Effect of Shortening Day Length on Immune Function in Siberian Hamsters

In order to understand the effect of gradual changes in photoperiod on immune function, adult female Siberian hamsters (Phodopus sungorus) were randomly divided into the control group (12L:12D, Con, n = 11) and the shortening day length group (SD, n = 11), in which day length was reduced from 12:12 h to 8:16 h light-dark cycle at the pace of half an hour every week. Meanwhile the winter immunoenhancement hypothesis, which holds that animals’ immune function would be enhanced in winter or winter-like conditions, was tested. Gradual shortening day length had no effect on body mass and body composition including wet carcass mass, the subcutaneous, retroperitoneal, mesenteric and total body fat masses in Siberian hamsters. The masses of liver and small intestine with contents were higher in the SD group than in the Con group, however other organ masses such as brain, heart, kidney and so on did not differ between the two groups. Phytohemagglutinin (PHA) response after 24 h of PHA injection was enhanced by the shortening photoperiod, which supported the winter immunoenhancement hypothesis. The masses of spleen and thymus, white blood cells, bacteria killing capacity indicative of innate immunity were not affected, which did not support this hypothesis. In summary, gradually decrease in day length increased cellular immunity, but had no effect on other immunological parameters in Siberian hamsters.

Comparative studies between humans and golden Syrian hamsters via thromboelastography

Background:Thromboelastography(TEG)is a widely utilized clinical testing method for real-time monitoring of platelet function and the thrombosis process.Lipid metab-olism disorders are crucial risk factors for thrombosis.The lipid metabolism charac-teristics of hamsters resemble those of humans more closely than mice and rats,and their relatively large blood volume makes them suitable for studying the mechanisms of thrombosis related to plasma lipid mechanisms.Whole blood samples from golden Syrian hamsters and healthy humans were obtained following standard clinical pro-cedures.TEG was employed to evaluate coagulation factor function,fibrinogen(Fib)function,platelet function,and the fibrinolytic system.Methods:The whole blood from hamster or healthy human was isolated following the clinical procedure,and TEG was employed to evaluate the coagulation factor func-tion,Fib function,platelet function,and fibrinolytic system.Coagulation analysis used ACLTOP750 automatic coagulation analysis pipeline.Blood routine testing used XN-2000 automatic blood analyzer.Results:TEG parameters revealed that hamsters exhibited stronger coagulation fac-tor function than humans(reaction time[R],p=0.0117),with stronger Fib function(alpha angle,p<0.0001;K-time[K],p<0.0001).Platelet function did not differ signifi-cantly(maximum amplitude[MA],p=0.077).Hamsters displayed higher coagulation status than humans(coagulation index[CI],p=0.0023),and the rate of blood clot dissolution in hamsters differed from that in humans(percentage lysis 30 min after MA,p=0.02).Coagulation analysis parameters indicated that prothrombin time(PT)and activated partial thromboplastin time(APTT)were faster in hamsters than in hu-mans(PT,p=0.0014;APTT,p=0.03),whereas the Fib content was significantly lower in hamsters than in humans(p<0.0001).No significant difference was observed in thrombin time(p=0.1949).Conclusions:In summary,TEG could be used to evaluate thrombosis and bleeding parameters in whole blood samples from hamsters.The platelet function of hamsters closely resembled that of humans,whereas their coagulation function was signifi-cantly stronger.

Characterization of SHARPIN knockout Syrian hamsters developed using CRISPR/Cas9 system

Background : SHARPIN (SHANK- associated RH domain interactor) is a component ofthe linear ubiquitination complex that regulates the NF- κB signaling pathway. To betterunderstand the function of SHARPIN, we sought to establish a novel geneticallyengineered Syrian hamster with SHARPIN disruption using the CRISPR/Cas9 system.Methods : A single- guide ribonucleic acid targeting exon 1 of SHARPIN gene was designedand constructed. The zygotes generated by cytoplasmic injection of the Cas9/gRNA ribonucleoprotein were transferred into pseudopregnant hamsters. Neonatalmutants were identified by genotyping. SHARPIN protein expression was detectedusing Western blotting assay. Splenic, mesenteric lymph nodes (MLNs), and thymicweights were measured, and organ coefficients were calculated. Histopathologicalexamination of the spleen, liver, lung, small intestine, and esophagus was performedindependently by a pathologist. The expression of lymphocytic markers and cytokineswas evaluated using reverse transcriptase- quantitative polymerase chain reaction.Results : All the offspring harbored germline- transmitted SHARPIN mutations.Compared with wild- type hamsters, SHARPIN protein was undetectable in SHARPIN −/−hamsters. Spleen enlargement and splenic coefficient elevation were spotted inSHARPIN −/− hamsters, with the descent of MLNs and thymuses. Further, eosinophilinfiltration and structural alteration in spleens, livers, lungs, small intestines, and esophagiwere obvious after the deletion of SHARPIN. Notably, the expression of CD94 and CD22 was downregulated in the spleens of knockout (KO) animals. Nonetheless,the expression of CCR3, CCL11, Il4 , and Il13 was upregulated in the esophagi. Theexpression of NF- κB and phosphorylation of NF- κB and IκB protein significantly diminishedin SHARPIN −/− animals.Conclusions : A novel SHARPIN KO hamster was successfully established using theCRISPR/Cas9 system. Abnormal development of secondary lymphoid organs andeosinophil infiltration in multiple organs reveal its potential in delineating SHARPINfunction and chronic inflammation.

β-Glucan Fiber from Spent Brewer’s Yeast Reduces Early Atherosclerosis Greater Than Psyllium in Hypercholesterolemic Syrian Golden Hamsters

β-Glucans, mostly from oats, have been shown to reduce blood concentrations of total and LDL-cholesterol in animals and humans. After processing, spent brewer’s yeast, a by-product of the fermentation process, contains 85% - 90% β-glucans. The purpose of this study was to evaluate the effect of yeast-derived β-glucan fiber on plasma lipids and early atherosclerosis development in hamsters consuming a semi-purified hypercholesterolemic diet (HCD). Animals were fed either the HCD or the HCD containing psyllium or β-glucan fiber from yeast for 12 weeks. Both the psyllium and β-glucan fiber from yeast showed significant decreases in plasma total cholesterol, non-HDL-C, triacylglycerol, and aortic fatty streak area when compared to the HCD. Also, the β-glucan fiber from yeast had significantly less aortic fatty streak area compared to the psyllium diet. Findings from this study show that while both β-glucan fiber from yeast and psyllium produced similar reductions in plasma lipid and lipoprotein concentrations, the β-glucan fiber from yeast prevented the development early atherosclerosis better than psyllium in the hamsters.

High Body Mass Has No Effect on Cellular and Innate Immunity in Siberian Hamsters (<i>Phodopus sungorus</i>)

Body mass is considered to be related with immune function in animals. Our aim was to test the hypothesis that cellular and innate immunity would be suppressed in high body mass of Siberian hamsters (Phodopus sungorus). Six heavier (high body mass, HBM) and six lighter (low body mass, LBM) hamsters were selected from 28 male hamsters. Body mass, body fat mass, wet spleen mass and blood glucose levels were significantly higher in the HBM group than in the LBM group. However, phytohaemagglutinin response, serum bacteria killing capacity and white blood cells did not differ between the two groups, suggesting cellular and innate immunity was?not impaired in high body mass of hamsters. There was no correlation between cellular, innate immunity and body mass, body fat mass and glucose levels, suggesting cellular and innate immunity was?not suppressed by higher body mass, body fat mass and glucose levels. In summary, cellular and innate immunity was not impaired in the HBM hamsters compared with the LBM hamsters.

The Uniform Carcinogenic Action of Alkylnitrosoureas in Syrian Hamsters

The carcinogenic effects of a number of alkylnitrosoureas in Syrian golden hamsters have been compared by administering them by gavage as solutions in corn oil/ethyl acetate.The compounds were methyl-,ethyl-,2-hydroxyethyl-,2-oxopropyl-,and 2-phenylethylnitrosourea and the dialkylnitrosoureas dimethyl- and diethylnitrosourea,ethylnitrosohydroxyethylurea, ethylnitroso-2-oxopropylurea,2-oxopropylnitrosochloroethylurea,and hydroxyethylnitroso- ethylurea.All were given at approximately equimolar doses and,in most cases,to male and female hamsters.Most of the hamsters died with tumors associated with the treatments.Methyl- nitrosourea,ethylnitrosourea,and hydroxyethylnitrosourea,but not oxopropylnitrosourea, gave rise to a high incidence of tumors of the forestomach,while the dialkylnitrosoureas pro- duced smaller numbers of forestomach tumors.All of the alkylnitrosoureas induced hemangio- sarcomas of the spleen,which was the most common tumor produced by these carcinogens. Tumors of other types were uncommon,except that ethylnitrosourea and ethylnitrosohydroxy- ethylurea induced tumors of the cervix in about half of the animals and ethylnitrosooxopropyl- urea induced some nervous system tumors.The small number of common target organs of alkylnitrosoureas in hamsters contrasted sharply with the broad spectrum of tumors they in- duced in rats,depending on the nature of the alkyl groups,and with a quite different order of potency in the latter species,1989 Academic Press.Inc.

Modulating Effects of Chlorogenic Acid on Lipids and Glucose Metabolism and Expression of Hepatic Peroxisome Proliferator-activated Receptor-α in Golden Hamsters Fed on High Fat Diet

Objective To examine the effects of chlorogenic acid （CGA） on lipid and glucose metabolism under a high dietary fat burden and to explore the possible role of peroxisome proliferator-activated receptor-α （PPAR-α） in these effects. Methods Twenty male golden hamsters were randomly divided into CGA treatment group （n=10, given peritoneal injection of CGA solution prepared with PBS, 80 mg CGA/kg body weight daily）, and control group （n=10, given PBS i.p. at the average volume of the treatment group）. Animals in both groups were given 15% high fat diet. Eight weeks after treatment with CGA, the level of biochemical parameters in fasting serum and tissues and the expression of hepatic mRNA and protein PPAR-α were determined. Results Eight weeks after treatment with CGA, the levels of fasting serum triglyceride （TG）, free fatty acid （FFA）, total cholesterol （TC）, low density lipoprotein cholesterol （LDL-C）, high density lipoprotein cholesterol （HDL-C）, glucose （FSG）, and insulin （FSI） were significantly lower in the GGA treatment group than in the control group. CGA also led to higher activity of hepatic lipase （HL） lower contents of TG and FFA in liver, and lower activity of lipoprotein lipase （LPL） in skeletal muscle. Furthermore, CGA significantly elevated significantly elevated the expression level of mRNA and protein expression in hepatic PPAR-α. Conclusion CGA can modify lipids and glucose metabolism, which may be attributed to PPAR-α facilitated lipid clearance in liver and improved insulin sensitivity.

Protective effects of ursodeoxycholic acid on chenodeoxycholic acid-induced liver injury in hamsters

AIM： TO investigate the effects of ursodeoxycholic acid （UDCA） on chenodeoxycholic acid （CDCA）-induced liver injury in hamsters, and to elucidate a correlation between liver injury and bile acid profiles in the liver.METHODS： Liver injury was induced in hamsters by administration of 0.5% （w/w） CDCA in their feed for 7 d. UDCA （50 mg/kg and 150 mg/kg） was administered for the last 3 d of the experiment.RESULTS： At the end of the experiment, serum alanine aminotransferase （ALl） increased more than 10 times and the presence of liver injury was confirmed histologically. Marked increase in bile acids was observed in the liver. The amount of total bile acids increased approximately three-fold and was accompanied by the increase in hydrophobic bile acids, CDCA and lithocholic acid （LCA）. UDCA （50 mg/kg and 150 mg/kg） improved liver histology, with a significant decrease （679.3 ±77.5 U/L vs 333.6 ± 50.4 U/L and 254.3 ±35.5 U/ L, respectively, P 〈 0.01） in serum ALT level. UDCA decreased the concentrations of the hydrophobic bile acids, and as a result, a decrease in the total bile acid level in the liver was achieved.CONCLUSION： The results show that UDCA improves oral CDCA-induced liver damage in hamsters. The protective effects of UDCA appear to result from a decrease in the concentration of hydrophobic bile acids, CDCA and LCA, which accumulate and show the cytotoxicity in the liver.

Pravastatin activates PPARα/PPARγexpression in the liver and gallbladder epithelium of hamsters

BACKGROUND:Our earlier study with cultured gallbladder epithelial cells demonstrated that statins(HMG-CoA reductase inhibitors)activate the expression of PPARαand PPARγ, consequently blocking the production of pro-inflmmatory cytokines.The present study used hamsters to investigate the effects of pavastatin on PPARα/PPARγexpression in the liver and gallbladder epithelium,and to determine whether pravastatin suppresses cholesterol crystal formation in the gallbladder. METHODS:A total of 40 Golden Syrian male hamsters(4 weeks old)were randomly assigned to four groups(basal diet control; basal diet+pavastatin;high cholesterol diet;high cholesterol diet+pravastatin).All hamsters were 11 weeks old at the end of the experiment.The liver,gallbladder and bile were harvested. Immunohistochemical staining and Western blotting for PPARαand PPARγwere performed in the liver and gallbladder. A drop of fresh bile was examined for cholesterol crystals under a microscope. RESULTS:In the gallbladder and liver of the hamsters, pravastatin activated the PPARαand PPARγexpression of gallbladder epithelial cells and hepatocytes,and particularly the response of PPARγwas much stronger than that of PPARα. Pravastatin suppressed the formation of cholesterol gallstones or crystals in the gallbladder. CONCLUSION:Pravastatin is an effective medication to activate PPARs(especially PPARγ)in the liver and the gallbladder epithelium of hamsters,and contributes to the prevention of gallstone formation.

The role of leptin in striped hamsters subjected to food restriction and refeeding

Food restriction （FR） and refeeding （Re） have been suggested to impair body mass regulation and thereby making it easier to regain the lost weight and develop over-weight when FR ends. However, it is unclear if this is the case in small mammals showing seasonal forging behaviors. In the present study, energy budget, body fat and serum leptin level were measured in striped hamsters that were exposed to FR-Re. The effects of leptin on food intake, body fat and genes expressions of several hypothalamus neuropeptides were determined. Body mass, fat content and serum leptin level decreased during FR and then increased during Re. Leptin supplement significantly attenuated the increase in food intake during Re, decreased genes expressions of neuropepetide Y （NPY） and agouti-related protein （AgRP） of hypothalamus and leptin of white adipose tissue （WAT）. Hormone-sensitive lipase （HSL） gene expression of WAT increased in leptin-treated hamsters that were fed ad libitum, but decreased in FR-Re hamsters. This indicates that the adaptive regulation of WAT HSL gene expression may be involved in the mobilization of fat storage during Re, which partly contributes to the resistance to FR-Re-induced overweight. Leptin may be involved in the down regulations of hypothalamus orexigenic peptides gene expression and consequently plays a crucial role in controlling food intake when FR ends.

Endocrine status and scent attractiveness in male dwarf hamsters Phodopus sungorus injected with thymus-dependent and thymus-independent antigens

We studied the influences of immune activation by thymus-dependent(sheep red blood cells,SRBC)and independent(bacterial lipopolysaccharide,LPS)antigens on odor signals and endocrine status in dwarf hamsters.Administration of SRBS to mature males resulted in a drop of sexual scent attractiveness of soiled bedding collected during 5 days after injection.This effect was accompanied with a decline of fecal testosterone.Reduction of the male scent attractiveness after SRBC treatment had maximum manifestation in males of dwarf hamsters with low humoral immune response to this challenge.Contrary to the effects of SRBC,males injected with LPS showed an increase of scent attractiveness.Differences in the time that mature females spent sniffing olfactory stimuli(LPS vs control),correlated positively with differences in concentration of testosterone in feces collected from LPS and saline treated males.We discuss the adaptive meaning of the opposite olfactory effects,which induced by activation of the nonspecific innate immunity with LPS and by activation of specific acquired immunity with SRBC.

Dose-dependent and combined effects of N-methyl-D-aspartate receptor antagonist MK-801 and nitric oxide synthase inhibitor nitro-L-arginine on the survival of retinal ganglion cells in adult hamsters

This study investigated the effects of daily intraperitoneal injections of N-methyl-D-aspartate receptor antagonist MK-801 and nitric oxide synthase inhibitor nitro-L-arginine （L-NA） on the survival of retinal ganglion cells （RGCs） at 1 and 2 weeks after unilateral optic nerve transection in adult hamsters. The left optic nerves of all animals were transected intraorbitally 1 mm from the optic disc and RGCs were retrogradely labeled with Fluorogold before they received different daily dosages of single MK-801 or L-NA as well as daily combinational treatments of these two chemicals. All experimental and control animals survived for 1 or 2 weeks after optic nerve transection. Our results revealed that the mean numbers of surviving RGCs increased and then decreased when the dosage of MK-801 （1.0, 3.0 and 4.5 mg/kg） and L-NA （1.5, 3.0, 4.5 and 6.0 mg/kg） increased at both 1 and 2 weeks survival time points. Daily combinational use of 1.0 mg/kg MK-801 and 1.5 mg/kg L-NA lead to a highest RGC number that was even higher than the sum of the RGC numbers in 1.0 mg/kg MK-801 and 1.5 mg/kg L-NA subgroups at 2 weeks. These findings indicated that both MK-801 and L-NA can protect axotomized RGCs in a dose-dependent manner and combinational treatment of these chemicals possesses a potentiative and protective effect.

Garbanzo Diet Lowers Cholesterol in Hamsters

The present study was conducted to investigate the effect garbanzo containing diet on cholesterol in hamster fed cholesterol containing high fat diet. It was hypothesized that garbanzo diet would lower cholesterol in hamsters, based on previous observation of the bile acid binding potential of garbanzo. Garbanzo (Cicer arietinum), Bengal gram (Cicer arietinum), lentils (Lens culinaris), soy protein isolate (SPI) or casein (control) diets were fed to hamsters for three weeks. Initial and final animal weights, feed intakes and plasma triglycerides values were similar among all the treatments. Garbanzo containing diet significantly lowered total plasma cholesterol (TC) compared with casein control. There was 17% reduction in low density lipoprotein cholesterol (LDL-C) in hamsters fed the garbanzo diet;this difference was not significant due to high variability in within treatment values. Plasma cholesterol values with lentils diet were similar those with the control diet. Liver lipid and liver cholesterol values with lentils diet were higher than all the other treatments. Data suggest that garbanzo diet has the potential to lower the risk of atherosclerosis and improve human health.

Effect of Cholesterol Content in Diet on Atorvastatin(ATO)-induced Liver Injury in Golden Hamsters

[Objectives]The objective of this study was to investigate the effect of cholesterol content in high-fat diet on atorvastatin(ATO)-induced liver injury in golden hamsters and compare the degree of liver injury caused by two high-fat diets with different cholesterol proportions.[Methods]Male golden hamsters were randomly and evenly divided into different groups and given different high-fat diets for 14 consecutive days by gavage to establish hyperlipidemia models.From the 15th d on,the hamsters in the model groups were given ATO at a dose of 5 mg/kg,one a day,for 9 consecutive days.Blood was sampled from the orbital veins of the hamsters for the determination of biochemical indicators.Liver tissues of the hamsters were sampled,paraffin-embedded,sliced,stained by HE(hematoxylin-eosin)method and observed under an optical microscope.[Results]Compared with standard diet group,the body weight increased significantly(P<0.05),the serum TC,TG and LDL-C levels increased significantly(P<0.05),the serum HDL-C level declined significantly(P<0.05),and the ALT and AST levels increased significantly(P<0.05)in the high-fat diet groups.This trend was more obvious in the high-fat II group than the high-fat I group.After ATO intervention,the HDL-C,TBIL and TBA levels increased significantly(P<0.05),and the liver ALT and AST levels further increased(P<0.05)in the model groups.This trend was more obvious in the model II group than the model I group.The morphological inspection shows that the fat deposition in the liver tissues was severe;the hepatocytes in the model groups were obviously damaged;the liver injury in the hamsters fed high-fat diet containing 0.2%cholesterol and intervened with ATO was relatively mild but severer than the high-fat diet groups.[Conclusions]Hamster models of hyperlipidemia were successfully established in this study.High-fat diet could cause liver injury.While lowering blood lipid level,ATO aggravated liver injury.Among the high-fat diets with different proportions of cholesterol,the diet containing 0.2%cholesterol had little effect on ATO-induced liver injury.

Temperature determines the shift of thermal neutral zone and influences thermogenic capacity in striped hamsters

The thermoneutral zone(TNZ)reflects the adaptation of mammals to their natural habitat.However,it remains unclear how TNZ shifts in response to variations in ambient temperature.To test the hypothesis that ambient temperature plays a key role in determining TNZ variations between seasons,we measured metabolic rate,body temperature,and cytochrome c oxidase(COX)activity of several visceral organs in striped hamsters(Cricetulus barabensis)either acclimated to semi-natural conditions over a year,or subjected to a gradual decrease in mean temperature from 30±1°C to-15±1°C.The TNZ range in striped hamsters differed seasonally,with a wider TNZ and a lower lower-critical temperature in winter compared to summer.The hamsters showed a consider-able leftward shift of lower-critical temperature from 30°C to 20°C after the ambient temperature of acclimation from 30°C down to-15°C,whereas the upper-critical temperature of TNZ remainedfixed at 32.5°C.The rest-ing metabolic rate in thermoneutral zone(RMRt),nonshivering thermogenesis(NST),and COX activity of brown adipose tissue,liver,skeletal muscle,brain,and kidneys,increased significantly in hamsters acclimated at lower ambient temperatures.Following acute exposure to 5°C and-15°C,hamsters acclimated to 32.5°C had signifi-cantly lower maximal NST and lower serum thyroid tri-iodothyronine(T3)levels compared to those kept at 23°C.Thesefindings suggest that acclimation to the upper-critical temperature of TNZ impairs the hamsters’thermo-genic capacity to cope with extreme cold temperature.Reduced ambient temperature was mainly responsible for the leftward shift of TNZ in striped hamsters,which reflects the adaptation to cold environments.

Increased pathogenicity and aerosol transmission for one SARS-CoV-2 B.1.617.2 Delta variant over the wild-type strain in hamsters

During the two-year pandemic of coronavirus disease 2019(COVID-19), its causative agent, severe acute respiratory syndrome coronavirus 2(SARS-CoV-2), has been evolving. SARS-CoV-2 Delta, a variant of concern, has become the dominant circulating strain worldwide within just a few months. Here, we performed a comprehensive analysis of a new B.1.617.2 Delta strain(Delta630) compared with the early WIV04 strain(WIV04) in vitro and in vivo, in terms of replication, infectivity, pathogenicity, and transmission in hamsters. When inoculated intranasally, Delta630 led to more pronounced weight loss and more severe disease in hamsters. Moreover, 40%mortality occurred about one week after infection with 10^(4)PFU of Delta630, whereas no deaths occurred even after infection with 10^(5)PFU of WIV04 or other strains belonging to the Delta variant. Moreover, Delta630outgrew over WIV04 in the competitive aerosol transmission experiment. Taken together, the Delta630 strain showed increased replication ability, pathogenicity, and transmissibility over WIV04 in hamsters. To our knowledge, this is the first SARS-CoV-2 strain that causes death in a hamster model, which could be an asset for the efficacy evaluation of vaccines and antivirals against infections of SARS-CoV-2 Delta strains. The underlying molecular mechanisms of increased virulence and transmission await further analysis.

Females choose gentle, but not healthy or macho males in Campbell dwarf hamsters （Phodopus campbelli Thomas 1905）

Androgen-dependent male sexual traits （STs） as well as immunocompetence are theoreticallyassumed to be key indicators of a male＇s quality for the mate-choosing female. We studied matechoice by sexually motivated （SM） females of Campbell＇s dwarf hamsters. Females chose between2 tethered male siblings that differed in expression of STs. Males were unrelated to the female andable to contact and copulate with her. In both males, we measured sex-related morphology ofbody mass, mid-ventral specific skin gland, ano-genital distance, and external testicular diameter.We also estimated levels of blood testosterone and cortisol, specific T- and B-cell immune re-sponses to antigens, as well as aggressive and sexual dominance in sibling males through add-itional encounter experiments with another SM female （male sibs could freely compete for thefemale）. We found that SM females chose a partner among 2 male sibs and spent over 80% of theirtime on average with the preferred male compared with the non-preferred one. Her choice was notassociated with the first visit of the chosen male, with a higher expression of sex-related traits,higher levels of blood testosterone, or with aggressive dominance. The choice was not associatedwith the intensity of T-cell immune response to phitohemagglutinin （PHA）. Instead there was a ten-dency for a negative relationship with the expression of STs and B-cell response to the antigenchallenge. The only character that unambiguously influenced female choice was the non-aggressive male to female grooming during sexual contact. There was no difference in breedingsuccess between preferred and non-preferred males paired with virgin females.

Effect of losing a fight on later agonistic behavior toward unfamiliar conspecifics in male Syrian hamsters

In many species, agonistic interactions result in social relationships that are stable over time. In Syrian hamsters, two unfamiliar males that are placed together will fight vigorously and a clear winner/loser relationship is usually established. In subsequent interactions, the loser will flee soon after detecting the familiar winner. Here we tested the hypothesis that losing a fight with a conspecific will affect future agonistic interactions not only toward that individual （i.e., the familiar winner） but also toward unfamiliar conspecifics. To test this hypothesis we paired two Syrian hamster males in three trials on one day in which the loser had tile opportunity to escape the winner. The next day the loser was paired with an unfarniliar male, also for three trials. If he lost again, he was tested on a third day with a third unfamiliar male. Subjects were those males that were losers on all three days. The latency to escape on the first trial on Days 2 and 3 was significantly shorter than on the first trial on Day l, indicating that losing against the first male affected the response toward unfamiliar males. However, the latency to escape on the first trial on Days 2 and 3 was significantly longer than that on the third trial on the preceding day, indicating that a loser treats unfamiliar males differently than a familiar winner. These results suggest that a defeat during an interaction with one male affects later agonistic behavior towards other, unfamiliar males [Current Zoology 57 （4）： 449-452, 2011].

Strategies of behavior,energetic and thermogenesis of striped hamsters in response to food deprivation

The life history of many animals includes periods of food shortage.Two behavioral strategies are involved in small mammals in response to food shortage:an increase in activity behavior,representing the increased foraging or migratory behavior,and a decrease in activity level,serving as a mechanism for conserving energy.However,it is uncertain whether animals adopt both strategies in response to food shortage,and whether hormone and neuroendocrine mechanisms are involved in both strategies.In the present study,changes in behavior and metabolic rate were examined in food-deprived striped hamsters(Cricetulus barabensis).The effects of leptin supplement on activity behavior,metabolic rate and hypothalamic neuropeptide gene expression were also examined.The behavior of food-deprived hamsters significantly changed with photoperiod phases:with increasing activity during the dark phase compared to those fed ad libitum,whereas decreasing activity and simultaneously increasing resting behavior during the light phase.Resting metabolic rate,body mass,and masses of fat depots and digestive tracts significantly decreased in food-deprived hamsters compared with ad libitum controls.Leptin supplement tended to attenuate the increased activity in the dark phase.Gene expression of hypothalamic neuropeptide Y(NPY)was significantly upregulated in food-deprived hamsters,while was significantly attenuated by exogenous leptin.These findings suggest that both behavior strategies are important behavioral adjustments in free-living animals to cope with food shortage.Leptin and hypothalamic NPY gene expression may be involved in the adjustments of physiology and behavior in animals demonstrating a hyperactivity strategy in response to food shortage.

Effects of short photoperiod on energy intake,thermogenesis,and reproduction in desert hamsters(Phodopus roborovskii)

Desert hamsters(Phodopus roborovskii)are the least known species in the genus Phodopus with respect to ecology and physiology,and deserve scientific attention,particularly because of their small body size.Here,the responses of energy metabolism and reproductive function to short photoperiods in desert hamsters were investigated.Male and female desert hamsters were acclimated to either long day(LD)(L:D 16:8 h)or short day(SD)photoperiods(L:D 8:16 h)for three months,and then the females were transferred back to an LD photoperiod for a further five months,while at the end of the SD acclimation the males were killed and measurements were taken for serum leptin as well as molecular markers for thermogenesis.We found that like the other two species from the genus Phodopus,the desert hamsters under SD decreased body mass,increased adaptive thermogenesis as indicated by elevated mitochondrial protein content and uncoupling protein-1 content in brown adipose tissue,and suppressed reproduction compared to those under LD.However,different from the other two species,desert hamsters did not show any differences in energy intake or serum leptin concentration between LD and SD.These data suggest that different species from the same genus respond in different ways to the environmental signals,and the desert adapted species are not as sensitive to change in photoperiod as the other two species.