Cricetus Research Articles

Seasonal variations in the daily rhythm of pineal gland and/or circulating melatonin and 5-methoxytryptophol concentrations in the European hamster, Cricetus cricetus

Day-night variations in pineal and/or circulating melatonin and 5-methoxytryptophol (5-ML) concentrations were measured monthly throughout the year in female European hamsters, Cricetus cricetus, maintained under natural conditions. Pronounced seasonal variations in the day-night rhythm of both melatonin and 5-ML were observed. As previously reported for melatonin, the daily rhythm of both methoxyindoles disappeared in spring and early summer, while a clear day-night rhythm occured in autumn, winter, and early spring. The amplitude of the day-night variations appeared to be maximum from October until January. An inverse relationship existed between the rhythms of melatonin and 5-ML.

Characterization of Melatonin Binding Sites in the Pars Tuberalis of the European Hamster

Melatonin binding sites in the pars tuberalis of the European hamster (Cricetus cricetus) have been characterized using the radioligand 2-[(125) I]iodomelatonin. Specific 2-[(125) I]iodomelatonin binding was assessed using radioreceptor studies of pars tuberalis membrane preparations. Saturation studies revealed a single, high affinity site (K(d) 39.8 (± 7.6 SEM) pM and B(max) 4.1 (± 0.5 SEM) fmol/mg protein, n=4). Kinetic experiments showed the 2-[(125) I]iodomelatonin binding to be rapid, saturable and reversible. The K(d) calculated from the dissociation and association rate constants was 19.4 pM. The order of potency of different indoles for inhibition of 2-[(125) I]iodomelatonin binding was 6-chloromelatonin > melatonin > 6-hydroxymelatonin > N-acetylserotonin > 5-methoxytryptophol > serotonin > 5-methoxytryptamine. GTP caused a dose-dependent inhibition of the 2-[(125) I]iodomelatonin binding. A saturation study showed that GTP reduced the number of binding sites by a third without altering their affinity. These results imply the presence of a G-protein-coupled melatonin receptor in the pars tuberalis of sexually active European hamsters.

Pinealectomy and constant illumination increase the density of melatonin binding sites in the pars tuberalis of rodents

We report here the effects of pinealectomy and light exposure on the melatonin receptor density in the pars tuberalis of the rat and the European hamster using quantitative autoradiography. Scatchard analysis revealed that 24 and 72 h of constant light exposure (LL) before sacrifice did not modify the K d value of melatonin for its receptors in rats and European hamsters (about 70 pM). In contrast, the B max value was significantly increased in both species when the animals were kept in constant illumination for 72 h before sacrifice (50%–70% compared with the controls). A similar increase was also observed in rats pinealectomized 3 days before sacrifice and then kept in either constant illumination or in 12L/12D. Pinealectomy or constant light exposure are known to result in a clear decrease in the concentration of circulating melatonin. We demonstrate here that they also result in an increase in the density of melatonin receptors. This could suggest a direct effect of melatonin on its own receptors.

Endogenous, photoperiodic and hormonal control of the body weight rhythm in the female european hamster, Cricetus cricetus

1. 1. Body weight and hibernation rhythms were followed on normal and castrated female European hamsters raised in different conditions of photoperiod and ambient temperature. 2. 2. In the normal females, the photoperiod was more effective than the ambient temperature regarding the control of the body weight rhythm. 3. 3. In the castrated females, testosterone was more effective than oestradiol in suppressing both body weight and hibernation rhythms. 4. 4. In short photoperiod conditions, the existence of endogenous rhythmicity depends upon prior photoperiodic exposure of the animals.

Day and nighttime concentrations of 5-methoxytryptophol and melatonin in the retina and pineal gland from different classes of vertebrates

5-Methoxytryptophol (ML) and melatonin concentrations were determined by radioimmunoassay in the retinae and pineal glands of frogs ( Rana esculenta), chickens ( Gallus domesticus), quails ( Coturnix coturnix), and European hamsters ( Cricetus cricetus), killed in the afternoon (1500–1700 hr) and around midnight (2400-0200 hr). ML was only detectable in significant amounts in the frog retina. In the pineal gland ML levels showed the opposite profile to retinal ML, with measurable levels in the chicken, quail, and hamster and undetectable levels in the frog (<2.0 pg/gland). A significant day/night variation was observed in the bird pineal only, with higher levels occurring during the day. In contrast to ML, the interspecies variation in melatonin content was similar in the retina and pineal, with the highest concentrations occurring in the chicken > quail ⪢ frog > hamster. Significantly higher night levels of melatonin were observed in the retina of the chicken and quail and in the pineal of the chicken, quail, and frog. The ratio of ML:melatonin concentrations in the retina and pineal also showed interspecies variations. In the birds the amount of ML was minimal in comparison with the amount of melatonin (1–4% retina; 0.3–12% pineal). The highest ML:melatonin occurred in the retina of the frog and in the pineal of the European hamster.

The Modulation of the Calcium Transport by Skeletal Muscle Sarcoplasmic Reticulum in the Hibernating European Hamster

Calcium transport of skeletal muscle sarcoplasmic reticulum was comparatively studied in hibernating and summer active European hamsters (Cricetus cricetus L.). Crude homogenates from psoas, soleus and mixed skeletal muscles were used. Protein yield was strongly reduced in the muscle homogenates of hibernating hamsters. The calcium concentration in the muscle of hibernating hamsters was increased to a much higher content than in the serum. In the same animals the maximal rate of calcium uptake and the calcium storing capacity of sarcoplasmic reticulum were augmented by 43% and respectively 17%. Kinetic experiments with various concentrations of free calcium revealed in the hibernating animals higher uptake rates and a lower apparent calcium affinity than in the summer active hamsters. Some shift of calcium uptake rate and calcium affinity similar to that of a fast-twitch muscle was also observed in winter active animals kept at 22 degrees C under natural photoperiod. By contrast, the activity of the calcium dependent ATPase was not increased, suggesting a tighter coupling during hibernation between calcium dependent ATP-hydrolysis and calcium transport. No seasonal difference was observed in the calcium release by KCl-caffeine from calcium loaded vesicles of sarcoplasmic reticulum. Proportion and size of fibre types were studied with cold cross sections from psoas and soleus muscles. An average atrophy of about 25% was found during hibernation in both muscles. Cytochemistry revealed, however, a different reduction of cross area between type-I- and type-II-fibres, which reaches values up to 46% in the type-II-fast-fibres of the slow soleus muscle. Electron microscopy did not show any definite change in the distribution and amount of sarcoplasmic reticulum. The results suggest that during hibernation a modulation in the properties of calcium transport ATPase of sarcoplasmic reticulum occurs to better support the calcium transport function at low temperatures, which in turn warrants the restoration of ion homeostasis in the course of the arousal.

Seasonal change in the temporal organization of wheel-running activity of the European Hamster,Cricetus cricetus

In this paper we demonstrate that a dramatic annual change in the temporal organization of locomotor activity goes hand in hand with the seasonal cycle of reproduction. Activity levels increased when the animals entered reproductive conditions, which occurs naturally in spring and early summer. During the 2-3 months of reproduction, a well-defined activity rhythm was observed. During the rest of the year, the level of activity was dramatically reduced and almost no rhythmic organization was detected. The question arising from these observations is whether the loss of temporal organization reflects a weakening or arrhythmia of the underlying pacemaker or whether it is due to an uncoupling of the overt activity rhythm from the central clock.

Colon adenocarcinomas in European hamsters after application of N-nitroso-bis 2-oxypropyl-amine

In the European hamster (EH) weekly subcutaneous (s.c.) injections of N-nitrosobis-(2-oxypropyl)-amine (BOP) (LD50, males: 174 mg/kg, body weight (b.w.), females: 118 mg/kg b.w.) induced adenocarcinomas of the colon in 77% (1/10 LD50), 70% (1/20 LD50) and 87% (1/40 LD50) of the treated animals (combined incidence for both sexes (c.i.)). Cholangiocellular carcinomas, the second most common type of tumor were produced in a dose-dependent manner. Furthermore tumors were found in the respiratory tract, urinary tract the integumentum system and the exocrine pancreas. The presented data show a difference between the BOP-induced tumor spectrum in European hamsters and that of Syrian hamsters [5,8,11]. The high incidence of colon adenocarcinomas may provide a further model of colon carcinogenesis.

Seasonal changes in vasopressin in the brain of the garden dormouse (Eliomys quercinus L.)

The distribution of vasopressin in the brain of the garden dormouse (Eliomys quercinus L.) was examined by immunocytochemistry at different times of the year. In spring-summer, sexual dimorphism in the density of vasopressin labeling was observed in several areas of the brain. In these regions, such as the lateral septum and the nucleus of the vertical limb of the diagonal band of Broca, male garden dormice showed more vasopressin immunoreactivity than their female counterparts. In autumn-winter, at the time of hibernation, vasopressin was undetectable in the sexually dimorphically innervated brain regions in males as well as females. In early spring, there was large variation in vasopressin staining in the male brain, whereas the female brain was consistently lacking in vasopressin labeling. In brain regions that exhibited no sexually dimorphic innervation in the summer, vasopressin labeling remained the same throughout the year. The difference in the amount of vasopressin immunoreactivity in males in summer and winter correlated significantly with differences in testes weight. In early spring, because of interindividual variations in the start of sexual activation, testes size does not correlate with the density of vasopressin immunoreactivity. Similar seasonal variations in density of vasopressin labeling in the brain were also observed in the European hamster (Cricetus cricetus). In this animal, central vasopressin infusion during the winter prevents hibernation. The presence of a similar pattern of changing vasopressin content in another hibernator, the garden dormouse, suggests an important role for this neuropeptide in seasonal functions.(ABSTRACT TRUNCATED AT 250 WORDS)

“Synaptic” Ribbons and Spherules Lacking in the Pineal Gland of the European Hamster Appear After Ganglionectomy

"Synaptic" ribbons and spherules are typical organelles of the mammalian pinealocytes, that present quantitative day-night variations parallel to pineal melatonin levels. The European hamster is a wild photoperiodic mammal whose pineal melatonin concentrations do not vary during the 24 hr light-dark cycle. The aim of this study was thus to see if a rhythmic variation in synaptic structures was nevertheless present in this species. It was found that, in contrast to all of the photoperiodic species studied to date, the European hamster pinealocyte contains no ribbons, and virtually no spherules. Moreover, constant administration of melatonin does not result in the occurrence of these organelles; nevertheless, the pinealocytes have the potentiality to produce spherules and, to a lesser extent, ribbons, as they are observed in ganglionectomized animals and in the deep pineal of some hamsters after ablation of the superficial part of the gland. The formation of pineal synaptic structures, normally lacking in the European hamster, thus seems directly related to the noradrenergic innervation of the gland.

Characteristic of spontaneous intraperitoneal cysts in Golden hamsters and European hamsters

Epidemiological study of 340 Golden hamsters and 200 European hamsters bred as laboratory animals and necropsied between 1985 and 1989 in our facility (affiliation 2) revealed high incidence of spontaneous cysts. The incidence was in general higher in European (26 to 62%) than Golden hamsters (0 to 15%). The cysts, of different sizes, were localized first of all in the liver, and secondly (in European hamsters only), in the caecum wall. Light microscopic and electron microscopic examinations showed that the cysts are lined by flattened to cuboidal epithelial cells which, on their surface, have microvilli of different lengths and underneath a continuous basement membrane. These examinations lead further to the interpretation of the liver cysts as cystic distensions of the bile ducts. The cysts in the caecum wall could be interpreted as dilatations of the lymphatic vessels. As to the etiology, which remains unclear, several hypotheses are discussed.

Long-Term Lithium Treatment Does Not Suppress Hibernation in European Hamsters

European hamsters were fed LiCl-supplemented food for a long time before, during and after the hibernating season. Long-term administration of LiCl does not suppress hibernation, which occurs normally during the first part of the experiment. Moreover lithium-treated hibernating hamsters tolerate very high plasma lithium levels. This tolerance is not explained. The results are discussed in relation with the recent theories on the similarities between depression, seasonal affective disorder and hibernation.

Central vasopressin infusion prevents hibernation in the European hamster (Cricetus cricetus).

The amount of immunocytochemically detectable vasopressin in the brain of the European hamster (Cricetus cricetus) shows a seasonal variation; i.e., dense vasopressin immunoreactivity is present in the lateral septum during summer but is absent in autumn and winter [Buijs, R. M., Pévet, P., Masson-Pévet, M., Pool, C. W., De Vries, G. J., Canguilhem, B. & Vivien-Roels, B. (1986) Brain Res. 371, 193-196]. In the winter period the European hamster hibernates. Since vasopressin in the lateral septum is known to be involved in the control of body temperature, we investigated whether infusion of vasopressin in the lateral septum during autumn-winter could influence hypothermic patterns normally seen in hibernating animals. Hamsters whose lateral septum was infused with vasopressin showed almost no periods of hypothermia, whereas hamsters treated with control infusions displayed a normal hibernation pattern. The results indicate that persistence of vasopressin release in the lateral septum of the European hamster during winter can prevent hibernation.

Characterization of some previously unclassified Pasteurellaceae isolated from hamsters.

Bacteria isolated from purulent processes on the jaws of European hamsters (Cricetus cricetus) and from intestinal inflammatory processes in Syrian hamsters (Mesocricetus auratus), bred as laboratory animals have been shown to be phenotypically similar but not identical with Pasteurella pneumotropica. Deoxyribonucleic acid (DNA)-DNA hybridization studies indicate that with one exception, the strains represent two new species of the family Pasteurellaceae. In the absence of a close genomic relatedness to members of the genera Actinobacillus or Pasteurella or allied organisms, however, the two new taxa are described without any formal designation. The one exception was identified as Actinobacillus capsulatus, a species not previously isolated from hamsters.

Melatonin, Serotonin, 5‐Hydroxyindole‐3‐Acetic Acid and N‐Acetyltransferase in the Pineal of the European Hamster (Cricetus cricetus) Kept Under Natural Environmental Conditions: Lack of a Day/Night Rhythm in Melatonin Formation in Spring and Early Summer

In female European hamsters killed in spring and early summer, pineal melatonin content exhibited no day/night rhythm. Absolute levels measured were relatively low, being on the order of daytime levels detected in other hamster species. An absence of day/night changes in the activity of N-acetyltransferase was also observed. However, a marked rhythm in pineal serotonin (5-HT) was found, an abrupt large increase being observed at the beginning of the light period. The day/night rhythm of pineal 5-HIAA content is similar to that of 5-HT. This absence of rhythm in pineal melatonin formation might mean that in the European hamster it is not melatonin but another substance that is of importance in photoperiodism. An absence of melatonin rhythm, however, could also be simply a peculiar pattern of melatonin production observed at a given period of the year. In this case, melatonin would be able to transduce photoperiodic information in the European hamster, as in other photoperiodic species.

Thermotelemetric study on the hibernation of a common hamster, Cricetus cricetus (Linnaeus, 1758), under natural circumstances

By means of radio-thermotelemetry a study was made of the thermoregulatory patterns during hibernation of a common hamster, Cricetus cricetus (L., 1758) under natural conditions.

Adaptation of intestinal enzymes to seasonal and dietary changes in a hibernator: the European hamster (Cricetus cricetus).

Effects of diet, hibernation and seasonal variations on hydrolase activities were determined in mucosa and purified brush border membranes of the small intestine of European hamsters. Wild hamsters captured in April and fed for several weeks with an equilibrated laboratory chow (20% protein, 50% carbohydrates) exhibited a rise in disaccharidase activities (sucrase, isomaltase, lactase) but no changes in aminopeptidase N activity. During deep hibernation, in contrast to sucrase and isomaltase activities which showed only minor changes, lactase activity was significantly enhanced along the jejunoileum, and aminopeptidase N activity was maximum in the ileum. After a short period (48 h) of wakefulness and feeding following 10 days of starvation during the hibernation period, the activities of the disaccharidases and of aminopeptidase N returned to values measured in active animals. In contrast to the nutritional state, which has an important impact on the activities of intestinal enzymes, season has little effect on the intestine of the active animal under a controlled environment. The pattern of enzyme activities which occurs along the small intestine in the hibernating animal may be a prerequisite for optimum digestion during the short phases of waking during the hibernation period of the European hamster.

Photoperiodic regulation of body mass, food intake, hibernation, and reproduction in intact and castrated male European hamsters, Cricetus cricetus.

A group of sexually active male European hamsters were raised either in short-photoperiod conditions (SP; LD 8:16) or in long-photoperiod conditions (LP; LD 16:8) from their capture at the end of the hibernation period. Another group of hamsters was castrated in April and gonadectomized animals were maintained in SP and cold (7 degrees C) or in a succession of SP and LP plus cold. Another group, castrated in May or in September and raised in LP conditions, was transferred in September to SP conditions and cold. 1. Normal hamsters raised in continuous SP or LP apparently did not show signs of rhythmic behavior, except possibly in gonadal activity. 2. Body weight increased continuously, plasma testosterone levels oscillated between 1.5 and 2.5 ng/ml, and animals raised in SP and in cold did not enter hibernation. 3. Similar results were also found in castrated animals kept in SP conditions and cold. 4. The sequence LP-SP induced a decrease in food intake and body weight and a decrease in plasma testosterone levels and triggered entry into hibernation in both intact and castrated animals. 5. After 6 months continuously in SP and with exposure to cold spontaneous recrudescence in food intake and body weight occurred and hibernation ended in both intact and castrated animals. 6. In normal animals a spontaneous increase in plasma testosterone levels was observed. 7. In both normal and gonadectomized animals the phase of refractoriness could be broken by exposure to LP conditions. 8. The critical photoperiod lies between 15 and 15.5 h. These results demonstrate that the European hamster is a photoperiodic species.(ABSTRACT TRUNCATED AT 250 WORDS)

Time-course of blood acid-base state during arousal from hibernation in the European hamster.

1. Arterial blood was sampled at 15 min-intervals in European hamsters Cricetus cricetus fitted with indwelling catheters, from deep hibernation to full arousal. Temperature-corrected pH and PCO2, respectively pH* and P*CO2, were directly measured at 37 degrees C. 2. Deep hibernation corresponded to a respiratory acidosis: pH* = 7.01 +/- 0.01 (mean +/- SE), P*CO2 = 160 +/- 4 Torr (n = 9 animals). 3. Three periods could be distinguished in the arousal: (i) a period of hyperventilation (28 +/- 5 min), in which P*CO2 was reduced to 79 +/- 4 Torr, while cheek pouch temperature increased only by 0.9 +/- 0.2 degrees C; (ii) a period of metabolic acidification by lactate accumulation (84 +/- 6 min), corresponding to the period of peak thermogenesis; (iii) a progressive return to euthermic conditions (104 +/- 10 min), by simultaneous respiratory and metabolic alkalinization. 4. Over 60% of the blood CO2 stores accumulated at the beginning of the hibernation bout were released by hyperventilation during the first period, prior to the full development of thermogenesis. This is in agreement with the hypothesis of an inhibitory role of the respiratory acidosis in hibernation.

Influence of photoperiod and gonadal steroids on hibernation in the European hamster.

Torpor was monitored daily in adult male and female European hamsters (Cricetus cricetus) induced to hibernate by exposure to a cold environment (6 degrees C). The effect of photoperiodic manipulations or administration of exogenous gonadal steroids was examined in gonadectomized or intact hamsters. 1. Gonadal regression occurred in all short day, but only in some long day, cold-exposed hamsters. Entry into hibernation was not observed until reproductive regression had occurred. Thus, gonadal atrophy appears to be a necessary precondition for hibernation. 2. Castrated hamsters in the short day cold condition showed a significantly greater incidence of torpor than those in the long day cold condition. Hence, photoperiod affected torpor independently of its effect on the gonadal cycle. 3. Testosterone, when administered via silastic capsules at near physiological levels, completely inhibited torpor in gonadectomized male and female hamsters hibernating in the short day cold condition. 4. In ovariectomized females, torpor was unaffected by progesterone treatment, but partially inhibited by estradiol. A greater inhibition of torpor was observed when estradiol-primed females were administered both estradiol and progesterone simultaneously. Thus, the effect of both hormones may be functionally comparable to that of the single testicular hormone. 5. Estradiol inhibited torpor to a greater extent in intact and ovariectomized female hamsters hibernating in long days than those in short days, suggesting an effect of photoperiod on responsiveness to estradiol. These results indicate an inverse relationship between the gonadal and hibernation cycles, and a probable role for gonadal steroids to influence the timing of the hibernation season. However, non-gonadal factors must also be involved in controlling hibernation, since photoperiod affected the incidence of torpor in gonadectomized animals and because hamsters were able to terminate hibernation in the absence of gonadal hormones.