Cricetus Research Articles

The somatostatin system of the brain and hibernation in the European hamster (Cricetus cricetus).

The depression of physiological processes characteristic of mammalian hibernation is precisely regulated by the central nervous system, especially by the neuropeptidergic apparatus of the hypothalamus. Because of inhibitory influences on neuronal circuits within the brain and suppressive effects on the metabolism via the endocrine axis, somatostatin has been implicated in the regulation of hibernation. The somatostatin system of the brain was investigated with immunocytochemistry, in situ hybridization, and radioimmunoassays in euthermic summer, euthermic winter, and hibernating European hamsters (Cricetus cricetus). Numerous somatostatin-immunoreactive perikarya were observed in the periventricular hypothalamic nucleus. The striatum, amygdala, and cortex contained only scattered immunoreactive perikarya. These entities also contained immunoreactive fiber profiles, although the highest density of immunoreactive fibers was found in the median eminence. Immunocytochemistry and radioimmunoassays showed that the number of somatostatin-immunoreactive perikarya and fibers and the content of somatostatin in the hypothalamus and the median eminence was conspicuously lower in euthermic winter animals than in euthermic summer animals. This decrease was more pronounced in hibernating specimens. In situ hybridization also demonstrated a decrease in the expression and synthesis rate of somatostatin in euthermic winter animals; again, this was even more dramatic in hibernating hamsters. These changes were less pronounced or non-significant in the extrahypothalamic somatostatin-immunoreactive perikarya and fiber systems, as shown by immunocytochemistry and radioimmunoassay, respectively.

Environmental Control of the Seasonal Variations in the Daily Pattern of Melatonin Synthesis in the European Hamster,Cricetus cricetus

Nocturnal patterns of pineal melatonin concentrations were measured at hourly intervals in the European hamster,Cricetus cricetus,maintained under different natural or experimental environmental conditions. There were pronounced variations in the night peak of pineal melatonin both in the duration and the amplitude of the melatonin peak and in the onset and decline of melatonin synthesis. The duration of the melatonin peak increased proportionnally with increased dark period. The amplitude increased abruptly from LD 16/8 to LD 15/9 and remained constant in all other photoperiods. The onset of synthesis started 6:00 hours after the onset of darkness in LD 16/8, 15/9, and 14/10, while it started 4:00 hours after dark onset in shorter photoperiods (LD 12/12 and 10/14). This result is opposite to that observed in the rat. The decline of synthesis was delayed as darkness increased and was directly related to lights on in long photoperiods, while it was endogenous in short photoperiods. Temperature, under a long photoperiod, also seems to be implicated in the regulation of the amplitude of the melatonin peak.

Adrenergic signal transduction in the brainstem of euthermic and hibernating European hamsters.

Adrenergic signal transduction in the brainstem of euthermic and hibernating European hamsters.

The density of neuropeptide Y (NPY)-containing nerve fibres in the pineal gland of the European hamster ( Cricetus cricetus) exhibits an annual variation

The density of neuropeptide Y (NPY)-containing nerve fibres in the pineal gland of the European hamster ( Cricetus cricetus) exhibits an annual variation

In Syrian and European hamsters, the duration of sensitive phase to light of the suprachiasmatic nuclei depends on the photoperiod

Kight induction of the expression of Fos protein in the suprachiasmatic nuclei was used to investigate the photosensitive state of the clock in Syrian and European hamster kept under different photoperiods. We observed that the duration of the photosensitive phase is variable and tied to the length of the night. A maximal extension has been determined in both species studied. Finally, a 4 h lengthening of the phase of photosensitivity takes approximately 3 weeks, while 3 days only are needed for its shortening.

Diurnal and seasonal changes in sympathetic signal transduction in cardiac ventricles of European hamsters.

This investigation of the relationship between cardiac beta-adrenoceptors and adenosine 3',5'-cyclic monophosphate (cAMP) formation in cardiac ventricles of the nocturnally active European hamster both during euthermia under a 12:12-h dark-light cycle and during hibernation under constant-darkness conditions showed that neither the densities, affinities, nor distribution of the beta 1- and beta 2-receptor subtypes differed between the dark phase, light phase, and hibernation. Basal formation of cAMP by the cardiac adenylyl cyclase of euthermic hamsters was higher in ventricles obtained at night [core temperature (Tcore) = 37.8 degrees C] than in ventricles obtained during the day (Tcore = 36.4 degrees C). Basal formation of cAMP was also significantly lower in hibernating hamsters (Tcore = 7.0 degrees C) than in euthermic hamsters. When adenylyl cyclase activity was stimulated by isoprenaline, guanylylimidodiphosphate [Gpp(NH)p], or forskolin, the rank order of potency was the same in euthermic hamsters and hibernating hamsters: isoprenaline < Gpp(NH)p < forskolin. Functional competition curves indicated that in the euthermic hamsters beta 1-receptors were responsible for 67% of the response to isoprenaline at night and 62% of the response during the day. In hibernating hamsters, in contrast, most of the response to isoprenaline (58%) was mediated via beta 2-receptors. This shift in the relative importance of the receptor subtypes may facilitate arousal from hibernation by making the heart more sensitive to circulating epinephrine.

The neuroendocrine system in hibernating mammals: present knowledge and open questions

The present review describes the distribution and the function-dependent reactivity pattern of those peptidergic and aminergic components of the neuroendocrine system of hibernating mammals that have been studied by histological, pharmacological and physiological techniques. Particular attention has been paid to the intrinsic connectivity of the peptidergic apparatus and its input systems. Since the reactivity patterns of the neuroendocrine system show remarkable fluctuations in relation to the various stages of hibernation and euthermia, these fluctuations have been analyzed with respect to (1) their causative role in the regulation of hibernation and (2) their secondary response to physiological changes during hibernation. The author's investigations described in this review have mainly been performed in European hedgehogs (Erinaceus europaeus), European and golden hamsters (Cricetus cricetus, Mesocricetus auratus), dormice (Glis glis), and in Richardson's and Columbian ground squirrels (Spermophilus richardsonii, Spermophilus columbianus), by the use of light- and electron-microscopic immunocytochemistry and histochemistry, in situ hybridization, radioimmunoassays and stereotaxically guided application techniques. These experiments were also performed in hypothermic animals. The (partially published) results obtained by the author and his associates are reviewed with reference to the body of evidence found in the recent literature. With respect to their reactivity patterns, several neuropeptide and transmitter systems can be regarded as candidates for control systems of hibernation. Neuronal complexes immunoreactive for endogenous opiates, in particular enkephalin, and also for vasopressin, somatostatin, substance P, corticotropin-releasing factor and serotonin are probably involved in the neuroendocrine control of hibernation.

Seasonal and daily rhythms of body temperature in the European hamster (Cricetus cricetus) under semi-natural conditions.

Body temperature of five European hamsters exposed to semi-natural environmental conditions at 47 degrees N in Southern Germany was recorded over a 1.5-year period using intraperitoneal temperature-sensitive radio transmitters. The animals showed pronounced seasonal changes in body weight and reproductive status. Euthermic body temperature changed significantly throughout the year reaching its maximum of 37.9 +/- 0.2 degrees C in April and its minimum of 36.1 +/- 0.4 degrees C in December. Between November and March the hamsters showed regular bouts of hibernation and a few bouts of shallow torpor. During hibernation body temperature correlated with ambient temperature. Monthly means of body temperature during hibernation were highest in November (7.9 +/- 0.8 degrees C) and March (8.2 +/- 0.5 degrees C) and lowest in January (4.4 +/- 0.7 degrees C). Using periodogram analysis methods, a clear diurnal rhythm of euthermic body temperature could be detected between March and August, whereas no such rhythm could be found during fall and winter. During hibernation bouts, no circadian rhythmicity was evident for body temperature apart from body temperature following ambient temperature with a time lag of 3-5 h. On average, hibernation bouts lasted 104.2 +/- 23.8 h with body temperature falling to 6.0 +/- 1.7 degrees C. When entering hibernation the animals cooled at a rate of -0.8 +/- 0.2 degrees C.h-1; when arousing from hibernation they warmed at a rate of 9.9 +/- 2.4 degrees C.h-1. Warming rates were significantly lower in November and December than in January and February, and correlated with ambient temperature (r = -0.46, P < 0.01) and hibernating body temperature (r = -0.47, P < 0.01). Entry into hibernation occurred mostly in the middle of the night (mean time of day 0148 hours +/- 3.4 h), while spontaneous arousals were widely scattered across day and night. For all animals regression analysis revealed free-running circadian rhythms for the timing of arousal. These results suggest that entry into hibernation is either induced by environmental effects or by a circadian clock with a period of 24 h, whereas arousal from hibernation is controlled by an endogenous rhythm with a period different from 24 h.

The presence of opioidergic pinealocytes in the pineal gland of the European hamster (Cricetus cricetus): an immunocytochemical study

By use of antibodies raised against leu-enkephalin and met-enkephalin immunoreactive, opioidergic bi- and multipolar cells were demonstrated in the pineal gland of the European hamster. Ultrastructural analysis of these opioidergic cells revealed them to be pinealocytes. Processes emerged from the cell bodies and terminated in club-shaped swellings containing many small clear and some larger granular vesicles. Some of the terminals made synapse-like contacts with non-immunoreactive pinealocytes. The presence of the opioidergic pinealocytes strongly indicates that the pineal gland of the European hamster, in addition to its pinealopetal nervous regulation, is regulated by intrapineal peptidergic pinealocytes via a synaptic mechanism. A possible paracrine role of the opioidergic cells must also be considered.

Are the annual reproductive and body weight rhythms in the male European hamster (Cricetus cricetus) dependent upon a photoperiodically entrained circannual clock?

Most of the data obtained so far on the European hamster (Cricetus cricetus) suggest direct photoperiodically driven seasonal changes in sexual activity and body weight. The results of the present long-term study support the hypothesis that these annual changes are the expression of photoperiodically driven endogenous circannual rhythms. When subjected following capture (April-May) to constant conditions of long photoperiod (LP) and constant temperature a large number of the European hamsters present, in September-December, complete gonadal atrophy associated with a decrease in body weight. A sexual reactivation as well as an increase in body weight are observed in the same animals between January and April. Of the six animals that survived long enough, two only presented partial gonadal atrophy during the second year. These observations clearly demonstrate that the decline in sexual activity in subjective autumn does not require a decrease in photoperiod, at least in the first year. Theoretically, the observed rhythms, if circannual in nature, would be generated by a self-sustained annual oscillator (circannual clock) able to function in the absence of a photoperiodic input. Pinealectomy makes animals unable to detect or measure photoperiodic information. Of the six European hamsters tested (pinealectomized in June and then kept continuously under LP), five showed clear annual rhythms in body weight and reproductive capacities for two consecutive years. Clearly endogenous annual rhythms were expressed in these conditions. To be entrained to a 1-year period, such a circannual clock should, however, be able to react to either LP and/or to short-photoperiod (SP), at least at certain periods of the annual cycle. In animals exposed to LP in August or October, after gonadal atrophy had been established by exposure to natural SP, gonadal regrowth started in December or January, about 2 to 3 months earlier than in animals kept outside or in experimental SP. With the same experimental conditions, exactly the same results were obtained in pinealectomized animals; thus stimulatory effect of LP or LP-induced phase advance of the circannual clock can be excluded. The absence of the SP information would then induce such reaction. In animals kept under constant LP and temperature following capture, however, pinealectomy in January--when all animals are sexually active--induces gonadal atrophy within--weeks. This clearly demonstrates that LP is stimulatory at this time of the subjective year.

The presence of opioidergic pinealocytes in the pineal gland of the European hamster ( Cricetus cricetus ): an immunocytochemical study

The presence of opioidergic pinealocytes in the pineal gland of the European hamster ( Cricetus cricetus ): an immunocytochemical study

Search for rhythmicity during hibernation in the European hamster.

Temporal patterns of hibernation were studied by continuous monitoring of body temperature by radiotelemetry over 6 months in European hamsters, Cricetus cricetus, at constant temperature and photoperiod. Entrances into hibernation occurred mostly at the end of the night (0000-0800 hours), while arousals were randomly distributed between day and night. This is at variance with a control of bout duration by a clock with a period of 24 h. Consequently, the timing of entrances implies a phase-resetting of the circadian clock on each arousal. Persistence of circadian rhythmicity with a period different from 24 h during deep hibernation was investigated examining whether the durations of torpor bouts were integer multiples of a constant period. A non-parametric version of the classical contingency test of periodicity was developed for this purpose. Periods ranging from 21 to 29 h were tested. Nine animals out of ten showed at least one significant period in this range (P < 0.01), either below 24 h (21.8 +/- 0.5 h, n = 4) or above (27.3 +/- 0.5 h, n = 7). However, we have found a theoretical model of bout durations for which the contingency test of periodicity sometimes gives false significant results. This indicates that the power of the test is weak. With this reservation our results suggest that a circadian oscillator controls the duration of a bout of hibernation, which would occur after an integer, but variable and possibly temperature-dependent number of cycles.

Induction of arousal in hibernating European hamsters ( Cricetus cricetus L.) by vasopressin infusion in the lateral septum

Vasopressin immunostaining in the lateral septum of the European hamster ( Cricetus cricetus L.) disappears in autumn, at the time of the first appearance of hypothermic periods characteristic to hibernation. Previous results have shown that chronic administration of vasopressin in the lateral septum during winter prevents the expression of hypothermic periods, suggesting a role for this peptide in hibernation. It is now observed that acute infusion of vasopressin, and in 50% of the cases, of a specific vasopressin V 1 receptor agonist, during a hypothermic period results in an immediate termination of hypothermia. Infusion of oxytocin or a vasopressin V 2 receptor agonist were without effect. The results indicate that the seasonal variation in central vasopressin activity, possibly through an interaction with V 1 receptors, may play an important role in the expression of hibernation in the European hamster.

Circadian changes in susceptibility of voles and golden hamsters to acute rodenticides

Abstract In common voles (Microtus arvalis) and golden hamsters (Mesocricetus auratus) circadian changes in the susceptibility to acute dosing of rodenticides, zinc phosphide and crimidine, were investigated. Animals were dosed at four different times of day (2.00, 8.00, 14.00, 20.00 h) and mortality, convulsive seizure, latency period to first seizure, and running wheel activity were studied. Both voles and hamsters showed the highest susceptibility to zinc phosphide during the light period. In case of crimidine, circadian pattern of susceptibility was noted only in hamsters with the highest mortality during the beginning of the dark period. The data demonstrate that circadian changes in susceptibility to rodenticides have to be taken into account.

Characterization of two Metabacterium sp. from the gut of rodents. 1. Morphology and histochemical examination of a new Metabacterium sp. from the gut of the European hamster (Cricetus cricetus)

A new giant Gram-negative non-cultivatable symbiotic endospore-forming bacterium was found in the gut of the European hamster. This "Metabacterium" sp., provisionally named "Metabacterium criceti", sp. n., has a length of approximately 20 microns and thickness of 4 microns. It forms 1 to 2 cylindrical endospores, approximately 9 microns long and 1.4 microns thick. TEM-micrographs show a cell wall structure characteristic of Gram-negative bacteria. Vegetative cells are filled with granules 0.3 micron in diameter which resemble starch granules. The reproduction occurs with binary fission and by formation of two endospores. Of thirteen biochemical components sought, four, i.e. glycogen, triacylglycerols, peroxidase and alkaline phosphatase, were not found. Starch, acid mucosubstances, DNA, RNA, lipids, proteins, adenosine triphosphatase and acid phosphatase were found in different patterns, depending on the developmental stage of the bacterium. In the vegetative cell stage all these components, with the exception of starch, were found. In the endospore-bearing cell stage, only the starch-like cell component granules could be detected. In free endospores only DNA, RNA and acid phosphatase were found. Some of the components, i.e. DNA, lipids, starch-like granules, were linked to certain cell substructures, the distribution of others, viz. polysaccharides, RNA, adenosine triphosphatase and proteins was diffuse. The lipids, found only in vegetative cells, were associated with the cell wall.

Seasonal changes in melatonin binding sites in the pars tuberalis of male European hamsters and the effect of testosterone manipulation.

Seasonal changes in specific 2-[125I]iodo-melatonin binding were assessed in the pars tuberalis of male European hamsters (Cricetus cricetus) kept under natural environmental conditions. Saturation studies were performed on pars tuberalis membrane preparations every 5-7 weeks for 13 months. The maximum number of melatonin binding sites occurred in spring and summer (Bmax, 4.0 +/- 0.3 fmol/mg protein, n = 9) with significantly reduced binding in winter (Bmax, 1.2 +/- 0.2 fmol/mg protein, n = 2). As an assay control, simultaneous saturation studies were performed on rat pars tuberalis membranes. No summer-winter difference in binding site density was observed in the rat studies. In both hamsters and rats no seasonal changes in binding affinity were found. Although an apparent correlation between Bmax, values and paired testes weight of the hamsters was noted, in early spring the increase in the number of melatonin binding sites preceded the elevation in testicular weight. Castration during the period of sexual activity or sexual inactivity also failed to reduce the elevated number of binding sites observed in the spring and summer. In addition, testosterone implanted sc 5 weeks before had no effect on the low 2-[125I]iodo-melatonin binding site density found in winter (November). These results suggest that the observed seasonal variation in the number of melatonin binding sites is independent of seasonal changes in circulating testosterone concentrations.

Seasonal changes in melatonin binding sites in the pars tuberalis of male European hamsters and the effect of testosterone manipulation

Seasonal changes in specific 2-[125I]iodo-melatonin binding were assessed in the pars tuberalis of male European hamsters (Cricetus cricetus) kept under natural environmental conditions. Saturation studies were performed on pars tuberalis membrane preparations every 5-7 weeks for 13 months. The maximum number of melatonin binding sites occurred in spring and summer (Bmax, 4.0 +/- 0.3 fmol/mg protein, n = 9) with significantly reduced binding in winter (Bmax, 1.2 +/- 0.2 fmol/mg protein, n = 2). As an assay control, simultaneous saturation studies were performed on rat pars tuberalis membranes. No summer-winter difference in binding site density was observed in the rat studies. In both hamsters and rats no seasonal changes in binding affinity were found. Although an apparent correlation between Bmax, values and paired testes weight of the hamsters was noted, in early spring the increase in the number of melatonin binding sites preceded the elevation in testicular weight. Castration during the period of sexual activity or sexual inactivity also failed to reduce the elevated number of binding sites observed in the spring and summer. In addition, testosterone implanted sc 5 weeks before had no effect on the low 2-[125I]iodo-melatonin binding site density found in winter (November). These results suggest that the observed seasonal variation in the number of melatonin binding sites is independent of seasonal changes in circulating testosterone concentrations.

Host specificity of cloned Spironucleus sp. originating from the European hamster.

In vivo experiments with a clone of the intestinal flagellate Spironucleus sp. originating from the laboratory European hamster (Cricetus cricetus), and the comparison with a spontaneous infection from laboratory bred European hamsters suggest high specificity of this clone for the homologous host. Only the Syrian golden hamster (Mesocricetus auratus) could be infected experimentally, though the mean intensity of infection was lower. Other heterologous recipients, mice and rats of one outbred and one inbred strain each, could not be infected. Even immunodeficient mice (athymic and C.B-17-scid) remained uninfected after inoculation of 5 x 10(5) cysts per mouse. This is the second Spironucleus clone, after the rat isolate (Schagemann et al., 1990), with a high level of host specificity suggesting heterogeneity within the genus Spironucleus.

Lack of tumorigenic activity of 1,1-dimethylhydrazine in Syrian golden hamsters treated by subcutaneous injection.

Syrian golden hamsters were treated throughout their lifespan by weekly subcutaneous injections of 1,1-dimethylhydrazine (1,1-DMH) at doses of 0, 8, 17 and 35 mg/kg body weight. In contrast to our previous study using European hamsters, no treatment-related tumors occurred in this study.

Viscosity of water in hibernating and nonhibernating mammals estimated by proton NMR relaxation times

Longitudinal ( T 1) and transverse ( T 2) nuclear magnetic resonance relaxation times were measured in vitro at 37, 30, 25, 15, and 5 °C on serum, brain, liver, kidney, and heart samples from a hibernator, the European hamster, active in summer (SA), active in winter, or in the hibernating state in winter; from a less efficient hibernator, the golden hamster; and from a homeotherm, the rat. T 1 and T 2 relaxation times varied between species and in the European hamster between the active and hibernating subjects. Despite the major relaxation time differences between the organs, NMR relaxation time measurements showed a general trend to an increase in the viscosity of water for the European hamster in the active state. Although these modifications were not directly related to the process of hibernation itself, the relaxation times observed in the hibernating animals were closer to those seen in the rat. This evidenced that changes of physical properties of water reflect a better adaptation to low temperatures of the hamster, as compared to the nonhibernator, given that the low water viscosity of SA hamster allows the decrease of the viscosity with temperature during the hibernating state. These in vitro studies permit the study the viscosity which is an important physicochemical parameter involved in NMR longitudinal relaxation time of water proton. More detailed studies of other physiological parameters must be undertaken by further in vivo measurements.