Recovery of a new herpesvirus from the ground squirrel (Citellus citellus).

A new herpesvirus recovered from the kidneys of mature ground squirrels (Citellus citellus) produced an effect in tissue culture cells resembling that of herpesviruses, including the formation of multinucleated syncytia and type A intranuclear inclusions. The isolate caused latent infection in the natural host, but it proved fatal for intracerebrally inoculated suckling mice and it produced pocks on the chorioallantoic membrane of embryonated eggs. Electron-microscopic examination of infected cells revealed intranuclear virus particles exhibiting a size and ultrastructure characteristic of herpesviruses. The isolate was ether-resistant and a DNA nucleic acid type was inferred from observations on inhibition by fluorinated pyrimidine. This ground squirrel herpesvirus was found to be antigenically distinct from Herpesvirus hominis and from ground squirrel cytomegalovirus, with no detectable cross-reactivity.     

Seasonal changes of the ovarian atretic follicles of the ground squirrel (Citellus citellus L.)

The ovaries of 84 ground squirrels (C. Citellus L.) were studied during the four seasons of the year. The ovarian atretic follicles were examined by histological methods and by electron microscopy. The histoenzyme activities of NAD.H2-tetrazolium reductase, glucose-6-phosphate dehydrogenase, and 3 beta-hydroxy-delta 5-steroid dehydrogenase were photometrically demonstrated. The steroid-producing atretic follicles were mainly described as they reached their highest enzyme activity during the lactation period in April. The atresia of the primordial and primary follicles was manifested by disappearance of the oocyte and preservation of the granulose cells surrounded by basal lamina. Atresia of follicles with two oocytes was a typical process for the ground squirrel. Later on the oocytes and the granulose cells around it disappeared. The remaining part of the follicle continued its development and reached maturity. Atresia was observed mainly in March, April, and May.     

Circannual fluctuations of the serum cortisol in the European ground squirrel, Citellus citellus L

1. Serum cortisol levels were measured throughout an annual cycle in male European ground squirrels, Citellus citellus L. 2. A circannual rhythm of these levels in euthermic animals was found: the highest being in late October, November and December, the lowest in May, early October and March. 3. The levels varied in the hibernating period as well: strongly reduced during the first part (October-December) and significantly elevated in the second one (January-March). 4. A significant elevation of the cortisol levels was marked 18-20 hr after full arousal from hibernation in October.     

Studies on the estrus cycle of the ground squirrel (Citellus citellus L.) at experimentally induced hibernation

Eighty-five ground squirrels (C. citellus L.) were examined immediately after arousal (March-June). It was established that the animals were in estrus at the end of March; in April they were pregnant; in May they were in lactation; and in June they were already at rest, a postlactation period. Fifteen ground squirrels were treated with Hibernal and then placed in a chamber for 30 days at external temperature, 8-12 degrees C. In this case the estrus cycle of hypothermic ground squirrels was not changed. A retarded involution of corpus luteum persisted for a month and cystic follicles appeared in the ovary.     

Diabetes mellitus in the 13-lined ground squirrel (Citellus tridecemlineatus).

Spontaneous diabetes mellitus was diagnosed in six of 126, 13-lined ground squirrels, Citellus tridecemlineatus. Serum glucose values were significantly higher in the diabetic ground squirrels than in the non-diabetic ground squirrels, while serum insulin values of fasted diabetic squirrels were significantly lower than fasted nondiabetic ground squirrels. In addition, the classic diabetic signs of poly-dipsia, polyuria, glycosuria, ketonuria, polyphasia, and weight loss were present. The proportion of islet tissue to total pancreatic area in diabetic ground squirrels was less than 25% of that in the nondiabetic ground squirrels. Both the number and size of the islets of Langerhans in diabetic ground squirrels were less than those in nondiabetic ground squirrels.     

Seasonal dependence of the activity of antioxidant defence enzymes in the ground squirrel (Citellus citellus): the effect of cold.

1. The activity of antioxidant defense enzymes (SOD, CAT, GSH-Px and GST) was analysed during the autumn and winter in the ground squirrel adapted to 30 degrees C and subsequently exposed to cold for 6 and 24 hr. 2. The liver CAT activity as well as the IBAT CAT and GSH-Px activities differed between animals adapted to 30 degrees C, studied in autumn, and those studied in winter. 3. MnSOD activity in the liver was increased in autumn but decreased in winter after 6 hr cold exposure reaching the control level 24 hr later. Cold exposure induced a decrease in CAT activity (except after 24 hr cold exposure in winter) and an increase in GSH-Px activity. Lower GST activity was found after 24 hr exposure to cold in winter. 4. The IBAT SOD activity decreased under the influence of cold during both seasons with a tendency to return to the control level only in winter. Cold exposure produced a decrease in GST in both seasons and CAT activity in autumn. GSH-Px activity was increased in winter only. 5. The results indicate a seasonal dependence of the activity of antioxidant defence enzymes in the ground squirrel. Seasonal influence was evidenced in animals exposed to cold as well.     

Antioxidant defenses in the ground squirrel Citellus citellus. 2. The effect of hibernation

In spring and autumn, the ground squirrel Citellus citellus is awake and active but in winter it usually hibernates. Reawakening from hibernation involves intense metabolic activity in the interscapular brown adipose tissue (IBAT). The IBAT of hibernation animals showed significant increases in the activities of superoxide dismutase (both copper-zinc and manganese-containing enzymes), glutathione peroxidase, and in the amount of ascorbate present. Glutathione peroxidase also increased in the liver, as did ascorbate in the plasma. These changes were not merely a consequence of exposure to low environmental temperatures. It is proposed that antioxidant defenses are increased in the IBAT of ground squirrels at the onset of hibernation in order to protect the tissue from reactive oxygen species generated as a result of the intense metabolic activity sustained by this tissue during reawakening.     

Distribution of superoxide dismutase in the ground squirrel (Citellus citellus): effect of the hibernation and arousal

The activity of superoxide dismutase (SOD) was studied in the liver, kidney, interscapular brown adipose tissue (IBAT), lung, heart and spleen of the active and hibernating ground squirrel (Citellus citellus). One group was examined immediately after the arousal from the hibernation. A considerable activity of this enzyme was found in homogenates of all tissues studied except the lung. This activity was lower in the liver and lung of the ground squirrel than in the rat (P less than 0.01). In the other tissues studied the enzyme activity was about the same level in both animals. In the ground squirrel hibernation didn't produce the significant change in SOD activity, as compared with the active state, except in the spleen. Tested immediately after the arousal, SOD activity was significantly higher in all tissues studied except in the IBAT, as compared with the hibernating ones (P less than 0.01).     

Antioxidant defenses in the ground squirrel Citellus citellus. 1. A comparison with the rat

The antioxidant defenses of the liver, erythrocytes, blood plasma, and interscapular brown adipose tissue (IBAT) of male ground squirrels were compared with those of male rats kept under identical conditions and fed the same diet. Superoxide dismutase (SOD), ascorbate, vitamin E, catalase, glutathione, and enzymes of glutathione metabolism were measured. In general, antioxidant defenses in erythrocytes were lower in ground squirrels than in rats. The same was true in liver, except that catalase-specific activity was higher. In IBAT, ascorbate, vitamin E, catalase, and glutathione reductase were higher than in rat and more of the SOD activity present was cyanide-insensitive (MnSOD). It is suggested that IBAT in ground squirrels may need a relatively greater antioxidant defense because of its important role in thermogenesis, especially in reawakening from hibernation. No major differences in antioxidant defenses between male and female ground squirrels were observed, except that the SOD activity of IBAT was higher in females.     

Nonphotic entrainment in a diurnal mammal, the European ground squirrel (Spermophilus citellus).

Entrainment by nonphotic, activity-inducing stimuli has been investigated in detail in nocturnal rodents, but little is known about nonphotic entrainment in diurnal animals. Comparative studies would offer the opportunity to distinguish between two possibilities. (1) If nonphotic phase shifts depend on the phase of the activity cycle, the phase response curve (PRC) should be about 180 degrees out of phase in nocturnal and diurnal mammals. (2) If nonphotic phase shifts depend on the phase of the pacemaker, the two PRCs should be in phase. We used the diurnal European ground squirrel (Spermophilus citellus) in a nonphotic entrainment experiment to distinguish between the two possibilities. Ten European ground squirrels were kept under dim red light (<1 lux) and 20 +/- 1 degrees C. During the entrainment phase of the experiment, the animals were confined every 23.5 h (T) to a running wheel for 3 h. The circadian rhythms of 6 squirrels entrained, 2 continued to free run, and 2 possibly entrained but displayed arrhythmicity during the experiment. In a second experiment, a photic pulse was used in a similar protocol. Five out of 9 squirrels entrained, 1 did not entrain, and 3 yielded ambiguous results. During stable entrainment, the phase-advancing nonphotic pulses coincided with the end of the subjective day, while phase-advancing light pulses coincided with the start of the subjective day: mean psi(nonphotic) = 11.4 h; mean psi(photic) = 0.9 h (psi defined as the difference between the onset of activity and the start of the pulse). The data for nonphotic entrainment correspond well with those from similar experiments with nocturnal Syrian hamsters where psi(nonphotic) varied from 8.09 to 11.34 h. This indicates that the circadian phase response to a nonphotic activity-inducing stimulus depends on the phase of the pacemaker rather than on the phase of the activity cycle.     

Cytology of oocytes in ground squirrels (Citellus citellus L.)

Oocytes of primordial, primary, growing, and Graaf follicles of the ovaries of 96 ground squirrels (Citellus citellus L.) were studied during the four seasons of the year. Multilamellar bodies in the oocytes were observed by electron microscopy. The bodies underwent changes during the follicle growth. The vesicles included in the multilamellar bodies were filled with an amorphous substance, while in Graaf follicles trapezoidal, rhomboidal, and hexagonal inclusions were found. The primordial follicle of the oocyte had no Balbiani body. In the hibernating ground squirrel the functions of the Balbiani body were probably performed by the multilamellar bodies, which were considered to be analogous to the Balbiani body.     

Natural entrainment without dawn and dusk: the case of the European ground squirrel (Spermophilus citellus).

Observational data collected in the field and in enclosures show that diurnal, burrow-dwelling European ground squirrels (Spermophilus citellus) never were above ground during twilight at dawn or at dusk. The animals emerged on average 4.02 h (SD = 0.45) after civil twilight at dawn and retreated in their burrows on average 2.87 h (SD = 0.47) before civil twilight at dusk. Daily patterns of light perceived by these burrowing mammals were measured with light-sensitive radio collar transmitters in an enclosure (the Netherlands) and in the field (Hungary). The observational data are corroborated by the telemetry data, which show clear daily patterns of timing of light perception including light perceived from the burrow entrances. The first light was observed by the animals on average 3.54 h (enclosure, SD = 0.45) and 3.60 h (field, SD = 0.31) after civil twilight at dawn, whereas the final observed light was on average 3.04 h (enclosure, SD = 0.64) and 2.02 h (field, SD = 0.72) before civil twilight at dusk. Thus, the animals do not perceive the rapid natural light-dark (LD) transitions that occur at civil twilight. Instead, they generate their own pattern of exposure to light within the natural LD cycle. The classical phase response model for entrainment by light or dark pulses cannot explain how the circadian system of this species remains entrained to the external, natural LD cycle while the major LD transitions are created by its own behavior.     

Mitotic activity of stomach epithelium in the ground squirrel, Citellus erythrogenys Brandt

1. During hibernation the epithelial cells of the stomach in ground squirrels divide upon spontaneous emergence from hibernation. In torpor periods, mitoses are blocked up. 2. In animals which have come out of hibernation in spring, one peak of mitosis has been recorded in the first few hours after emergence, and another 3 or 4 days later. 3. In summer the mitotic index is low.     

Heat production in the ground squirrel Citellus pygmaeus during arousal from hibernation]

Heat production has been both measured experimentally (Qcal) and calculated from oxygen consumption (QO2) in arousing ground squirrels during the rise of their body temperature. Studies were made on total heat production during all the period of their warming as well as on the heat production at various stages of arousal. Qcal was evaluated by changes in body temperature and those in heat losses via convection and irradiation (calorimetrically). During arousal of animals, their body temperature, heat losses, Qcal and QO2 Gradually increase. However, the increase in heat losses is 3-4 times lower as compared to the intrinsic heat production measured both calorimetrically and by oxygen consumption. Limitation of heat losses (due to the constriction of subcutaneous blood vessels) together with activation of the metabolism in muscles and other tissues provide for significant heat accumulation and the increase in body temperature of arousing ground squirrels.