Cricetus Research Articles

Non-gonadal mediated effect of photoperiod on hibernation and body weight cycles of the European hamster

1. 1. Sexually active male European hamsters raised under short photoperiod display high levels of plasma testosterone, high body weight and do not hibernate. 2. 2. Castrated males in May, raised under the same conditions, do not hibernate and do not present the physiological body weight rhythm. 3. 3. Normal and castrated animals under natural conditions enter hibernation and display a normal body weight rhythm. 4. 4. Normal and castrated animals not submitted to the natural succession of long and short days do not enter hibernation. 5. 5. Photoperiod directly controls body weight and hibernation without gonadal interactions.

PH-temperature interactions on protein function and hibernation: GDP binding to brown adipose tissue mitochondria.

1. [3H]GDP binding to the uncoupling protein of brown adipose tissue was determined on mitochondria isolated from hibernating European hamsters, at two temperatures, 35 and 15 degrees C, and four values of 25pH (pH corrected to 25 degrees C): 6.4, 6.8, 7.2 and 7.6, encompassing the physiological range of pH. Buffer composition was adjusted to get the same pH-temperature relationship as for mammalian blood, in which this relationship is mainly determined by protein imidazole buffers. 2. The maximal binding capacity was independent both of temperature and pH. The dissociation constant KD was highly pH-dependent, but was independent of temperature when 25pH was held constant. Under these conditions, the uncoupling protein thus fully conserves its regulatory properties over the temperature range studied (eurythermal adaptation). 3. The temperature coefficient of the apparent pK' for the pH effect (-0.012 +/- 0.004) differed significantly from that of GDP terminal phosphoryl group, but not from that of blood protein imidazole buffer groups, in good agreement with the imidazole alphastat theory. 4. The results indicate that GDP reaction with the protein involves an electrostatic binding with a titratable group of the protein, probably a sulfhydryl. 5. pH modulation of the uncoupling of brown adipose tissue mitochondria probably permits a reversible control of thermogenesis in the hibernation cycle, heat dissipation being inhibited by respiratory acidosis in deep hibernation, but facilitated by the hyperventilation of arousal.

Effect of pinealectomy and a constant high level of circulating melatonin or of 5-methoxytryptamine on the vasopressinergic innervation in the brain of the European hamster (Cricetus cricetus, L).

In the European hamster (Cricetus cricetus,L.) pinealectomy as well as a constant high level of either circulating melatonin or 5-methoxytryptamine induced marked changes in the immunocytochemically demonstrable central vasopressinergic innervation. When compared to control animals, a drastic decrease of AVP-immunoreaction was observed in the diagonal band of Broca, the lateral septum, the medial amygdala and the ventral hypothalamus. The results obtained suggest that part of the central vasopressinergic innervation is involved in pineal dependent seasonal functioning of the animal.

Induction of malignant peripheral nerve sheath tumors in European hamsters with 1,1-dimethylhydrazine (UDMH)

A rate of up to 43% of malignant peripheral nerve sheath tumors (PNST) was induced in European hamsters (EH) after weekly s.c. administration of 1,1-dimethylhydrazine (UDMH). The overall neoplastic response in the treated EH was also elevated as compared to the untreated controls. Histologically, the malignant PNST were neurofibrosarcomas and melanotic as well as unpigmented schwannomas. The occurrence of melanotic schwannomas is briefly discussed with regard to the histogenesis of this rare tumor type.

Brain serotonin levels and metabolism in the non-hibernating bulbectomized european hamster

Serotonin levels and turnover were measured in different brains areas of full bulbectomized and partially bulbectomized European hamsters and their controls. Full bulbectomized hamsters did not hibernate and ate more than the two other groups in which hibernation patterns were similar. The levels of serotonin were of the same magnitude in the three groups. The turnover rates were slower in amygdala and hypothalamus in the full lesioned animals. These results were discussed for their implications in the mechanism of entrance into hibernation.

Does serotonin play a role in entrance into hibernation?

To study the role of brain serotonin in entrance into hibernation, intraventricular injections of 5,7-dihydroxytryptamine, electrolytic lesions of small parts of the median raphe nucleus, and chemical lesions of the same nucleus were undertaken on the European hamster in winter. All the lesions led to a variable decrease of serotonin levels in all parts of the brain areas examined. However, hibernation was suppressed only in those animals whose serotonergic neurons were destroyed in a small anterior part of the median raphe nucleus. Electrolytic lesions as well as chemical lesions in the other parts of the median raphe nucleus or the 5,7-dihydroxytryptamine injections into lateral ventricles do not prevent hibernation. These data suggest that in the European hamster only a specific group of serotonergic neurons of the median raphe nucleus are involved in the process of entrance into hibernation.

Fluorescence anisotropy of kidney lipids and membranes of a hibernating mammal

The fluorescence anisotropy of lipids and membranes isolated from kidneys of European hamsters ( Cricetus cricetus L.) has been estimated using 1.6-diphenyl-1.3.5-hexatriene as a probe. We have compared in this study the results obtained for two critical periods for a hibernator: winter (torpid state), and summer (active state). The differences were of very low magnitude. A slight increase in anisotropy was noticed in the kidney lipids and microsomal membrane preparations from torpid animals. In contrast, a small decrease in anisotropy was observed in the microsomal lipid extracts of torpid animals. A difference in triglyceride content of winter and summer total kidney lipids was detected, as well as a difference in microsomal protein content between winter and summer membrane preparations. It is hypothesized that the latter observations may explain why the behavior of kidney total lipids and microsomal preparations were different from that presented by kidney microsomal lipids in respect to fluorescence anisotropy. Therefore, only a little, if any, homeoviscous adaptation is exhibited by kidney membranes during hibernation of this mammal.

Seasonal variation in vasopressin innervation in the brain of the European hamster ( Cricetus cricetus)

Using immunocytochemistry, vasopressin innervation was determined in the brain of the European hamster ( Cricetus cricetus) during different seasons. It was found that the spring period coincides with a dense vasopressin innervation in many brain regions in the male hamster, and lower vasopressin fibre density in some brain regions in the female hamster. In autumn just before hibernation an almost complete disapperance of vasopressin innervation is noted in those brain regions that are sexually dimorphically innervated in spring. These results suggest that vasopressin activity in certain areas of the brain might be required for some-seasonal functions to find expression.

Cemento-fibrous dysplasia of the periodontal membrane (studies of the European hamster maxillary incisor).

The periodontal membrane of European hamster maxillary incisors showed histologic changes consisting of an irregularly orientated, less vascularized connective tissue which included abundant cementicle-like structures. The changes were multifocal and bilateral, growing towards the alveolar bone (Grade 1), causing atrophy of the alveolar bone due to compression (Grade 2) and reaching the periosteal membranes (Grade 3). In a few animals, the lesions were seen after one year. They were seen in 80% of hamsters more than 2 years old. Carcinogenic exposure did not alter the latency and incidence of the alterations. The lesions were thought to be a spontaneously occurring disease representing a nodular cemento-fibrous dysplasia of the periodontium. As, morphologically, no exact attribution to other odontogenic or mesenchymal growth could be made, the entity of this periodontal lesion was considered. Although the changes observed in the periodontal membrane of the maxillary incisors of the European hamster were not exactly comparable to odontogenic cemental lesions in man, they may serve as a model to further clarify the nature of fibro-osseous lesions.

Circannual variations of GABA content in cytosolic and crude synaptosomal fractions in some brain areas of the european hamster

In the European hamster, Cricetus cricetus, a common hibernator, over a year, the γ-aminobutyric acid (GABA) content has been followed, in the cytosolic and crude synaptosomal fractions of the olfactocy bulbs, hypothalamus and cerebellum. In these 3 areas, the GABA content shows circannual variations of endogenous origin: in this period, in both fractions two peaks can be observed, at the beginning of spring and in autumn. These circannual variations do not follow the circannual variation of food intake or body weight.

Intracellular pH in hibernation and respiratory acidosis in the European hamster.

Intracellular pH was determined (DMO method) in European hamsters, in the spontaneously-occurring respiratory acidosis of hibernation, in hypercapnia due to breathing 12% CO2 in air in euthermy in spring, and in euthermicnormocapnic controls. From euthermy to hibernation, the temperature coefficient of pH was lowest in blood plasma and brain, intermediate in striated muscles (thigh muscles and diaphragm), and highest in heart and liver (Fig. 1). Correspondingly, the estimated dissociation ratio of the protein imidazole buffer groups, alpha Im, decreased markedly in plasma and brain, denoting an acid titration, but varied little in liver and heart. Striated muscles were intermediate (Fig. 2). Like in other mammals, intracellular responses to short-term euthermic respiratory acidosis were characterized by a partial metabolic compensation in the brain and a small metabolic acidification in striated muscles. In hibernation, a powerful metabolic compensation took place in liver and heart, nearly restoring alpha Im, but none occurred in brain (Figs. 3 to 5). The existence of an intracellular acidosis in brain and striated muscles during hibernation is in keeping with an inhibitory role of acidosis, whereas the homeostasis of intracellular alpha Im in liver and heart would subserve the eurythermal functioning of metabolic regulations in these organs, like in most organs of ectotherms.

Fluorescence polarization study of lipids and membranes prepared from brain hemispheres of a hibernating mammal

The physical behavior of total lipids, microsomes and microsomal lipids prepared from brain hemispheres of European Hamsters ( Cricetus cricetus ) was approached by the measure of the fluorescence polarization of the probe 1,6-diphenyl 1,3,5-hexatriene. We compare in this study the results obtained for two critical periods for a hibernator: winter (torpid state) and summer (active state). An increase in fluidity was noticed in the winter lipid and membrane preparations. The difference was however of very low magnitude, suggesting that only the microenvironment of some proteins was involved, rather than the bulk membrane fluidity.

Skin tumor formation in the European hamster (Cricetus cricetus L.) after topical initiation with 7,12-dimethylbenz[a]anthracene (DMBA) and promotion with 12-O-tetradecanoylphorbol-13-acetate (TPA).

Initiation with the carcinogen 7,12-dimethylbenz[a]anthracene followed by promotion with the hyperplasiogenic phorbol ester 12-O-tetradecanoylphorbol-13-acetate carried out on the dorsal skin of European hamsters (Cricetus cricetus L.) led to the formation of a broad spectrum of skin tumors in terms of a two-stage principle. Tumor formation involved the epidermis and its appendages, the connective tissue, and the vascular and pigmentary system. With regard to the sensitivity to initiation with DMBA alone and initiation with DMBA and promotion with TPA the European hamster occupies a special position since all of the DMBA-TPA sensitive two-stage target organs known from the mouse, rabbit, Syrian golden hamster and rat are combined in this animal.

The effect of cigarette smoke exposure in European hamsters

The effects of 2 types of research cigarettes, differing in their total smoke delivery and condensate were examined. Two groups of European hamsters were exposed in a smoking chamber to the cigarette smoke of both types of cigarettes for 130 weeks. Exposure related alterations were found in the respiratory tract and forestomach. However, smoke exposure over this period had no effect on mortality and led to no neoplastic response.

Hyperphagia and obesity after olfactory bulbectomy performed at different times of the year in the European hamster

Olfactory bulbectomy was performed on wild male European hamsters at different phases of their circannual body weight rhythm. Olfactory bulbectomy was always followed by an immediate hyperphagia the magnitude of which varied with the time of the year it was performed. The bulbectomy did not affect the phase of the circannual body weight rhythm, although in certain cases the rhythm is attenuated or apparently phase-shifted. Hyperphagia was delayed by food restriction but reappeared when animals were placed on ad lib food. The possible role of olfactory bulbs in the regulation of body weight, and the possibility that the maintenance expenditure of the bulbectomized animals is higher than that of the controls are discussed.

Changes in lipid composition of the brain cellular membranes of an hibernating mammal during its circannual rhythm

The lipid composition of whole brain hemispheres and subcellular fractions of European Hamsters ( Cricetus cricetus) was investigated at four different periods of the year. 1. 1. No difference was observed in winter between hibernating animals and active animals awake for 24 hr. 2. 2. A slight increase of cholesterol/phospholipid molar ratio was observed in winter. 3. 3. A slight increase of the ratio ethanolamine phosphoglycerides/choline phosphoglycerides was observed in summer and autumn. 4. 4. Some changes in sugar moieties proportions of gangliosides were observed with a tendency of increased polysialylation in winter. 5. 5. An increase of docosahexaenoic acid was observed in summer, while a slight increase of linoleic acid and of the monounsaturated fatty acids was observed in winter. These changes were mainly exhibited in the synaptosomal fraction. All the changes observed were of very small magnitude and might not be sufficient for the maintenance of a fluid state of membranes during hibernation.

The carcinogenic effect of nitrosomethyldodecylamine in European hamsters

Laboratory-bred European hamsters received nitrosomethyldodecylamine (NMDA) subcutaneously in olive oil once weekly for life. The animals showed mainly mucoepidermoid carcinomas of the lung, carcinomas of the urinary bladder and squamous cell carcinomas and sarcomas at the injection site. The tumour incidence was 90% in males and 70% in females, while the average tumour latency was 32 ± 6 weeks for both sexes. Males had an average survival time of 29 ± 17 weeks and females 24 ± 19 weeks.

The carcinogenic effect of 1,1-diethyl-3-methyl-3-nitrosourea in European hamsters

Laboratory-bred European hamsters received subcutaneous injections of 1,1-diethyl-3-methyl-3-nitrosourea once weekly for life. The animals developed mainly squamous cell carcinomas of the nasal and oral cavities and malignant sarcomas (schwannomas) of the glandular stomach. The average tumour latency was shorter in females (24 weeks) than in males (28 weeks), while tumour incidence was 80% for both sexes.

Effects of bulbectomy on hibernation, food intake and body weight in the european hamster, Cricetus cricetus

Bulbectomy was performed on European male wild hamsters in autumn, habitual phase of weight decline and entrance into hibernation. Total bulbectomy suppresses both nest building behavior and hibernation, and is followed by an immediate increase in food intake and obesity. The body weight curve of totally bulbectomized animals is in opposition of phase with that of the controls. Incomplete bulbectomy suppresses nest building behavior but hibernation is present with a diminution of periodic arousals. Hyperphagia starts in spring after the terminal arousal; it is similar to that of the total bulbectomized animals. Anosmic animals do not differ from the control animals.

A morphometric study of the pulmonary Clara cell in normal and nitrosoheptamethyleneimine-treated European hamsters

Previous studies have identified the bronchial Clara cell as the progenitor of the lung tumors induced in European hamsters by nitrosoheptamethyleneimine (NHMI). Using stereological methods, we compared the ultrastructure of Clara cells from untreated animals and lung tumor cells, induced by NHMI, in the European hamster. The composition and volume of the cytoplasm was significantly altered in the tumor cells whereas the nuclei did not show any measurable changes in size or structure when compared with the controls.