Phospholipid composition of hibernating ground squirrel (Citellus lateralis) kidney and low-temperature membrane function.

1. Phospholipid analysis of kidney lipids from active and hibernating ground squirrels (Citellus lateralis) indicate that molar quantities of phosphatidyl choline increase, while sphingomyelin decreases in hibernating animals. 2. Both of these changes are in such a direction as to enhance membrane fluidity and possibly contribute to low-temperature membrane function in these organisms.     

Circannual rhythmicity in the hibernating ground squirrel Citellus lateralis under constant light and hyperthermic ambient temperature

• 1.1. In order to elucidate some of the parameters of the circannual rhythm in heterothermichomothermic mammals, the ground squirrel Citellus lateralis was maintained for 3 years under constant. high ambient temperature (34 C).
• 2.2. Results indicate that the ground squirrel continues to exhibit a circannual cycle of body weight fluctuations despite the high temperature.
• 3.3. Furthermore, although alternating periods of heterothermy-homothermy were not possible at 34 C, the body weight cycle did free run under this constant environmental condition, and thus demonstrates the true endogenous nature of the circannual rhythm.

     

Fine structural changes in Sertoli and Leydig cells during the reproductive cycle of the ground squirrel, Citellus lateralis

During spermatogenesis in sexually mature ground squirrels Leydig and Sertoli cells were morphologically well differentiated. For Leydig cells the most prominent organelles were lipid droplets, mitochondria with tubulo-vesicular cristae and abundant agranular reticulum organized as a mass of anastomosing tubules. These morphological criteria suggest that the Leydig cells were steroidogenically active. Sertoli cells exhibited a topographical distribution of certain organelles with basal regions containing stacks of granular reticulum, and large areas of agranular reticulum. The cytoplasm surrounding maturing germ cells contained numerous microtubules, and an adluminal layer of spermatids at a certain stage of spermiogenesis became enveloped by Sertoli cytoplasm containing an enormous proliferation of agranular reticulum. The presence of these organelles in Sertoli cells suggests that during spermatogenesis they are active in the synthesis of proteins and steroids. In particular the mass of agranular reticulum surrounding late stage spermatids indicates that steroids may be required for spermatid maturation and/or spermiation. By contrast Leydig and Sertoli cells observed during testicular regression, when only spermatogonia remain in the seminiferous tubules, had undergone structural changes. Leydig cells were still numerous and large with abundant agranular reticulum that was now organized as a loose assemblage of single unbranched tubules. Sertoli cells were drastically reduced in both cytoplasmic volume and content of organelles.     

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.     

The influence of hibernation on testis growth and spermatogenesis in the golden-mantled ground squirrel, Spermophilus lateralis

Testis size and spermatogenesis were monitored serially in individual golden-mantled ground squirrels before, during, and after the hibernation season. During hibernation, animals spent 81% of days in torpor at body temperatures of 3-4 degrees C. Torpor bouts of 6 days duration were interspersed with brief arousals from torpor during which animals were normothermic. In the 5 mo between December (when animals entered hibernation) and April (when torpor was spontaneously terminated), the estimated mass of testes increased gradually from 500 to 1100 mg, but spermatogenesis did not advance beyond pachytene spermatocytes, which were present before hibernation began. In contrast, during the month after torpor was terminated, testes increased rapidly to 3500 mg and after 31 days, spermatozoa were found in the epididymides. We suggest that the limited testis growth that occurred during the hibernation season was restricted to intervals during which squirrels were aroused from torpor. The major portion of gonadal growth and spermatogenesis in the laboratory, and presumably in the field, occurs after ground squirrels have regained the normothermic state. Since males are reproductively mature when first trapped in spring, these findings suggest that males are normothermic for several weeks before they emerge from their hibernacula in the spring.     

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.     

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.     

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).