Temporal Synergism of Corticosterone and Prolactin in the Syrian Hamster, Mesocricetus auratus

To augment the limited work reported in the literature regarding testing of the hormonal temporal synergism hypothesis in Syrian hamsters (Joseph MM, Meier AH. Proc Soc Exp Biol Med. 1974;146:1150-5), a large experiment with female hamsters was conducted. Forty-eight received corticosterone at 18:00 h on January 21, 23, 25, 27, and 29 and ovine prolactin at one of six times of day beginning January 22 for 8 days; 36 received saline (at 18:00) and prolactin at one of the six times of day for 8 days; 35 received only prolactin at one of the six times of day for 8 days; and 16 received no injections. Twelve hamsters receiving corticosterone and prolactin and eight uninjected hamsters were on running wheels. The corticosterone and prolactin group not on wheels had a body weight gain and no circadian rhythm of weight gain, but did have circadian rhythms of response in organ weight, per 100 g of body weight, and in weights of fat pads and uteri. The corticosterone and prolactin group with access to running wheels gained in body weight and had larger ovaries and smaller fat pads. Hamsters receiving saline and prolactin had a body weight gain, but had no circadian rhythms of response in organ weights. The hamsters receiving only prolactin gained in body weight but had no rhythms of response, except for unexpected circadian rhythms in body weight gain and weights of fat pads. The uninjected hamsters had a modest weight gain. Most or all hamsters with access to running wheels freeran, and the corticosterone injections did not appear to synchronize the locomotor activity rhythms. In conclusion, corticosterone does interact with the injection time effect of prolactin on weights of fat pads, paired ovaries, and uteri. The mechanism of that effect, in terms of circadian rhythm theory, is unclear.     

Temporal Synergism of Corticosterone and Prolactin in the Syrian Hamster,Mesocricetus auratus

To augment the limited work reported in the literature regarding testing of the hormonal temporal synergism hypothesis in Syrian hamsters (Joseph MM, Meier AH. Proc Soc Exp Biol Med. 1974;146:1150-5), a large experiment with female hamsters was conducted. Forty-eight received corticosterone at 18:00 h on January 21, 23, 25, 27, and 29 and ovine prolactin at one of six times of day beginning January 22 for 8 days; 36 received saline (at 18:00) and prolactin at one of the six times of day for 8 days; 35 received only prolactin at one of the six times of day for 8 days; and 16 received no injections. Twelve hamsters receiving corticosterone and prolactin and eight uninjected hamsters were on running wheels. The corticosterone and prolactin group not on wheels had a body weight gain and no circadian rhythm of weight gain, but did have circadian rhythms of response in organ weight, per 100 g of body weight, and in weights of fat pads and uteri. The corticosterone and prolactin group with access to running wheels gained in body weight and had larger ovaries and smaller fat pads. Hamsters receiving saline and prolactin had a body weight gain, but had no circadian rhythms of response in organ weights. The hamsters receiving only prolactin gained in body weight but had no rhythms of response, except for unexpected circadian rhythms in body weight gain and weights of fat pads. The uninjected hamsters had a modest weight gain. Most or all hamsters with access to running wheels freeran, and the corticosterone injections did not appear to synchronize the locomotor activity rhythms. In conclusion, corticosterone does interact with the injection time effect of prolactin on weights of fat pads, paired ovaries, and uteri. The mechanism of that effect, in terms of circadian rhythm theory, is unclear.     

Sleep Deprivation Alters the Cell Population Kinetics In the Jejunum of the Male Syrian Hamster (Mesocricetus auratus)

The proliferative and functional units of the jejunum were studied every 3 hr during 24 hr in groups of control and sleep-deprived hamsters. Peaks in kinetic parameters were evident during the sleep period in control hamsters; in the absence of sleep, peak values were significantly reduced. Sleep deprivation was associated with reduction of G₂ to M flux and reduction of the circadian rhythm in mitotic index from 74% to 25%. the reduction in the number of cells passing through M was reflected by a drop in labelling index 9 hr later. These findings are consistent with the theory that sleep promotes restorative processes.     

Experimental iron deficiency in Syrian hamsters (Mesocricetus auratus)

An animal model was developed in which the effect of iron deficiency on the oral mucosa could be studied. Iron deficiency was induced by feeding hamsters a low-iron powdered diet together with withdrawal of 0.5 ml of blood weekly, for a period of 9 weeks. At the end of this period the mean haematological values for control animals were, Hb 15.9 g/dl, plasma iron 40.3 mumol/l, TIBC 90.5 mumol/l and transferrin saturation 44.5%, compared with 7.4, 7.2, 111.4 and 6.5 respectively for experimental animals. These results were reproducible in successive groups of animals and indicate that this is a useful model for the study of iron deficiency anaemia.     

Age affects hibernation in Syrian hamsters (Mesocricetus auratus)

In this study, we aimed to show how age affects hibernation in the Syrian hamster. Experimentally, we used 30 male animals differing in age. The old animals were 20 months of age and the adults were 8 months of age at the end of the test. The young animals were 3 weeks old at the start of testing and 5 months old at the end of the testing period. The torpor observation started October 15, 1996, and ended March 11, 1997, in the laboratory colony maintained under natural photoperiod and outdoor air. Observations were performed around noon daily. Three measures (i.e., prehibernation period [hibernation latency], proportion of hibernation spent in torpor, and proportion of animals in torpor), all of which reflect the strength of occurrence of hibernation, indicated that the older hamsters (1) started hibernation earlier, (2) spent more time in torpor, and (3) had a higher chance of being in torpor than the younger ones during the hibernation season. (Chronobiology International, 17(5), 623-630, 2000)     

Chromosome replication in fibroblasts of the Syrian hamster (Mesocricetus auratus)

The BrdU/Hoechst 33258/Giemsa method for sub-dividing S-phase in asynchronous cell populations has been re-evaluated and modified to give better definition and more even distribution of sub-phases. A reference pattern of early-relicating euchromatic bands is given for all chromosomes at Sk2 in primary cultures of skin fibroblasts. The overall band patterns at each sub-phase have allowed more objective definitions of early and late replication for these cells, and show that in both classes of chromatin light G-bands preceed dark G-bands. Asynchrony between homologous bands is observed at all stages of S, albeit with a variable frequency. The observed in vitro replication patterns and programme for the chromosomes of skin fibroblasts does not appear to be affected by the age or sex of the source.     

Indicators of Postoperative Pain in Syrian Hamsters (Mesocricetus auratus)

Despite the use of Syrian hamsters (Mesocricetus auratus) in research, little is known about the evaluation of pain in this species. This study investigated whether the frequency of certain behaviors, a grimace scale, the treat-take-test proxy indicator, body weight, water consumption, and coat appearance could be monitored as signs of postoperative pain in hamsters in a research setting. Animals underwent no manipulation, anesthesia only or laparotomy under anesthesia. An ethogram was constructed and used to determine the frequencies of pain, active and passive behaviors by in-person and remote videorecording observation methods. The Syrian Hamster Grimace Scale (SHGS) was developed for evaluation of facial expressions before and after the surgery. The treat-take-test assessed whether surgery would affect the animals’ motivation to take a high-value food item from a handler. The hypothesis was that behavior frequency, grimace scale, treat-take-test score, body weight, water consumption, and coat appearance would change from baseline in the surgery group but not in the no-intervention and anesthesia-only groups. At several time points, pain and passive behaviors were higher than during baseline in the surgery group but not the anesthesia-only and no-intervention groups. The SHGS score increased from baseline scores in 3 of the 9 animals studied after surgery. The frequency of pain behaviors and SHGS scores were highly specific but poorly sensitive tools to identify animals with pain. Behaviors in the pain category were exhibited by chiefly, but not solely, animals that underwent the laparotomy. Also, many animals that underwent laparotomy did not show behaviors in the pain category. Treat-take-test scores, body weight, water consumption, and coat appearance did not change from baseline in any of the 3 groups. Overall, the methods we tested for identifying Syrian hamsters experiencing postoperative pain were not effective. More research is needed regarding clinically relevant strategies to assess pain in Syrian hamsters.

Pain experienced by laboratory animals can affect both animal welfare and research results. Little is known about the evaluation of pain in Syrian hamsters (Mesocricetus auratus) in the laboratory setting. However, various research models using Syrian hamsters involve surgery and are presumed to cause pain.^16,47,49 In 2018 alone, the USDA reported that 35,695 hamsters were used for research studies involving painful procedures.⁴⁸ Previously published behaviors exhibited by hamsters in response to pain include hunched posture with head down, reluctance to move, increased depression or aggression, extended sleep periods, and weight loss.^7,8,10,16,21 How these behaviors are affected by factors such as the type of painful stimulus, anesthetic protocol, handling procedures, and environmental conditions is unclear. The practicality of observing these signs in the research environment is uncertain and likely complicated by the nocturnal nature of Syrian hamsters and an assumed propensity of this species to mask pain, much like other prey species.^8,14,16A significant need exists for published data investigating whether behavioral observations or other clinical indicators can help recognize, quantify, or monitor pain in hamsters in a research setting. Detailed behavioral observations and well-controlled studies are needed to develop a system to assess postoperative pain in laboratory animals.^8,33 Moreover, little information is available on the efficacy of analgesic agents in hamsters.¹ The few studies of analgesics in hamsters rely on the mitigation of evoked pain responses (such as using a hot plate), which has limited relevance to clinical situations such as postoperative pain.^8,32,36,51 To date, no published literature has evaluated the efficacy or safety of analgesics to treat postoperative pain in hamsters. Validated real-time and practical methods for evaluating pain in Syrian hamsters would support the evaluation of analgesic efficacy in this species.Various assessments have been developed to identify signs of pain in other species. Behavioral ethograms have been used to evaluate pain and analgesic efficacy in mice, rats, rabbits, and guinea pigs in the research environment.^{5,6,20,23,25,34,35,39-41,53} Another tool used to evaluate pain in animals is the grimace scale, which has been developed for mice, rats, rabbits, ferrets, cats, sheep, pigs, horses, and even harbor seals.^{3,4,9,11,13,15,19,22,26,30,37,45,50} The use of a proxy indicator, such as burrowing and time-to-integrate-to-nest in mice and time-to-consume in guinea pigs, can be used as an additional tool for the evaluation of pain.^{5,17,18,35,38}Because none of the previously mentioned assessment techniques were specific to hamsters, we here explored using these approaches to detect pain in Syrian hamsters that underwent laparotomy in a laboratory setting. We developed a species-specific ethogram and the Syrian Hamster Grimace Scale (SHGS). We also devised a novel proxy indicator of pain for use in Syrian hamsters, the treat-take-test (TTT), which is based on hamsters’ natural behavior to hoard food.^16,46,49,52 Although water intake, body weight, and coat appearance are non-specific indicators of pain, we also measured these parameters.^5,19,23,33 Furthermore, we analyzed the effects of the presence of an observer and time of day. We hypothesized that behavior frequency, grimace scale, treat-take-test score, body weight, water consumption, and coat appearance would change from baseline in the surgery group but not in the no-intervention and anesthesia-only groups.     

Cytological sub-division of S-phase in the Syrian hamster (Mesocricetus auratus)

Using BrdU/Hoechst 33258/Giemsa methods for detecting replicating chromosome bands, a method is described by which the DNA synthesis phase may be sub-divided on the basis of distinctive patterns displayed by certain chromosomes. — Applied to asynchronous populations successively sampled through one cell cycle, cells in S can be unscrambled and replaced in their correct time sequence. — This helps to overcome the sampling-time variable inherent in such populations, and allows a clearer picture of the progression of events both qualitatively and quantitatively.     

Photoperiodic control of meiosis in the male Syrian hamster (Mesocricetus auratus)

Male Syrian hamsters exposed to short photoperiods of 6 h light/day (6L:18D) show regression of the testes within 12 weeks. Chromosome preparations of the meiotic stages (pachytene, metaphase I (MI) and metaphase II (MII)), testicular weights relative to body weights, sperm counts, seminiferous tubule diameter and histological appearance were examined at intervals during regression and subsequent recovery in a long photoperiod (14L:10D). The fall of testicular weight was associated with the decrease in tubule diameter. Spermatogenesis and sperm count were reduced rapidly and finally ceased after 10 weeks in short days. The numbers of MI and MII cells relative to 100 pachytene cells progressively decreased during the short-day treatment, although the ratio of MI:MII stayed constant whenever there was meiotic activity (except in the first week of the recovery phase). This suggests that an increasing proportion of pachytene cells did not progress to MI with increased time in short days, but cells which did reach MI progressed to MII in the same proportions as in the control testes. Meiosis ceased after 10 weeks in short days. Recovery in the long days was marked by a peak in the number of MI and MII cells/100 pachytene cells soon after the return to long days. This preceded the return (to control values) of the sperm count by 10 weeks. Initial recovery in the first 3 weeks was very rapid in all the determined values.     

Analysis of ear sebum of the Syrian hamster (Mesocricetus auratus) reveals pronounced sexual dimorphism

External ear of male and female Syrian hamsters (Mesocricetus auratus) were extracted with hexane and separated by class on thin-layer chromatography (TLC). Separated lipid classes were eluted and saponified, and non-saponifiable lipids further characterized by TLC, gas-liquid chromatography (GLC), UV and IR spectroscopy and functional group analyses. Many sex differences were observed, most notably the presence of sex-specific sterols of males and females. Mature animals were found to have greater quantities of ear sebum, but the characteristic qualitative lipid profiles of each sex were apparent in immature animals.     

光照周期对叙利亚地鼠生长发育和繁殖的影响

对离乳雄性叙利亚地鼠（Ｍｅｓｏｃｒｉｃｅｔｕｓａｕｒａｔｕｓ）和雌性叙利亚地鼠各３０只分别给以长光照（１６Ｌ：８Ｄ）、中光照（１２Ｌ：１２Ｄ）和短光照（８Ｌ：１６Ｄ）三种光周期处理,研究光周期对叙利亚地鼠生长发育和繁殖的影响。１３周龄时,短光照处理组雄性地鼠的体重显著（Ｐ＜０．０５）高于长光照和中光照组的体重;雌性地鼠９周龄时长光照组的体重显著（Ｐ＜０．０１）高于另外两个处理组的体重,较高的日食量可能是长光照组具有较大体重的原因之一,雄性地鼠的睾丸、副睾和肾上腺重量及雌性地鼠的卵巢、子宫和肾上腺重量表现了随着光照时间的延长而递增的趋势。长光照条件有利于雌性地鼠的正常发情和繁殖。每天１６ｈ的光照对繁殖地鼠是比较适宜的。     

Cell-specific variation of X chromosome replication in the Syrian hamster (Mesocricetus auratus)

The sub-division of S-phase in Syrian hamsters, on the basis of BrdU/Hoechst 33258/Giemsa banding, has allowed a quantitative comparison of the replication of individual chromosome bands within defined subphases of S. This analysis has shown that in hamsters, as has been reported in humans, there are distinct patterns of early replication in vitro in the early X, the late X in fibroblasts, and the late X in lymphocytes. In addition, it has been possible to show that, although the pattern of replication of the late X in fibroblasts differs from that in lymphocytes, the time in S at which bands first appear on this chromosome is the same in the two cell types. — No significant heterogeneity can be ascribed to differences between individuals, adult or embryonic sources, culture media, or time of exposure to BrdU. — The absence of any detectable heterogeneity in the replication band frequencies in autosomal heterochromatic arms suggests that the cell-specific variability of the late-replicating X is a feature of facultative rather than constitutive heterochromatin.     

Enhanced longevity in tau mutant Syrian hamsters,Mesocricetus auratus

The single-gene mutation tau in the Syrian hamster shortens the circadian period by about 20% in the homozygous mutant and simultaneously increases the mass-specific metabolic rate by about 20%. Both effects might be expected to lead to a change in longevity. To test such expectations, the life span of male and female hamsters from three genotypes (wild-type, heterozygous, and homozygous tau mutants, all derived from heterozygote crosses to randomize the genetic background) was recorded in constant darkness. Male hamsters lived significantly longer than females: the overall average life span was 96.9 weeks (SE = 2.5, n = 118) for males and 82.0 weeks (SE = 2.1, n = 99) for females. To our surprise, male and female homozygous mutant hamsters lived significantly longer rather than shorter compared to wild-types. For males, the difference between the two genotypes was on average 14%; for females, the difference was 16%. The mortality rate of wild-type males was significantly different from that of homozygous tau males but not different from that of heterozygotes. Overall, survival of wild-type females was statistically distinguishable from both heterozygous and homozygous mutant females. Male and female wild-type hamsters were heavier than homozygote mutants throughout the entire life span, and heterozygous mutants had intermediate weights. There was no correlation between body mass and life span, and the causes of the extended life span in tau mutant hamsters remain unresolved.     

Cloning and characterization of corticotropin-releasing factor and urocortin in Syrian hamster (Mesocricetus auratus)

Corticotropin-releasing factor and urocortin belong to a superfamily of neuropeptides that includes the urotensins-I in fishes and the insect diuretic peptides. Sequence analysis suggests that urocortin is the mammalian ortholog of urotensin-I, although the physiological role for this peptide in mammals is not known. Within the Rodentia, hamsters belong to a phylogenetically older lineage than that of mice and rats and possess significant differences in hypothalamic organization. We have, therefore, cloned the coding region of the Syrian hamster (Mesocricetus auratus) corticotropin-releasing factor and urocortin mature peptide by polymerase chain reaction. Hamster urocortin was prepared by solid-phase synthesis, and its pharmacological actions on human corticotropin-releasing factor R1 and R2 receptors were investigated. The deduced hamster corticotropin-releasing factor amino acid sequence and cleavage site is identical to that in rat, whereas the urocortin sequence is unique among the urocortin/urotensin-I/sauvagine family in possessing asparagine and alanine in positions 38 and 39, respectively. The hamster urocortin carboxy terminus sequence bears greater structural similarity to the insect diuretic peptide family, suggesting either retrogressive mutational changes within the mature peptide or convergent sequence evolution. Despite these changes, human and hamster urocortin are generally equipotent at cAMP activation, neuronal acidification rate, and R1/R2 receptor affinities.     

Pathophysiological studies of trinitrobenzene sulfonic acid-induced colitis in Syrian hamsters (Mesocricetus auratus)

We developed a colitis model in Syrian hamsters (Mesocricetus auratus) to investigate the relationship between colitis and neutrophil elastase (NE). Colitis was induced by a single intracolonic dose of trinitrobenzene sulfonic acid (TNBS; 90 mg/ml) dissolved in 15% (vol/vol) ethanol. The ulcer area, tissue myeloperoxidase (MPO) activity, and luminal NE activity all were increased on Days 1 and 5, corresponding with the acute inflammatory histopathological changes. These acute inflammatory parameters subsequently decreased by Day 14, and chronic inflammatory histopathological changes became evident. Recurrence of inflammation was not observed during the period up to Day 28. To evaluate our colitis model, the effects of prednisolone were examined. Prednisolone was administered orally once on the day before induction of colitis, and animals were treated twice daily thereafter. Although prednisolone had little effect on the tissue MPO activity, prednisolone inhibited the ulcer area and NE activity. In addition, the effects of an NE-specific inhibitor (ONO-6818) on our TNBS-induced colitis model were examined. In the subcutaneous treatment study, ONO-6818 was administered once before the induction of colitis. Although ONO-6818 had little effect on the tissue MPO activity, the ulcer area and NE activity were decreased in the ONO-6818-treated group. The inhibitory effects on the ulcer area and NE activity were confirmed after oral treatment with ONO-6818 after induction of colitis. We conclude that our colitis model is useful for investigating the relationship between colitis and NE, and inhibition of NE activity can prevent the progression of ulceration.     

Routine chromosome screening in Syrian hamsters (Mesocricetus auratus) using orbital sinus blood

Blood from the posterior orbital sinus of Syrian hamsters, obtained under halothane anaesthesia, can be cultured to give large numbers of metaphase chromosome spreads for analysis. The procedure has been used for rapid routine screening of the karyotypes of all offspring in a breeding colony where translocations are present. Results can be obtained within 3 days of collecting the blood sample.