasonal differences of the FFR of active ground squirrel heart are associated with changes in the ratio of activities of the calcium-transporting system in the hibernation period.     

Analysis of the brain bioelectrical activity of the suslik Citellus parryi during hibernation

Computer analysis has been made of the diurnal rhythm of the brain activity in the ground squirrel Citellus parryi during hibernation (body temperature 7-8 degrees C). The data obtained are presented in the form of graphical plots with two-dimensional density of probability of distribution of intermittent bursts of spindles and isoelectric EEG.     

Characteristics of higher nervous activity in the suslik Citellus fulvus during its active period

In experiments on active ground squirrels, it was possible to form motor defensive conditioned reflexes and to re-arrange the conditioned reflexes from visual and auditory analysers. It was originally demonstrated that repetitive alteration of the informational content of the conditioned stimuli results in neurotic disturbances in animals.     

The evaluation of the sizes of erythrocytes of the hibernating ground squirrel Citellus undulatus Pallas

A topographical image of individual erythrocytes of the ground squirrel Citellus undulatus Pallas, in unfixed unstained smears was first obtained by scanning probe microscopy for two states of the animal: hibernation and the active state. The scannig of single discocytes, i.e. erythrocytes having a typical discal form, was fulfilled. For the active male, the diameter of the discocyte was found to be approximately 6500 nm. For the hibernating female, the diameter is approximately 6000 nm. According to the data of light microscopy, the discocyte diameters are: 6610 +/- 100 nm for the active state of animal and 6430 +/- 160 nm for the hibernating state.     

Role of the nonspecific modification of erythrocyte membrane lipids during hibernation in the suslik Citellus parryi

Studies have been made on the content of cholesterol, phospholipids, fatty acid composition, the intensity of lipid peroxidation, the activity of Na+, K+-ATPase, as well as on the peroxide hemolysis in the erythrocytes in prehibernating and hibernating ground squirrels. Changes in partial content of cholesterol and in fatty acid composition of membranes are presumably due to the excessive lipid peroxidation during hibernation resulting from the decrease in the activity of antioxidative enzymes, which also accounts for the increase in peroxide hemolysis of erythrocytes.     

Seasonal shifts in the chemical makeup of the fatty tissue of the Arctic suslik, Citellus parryi

Fat stores in three forms of adipose tissue (brown, subcutaneous and visceral) differ in their composition in five populations of the ground squirrel C. parryi. Oleic aicd content is always several times higher in subcutaneous and visceral fat during spring period as compared to the content of linoleic acid. Linoleic and linoleic acids content increased in autumn animals, although in the most northern population it remained unchanged.     

Variability in several ecologic-physiologic traits of different populations of the Asiatic Arctic suslik Citellus parryi]

In several geographic populations of the Arctic ground squirrel C. parryi, studies have been made on changes in oxygen consumption during decrease of the ambient temperature from 25 to 3-4 degrees, thermal preference, hemoglobin content of the blood and composition of the adipose tissue (both brown and white, subcutaneous and visceral). Significant shifts of these indices were found. In animals from various parts of the species area, different sensitivity to cooling was found, as indicated by determinations of oxygen consumption at different temperatures and the prefered temperature: different hemoglobin content of the blood was also found together with differences in the level of two unsaturated fatty acids - the oleic and linoleic ones. Comparison of these data with similar results obtained on various populations of the Siberian ground squirrel C. undulatus revealed obvious differences between these close species with respect to the indices studied.