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13 November 2015, Volume 35 Issue 4

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Effect of dopamine on food hoarding in Mongolian gerbils (Meriones unguiculatus)

YANG Huidi, WANG Qian, WANG Dehua

2015, 35(4):  349-358. 

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Food deprivation-induced food-hoarding in Mongolian gerbils (Meriones unguiculatus) shows a bimodal pattern. Although our previous study implicated the neurotransmitter dopamine (DA) in the brain in food hoarding, little is known about how DA is involved in this behavior. Here we tested the effects of the DA receptor antagonist haloperidol or the agonist apomorphine on food-hoarding and neuronal activation indicated by Fos-immunoreactive (ir) labeling in food-deprived male Mongolian gerbils. Males received i.p. injections of haloperidol (1 mg/kg) or apomorphine (0.3 mg/kg). Haloperidol treatment inhibited food deprivation-induced increases in food-hoarding in male gerbils displaying high levels of food-hoarding (HFH). In contrast, apomorphine stimulated this behavior in males displaying low levels of food hoarding (LFH). Furthermore, haloperidol significantly increased Fos-ir labeling in the caudate putamen (CP) and nucleus accumbens (NAcc), but decreased Fos-ir and TH-ir/Fos-ir expression in the substantia nigra (SN). Conversely, apomorphine decreased Fos-ir labeling in the CP and NAcc. Together, these data indicate that the mesolimbic dopamine system is involved in mediating food-hoarding behavior induced by food deprivation.

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The trade-off between the energy allocation to maintenance and reproduction in striped hamster is independent of temperature

ZHAO Zhijun

2015, 35(4):  359-368. 

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The present study was aimed at examining the energy budget during lactation in small mammals, within which the factors limiting maximum sustained energy intake (SusEI) and the physiological mechanisms underpinning the limitation would be further explored. Body mass, food intake, litter size and litter mass during lactation were determined in striped hamsters raising natural litters (Con), minus 2-3 (Minus) and plus 2-3 pups (Plus) at 21℃, 30℃ and 5℃. Basal metabolic rate (BMR), nonshivering thermogenesis (NST), cytochrome c oxydase (COX) activity of brown adipose tissue (BAT), serum T₃, T₄ and prolactin levels also were measured. Females increased food intake, but decreased body mass throughout lactation, during which the differences between 21 and 30℃ were not significant. Maximum asymptotic food intake averaged 14g/d, and it was lower by 20.3% and 18.6% in Minus group than Con and Plus groups, respectively. The effect of temperature on food intake was significant. Food intake was increased to 16g/d at 5℃, which was significantly higher than that at 21 and 30℃ (by 14%, P<0.05). Litter size decreased significantly in Plus group, but did not change in Con and Minus groups throughout the lactation. Mean litter size was 4.5±0.3, 2.6±0.3 and 4.6±0.3 in Con, Minus and Plus groups, respectively, at weaning (P<0.01), and no difference was observed between Con and Plus groups. On weaning day, litter mass was not different between Con and Plus groups, but it was significantly lower in Minus group (33.9±3.8 g) than Con (50.9±2.2 g) and Plus groups (49.0±1.8 g). Mean pup body mass was 13.7±0.7 g in Minus group, which was higher by 17.9% and 24.9% than that in Con (11.6±0.5 g) and Plus (10.9±0.6 g) groups (P<0.05), respectively. BMR, NST, BAT COX activity, serum T₃, T₄ and prolactin levels were significantly higher at 5℃ than 21℃ and 30℃, whereas no differences were observed between 21℃ and 30℃. It suggested that SusEI was 5×BMR in striped hamster raising different litter size at 5℃, 21℃ and 30℃. Cold-exposed hamsters were able to increase energy intake to cope with the energy expenditure for thermogenesis, showing a trade-off energetic budget between maintenance and reproductive output. The finding provided support for the “heat dissipation limitation hypothesis”, but was also consistent with the prediction of the “peripheral limitation hypothesis”.

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Effect of fasting duration on immune function in female Mongolian gerbils (Meriones unguiculatus)

XU Deli, WANG Dehua

2015, 35(4):  369-378. 

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The immune system protects animals from the effects of pathogens including bacteria and viruses, hence it plays an important role in their survival. However, immune function is affected greatly by food shortage. Our previous research showed that 3 days of fasting suppressed phytohaemagglutinin (PHA) response in female Mongolian gerbils (Meriones unguiculatus). The duration of fasting might play a key role in influencing animals’ immunity. In order to clarify this question, we investigated how different fasting durations would have effects on immunity in gerbils. Fifty-five adult female gerbils were randomly divided into 4 groups that, in turn, were subjected to 1 day, 2 days, and 3 days of fasting or fed ad libitum, respectively. Half of each treatment group received phosphate buffered saline or PHA injection. We found that PHA response indicative of T-cell-mediated immunity was suppressed gradually with duration of fasting. Similarly, fasting led to spleen and thymus atrophy in gerbils. These results indicate that the duration of fasting had an important effect on immunity. Moreover, body fat mass, blood glucose and leptin levels decreased gradually with duration of starvation, which were all positively correlated with PHA response. However, white blood cells and corticosterone concentrations were not affected by fasting. Taken together, the duration of fasting had an important effect on immunity in gerbils. Suppression of T-cell-mediated immunity might be due to the gradual decrease of body fat mass, blood glucose and leptin levels with the time of fasting.

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The roles of leptin on energy balance and thermoregulation in post-fattening Daurian ground squirrels

XING Xin, TANG Gangbin, SUN Mingyue, YANG Ming, WANG Dehua

2015, 35(4):  379-388. 

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The post-fattening period is regarded as the transitive period from euthermia to hibernation in fat-storing hibernators, within which hibernators are characterized by gradually decreased food intake, body mass and body temperature (T_b). This study sought to test the effects of leptin on energy balance and thermoregulation in post-fattening Daurian ground squirrel (Spermophilus dauricus), a typical fat-storing hibernator. The animals were treated with leptin (0.5μg/day), leptin antagonist (0.5μg/day leptin + 5μg/day leptin antagonist) or artificial cerebrospinal fluid (control group) through intracerebroventricular injection for 4 weeks. The last week of administration was coupled with cold exposure (5±1^oC) in constant darkness for facilitating torpor. Body mass, energy intake, resting metabolic rate (RMR) and T_b were measured throughout the experiment. The mass of white adipose tissue (WAT), uncoupling protein 1 (UCP1) content in brown adipose tissue and the concentration of energetics-related hormones in serum were measured at the end of drug administration. The results showed that food intake, body mass and T_b spontaneously decreased after fattening. In the control group, 50% animals fell into the torpid state after cold exposure. Leptin administration had no effect on ratio of animals entering torpor. However, the hibernation expression and T₄ concentration in the leptin antagonist group were significantly higher than those in the leptin-administrated group. Leptin and leptin antagonist administrations decreased WAT mass by about 25% compared with that in the control group. There were no significant effects of leptin and leptin antagonist administration on energy budget and UCP1 content. Our results suggest that leptin has limited roles on energy regulation but can affect the torpor patterns in the post-fattening Daurian ground squirrels.

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Trade-off between growth and reproduction in male offspring of Brandt’s voles from low body mass parents

WANG Tongliang, ZHANG Xueying, FU Rongshu, WANG Dehua

2015, 35(4):  389-397. 

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The perinatal period is critical for phenotypic plasticity in animals. Numerous physiological and environmental factors could chronically modify animals’ growth and metabolic phenotype. Parental effects are a major driver of phenotypic plasticity. The present study was designed to explore the effects of parental body-mass on offspring growth, body-mass and energy metabolism in Brandt's voles (Lasiopodomys brandtii). The offspring (litter sizes from 6 to 8) from high body-mass parents (female, 51.5 ± 1.6 g; male, 60.4 ± 2.5 g) were defined as parental high group (HBM), and those from low body-mass parents (female, 35.5 g ± 1.2 g; male, 49.6 g± 2.8 g) as parental low group (LBM). Body mass and energy intake from age of 4 weeks to 13 weeks, resting metabolic rate (RMR), nonshivering thermogenesis (NST), glucose tolerance, body composition, organ mass, and serum leptin concentration in the adults were recorded. Our results showed that:（1）gross energy intake and digestible energy intake of offspring in the LBM group were significantly higher than those of the HBM group. The wet and dry masses of testes in the LBM group were significantly lower than those of the HBM group.（2） RMR in the LBM group was significantly higher than that of the HBM group in male offspring. （3）No significant differences in body-mass, NST, serum leptin, and glucose tolerance were detected between these two groups. These results suggest that low parental body-mass resulted in the trade-off between growth and reproduction in male offspring, indicative of the increases in RMR and energy intake but the depression of reproductive organs.

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Hibernation and energy consumption of Daurian ground squirrels (Spermophilus dauricus) under light-dark cycle conditions

LV Zheng, CAI Luna, SONG Shiyi, LIU Xinyu, PENG Xia, YANG Ming

2015, 35(4):  398-404. 

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To understand the influence of photoperiod on hibernation in fat-storing hibernators, Daurian ground squirrels (Spermophilus dauricus) were implanted with iButtons and then moved into 5℃ with 12h light:12h dark(12L:12D) after reaching maximum body mass.  Three kinds of status were detected in Daurian ground squirrels, deep hibernation, less hibernation and no hibernation. Torpor bout patterns included deep hibernation bouts (DHB), short hibernation bouts (SHB) and daily torpor bouts (DTP). Tbmin during hibernation bouts, bout duration, duration of inter-bout euthermia, cooling rate and warming rate displayed significant differences in different torpor bout patterns. There were no significant differences in Tbmax during inter-bout euthermia. Daily energy consumption in animals with DTBs was the highest, less in animals with SHB and the lowest in animals with DHBs. The time at which torpor was entered usually happened in the dark phase，while awakening from hibernation occurred mostly during the light phase. The results indicate that, compared with animals under constant darkness during hibernation, duration of hibernation in daurian ground squirrels was reduced under light-dark cycle conditions. Also torpor bouts were influenced by showing elevated Tbmin during torpor bouts, reduced bout duration and duration of inter-bout euthermia and increased energy consumption during hibernation. Hibernating and awakening times showed obvious light-dark rhythm under Light-dark cycle.

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No simultaneous increase of humoral immune response and resting metabolic rate in striped hamsters followed a single KLH challenge

ZHANG Zhiqiang, HUANG Shuli, ZHAO Zhijun

2015, 35(4):  405-411. 

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Life history theory predicts that immune function, like other physiological activities such as thermogenesis and reproduction is energetically expensive. However, little experimental evidence for the energy cost to mount an immune response is available, and such costs may be affected by immunological parameters and assays selected. Therefore, the aim of this study was to explore the energetic cost of mounting an immune response in small mammals. We measured body mass and resting metabolic rate (RMR) at days 0 (before injection), and 5 and 10 days post-injection after a keyhole limpet haemocyanin (KLH) antigen challenge in male and female striped hamsters, Cricetulus barabensis. Concentrations of serum anti-IgM and IgG antibodies were measured by an ELISA assay using orbital venous blood samples. The results showed that: (1) Body masses of males were higher than for females, though no significant differences were found between the experimental and control groups by sex and time period after KLH challenge. (2) Concentrations of serum anti-IgM and IgG antibodies were higher in all KLH-challenged groups (i.e. females and males) than those of the controls. (3) RMR did not show apparent differences between control and KLH challenged groups by sex, and before-and-after KLH-challenge or within the different sampling time points (5 and 10 days post KLH injection). These results indicate that a single KLH challenge activated the humoral immunity of striped hamsters, but did not effect changes on body masses or energy expenditure under unlimited food availability. Possible explanations for these findings include that the cost of an enhancement of the humoral immunity may be at the expense of a reduction of another component of the immune system or that striped hamsters can build a humoral response to a mild immunological challenge without simultaneous extra energy cost.

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Effects of cold temperatures on energy metabolism, antioxidants and oxidative stress in striped hamsters

CHEN Kexin, WANG Guiying, ZHAO Zhijun

2015, 35(4):  412-421. 

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The present study examined the effects of cold exposure on energy metabolism of striped hamsters, antioxidant activity and super-oxidative damage to organs or tissues, as well as the inter-relationships among the different organs and tissues. Body mass, food intake, superoxide dismutase (SOD) and catalase (CAT) activity, and H₂O₂ and malonadialdehyde (MDA) levels were measured in striped hamsters exposed to cold temperatures. Cold exposure increased food intake, but had no effect on body mass. MDA levels in heart and muscle, and SOD activity in skeletal muscle, were significantly increased in the hamsters exposed to cold for 42 days relative to those in their counterparts maintained at room temperature.The decreases in ambient temperature significantly decreses H₂O₂ levels of brain and kidneys, and SOD activity of liver and skeletal muscle, whereas increased MDA levels of brain, liver, lung and kidney, and SOD activity in brain and small intestine were significantly increased in the hamsters exposed to 8, 0 and -8 °C compared to those maintained at 21 °C. The correlations of antioxidant and super-oxidative radicals differed significantly among the different organs and tissues: the correlations within the same tissues were 100% in kidney, 66.7% in liver and 50.0% in muscle. These findings suggest that: 1) super-oxidative radical production is associated with the duration and gradient of cold exposure; 2) super-oxidative radical levels differ significantly among the different organs and tissues; 3) antioxidant activity is significantly correlated with super-oxidative radicals levels in some organs and tissues, which may be an important defensive system against the oxidative damages.

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Differential gene expression associated with glycometabolism in the white adipose tissue during fattening and hibernation in Daurian ground squirrel (Spermophilus dauricus)

MEN Liyuan, SONG Shiyi, LIU Xinyu, PENG Xia, LV Zheng, LIU Shuai, CAI Luna, YANG Ming

2015, 35(4):  422-430. 

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In order to study the mechanism of glycometabolism in the fattening progress and hibernation in fat-storing hibernators, we used next generation transcriptome sequencing technology (RNA-Seq) to detect differentially expressed genes associated with glycometabolism in the white adipose tissue, aldolase, enolase and so on; FBPase gene expression was up-regulated 9.6-fold and some other genes such as phosphoenolpyruvate carboxykinase, aldolase, citrate synthase at were down-regulated 1.2-fold to 2-fold Finished-Fattening expression levels of genes was significantly reduced in Hibernation, including hexokinase, aldolase, isocitrate dehydrogenase, 6-phosphogluconate and so on. It suggests that the increase in expression of hexokinase and other enzymes could be directly linked to the enhancement of glycometabolism at Rapid-Fattening in the Daurian ground squirrel; the down-regulation of aldolase and citrate synthase genes could be the reason for weakened glycometabolism at Finished-Fattening; the low expression of hexokinase, pyruvate dehydrogenase and other genes may be part of a general mechanism to coordinate glycometabolism reduction to an extreme level in hibernation. The initial regulation for glycometabolism pathways at the molecule level had been started in the active season before hibernation in the Daurian ground squirrel. compared with Rapid-Fattening ; of the Daurian ground squirrel (Spermophilus dauricus) and measured blood glucose at four physiological stages: Initial-Fattening, Rapid-Fattening, Finished-Fatteningene expression of fructose-1,6-bisphosphatase(FBPase) was down-regulatedcompared with Initial-Fattening, included hexokinase (HK) 8.3-fold and a sampling of genes that were up-regulated at Rapid-Fattening and Hibernation. Results show that there were no differences in blood glucose among stages of Initial-Fattening, Rapid-Fattening and Finished-Fattening but all were significantly higher than during Hibernation; G

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The role of the sperm-specific lactate dehydrogenase (LDH-C₄) in plateau pika brain

XU Lina, WEI Lian, WANG Yang, LI Xiao, WEI Linna, WEI Dengbang

2015, 35(4):  431-437. 

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The plateau pika (Ochotona curzoniae) has a strong adaptability to a hypoxic plateau environment. We found that the sperm-specific lactate dehydrogenase (LDH-C₄) gene is expressed in plateau pika brain. In order to shed light on the role of LDH-C₄ in plateau pika brain, we determined the expression levels of Ldh-c gene in plateau pika brain by real-time PCR and western blot. After injecting N-isopropyl oxamate, a LDH-C₄ specific inhibitor, in skeletal muscle of hind legs, the activities of LDH, and the contents of LD and ATP in plateau pika brain were measured. The results indicated that the expression levels of Ldh-c mRNA and protein were 0.38±0.05 and 0.74±0.13. Thirty minutes after 1 mL 1 mol/L N-isopropyl oxamate in was injected  into the biceps femoris muscle, the concentration of N-isopropyl oxamate in blood was 0.08 mmol/L；the LDH activities, the contents of LD and ATP in the brains of the inhibitor group were decreased significantly compared with that of the control group, and the inhibition rates of N-isopropyl oxamate to LDH, LD and ATP in plateau pika brain were 30.78%, 46.47% and 21.04%, respectively. These results indicated that the sperm-specific lactate dehydrogenase gene is expressed in plateau pika brain, and the pika brain got at least 20% ATP for its life activities by catalyzing anaerobic glycolysis. As a result, the plateau pika may reduce dependence on oxygen and enhance the adaptation to the hypoxic environments.

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Effects of cold exposure on energy regulation and hypothalamic neuropeptideexpression levels in Tupaia belangeri

ZHANG Hao, ZHENG Jia, ZHU Wanglong, LIU Jihong, SUN Shuran, GAO Wenrong, WANG Zhengkun

2015, 35(4):  438-444. 

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Tupaia belangeri is a species which is distributed in tropical and subtropical regions. In the present study, we tested the hypothesis that hypothalamic neuropetides were cues to induce adjustments in body mass regulation and metabolism in cold-exposed tree shrews (Tupaia belangeri)> Body mass, food intake and thermogenic capacity, serum leptin levels and hypothalamic neuropeptide expression levels were measured. The animals were subjected to either 5℃ for 28 days in cold-exposed, or maintained under 25℃ for 28 days. The results showed a significant increase in body mass and food intake in the cold exposure group, accompanied by a significant decrease in serum leptin levels, hypothalanic cocaine and amphetamine regulated transcript peptide (CART) mRNA and pro-opiomelanocortin (POMC) mRNA levels. Neuropeptide Y(NPY) mRNA was significantly increased in the cold exposure group, but there were no changes in hypothalamic agouti-related protein (AgRP) mRNA levels between the control and cold acclimation groups. All of the results suggest that hypoleptinemia partially contributes to cold-induced hyperphagia, which might involve the elevation of hypothalamic NPY, CART and POMC gene expression.

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Progress of research on the metabolism characteristics in three small mammals in Hengduan Mountain region

WANG Zhengkun, GAO Wenrong, ZHU Wanlong

2015, 35(4):  445-452. 

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Metabolic rate is an important parameter in animal physiological ecology which can reflect the energy consumption levels between different species and individuals. It has important significance in the process of adaption to the environment for animals. Many different physical and biological factors could affect the metabolic characteristics of the animals. The present paper mainly summarizes the effects of body-mass and temperature on metabolic rate in three small mammals (Tupaia belangeri, Eothenomys miletus,and Apodemus chevrieri) in Hengduan Mountain region. In addition, compared the similarities and differences of metabolic rate between three small mammals in Hengduan Mountain region and some small mammals from other regions, given some special metabolic characteristics about differences between small mammals from Hengduan Mountain region; Moreover, we studied the origin issue of tree shrews by comparing their metabolic characteristics.