Ultrastructural changes in the mitochondria of brown adipose cells during the hibernation cycle of Citellus lateralis

Summary The mitochondrial structure in the brown adipose cells of the golden mantled squirrel, Citellus lateralis, was examined throughout the year in biopsy samples. The mitochondria showed remarkable and apparently reversible changes in size and internal structure related to the physiologic activity of the animal. In the active animal the size of the largest mitochondria was 2.4 m × 1.5 m; during hibernation it increased to 7 m × 2.5 m; and during arousal it reached 11.2m × 5.3 m. The cristae of the mitochondria in the brown adipose cells of the animals in hibernation phase formed loops, whorls and mesh-like interconnections. During the arousal phase they underwent further configurational changes. The most remarkable structure was associated with mitochondria of most unusual proportions which by dissolution gave rise to a new generation. This was a common finding during arousal but did not occur in any other phase of the hibernation cycle. The new mitochondria were virtually indistinguishable from those of brown adipose cells of any active animal.Supported by a grant from the Medical Research Council of CanadaThe author is grateful to colleagues, Dr. G. Dempster and Dr. W.A. Spencer, for many valuable suggestions in the course of the work     

The glyceride fatty acid composition and lipid content of brown and white adipose tissue of the hibernator Citellus lateralis

Glyceride and total phosphatide levels of brown and white fat of Citellus lateralis have been followed throughout the year in biopsy samples. Extraction of the glycerides for fatty acid analysis is described. As much as 20% of the phosphatide of brown fat was found in the upper fat layer of a centrifuged tissue homogenate. This phosphatide appeared to be present as a low-density lipoprotein, and may be associated with the lipid globules of the intact cell. Glyceride and phosphatide levels varied considerably in brown fat, and no particular level was consistently observed to be associated with any part of the hibernation cycle. Fatty acid composition of the glycerides also varied widely. The degree of unsaturation was not related to the hibernation cycle, although there appeared to be a differential utilization of fatty acids during a few weeks prior to spring arousal. A decrease in tissue glyceride levels was observed in both brown and white fat during arousal from hibernation at 2°C, the loss from brown fat being double the loss from white fat.     

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.     

温度对达乌尔黄鼠冬眠的影响

达乌尔黄鼠(Citellus dauricus)是我国北方主要的农牧业以及保健事业上的害鼠之一。冬眠是该鼠的重要特征。黄鼠每年仅生殖一次,因而冬眠期间黄鼠存活率的高低直接影响着它们数量的多少和危害的程度。我们就温度对黄鼠冬眠的影响问题进行了研究,目的是寻求影响黄鼠冬眠后成活的种种因素,为种群动态的研究提供依据。     

Ultrastructural changes in Paneth cells during hibernation in the ground squirrel Spermophilm lateralis

Summary The ultrastructure of Paneth cells from jejuno-ileal segments of the small intestine of the ground squirrel, S. lateralis, was examined under normal euthermic conditions and during the profoundly depressed metabolic conditions of natural hibernation. Paneth cells obtained from hibernating animals gave evidence of markedly reduced activity when compared to Paneth cells from euthermic animals. In hibernating animals, the nuclei were smaller, with less prominent nucleoli and with an increased proportion of heterochromatin. In hibernating animals, the rough endoplasmic reticulum was fragmentary and poorly organized, in contrast to the typical arrangement of concentric lamellae seen in euthermic animals. Although the total number of ribosomes was decreased in hibernating animals, there were proportionally more free ribosomes than in euthermic animals. Paneth cells from hibernating animals also contained a greater number of apical secretory granules which were smaller and more variable in electron density than granules from control animals. These ultrastructural features indicate that during hibernation the Paneth cell is relatively quiescent.Supported by U.S.P.H.S. grants RR 05411 and RR 05583 from the N.I.H.     

The optimal depot fat composition for hibernation by golden-mantled ground squirrels (Spermophilus lateralis)

Golden-mantled ground squirrels (Spermophilus lateralis) are herbivores that hibernate during winter. Although little is known about the nutritional/physiological constraints on hibernation, numerous studies have demonstrated that increasing the amount of linoleic acid (a polyunsaturated fatty acid) in the diet enhances hibernation. This is probably because high linoleic acid diets reduce the melting points of the depot fats produced for hibernation which makes them more metabolizable at low body temperatures. This suggests that a major limitation on hibernation may be obtaining enough linoleic acid in the diet for proper hibernation. In all previous studies, however, the amount of linoleic acid in the diets of free-ranging animals was either not considered, or the range of dietary linoleic acid contents in the experiments was less than that of natural diets. It is thus not known whether the amount of linoleic acid available to hibernators under natural conditions actually limits their torpor patterns. A series of laboratory feeding and hibernation experiments were conducted with S. lateralis and artificial diets with different linoleic acid contents that were either below or above the linoleic acid content of the natural diet. The results demonstrated that when dietary linoleic acid contents are either below or above natural levels, hibernation ability is greatly reduced. Hibernation ability was reduced when the squirrels were maintained on a high linoleic acid diet probably by the production of toxic lipid peroxides in brown adipose tissues. The results indicate that there is an optimal level of dietary linoleic acid for proper hibernation, and this is equal to that of the natural diet. The amount of linoleic acid available in the diet thus does not limit hibernation under normal natural conditions.Abbreviations BAT brown adipose tissue - bm body mass - FA fatty acid - PUFA polyunsaturated fatty acid - T _a ambient temperature - T _b body temperature - WAT white adipose tissue     

冬眠周期长短不同的蒙古黄鼠（Citellus dauricus）...

Adult Mongolian ground squirrels (Citellus dauricus) were kept at 5 degrees C in winter and divided into four experimental groups according to the bout length. The first group was not hibernating until decapitation. The bout length of the second group was between 4-10 days, the third group 11-17 days and the fourth group longer than 20 days. All pineals were sampled at the end of January. Morphometric analytical procedures were used to study the ultrastructure of the distal part of the pineal gland. The statistical results demonstrated that 1) the euthermic animals have larger cross areas of pinealocyte, longer and narrower Golgi apparatus and more number of saccules of each Golgi apparatus (P less than 0.01). But they also have smaller volume density of vaculoes, less lipid droplets and associated vesicles around Golgi apparatus (P less than 0.01). 2) the hibernating animals with variety of bout length had no significant differences in the number of mitochondria, lipid droplets, lysosomes, the size of Golgi apparatus and the cross areas of nucleus and cytoplasm (P greater than 0.05). However, the number and the cross areas of vacuoles were significantly increased with the bout length (P less than 0.01). This might suggest that the bout length was not related to the metabolic activity of pinealocytes in Citellus dauricus and vacuoles might play some important roles in maintenance of individual bout of hibernation in this species.     

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.     

Pineal melatonin: circadian rhythm and variations during the hibernation cycle in the ground squirrel, Spermophilus lateralis

Variations in pineal melatonin content throughout a 24-hour period and during different phases of the hibernation bout cycle were studied in the golden-mantled ground squirrel (Spermophilus lateralis). In addition to pineal melatonin, the circadian variation in the activities of pineal N-acetyltransferase (NAT) and hydroxyindole-O-methyltransferase (HIOMT) were also investigated in summer animals maintained at 22 +/- 2 degrees C, on a light:dark (L:D) schedule of 12:12 hr for 1 month (lights on at 08.00 hr). Pineal glands were collected from six animals in each group at 1200, 1600, 2000, 2400, 0200, 0400, and 0800 hr. Changes in pineal melatonin content during the hibernation bout cycle were investigated in ground squirrels housed at 4 +/- .05 degrees C in relative darkness (1.9-3.4 lux; 10:14 LD). Pineal glands were obtained between 12:00 and 18:00 hr from 30 animals during one of three phases of the cycle (deep hibernation, euthermic interbout, and entrance into hibernation). Pineal melatonin was also measured for comparison in six winter euthermic animals that were housed at 22 +/- 2 degrees C, on a L:D schedule of 10:14 hr. Melatonin was measured in individual pineal glands by radioimmunoassay. The daily melatonin rhythm in S. lateralis was characterized by a marked increase in pineal melatonin during the dark phase, in which peak nighttime values were nearly 20-fold greater than daytime basal levels. The daily rhythm for NAT activity paralleled the changes in melatonin, showing a peak activity at 0200 hr that was 45 times greater than mean daytime values.(ABSTRACT TRUNCATED AT 250 WORDS)