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.

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.

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.

Seasonal differential expression of KiSS-1/GPR54 in the striped hamsters(Cricetulus barabensis)among different tissues

Kisspeptins and G protein coupled receptor(GPR54)play significant roles in regulating reproductive activity among seasonally reproductive animals;however,the mechanisms of KiSS-1 and GPR54 gene affecting the seasonal reproduction in striped hamster are still unknown.In this study,real-time quantitative polymerase chain reaction was employed to examine the expression profiles of KiSS-1 and GPR54 in the hypothalamus,ovaries,testes,uterus and epididymis of striped hamsters across 4 different seasons.Our results showed that,across different seasons,the KiSS-1 expression mode of male striped hamsters and the GPR54 expression mode of female striped hamsters were consistent with the seasonal photoperiod in the hypothalamus.Meanwhile,across different seasons,the expression profile of KiSS-1 in the testes and the GPR54 expression profile of male striped hamsters in the hypothalamus were consistent with the intensity of their seasonal reproductive activity.Among different tissues,the expression trend for GPR54 is consistent across 4 seasons,while that for KiSS-1 is tissue-dependent.The expression trend for GPR54 across 4 seasons is the same regardless of gender,while that for KiSS-1 is dramatically different and sex-dependent across different seasons.These results suggest that the expressions of KiSS-1 and GPR54 in the striped hamsters were regulated by complicated mechanisms,and the regulatory mechanisms in the striped hamsters are seasonal-dependent and sex-dependent.This research will provide a theoretical basis for studying how KiSS-1 and GPR54 affect seasonal reproduction and the mechanisms behind their influence.

Correlations between phytohemagglutinin response and leukocyte profile,and bactericidal capacity in a wild rodent

phytohemagglutinin(PHA)-induced swelling is widely used to investigate cell-mediated and innate immunity across different vertebrate taxa.However,its physiological mechanism is still an open question due to the complexity of the involved immune components.In the present study,we measured the synchronous variations of PHA response,the proportion of different subtypes of leukocytes,as well as serum bactericidal capacity in circulation blood at 6,12 and 24 h after PHA versus PBS injection in striped hamster,Cricetulus barabensis.First,the results showed that PHA responses reached a peak at 6 h postinjection,then sharply declined at 12 h and 24 h postinjection.Serum bactericidal capacity was higher at 6 h and 12 h than at 24 h.The proportion of different subtypes of leukocytes,as well as the ratio of neutrophils to lymphocytes did not display significant changes across different time points.Second,PHA response was positively correlated with the proportion of neutrophils and serum bactericidal capacity.The proportion of monocytes was negatively correlated with that of eosinophils and neutrophils.The proportion of basophils was negatively correlated with that of lymphocytes.Our results indicate that earlier enhanced PHA response is important for the striped hamster to cope with changing environmental conditions due to its small body mass,and the increased components of innate immunity in circulation blood may contribute to the enhancement of PHA swelling response.