Regulation of body weight and thermogenesis in seasonally acclimatized Brandt's voles (Microtus brandti)

The function of brown adipose tissue at different sites of the body in Brandt's voles during cold acclimation

Ambient temperatures have great impacts on thermoregulation of small mammals. Brown adipose tissue (BAT), an obligative thermogenic tissue for small mammals, is localized not only in the interscapular depot (iBAT), but also in supraclavicular, infra/subscapular, cervical, paravertebral, and periaortic depots. The iBAT is known for its cold-induced thermogenesis, however, less has been paid attention to the function of BAT at other sites. Here, we investigated the function of BAT at different sites of the body during cold acclimation in a small rodent species. As expected, Brandt's voles (Lasiopodomys brandtii) consumed more food and reduced the body mass gain when they were exposed to cold. The voles increased resting metabolic rate and maintained a relatively lower body temperature in the cold (36.5 ± 0.27 °C) compared to those in the warm condition (37.1 ± 0.36 °C). During cold acclimation, the uncoupling protein 1 (UCP1) increased in aBAT (axillary), cBAT (anterior cervical), iBAT (interscapular), nBAT (supraclavicular), and sBAT (suprascapular). The levels of proliferating cell nuclear antigen (PCNA), a marker for cell proliferation, were higher in cBAT and iBAT in the cold than in the warm group. The pAMPK/AMPK and pCREB/CREB were increased in cBAT and iBAT during cold acclimation, respectively. These data indicate that these different sites of BAT play the cold-induced thermogenic function for small mammals.

Neuroendocrine control of brown adipocyte function by prolactin and growth hormone

Growth hormone (GH) is fundamental for growth and glucose homeostasis, and prolactin for optimal pregnancy and lactation outcome, but additionally, both hormones have multiple functions that include a strong impact on energetic metabolism. In this respect, prolactin and GH receptors have been found in brown, and white adipocytes, as well as in hypothalamic centers regulating thermogenesis. This review describes the neuroendocrine control of the function and plasticity of brown and beige adipocytes, with a special focus on prolactin and GH actions. Most evidence points to a negative association between high prolactin levels and the thermogenic capacity of BAT, except in early development. During lactation and pregnancy, prolactin may be a contributing factor that limits unneeded thermogenesis, downregulating BAT UCP1. Furthermore, animal models of high serum prolactin have low BAT UCP1 levels and whitening of the tissue, while lack of Prlr induces beiging in WAT depots. These actions may involve hypothalamic nuclei, particularly the DMN, POA and ARN, brain centers that participate in thermogenesis. Studies on GH regulation of BAT function present some controversies. Most mouse models with GH excess or deficiency point to an inhibitory role of GH on BAT function. Even so, a stimulatory role of GH on WAT beiging has also been described, in accordance with whole-genome microarrays that demonstrate divergent response signatures of BAT and WAT genes to the loss of GH signaling. Understanding the physiology of BAT and WAT beiging may contribute to the ongoing efforts to curtail obesity.

Fat accumulation in striped hamsters (Cricetulus barabensis) reflects the temperature of prior cold acclimation

BACKGROUND

Proper adjustments of metabolic thermogenesis play an important role in thermoregulation in endotherm to cope with cold and/or warm ambient temperatures, however its roles in energy balance and fat accumulation remain uncertain. Our study aimed to investigate the effect of previous cold exposure (10 and 0 °C) on the energy budgets and fat accumulation in the striped hamsters (Cricetulus barabensis) in response to warm acclimation. The body mass, energy intake, resting metabolic rate (RMR) and nonshivering thermogenesis (NST), serum thyroid hormone levels (THs: T3 and T4), and the activity of brown adipose tissue (BAT), indicated by cytochrome c oxidase (COX) activity and uncoupling protein 1 (ucp1) expression, were measured following exposure to the cold (10 °C and 0 °C) and transition to the warm temperature (30 °C).

RESULTS

The hamsters at 10 °C and 0 °C showed significant increases in energy intake, RMR and NST, and a considerable reduction in body fat than their counterparts kept at 21 °C. After being transferred from cold to warm temperature, the hamsters consumed less food, and decreased RMR and NST, but they significantly increased body fat content. Interestingly, the hamsters that were previously exposed to the colder temperature showed significantly more fat accumulation after transition to the warm. Serum T3 levels, BAT COX activity and ucp1 mRNA expression were significantly increased following cold exposure, and were considerably decreased after transition to the warm. Furthermore, body fat content was negatively correlated with serum T3 levels, BAT COX activity and UCP1 expression.

CONCLUSION

The data suggest that the positive energy balance resulting from the decreased RMR and NST in BAT under the transition from the cold to the warm plays important roles in inducing fat accumulation. The extent of fat accumulation in the warm appears to reflect the temperature of the previous cold acclimation.

RNA-seq transcriptome analysis provides new insights into the negative effects of tannic acid on the intestinal function of Brandt's voles (Lasiopodomys brandtii)

Tannic acid (TA), a significant plant secondary metabolite, is contained in the daily food of Brandt's voles. Its adverse effect on gut function has been shown in earlier research, but the underlying molecular mechanisms remain uncertain. In this study, male Brandt's vole (13 weeks old) were divided into two groups and given 0 (control) or 1,200 (TA-treated) mg•kg-1 TA for 18 days. Then RNA sequencing was used to conduct a thorough transcriptome analysis on the duodenum, jejunum, and ileum of Brandt's voles. Results showed that TA significantly increased serum total cholesterol concentration (P < 0.05) and decreased the nutrient digestibility (P < 0.05) of Brandt's voles. Furthermore, there were 174 differentially expressed genes (DEGs) in the duodenum, 96 DEGs in the jejunum, and 88 DEGs in the ileum between the control and TA-treated groups. Enrichment analysis revealed that many genes associated with bile secretion, fat digestion and absorption, innate immune response, and tight junction such as ABCG2, ABCG8, PEAK1, and IFR2, etc. were altered after TA treatment, which were verified by quantitative real-time PCR. These findings suggested that TA can change the expression of intestinal genes, thereby, altering nutrition metabolism and immunological function, eventually hindering the growth of Brandt's voles. The results of this study provide a theoretical basis for explaining how TA affects the gut function of Brandt's voles at the molecular level.

Seasonal adaptation of Mangalica pigs in terms of muscle morphology and metabolism

The skeletal muscle plays an important role in maintaining body temperature, which is mediated by thermogenesis and glucose or lipid metabolism. Mangalica is a native Hungarian pig that has cold tolerance and can live in grazing environments throughout the year. We evaluated the morphological and genetic aspects of Mangalica using muscle tissues to elucidate the mechanisms underlying the tolerance to seasonal effects in grazing environments. The muscle tissues in each season were analysed using morphological evaluation and electron microscopy. The cross-sectional area of skeletal muscle cells in summer was significantly larger than that in winter. The thickness of myofibrils in summer was significantly higher than in winter. The thickness of the Z-line in winter was significantly higher than in summer. The expression of MYH4 and GLUT4 was significantly lower in winter than in summer. The result of ATPase staining indicated significantly increase the muscle fibre ratio of type 1 in winter than that in summer. These findings indicate that the muscle fibre in Mangalica shifts from fast-twitch to slow-twitch fibre, and the metabolic physiology of the muscle was adapted to the cold environment. This study demonstrates that Mangalica gained tolerance to both seasonal heat and cold stresses that are caused by significant changes in ambient temperature in a year because of changes in their muscle fibre type and metabolic function. This study may contribute to elucidating the mechanism of thermogenetic adaptation in cold and heat environments among mammals.

Ambient Temperature Effects on the Spring and Autumn Somatic Growth Trajectory Show Plasticity in the Photoneuroendocrine Response Pathway in the Tundra Vole

Seasonal mammals register photoperiodic changes through the photoneuroendocrine system enabling them to time seasonal changes in growth, metabolism, and reproduction. To a varying extent, proximate environmental factors like ambient temperature (Ta) modulate timing of seasonal changes in physiology, conferring adaptive flexibility. While the molecular photoneuroendocrine pathway governing the seasonal responses is well defined, the mechanistic integration of nonphotoperiodic modulatory cues is poorly understood. Here, we explored the interaction between Ta and photoperiod in tundra voles, Microtus oeconomus, a boreal species in which the main impact of photoperiod is on postnatal somatic growth. We demonstrate that postweaning growth potential depends on both gestational and postweaning patterns of photoperiodic exposure, with the highest growth potential seen in voles experiencing short (8 h) gestational and long (16 h) postweaning photoperiods-corresponding to a spring growth program. Modulation by Ta was asymmetric: low Ta (10 °C) enhanced the growth potential of voles gestated on short photoperiods independent of postweaning photoperiod exposure, whereas in voles gestated on long photoperiods, showing a lower autumn-programmed growth potential, the effect of Ta was highly dependent on postweaning photoperiod. Analysis of the primary molecular elements involved in the expression of a neuroendocrine response to photoperiod, thyrotropin beta subunit (tshβ) in the pars tuberalis, somatostatin (srif) in the arcuate nucleus, and type 2/3 deiodinase (dio2/dio3) in the mediobasal hypothalamus identified dio2 as the most Ta-sensitive gene across the study, showing increased expression at higher Ta, while higher Ta reduced somatostatin expression. Contrastingly dio3 and tshβ were largely insensitive to Ta. Overall, these observations reveal a complex interplay between Ta and photoperiodic control of postnatal growth in M. oeconomus, and suggest that integration of Ta into the control of growth occurs downstream of the primary photoperiodic response cascade revealing potential adaptivity of small herbivores facing rising temperatures at high latitudes.

Melatonin reduced colon inflammation but had no effect on energy metabolism in ageing Mongolian gerbils (Meriones unguiculatus)

In photoperiod-sensitive wild animals, the secretion of melatonin (MT) is modulated by external photoperiod, and MT affects inflammation and the ageing process. The beneficial effects of MT in delaying the progress of ageing have been reported in laboratory mice and rats. However, little is known about MT in wild mammals. In the current study, we investigated energy metabolism, microbial community structure and colon homeostasis in ageing Mongolian gerbils (Meriones unguiculatus) through exogenous supplementation of MT to test the hypothesis that MT has beneficial effects on gut homeostasis in ageing gerbils. Exogenous MT supplementation had no effect on energy metabolism in Mongolian gerbils but reduced the levels of circulating tumor necrosis factor-α (TNF-α), immune globulin G (IgG) and corticosterone (CORT). The increase in the level of inflammation in ageing animals was related to changes in the structure and diversity of the gut microbiota. At the genus level, the relative abundance of Prevotella, Treponema, Corynebacterium, and Sphingomonas was increased in ageing animals and decreased significantly by the treatment of MT. Christensenella and Lactobacillus were attenuated in ageing animals, and tended to be enhanced by MT treatment. Functions related to glycosphingolipid biosynthesis-ganglio series and lipopolysaccharide biosynthesis (metabolisms of cofactors, vitamins and glycan) were increased in ageing animals and decreased significantly by the treatment of MT. Our data suggest that a supplement of MT could improve colon homeostasis through changing the composition of gut microbiota and reducing inflammation in ageing gerbils.

Disentangling the effects of obesity and high-fat diet on glucose homeostasis using a photoperiod induced obesity model implicates ectopic fat deposition as a key factor

OBJECTIVE

Obesity in laboratory rodents is generally induced by feeding them a high fat diet (HFD). This model does not permit separation of the impact of the HFD from the resultant obesity on metabolic defects such as impaired glucose homeostasis. In Brandt's voles we have previously shown that exposure to long photoperiod (LD: 16L: 8D) induces obesity even when they are fed a low fat diet. We show here that these voles are largely resistant to HFD. This model therefore permits some separation of the effects of HFD and obesity on glucose homeostasis. The objective was therefore to use this model to assess if glucose homeostasis is more related to diet or obesity METHODS: Male voles, which were 35 days old and born in LD, were exposed to SD and a low fat diet for 70 days. We then randomly separated the animals into 4 groups for another 63 days: SL (short day and low fat diet: n = 19) group; SH (short day and high-fat diet, n = 20) group; LL (long day and low-fat diet, n = 20) group; LH (long day and high-fat diet, n = 18) group. Glucose tolerance tests (GTT) were performed after treatment for 56 days, and body compositions of the voles were quantified at the end by dissection.

RESULTS

Consistent with our previous work LD voles were more obese than SD voles. Although total body weight was independent of dietary fat content, HFD did have an effect on fat storage. Photoperiod induced obesity had no effect on glucose homeostasis, and the fat content in both the liver and muscle. In contrast, HFD induced adiposity was linked with elevated fat deposition in muscle (but not in liver) and led to impaired glucose tolerance.

CONCLUSIONS

The contrasting effects of diet and photoperiod were consistent with the predictions of the 'lipotoxicity hypothesis'. This may contribute to our understanding of why some human individuals are able to be obese yet remain metabolically healthy.

Effects of exogenous melatonin on body mass and thermogenesis in red-backed vole (Eothenomys miletus) between Kunming and Dali regions

Melatonin (MEL) is an indole hormone synthesized and secreted by the pineal gland at night, which is involved in the regulation of body mass and thermogenesis in small mammals. To test the effects of exogenous MEL on body mass and thermogenic ability in two different red-backed vole (Eothenomys miletus) populations from two different regions (Kunming [KM] and Dali [DL]) with different annual variation in climatic variables, such as temperature, sunshine and rainfall. we traced the changes of energy balance in E. miletus from KM and DL, which were placed at 25 ± 1°C with photoperiod of 12 L:12 D, intraperitoneal injection of MEL was performed daily for 28 days. The results showed that body mass and food intake were significantly decreased, while resting metabolic rate (RMR) and nonshivering thermogenesis (NST) were significantly increased after MEL injection; Contents of total protein, mitochondrial protein, the activities of cytochrome C oxidase (COX) and α-glycerophosphate oxidase (α-PGO) in liver and brown adipose tissue (BAT) were enhanced; the activity of thyroxin 5'-deiodinase (T₄ 5'-DII) and uncoupling protein 1 (UCP1) in BAT were also increased. Serum leptin, triiodothyronine (T₃ ) levels and T₃ /T₄ ratio were significantly increased, thyroxine (T₄ ) levels was significantly decreased. Moreover, body mass and food intake in E. miletus from KM were higher than those from DL, but RMR and NST were lower than those from DL. Changes of body mass, food intake and thermogenic activity of KM were higher than those of DL when exposed to injection of MEL, indicating that E. miletus in KM were more sensitive to MEL. Furthermore, MEL was involved in the regulation of body mass and thermogenesis in E. miletus between KM and DL.

Tannic Acid Induces Intestinal Dysfunction and Intestinal Microbial Dysregulation in Brandt's Voles (Lasiopodomys brandtii)

Brandt's vole (Lasiopodomys brandtii) is a small herbivorous mammal that feeds on plants rich in secondary metabolites (PSMs), including tannins. However, plant defense mechanisms against herbivory by Brandt's voles are not clearly established. This study aimed to investigate the effects of dietary tannic acid (TA) on the growth performance, intestinal morphology, digestive enzyme activities, cecal fermentation, intestinal barrier function, and gut microbiota in Brandt's voles. The results showed that TA significantly hindered body weight gain, reduced daily food intake, changed the intestinal morphology, reduced digestive enzyme activity, and increased the serum zonulin levels (p < 0.05). The number of intestinal goblet and mast cells and the levels of serum cytokines and immunoglobulins (IgA, IgG, TNF-α, IL-6, and duodenal SlgA) were all reduced by TA (p < 0.05). Moreover, TA altered β-diversity in the colonic microbial community (p < 0.05). In conclusion, the results indicate that TA could damage the intestinal function of Brandt's voles by altering their intestinal morphology, decreasing digestive ability and intestinal barrier function, and altering microbiota composition. Our study investigated the effects of natural PSMs on the intestinal function of wildlife and improved our general understanding of plant-herbivore interactions and the ecological role of PSMs.

Analysis of differential metabolites and metabolic pathways in adipose tissue of tree shrews (Tupaia belangeri) under gradient cooling acclimation

In order to investigate the influence of gradient cooling acclimation on body mass regulation in tree shrews (Tupaia belangeri), white adipose tissue (WAT) and brown adipose tissue (BAT) in T. belangeri between the control group and gradient cooling acclimation group on day 56 were collected, body mass, food intake, thermogenic capacity, differential metabolites, and related metabolic pathways in WAT and BAT were measured, the changes of differential metabolites were analyzed by non-targeted metabolomics method based on liquid chromatography-mass spectrometry. The results shown that gradient cooling acclimation significantly increased body mass, food intake, resting metabolic rate (RMR), non-shivering thermogenesis (NST), and masses of WAT and BAT. 23 significant differential metabolites in WAT between the gradient cooling acclimation group and the control group, of which the relative contents of 13 differential metabolites were up-regulated and 10 differential metabolites were down-regulated. 27 significant differential metabolites in BAT, of which 18 differential metabolites decreased and 9 differential metabolites increased. 15 differential metabolic pathways in WAT, 8 differential metabolic pathways in BAT, and 4 differential metabolic pathways involved in both WAT and BAT, including Purine metabolism, Pyrimidine metabolism, Glycerol phosphate metabolism, Arginine and proline metabolism, respectively. All of the above results suggested that T. belangeri could use different metabolites of adipose tissue to withstand low temperature environments and enhance their survival.

Thermo-TRP channels are involved in BAT thermoregulation in cold-acclimated Brandt's voles

Transient receptor potential (TRP) channels, which can sense temperature, pressure and mechanical stimuli, were involved in many physiological and biochemical reactions. Whether thermosensitive TRP channels (Thermo-TRPs) are involved in thermoregulation in small mammals is still not clear. We measured the changes of thermo-TRPs at 4 °C, 23 °C and 30 °C in Brandt's voles (Lasiopodomys brandtii) to test the hypothesis that Thermo-TRPs are involved in cold-induced thermogenesis of brown adipose tissue (BAT) in small mammals. Results showed that air temperatures had no effect on body mass and rectal temperature, but the food intake and basal metabolic rate (BMR) in the 4 °C group were significantly higher than in the 30 °C group. Compared with 30 °C group, the protein contents of uncoupling protein 1(UCP1), TRP vanilloid 2 (TRPV2), TRP ankyrin 1 (TRPA1), TRP melastatin 2 (TRPM2), silent Information Regulator T1 (SIRT1), AMP-activated protein kinase (AMPK) and Calcium/calmodulin-dependent protein kinase II (CaMKII) in BAT increased significantly in 4 °C group, but there was no significant difference in the protein content of Thermo-TRPs in the hypothalamus among groups. Further, the expression of PRDM16 (PR domain containing 16) in inguinal white adipose tissue (iWAT) at 4 °C was significantly higher than that at 30 °C, but no difference was observed in the expression of other browning-related genes or TRPV2. In conclusion, TRP channels may participate in BAT thermoregulation through the CaMKII, AMPK, SIRT1 and UCP1 pathway in cold-acclimated Brandt's voles.

Roles of leptin on energy balance and thermoregulation in Eothenomys miletus

Leptin is a hormone mainly synthesized and secreted by white adipose tissue (WAT), which regulates various physiological processes. To investigate the role of leptin in energy balance and thermoregulation in Eothenomys miletus, voles were randomly divided into leptin-injected and PBS-injected groups and placed at 25°C ± 1°C with a photoperiod of 12 L:12 D. They were housed under laboratory conditions for 28 days and compared in terms of body mass, food intake, water intake, core body temperature, interscapular skin temperature, resting metabolic rate (RMR), nonshivering thermogenesis (NST), liver and brown adipose tissue (BAT) thermogenic activity, and serum hormone levels. The results showed that leptin injection decreased body mass, body fat, food intake, and water intake. But it had no significant effect on carcass protein. Leptin injection increased core body temperature, interscapular skin temperature, resting metabolic rate, non-shivering thermogenesis, mitochondrial protein content and cytochrome C oxidase (COX) activity in liver and brown adipose tissue, uncoupling protein 1 (UCP1) content and thyroxin 5'-deiodinase (T₄5'-DII) activity in brown adipose tissue significantly. Serum leptin, triiodothyronine (T₃), thyrotropin-releasing hormone (TRH) and corticotropin-releasing hormone (CRH) concentrations were also increased significantly. Correlation analysis showed that serum leptin levels were positively correlated with core body temperature, body mass loss, uncoupling protein 1 content, thyroxin 5'-deiodinase activity, nonshivering thermogenesis, and negatively correlated with food intake; thyroxin 5'-deiodinase and triiodothyronine levels were positively correlated, suggesting that thyroxin 5'-deiodinase may play an important role in leptin-induced thermogenesis in brown adipose tissue. In conclusion, our study shows that exogenous leptin is involved in the regulation of energy metabolism and thermoregulation in E. miletus, and thyroid hormone may play an important role in the process of leptin regulating energy balance in E. miletus.

Roles of Ghrelin and Leptin in Body Mass Regulation under Food Restriction Based on the AMPK Pathway in the Red-Backed Vole, Eothenomys miletus, from Kunming and Dali Regions

The phenotype plasticity of animals' physiological characteristics is an important survival strategy to cope with environmental changes, especially the change in climate factors. Small mammals that inhabit seasonally changing environments often face the stress of food shortage in winter. This study measured and compared the thermogenic characteristics and related physiological indicators in the adenosine-5'-monophosphate-activated protein kinase (AMPK) pathway in Eothenomys miletus between Kunming (KM, n = 18) and Dali (DL, n = 18) under food restriction and refeeding. The results showed that food restriction and the region have significant effects on body mass, the resting metabolic rate (RMR), hypothalamic neuropeptide gene expression, ghrelin levels in the stomach and serum, serum leptin level and the activity of AMPK, and malonyl CoA and carnitine palmitoyltransferase 1 (CPT-1) activity. Food restriction reduced the body mass, the gene expression of neuropeptide proopiomelanocortin (POMC), cocaine- and amphetamine-regulated transcription peptide (CART), and leptin level. However, the ghrelin concentration and AMPK activity increased. After refeeding, there was no difference in these physiological indexes between the food restriction and control groups. Moreover, the physiological indicators also showed regional differences, such as the body mass, POMC and CART gene expression, ghrelin concentration in the stomach and serum, and AMPK activity in DL changed more significantly. All these results showed that food restriction reduces energy metabolism in E. miletus. After refeeding, most of the relevant physiological indicators can return to the control level, indicating that E. miletus has strong phenotypic plasticity. Ghrelin, leptin, and the AMPK pathway play an important role in the energy metabolism of E. miletus under food restriction. Moreover, regional differences in physiological indicators under food restriction may be related to the different temperatures or food resources in different regions.

Comparative research of intestinal microbiota diversity and body mass regulation in Eothenomys miletus from different areas of Hengduan mountain regions

In order to investigate the effects of different areas on intestinal bacterial diversity and body mass regulation in Eothenomys miletus from Hengduan mountain regions, and to explore the community structure and diversity of intestinal microflora and their role in body mass regulation. E. miletus was collected from five areas including Deqin (DQ), Xianggelila (XGLL), Lijiang (LJ), Jianchuan (JC), and Dali (DL), we used 16S rRNA sequencing technology combined with physiological and morphological methods to study the intestinal microbiota diversity, abundance and community structure of the intestinal bacteria in winter, and to explore the influence of geographical factors, physiological indicators including food intake, resting metabolic rate (RMR), non-shivering thermogenesis (NST), neuropeptide Y (NPY), Agouti-Related Protein (AgRP), proopiomelanocortin (POMC), cocaine and amphetamine regulated transcription peptide (CART), and morphological indicators including body mass, body length and other nine indicators on the intestinal microflora diversity in E. miletus. The results showed that there were significant differences in metabolic indexes such as RMR, NST, NPY, AgRP, and morphological indexes such as body length, tail length and ear length among the five regions. Bacterial community in intestinal tract of E. miletus mainly includes three phyla, of which Firmicutes is the dominant phyla, followed by Bacteroidetes and Tenericutes. At the genus level, the dominant bacterial genera were S24-7(UG), Clostridiales (UG), and Lachnospiraceae (UG), etc. α diversity of intestinal microorganisms in DL and JC were significantly different from that in the other three regions. Genera of intestinal microorganisms in DL and JC were also the most. Moreover, Bacteroides, Ruminococcus, and Treponema could affect energy metabolism in E. miletus, which were closely related to the environment in which they lived. All of these results indicated that different areas in Hengduan Mountain had certain effects on the structure of intestinal microbial community in E. miletus, which were responded positively to changes in food abundance and other environmental factors. Furthermore, Firmicutes and Bacteroidetes play an important role in the body mass regulation in E. miletus.

Obligatory homeothermy of mesic adapted African striped mice, Rhabdomys pumilio, is governed by seasonal basal metabolism and year-round "thermogenic readiness" of brown adipose tissue

Small mammals undergo thermoregulatory adjustments in response to changing environmental conditions. Whereas small heterothermic mammals can employ torpor to save energy in the cold, homeothermic species must increase heat production to defend normothermia through the recruitment of brown adipose tissue (BAT). Here, we studied thermoregulatory adaptation in an obligate homeotherm, the African striped mouse (Rhabdomys pumilio), captured from a subpopulation living in a mesic, temperate climate with marked seasonal differences. Basal metabolic rate (BMR), non-shivering thermogenesis (NST) and summit metabolic rate (MSUM) increased from summer to winter, with NST and MSUM already reaching maximal rates in autumn, suggesting seasonal preparation to the cold. Typical of rodents, cold-induced metabolic rates positively correlate with BAT mass. Analysis of cytochrome c oxidase (COX) activity and UCP1 content, however, demonstrate that thermogenic capacity declines with BAT mass. This resulted in seasonal differences in NST being driven by changes in BMR. The increase in BMR is supported by a comprehensive anatomical analysis of metabolically active organs, revealing increased mass proportions in the cold season. The thermoregulatory response of R. pumilio is associated with the maintenance of body weight throughout the year (48.3±1.4 g), contrasting large summer-winter mass reductions often observed in Holarctic rodents. Collectively, bioenergetic adaptation of this Afrotropical rodent involves seasonal organ adjustments influencing BMR, combined with a constant thermogenic capacity dictated by trade-offs in thermogenic properties of BAT. Arguably, this high degree of plasticity was a response to unpredictable cold spells throughout the year. Consequently, the reliance on such a resource intensive thermoregulatory strategy may expose more energetic vulnerability in changing environments of food scarcity and extreme weather conditions due to climate change, with major ramifications for survival of the species.

Role of transient receptor potential vanilloid-1 in behavioral thermoregulation of the Mongolian gerbil Meriones unguiculatus

Ambient temperature considerably affects the physiology and behavior of mammals. Thermosensory and thermoregulatory abilities play an important role in the response to changing ambient temperature in endotherms. However, the molecular mechanisms of behavioral thermoregulation remain poorly understood. Transient receptor potential vanilloid-1 (TRPV1) is activated by changes in ambient temperature and is involved in acute thermoregulation. Here, we aimed to determine whether TRPV1 is involved in behavioral thermoregulation in wild rodents by conducting 2 experiments. In the first, 42 adult Mongolian gerbils (Meriones unguiculatus; 14 per treatment) were randomly assigned to 3 housing temperatures (4, 23, and 36°C) for 4 weeks. In the second, 20 gerbils (10 per treatment) were randomly injected with capsaicin (TRPV1 agonist) or AMG517 (TRPV1 antagonist). The results showed a significant decrease in food intake and non-shivering thermogenesis in the gerbils housed at 36°C. Additionally, there was a significant increase in the preference of gerbils housed at 4°C to low temperatures. The expression of TRPV1 protein in the brown adipose tissue (BAT) and liver was significantly positively correlated with that of protein kinase A (PKA). The expression of TRPV1 and PKA proteins in the BAT was positively correlated with the temperature preference of the gerbils. The gerbils injected with capsaicin preferred significantly lower temperatures than the control group gerbils. These findings suggest that TRPV1 and PKA are involved in behavioral thermoregulation in Mongolian gerbils.

Cold exposure increased hypothalamic orexigenic neuropeptides but not food intake in fattening Daurian ground squirrels

Energy balance and thermoregulation in many fat-storing seasonal hibernators show a circannual rhythm. To understand the physiological mechanisms of the seasonal pre-hibernation fattening related to the regulation of energy expenditure and thermogenesis, we cold-exposed fattening Daurian ground squirrels (Spermophilus dauricus) in late summer for 3 weeks. We predicted that cold-exposed squirrels would increase food intake rather than express torpor to accommodate both fattening and thermoregulatory fuel allocation. Food intake and body mass were quantified. After 3 weeks, body compositions, serum leptin concentration, expression of hypothalamic neuropeptides related to regulation of energy balance and uncoupling protein 1 (UCP1) in brown adipose tissue (BAT) were measured. There was no change in body mass after 3-weeks of cold exposure. Hypothalamic orexigenic neuropeptides and UCP1 levels in BAT were up-regulated after cold exposure. Food intake, serum leptin concentration and the expression of leptin signal suppressors, suppressor of cytokine signaling 3 and protein tyrosine phosphatase 1B, in hypothalamus showed no differences compared with controls. The core body temperature was unaffected by cold exposure. Our data suggest that cold exposure affected fattening mainly because of the increased heat loss, whereas energy balance and thermoregulation are under control of a strong circannual rhythm in the Daurian ground squirrels.

Continuous growth through winter correlates with increased resting metabolic rate but does not affect daily energy budgets due to torpor use

Small mammals that are specialists in homeothermic thermoregulation reduce their self-maintenance costs of normothermy to survive the winter. By contrast, heterothermic ones that are considered generalists in thermoregulation can lower energy expenditure by entering torpor. It is well known that different species vary the use of their strategies to cope with harsh winters in temperate zones; however, little is still known about the intraspecific variation within populations and the associated external and internal factors. We hypothesized that yellow-necked mice Apodemus flavicollis decrease their resting metabolic rate (RMR) from autumn to winter, and then increase it during spring. However, since the alternative for seasonal reduction of RMR could be the development of heterothermy, we also considered the use of this strategy. We measured body mass (m_b), RMR, and body temperature (T_b) of mice during 2 consecutive years. In the 1st year, mice decreased whole animal RMR in winter, but did not do so in the 2nd year. All mice entered torpor during the 2nd winter, whereas only a few did so during the first one. Mice showed a continuous increase of m_b, which was steepest during the 2nd year. The relationship between RMR and m_b varied among seasons and years most likely due to different mouse development stages. The m_b gain at the individual level was correlated positively with RMR and heterothermy. This indicates that high metabolism in winter supports the growth of smaller animals, which use torpor as a compensatory mechanism. Isotope composition of mice hair suggests that in the 1st year they fed mainly on seeds, while in the 2nd, they likely consumed significant amounts of less digestible herbs. The study suggests that the use of specialist or generalist thermoregulatory strategies can differ with environmental variation and associated differences in developmental processes.

Season and sex have different effects on hematology and cytokines in striped hamsters (Cricetulus barabensis)

Animals in the temperate zones face seasonal variations in environments and hence their immune responses change seasonally. In the current study, seasonal changes in hematological parameters and cytokines in striped hamsters (Cricetulus barabensis) were examined to test the winter immunoenhancement hypothesis, which states that immune function tends to increase in fall and winter compared with other seasons. Male and female hamsters were captured from the wild in the fall and winter of 2014 and in the spring and summer of 2015. Maximum body mass in both sexes and relative fatness in female hamsters occurred in the summer, indicating that body condition was the best during this season. All hematological parameters were not different between male and female hamsters, and were also not affected by the interaction of season and sex except neutrophil granulocytes (GRAN). Red blood cells (RBC) and haematocrit (PCV) were higher in the fall and winter, and hemoglobin concentration (HGB) was the highest in winter in hamsters compared with the spring and summer, implying that their oxygen-carrying capacity and oxygen affinity of the blood increased during these seasons. Compared with other seasons, the number of white blood cells (WBC) was higher in winter than in summer, intermediate granulocytes (MID), the percent of MID (MID%), GRAN and the percent of GRAN (GRAN%) were the highest in winter, which all supported the winter immunoenhancement hypothesis. However, the count of lymphocytes (LYMF) was the highest in spring, being inconsistent with this hypothesis. IL-2 levels, but not TNF-α, were influenced by seasons, sex and their interaction in hamsters. Regardless of sex, IL-4 titres were higher in spring and summer than in fall and winter in hamsters. INF-γ titres in male hamsters did not differ between the spring and summer, while its titres in female hamsters was lower in spring in contrast with winter and summer. Higher IL-2 and IL-4 levels during the breeding seasons might be crucial in controlling the increased possibilities of infections in these seasons. In summary, season and sex had disparate effects on different hematological profiles and the levels of cytokines in hamsters.

Thyroid hormones mediate metabolic rate and oxidative, anti-oxidative balance at different temperatures in Mongolian gerbils (Meriones unguiculatus)

Oxidative damage is a potential physiological cost of thermoregulation during seasonal adjustments to air temperature (T_a) in small mammals. Here, we hypothesized that T_a affects serum thyroid hormone levels and these hormones can mediate the changes in metabolic rate and oxidative damage. Mongolian gerbils (Meriones unguiculatus) were acclimated at different T_as (5 °C, 23 °C and 37 °C) for 3 weeks. Serum tri-iodothyronine (T3) levels increased at 5 °C but decreased at 37 °C compared to the control (23 °C). Protein carbonyls increased in liver at 37 °C compared with control, however, lipid damage (malonaldehyde, MDA) in both serum and liver was unrelated to T_a. After the effects of different T_as on thyroid hormone levels and oxidative damage markers were determined, we further investigate whether thyroid hormones mediated metabolic rate and oxidative damage. Another set of gerbils received 0.0036% L-thyroxin (hyperthyroid), 0.04% Methylimazol (hypothyroid) or water (control). Hypothyroid group showed a 34% reduction in resting metabolic rate (RMR) also 42% and 26% increases in MDA and liver protein carbonyl respectively, whereas hyperthyroid group had higher RMR, liver mass and superoxide dismutase (SOD) compared to control. Serum T3 or T3/T4 levels were correlated positively with RMR, liver mass, and SOD, but negatively with MDA and uncoupling protein 2 (UCP2). We concluded that high T_a induced hypothyroidism, decreased RMR and increased oxidative damage, whereas low T_a induced hyperthyroidism, increased RMR and unchanged oxidative damage. These data supported our hypothesis that thyroid hormones can be a cue to mediate metabolic rate and different aspects of oxidative and antioxidant activities at different T_as.

Seasonal variations in cellular and humoral immunity in male striped hamsters (Cricetulus barabensis)

Animals in the non-tropical zone usually demonstrate seasonal variations in immune function, which is important for their survival. In the present study, seasonal changes in immunity in striped hamsters (Cricetulus barabensis) were investigated to test the winter immunoenhancement hypothesis. Male hamsters were captured from the wild in the fall and winter of 2014 and in the spring and summer of 2015. Body mass, body fat mass and blood glucose levels of the hamsters were all highest in the summer, whereas relative fatness and thymus mass had no seasonal changes. Spleen mass was highest in the fall and white blood cells and phytohaemagglutinin (PHA) response indicative of cellular immunity were lowest in the summer among the four seasons, which supports the winter immunoenhancement hypothesis. IgG and IgM titers were lowest in the fall, which was against this hypothesis. Body fat mass had no correlations with cellular and humoral immunity, suggesting it was not the reason for seasonal changes in cellular and humoral immunity in males. Leptin titers were higher in spring and summer than in fall and winter. No correlation between leptin and cellular and humoral immunity suggested that leptin did not mediate their seasonal changes. Similarly, corticosterone levels were also higher in spring and summer than in fall and winter, which correlated negatively with cellular immunity but positively with IgG levels. This result implied that corticosterone has a suppressive effect on cellular immunity and an enhancing effect on humoral immunity. In summary, distinct components of immune systems exhibited different seasonal patterns. This article has an associated First Person interview with the first author of the paper.

Does Basal Metabolism Set the Limit for Metabolic Downregulation during Torpor?

The evolution of endothermic thermoregulation is rooted in the processes involving high metabolism, which allows the maintenance of high and stable body temperatures (T_b). In turn, selection for high endothermic metabolism correlates with increased size of metabolically active organs and thus with high basal metabolic rate (BMR). Endothermic animals are characterized by an MR several times that of similar-sized ectotherms. However, many small mammals are temporally heterothermic and are able to temporally decrease T_b and MR by entering daily torpor or hibernation. Both BMR and minimum MR during torpor (TMR_min) likely result from oxidative respiration in mitochondria of the same tissues. It should be expected that these two MRs are positively correlated, suggesting that the evolution of endothermy and higher BMR set the limit for the ability to reduce MR while entering torpor. Using published data for 96 mammal species, we tested the hypothesis that, among heterothermic mammals, the processes leading to the evolution of higher BMR limit the ability to downregulate metabolism during torpor. We found that body mass (m_b)-adjusted BMR was positively correlated with m_b- and T_b-adjusted TMR_min, in a phylogenetically corrected analysis. Phylogenetic path modeling indicated that the mechanisms underlying the evolutionary increase of BMR in endotherms most likely constrain their ability to reduce MR during torpor. Given that heterothermy is considered an ancestral state in mammals, these results suggest an increase in BMR during the evolution of endothermy in homeothermic animals, which leads to the loss of their ability to enter torpor.

Huddling remodels gut microbiota to reduce energy requirements in a small mammal species during cold exposure

BACKGROUND

Huddling is highly evolved as a cooperative behavioral strategy for social mammals to maximize their fitness in harsh environments. Huddling behavior can change psychological and physiological responses. The coevolution of mammals with their microbial communities confers fitness benefits to both partners. The gut microbiome is a key regulator of host immune and metabolic functions. We hypothesized that huddling behavior altered energetics and thermoregulation by shaping caecal microbiota in small herbivores. Brandt's voles (Lasiopodomys brandtii) were maintained in a group (huddling) or as individuals (separated) and were exposed to warm (23 ± 1 °C) and cold (4 ± 1 °C) air temperatures (Ta).

RESULTS

Voles exposed to cold Ta had higher energy intake, resting metabolic rate (RMR) and nonshivering thermogenesis (NST) than voles exposed to warm Ta. Huddling voles had lower RMR and NST than separated voles in cold. In addition, huddling voles had a higher surface body temperature (Tsurface), but lower core body temperature (Tcore) than separated voles, suggesting a lower set-point of Tcore in huddling voles. Both cold and huddling induced a marked variation in caecal bacterial composition, which was associated with the lower Tcore. Huddling voles had a higher α and β-diversity, abundance of Lachnospiraceae and Veillonellaceae, but lower abundance of Cyanobacteria, Tenericutes, TM7, Comamonadaceae, and Sinobacteraceae than separated voles. Huddling or cold resulted in higher concentrations of short-chain fatty acids (SCFAs), particularly acetic acid and butyric acid when compared to their counterparts. Transplantation of caecal microbiota from cold-separated voles but not from cold-huddling voles induced significant increases in energy intake and RMR compared to that from warm-separated voles.

CONCLUSIONS

These findings demonstrate that the remodeling of gut microbiota, which is associated with a reduction in host Tcore, mediates cold- and huddling-induced energy intake and thermoregulation and therefore orchestrates host metabolic and thermal homeostasis. It highlights the coevolutionary mechanism of host huddling and gut microbiota in thermoregulation and energy saving for winter survival in endotherms.

Huddling Conserves Energy, Decreases Core Body Temperature, but Increases Activity in Brandt's Voles (Lasiopodomys brandtii)

Huddling as social thermoregulatory behavior is commonly used by small mammals to reduce heat loss and energy expenditure in the cold. Our study aimed to determine the effect of huddling behavior on energy conservation, thermogenesis, core body temperature (T_b) regulation and body composition in Brandt's voles (Lasiopodomys brandtii). Adult captive-bred female Brandt's voles (n = 124) (~50 g) in 31 cages with 4 individuals each were exposed to cool (23 ± 1°C) and cold (4 ± 1°C) ambient temperatures (T_a) and were allowed to huddle or were physically separated. The cold huddling (Cold-H) groups significantly reduced food intake by 29% and saved digestible energy 156.99 kJ/day compared with cold separated groups (Cold-S); in cool huddling groups (Cool-H) the reduction in food intake was 26% and digestible energy was saved by 105.19 kJ/day in comparison to the separated groups (Cool-S). Resting metabolic rate (RMR) of huddling groups was 35.7 and 37.2% lower than in separated groups at cold and cool T_as, respectively. Maximum non-shivering thermogenesis (NSTmax) of huddling voles was not affected by T_a, but in Cold-S voles it was significantly increased in comparison to Cool-S. Huddling groups decreased wet thermal conductance by 39% compared with separated groups in the cold, but not in the cool T_a. Unexpectedly, huddling voles significantly decreased T_b by 0.25 - 0.50°C at each T_a. Nevertheless, activity of Cold-H voles was higher than in Cold-S voles. Thus, huddling is energetically highly effective because of reduced metabolic rate, thermogenic capacity and relaxed T_b regulation despite the increase of activity. Therefore, Brandt's voles can remain active and maintain their body condition without increased energetic costs during cold exposure. This study highlights the ecological significance of huddling behavior for maintenance of individual fitness at low costs, and thus survival of population during severe winter in small mammals.

Diversity of Thermogenic Capacity Predicts Divergent Obesity Susceptibility in a Wild Rodent

OBJECTIVE

The objective of the present study was to examine whether wild rodents exhibit diverse obesity susceptibility and what factors predispose subjects to this divergence in response to a high-fat diet (HFD).

METHODS

Sixty male and female Brandt's voles (Lasiopodomys brandtii) were fed an HFD for 8 weeks, and the upper (obesity prone [OP]) and lower (obesity resistant [OR]) one-third for mass gain were selected. Energy budgets and pathologic changes were measured. Another 30 males were fed a low-fat control diet (LFD) for 10 weeks and then fed an HFD for 12 weeks. The energetic parameters of the rodents on an LFD were analyzed for the correlation with body mass of the rodents on an HFD.

RESULTS

OP voles had higher energy intakes, higher levels of noradrenaline-induced nonshivering thermogenesis, and a greater impairment of insulin tolerance than OR voles. Unlike laboratory rodents, there were no differences in physical activity or resting metabolic rate between these groups of voles. The thermogenic capacity during LFD feeding was the strongest predictor for mass gain during HFD feeding.

CONCLUSIONS

This study suggests that a wild rodent species of Brandt's voles exhibits diverse obesity susceptibility in reaction to an HFD, providing a natural model to give insight into the mechanisms for divergent obesity susceptibility. This study also indicates that maximum thermogenic capacity has a predictive power for the development of obesity when an HFD was available.

Comparative analyses of basal rate of metabolism in mammals: data selection does matter

Basal rate of metabolism (BMR) is a physiological parameter that should be measured under strictly defined experimental conditions. In comparative analyses among mammals BMR is widely used as an index of the intensity of the metabolic machinery or as a proxy for energy expenditure. Many databases with BMR values for mammals are available, but the criteria used to select metabolic data as BMR estimates have often varied and the potential effect of this variability has rarely been questioned. We provide a new, expanded BMR database reflecting compliance with standard criteria (resting, postabsorptive state; thermal neutrality; adult, non-reproductive status for females) and examine potential effects of differential selectivity on the results of comparative analyses. The database includes 1739 different entries for 817 species of mammals, compiled from the original sources. It provides information permitting assessment of the validity of each estimate and presents the value closest to a proper BMR for each entry. Using different selection criteria, several alternative data sets were extracted and used in comparative analyses of (i) the scaling of BMR to body mass and (ii) the relationship between brain mass and BMR. It was expected that results would be especially dependent on selection criteria with small sample sizes and with relatively weak relationships. Phylogenetically informed regression (phylogenetic generalized least squares, PGLS) was applied to the alternative data sets for several different clades (Mammalia, Eutheria, Metatheria, or individual orders). For Mammalia, a 'subsampling procedure' was also applied, in which random subsamples of different sample sizes were taken from each original data set and successively analysed. In each case, two data sets with identical sample size and species, but comprising BMR data with different degrees of reliability, were compared. Selection criteria had minor effects on scaling equations computed for large clades (Mammalia, Eutheria, Metatheria), although less-reliable estimates of BMR were generally about 12-20% larger than more-reliable ones. Larger effects were found with more-limited clades, such as sciuromorph rodents. For the relationship between BMR and brain mass the results of comparative analyses were found to depend strongly on the data set used, especially with more-limited, order-level clades. In fact, with small sample sizes (e.g. <100) results often appeared erratic. Subsampling revealed that sample size has a non-linear effect on the probability of a zero slope for a given relationship. Depending on the species included, results could differ dramatically, especially with small sample sizes. Overall, our findings indicate a need for due diligence when selecting BMR estimates and caution regarding results (even if seemingly significant) with small sample sizes.

The roles of metabolic thermogenesis in body fat regulation in striped hamsters fed high-fat diet at different temperatures

The metabolic thermogenesis plays important roles in thermoregulation, and it may be also involved in body fat regulation. The thermogenesis of brown adipose tissue (BAT) is largely affected by ambient temperature, but it is unclear if the roles in body fat regulation are dependent on the temperature. In the present study, uncoupling protein 1 (ucp1)-based BAT thermogenesis, energy budget and body fat content were examined in the striped hamsters fed high fat diet (HF) at cold (5°C) and warm (30°C) temperatures. The effect of 2, 4-dinitrophenol (DNP), a chemical uncoupler, on body fat was also examined. The striped hamsters showed a notable increase in body fat following the HF feeding at 21°C. The increased body fat was markedly elevated at 30°C, but was significantly attenuated at 5°C compared to that at 21°C. The hamsters significantly increased energy intake at 5°C, but consumed less food at 30°C relative to those at 21°C. Metabolic thermogenesis, indicated by basal metabolic rate, UCP1 expression and/or serum triiodothyronine levels, significantly increased at 5°C, but decreased at 30°C compared to that at 21°C. A significant decrease in body fat content was observed in DNP-treated hamsters relative to the controls. These findings suggest that the roles of metabolic thermogenesis in body fat regulation largely depend on ambient temperature. The cold-induced enhancement of BAT thermogenesis may contribute the decreased body fat, resulting in a lean mass. Instead, the attenuation of BAT thermogenesis at the warm may result in notable obesity.

Role of thermal physiology and bioenergetics on adaptation in tree shrew (Tupaia belangeri): the experiment test

Ambient conditions, as temperature and photoperiod, play a key role in animals’ physiology and behaviors. To test the hypothesis that the maximum thermal physiological and bioenergetics tolerances are induced by extreme environments in Tupaia belangeri. We integrated the acclimatized and acclimated data in several physiological, hormonal, and biochemical markers of thermogenic capacity and bioenergetics in T. belangeri. Results showed that T. belangeri increased body mass, thermogenesis capacity, protein contents and cytochrome c oxidase (COX) activity of liver and brown adipose tissue in winter-like environments, which indicated that temperature was the primary signal for T. belangeri to regulate several physiological capacities. The associated photoperiod signal also elevated the physiological capacities. The regulations of critical physiological traits play a primary role in meeting the survival challenges of winter-like condition in T. belangeri. Together, to cope with cold, leptin may play a potential role in thermogenesis and body mass regulation, as this hormonal signal is associated with other hormones. The strategies of thermal physiology and bioenergetics differs between typical Palearctic species and the local species. However, the maximum thermal physiology and bioenergetic tolerance maybe is an important strategy to cope with winter-like condition of T. belangeri.

Exposure to short photoperiod regime reduces ventral subicular lesion-induced anxiety-like behavior in Wistar rats

Neurodegeneration of hippocampal structures is implicated in Alzheimer's disease (AD). Patients with AD exhibit 'sundown syndrome' featuring mood swings and anxiety. Although there are studies demonstrating circadian rhythm disruption associated with sundown phenomenon, the mechanisms underlying the emotional disturbances remain elusive. In the present study, we examined the relationship between subiculum (a key hippocampal output structure) and anxiety. Our study demonstrates that bilateral ventral subicular lesion (VSL) leads to anxiogenic behavior. In the elevated plus maze test, VSL rats made less number of entries into the open arms and spent significantly more time in the closed arms. Similarly, in the light-dark exploration test, VSL rats spent significantly more time in the dark chamber and made fewer entries into the light chamber. VSL also produced significant neurodegeneration in the paraventricular, suprachiasmatic and dorsomedial nuclei of the hypothalamus. Exposing VSL rats to a short photoperiod regime (SPR; 06/18h light-dark cycle) for 21days ameliorated the anxiety-like behavior. VSL rats on SPR also exhibited increased food consumption and higher core body temperature. Our study supports the hypothesis that the ventral subiculum regulates anxiety-like behavior and that SPR helps in the alleviation of such behavior. Even though the mechanisms underlying anxiolytic effects of light-dark cycle manipulation are yet to be elucidated, such non-pharmacological strategies can help to mitigate anxiety-like behavior. A proper understanding of the effectiveness of photoperiod manipulation will help in developing strategies in the management of emotional disturbances associated with affective and neurodegenerative disorders including AD.

Photoperiod induced obesity in the Brandt's vole (Lasiopodomys brandtii): a model of 'healthy obesity'?

Brandt's voles have an annual cycle of body weight and adiposity. These changes can be induced in the laboratory by manipulation of photoperiod. In the present study, male captive-bred Brandt's voles aged 35 days were acclimated to a short day (SD) photoperiod (8L:16D) for 70 days. A subgroup of individuals (n=16) were implanted with transmitters to monitor physical activity and body temperature. They were then randomly allocated into long day (LD=16L:8D) (n=19, 8 with transmitters) and SD (n=18, 8 with transmitters) groups for an additional 70 days. We monitored aspects of energy balance, glucose and insulin tolerance (GTT and ITT), body composition and organ fat content after exposure to the different photoperiods. LD voles increased in weight for 35 days and then re-established stability at a higher level. At the end of the experiment LD-exposed voles had greater white adipose tissue mass than SD voles (P=0.003). During weight gain they did not differ in their food intake or digestive efficiency; however, daily energy expenditure was significantly reduced in the LD compared with SD animals (ANCOVA, P<0.05) and there was a trend to reduced resting metabolic rate RMR (P=0.075). Physical activity levels were unchanged. Despite different levels of fat storage, the GTT and ITT responses of SD and LD voles were not significantly different, and these traits were not correlated to body fatness. Hence, the photoperiod-induced obesity was independent on disruptions to glucose homeostasis, indicating a potential adaptive decoupling of these states in evolutionary time. Fat content in both the liver and muscle showed no significant difference between LD and SD animals. How voles overcome the common negative aspects of fat storage might make them a useful model for understanding the phenomenon of 'healthy obesity'.

The increase in fat content in the warm-acclimated striped hamsters is associated with the down-regulated metabolic thermogenesis

It has been well known that metabolic thermogenesis plays an important role in the thermoregulation of small mammals under different temperatures, while its role in fat accumulation is far from clear. In the present study, several physiological, hormonal, and biochemical measures indicative of metabolic thermogenesis were measured in the weaning striped hamsters after acclimated to a warm condition (30°C) for 1, 3 and 4months. The warm-acclimated groups significantly decreased energy intake, and simultaneously decreased nonshivering thermogenesis compared to those housed at 21°C. Body fat content increased by 29.9%, 22.1% and 19.6% in the hamsters acclimated to 1, 3 or 4months, respectively relative to their counterparts maintain at 21°C (P<0.05). The cytochrome c oxidase (COX) activity of brain, liver, heart and skeletal muscle, and the ratio of serum tri-iodothyronine to thyroxine significantly decreased in warm-acclimated groups compared with 21°C group. COX activity and uncoupling protein 1 (UCP1) mRNA expression of brown adipose tissue (BAT) were significantly down-regulated under the warm conditions. COX activity of BAT, liver, heart and muscle were significantly negatively correlated with body fat content, and the correlation between UCP1 expression and body fat content tended to be negative. These findings suggest that the decrease in the energy spent on metabolic thermogenesis plays an important role in the fat accumulation. The attenuation of COX and UCP1-based BAT activity may be involved in body fat accumulation in animals under warm conditions.

The role of dietary fiber content on energy metabolism, thermogenesis, and leptin in Chevrier’s field mouse (Apodemus chevrieri)

Food quality and availability are important factors influencing the survival and reproduction of animals. The aim of the present study was to examine the effect of dietary fiber content high-fiber (HF) diet treatment or low-fiber (LF) diet treatment) on energy metabolism, thermogenesis, and leptin concentrations in Chevrier’s field mouse (Apodemus chevrieri (Milne-Edwards, 1868)) (Mammalia: Rodentia: Muridae). Mice on the HF treatment showed a lower body mass compared with LF treatment from day 27 to day 37, and a lower but insignificant body mass to day 71. Dry matter intake (DMI) and gross energy intake (GEI) were greater in HF compared with LF, whereas the digestible energy intake (DEI) was similar for both treatments. Nonshivering thermogenesis (NST) decreased in HF mice, whereas LF mice remained stable; no significant differences were detected in the basal metabolic rate (BMR), uncoupling protein 1 (UCP1) content in brown adipose tissue (BAT), or the levels of serum tri-iodothyronine (T3) and thyroxine (T4) between HF and LF mice. Although there were no differences in body fat content and serum leptin concentrations between HF and LF mice, serum leptin levels were positively correlated with body fat mass. These results support the hypothesis that A. chevrieri can compensate the poor-quality diet physiologically by way of increasing food intake and decreasing thermogenesis.

Leptin regulates energy intake but fails to facilitate hibernation in fattening Daurian ground squirrels (Spermophilus dauricus)

Body fat storage before hibernation affects the timing of immergence in Daurian ground squirrels (Spermophilus dauricus). Leptin is an adipose signal and plays vital role in energy homeostasis mainly by action in brain. To test the hypothesis that leptin plays a role in facilitating the process of hibernation, squirrels were administrated with recombinant murine leptin (1μg/day) through intracerebroventricular (ICV) injection for 12 days during fattening. From day 7 to 12, animals were moved into a cold room (5±1°C) with constant darkness which functioned as hibernaculum. Energy intake, body mass and core body temperature (Tb) were continuously monitored throughout the course of experiment. Resting metabolic rate (RMR) was measured under both warm and cold conditions. At the end of leptin administration, we measured the serum concentration of hormones related to energy regulation, mRNA expression of hypothalamic neuropeptides and uncoupling protein 1 (UCP1) levels in brown adipose tissue (BAT). Our results showed that during leptin administration, the cumulative food intake and increase of body mass were suppressed while Tb and RMR were unaltered. The proportion of torpid squirrels was not different between two groups. At the end of leptin administration, the expressions of hypothalamic neuropeptide Y and agouti gene-related protein were suppressed. There were no differences in UCP1 mRNA expression or protein content in BAT between groups. Our data suggest that leptin can affect energy intake via hypothalamic neuropeptides, but is not involved in the initiation of hibernation in fattening Daurian ground squirrels.

Effects of dietary tannic acid on the growth, hepatic gene expression, and antioxidant enzyme activity in Brandt's voles (Microtus brandti)

This study was designed to investigate the physiological and biochemical responses of Brandt's voles to the persistent presence of dietary tannic acid. The diet for animals in the experimental group was supplemented with 3% dietary tannic acid for 5weeks. The control group received a commercial lab chow. No significant differences were detected in body weight, organ (heart, kidney, and liver) weights, and organ parameters between animals from two groups. However, voles in the experimental group had significantly higher daily food intake, increased contents of proline and histidine in saliva and feces after protein hydrolysis, and elevated hepatic expression of transferrin than the control. Our results suggested the existence of adaptive strategies developed in Brandt's voles to overcome the adverse effects of dietary tannic acid. (1) Food consumption was increased to satisfy their nutritional demands. (2) The secretion of tannic-acid-binding salivary proteins was promoted. (3) The absorption of iron was enhanced. These alterations contributed to neutralize the negative effects of tannic acid and maintain body mass in animals supplemented with tannic acid. As the result of the consumption of tannic acid, hepatic expression of 3-hydroxy-3-methylglutaryl coenzyme A reductase was significantly decreased, while the overall potential of the antioxidant system, characterized by increased hepatic enzymatic activities of catalase and glutathione peroxidase, was enhanced. Our results also implied the involvement of tannic acid in the regulation of lipid metabolism and oxidative stress in voles.

Plasticity in the physiological energetics of Apodemus chevrieri: the role of dietary fiber content

Small mammals are usually adapted to cope with changes in food quality and availability. In order to investigate the adaptive strategy of small rodents responding to varying dietary fiber content, in the present study, Apodemus chevrieri individuals were acclimated to a high-fiber diet for four weeks and then a relatively low-fiber diet for another four weeks. The results show that body mass was relatively stable over the course of acclimation, but dry matter intake, gross energy intake and the mass of the digestive tract increased significantly and digestibility decreased significantly in high-fiber diet mice, while the digestible energy intake was similar for both high-fiber and low-fiber diet mice except for the first week. High-fiber/low-fiber diet mice showed only a significant lower basal metabolic rate and nonshivering thermogenesis compared to low-fiber diet mice on day R1. The high-fiber diet induced a decrease in serum leptin levels and brown adipose tissue mass associated with a reduction in the cytochrome c oxidase activity and uncoupling protein 1 content of brown adipose tissue. Body mass, thermogenic capacity, energy intake, serum leptin levels and digestive tract morphology returned to the control levels after 4 weeks of refeeding low-fiber diet. Further, serum leptin levels were positively related to body fat mass and negatively related to food intake. These data indicated that body mass, energy intake, serum leptin levels and organ morphological plasticity were the main strategies by which A. chevrieri copes with variations in dietary fiber content.

Plasticity in food intake, thermogenesis and body mass in the tree shrew (Tupaia belangeri) is affected by food restriction and refeeding

Physiological adjustments are important strategies for small mammals in response to variation in food availability. To determine the physiological mechanisms affected by food restriction and refeeding, tree shrews were restricted to 85% of initial food intake for 4 weeks and refedad libitumfor another 4 weeks. Changes in food intake, body mass, thermogenesis, body composition, mitochondrial cytochromecoxidase activity, uncoupling protein-1 content in brown adipose tissue and serum leptin levels were measured. The results showed that body mass, body fat mass and serum leptin levels significantly decreased in food restricted tree shrews, and increased when the restriction ended, showing a short “compensatory growth” rather than over-weight or obesity compared withad libitumcontrols. Resting metabolic rate, non-shivering thermogenesis, brown adipose tissue mass (mg), and uncoupling protein-1 content decreased significantly in response to food restriction, and returned to the control levels after the animals were refedad libitum, while the brown adipose tissue mass (%) and cytochromecoxidase activity remained stable during food restriction and refeeding. Food intake increased shortly after refeeding, which perhaps contributed to the rapid regaining of body mass. These results suggest thatTupaia belangerican adjust the status of its physiology integratively to cope with the lack of food by means of decreasing body mass, thermogenesis and serum leptin levels. Leptin may act as a starvation signal to predominantly mediate the reduction in body mass and energy expenditure.

Cold exposure inhibits hypothalamic Kiss-1 gene expression, serum leptin concentration, and delays reproductive development in male Brandt's vole (Lasiopodomys brandtii)

Cold commonly affects growth and reproductive development in small mammals. Here, we test the hypothesis that low ambient temperature will affect growth and puberty onset, associated with altered hypothalamic Kiss-1 gene expression and serum leptin concentration in wild rodents. Male Brandt's voles (Lasiopodomys brandtii) were exposed to cold (4 ± 1 °C) and warm (23 ± 1 °C) conditions from the birth and sacrificed on different developmental stages (day 26, day 40, day 60, and day 90, respectively). Brandt's voles increased the thermogenic capacity of brown adipose tissue, mobilized body fat, decreased serum leptin levels, and delayed the reproductive development especially on day 40 in the cold condition. They increased food intake to compensate for the high energy demands in the cold. The hypothalamic Kiss-1 gene expression on day 26 was decreased, associated with lower wet testis mass and testis testosterone concentration on day 40, in the cold-exposed voles compared to that in the warm. Serum leptin was positively correlated with body fat, testis mass, and testosterone concentration. These data suggested that cold exposure inhibited hypothalamic Kiss-1 gene expression during the early stage of development, decreased serum leptin concentration, and delayed reproductive development in male Brandt's voles.

Effects of dietary fiber content on energetics in nonreproductive and reproductive Brandt’s voles (Lasiopodomys brandtii)

Food quality can affect many physiological characteristics in small mammals. Reproduction is a highly energy-demanding period especially for the females to produce and feed their offspring. We hypothesized that energy intake was constrained at different levels in nonreproductive and reproductive females and thus they adopted diverse energy strategies in response to diet changes. Here, we tested the effects of low fiber diet (3.5% vs. 12.4%) on energy intake and thermogenesis in nonreproductive and reproductive Brandt’s voles (Lasiopodomys brandtii (Radde, 1861)), a herbivorous species. We found that the voles decreased food intake while keeping a stable digestible energy intake (DEI) in response to the low fiber diet, but DEI was increased in reproductive voles at peak lactation. Uncoupling protein 1 content in brown adipose tissue decreased in nonreproductive voles, but was stable in reproductive voles on the low fiber diet. Litter mass on day 18 of age tended to increase in the low fiber group compared with that in the control group. Our findings demonstrate that the voles have a target intake to maintain energy balance when diet composition changes and energy intake may be constrained at a high level for the reproductive voles to improve their offspring’s fitness.

High incubation temperatures enhance mitochondrial energy metabolism in reptile embryos

Developmental rate increases exponentially with increasing temperature in ectothermic animals, but the biochemical basis underlying this thermal dependence is largely unexplored. We measured mitochondrial respiration and metabolic enzyme activities of turtle embryos (Pelodiscus sinensis) incubated at different temperatures to identify the metabolic basis of the rapid development occurring at high temperatures in reptile embryos. Developmental rate increased with increasing incubation temperatures in the embryos of P. sinensis. Correspondingly, in addition to the thermal dependence of mitochondrial respiration and metabolic enzyme activities, high-temperature incubation further enhanced mitochondrial respiration and COX activities in the embryos. This suggests that embryos may adjust mitochondrial respiration and metabolic enzyme activities in response to developmental temperature to achieve high developmental rates at high temperatures. Our study highlights the importance of biochemical investigations in understanding the proximate mechanisms by which temperature affects embryonic development.

Seasonal changes in body mass, serum leptin levels and hypothalamic neuropeptide gene expression in male Eothenomys olitor

The present study examined seasonal changes in body mass and energy metabolism in the Chaotung vole (Eothenomys olitor) and the physiological mechanisms underpinning these changes. Seasonal changes in the following parameters were measured in male E. olitor, body mass, food intake, thermogenesis, enzyme activity, masses of tissues and organs, hormone concentrations and expression of hypothalamic arcuate nucleus energy balance genes including neuropeptide Y (NPY), agouti-related protein (AgRP), pro-opiomelanocortin (POMC), and cocaine- and amphetamine-regulated transcript (CART). Body mass was constant over the year, but the masses of tissues and organs differed significantly between seasons. There were significant changes in body fat mass and serum leptin levels over the four seasons. E. olitor showed significant seasonal changes in food intake and thermogenesis, uncoupling protein 1 (UCP1) content, enzyme activity, and serum tri-iodothyronine (T3) and thyroxine (T4) levels. Moreover, mRNA expression in the hypothalamus showed significant seasonal changes. All of our results suggested that E. olitor had constant body mass over the year, which was inconsistent with the prediction of the 'set-point' hypothesis. However, body fat mass and serum leptin levels were significantly different among the four seasons, providing support for the 'set-point' hypothesis. The changes in leptin, NPY, AgRP, POMC, and CART mRNA levels may play a role in the regulation of energy intake in E. olitor. Furthermore, the role of leptin and hypothalamic neuropeptide gene in the regulation of energy metabolism and body mass may be different in animals that are acclimated to different seasons.

The expression of leptin, hypothalamic neuropeptides and UCP1 before, during and after fattening in the Daurian ground squirrel (Spermophilus dauricus)

The Daurian ground squirrel (Spermophilus dauricus) accumulates large amounts of body fat during pre-hibernation fattening. Leptin, an adipose-derived hormone, plays important roles in energy balance and thermogenesis. We predicted that body fat accumulation would lead to the elevation of leptin concentration while its effect on satiety would be suppressed in hypothalamus during fattening. In addition, the uncoupling protein 1 (UCP1) in brown adipose tissue (BAT) would increase and correlated positively with leptin concentration before hibernation. Here, we measured serum leptin concentration and leptin mRNA in white adipose tissue (WAT), hypothalamic neuropeptides involved in energy regulation and UCP1 in BAT before, during and after fattening in squirrels. The fat mass gradually increased during fattening but serum leptin increased mainly in the late phase of fattening, which was consistent with leptin mRNA expression in WAT. During fattening, the mRNA of hypothalamic leptin receptor was up-regulated and correlated positively with serum leptin. Orexigenic neuropeptide Y mRNA increased by 67%; however agouti-related peptide remained unchanged before hibernation. There was no significant change in anorexigenic neuropeptide mRNA. No change in suppressor of cytokine signaling-3 and protein tyrosine phosphatase-1B was detected. UCP1 mRNA expression and protein content in BAT increased significantly after fattening. These changes were independent of environmental conditions and serum leptin concentration. Our results suggest that the dissociation of leptin production and adiposity during fattening may facilitate fat accumulation. No evidence of suppressed leptin signal was found in fattening squirrels. The UCP1 recruitment in post-fattening squirrels could occur without winter-like acclimation and increased leptin.

Leptin levels in free ranging striped mice (Rhabdomys pumilio) increase when food decreases: the ecological leptin hypothesis

Leptin is a hormone informing the body about its fat stores, reducing appetite and foraging and as such reducing fattening of individuals. In laboratory rodents, leptin secretion is highly correlated to the amount of adipose tissue. We compared this to the alternative ecological leptin hypothesis, which based on the behavioural effects of leptin predicts that leptin levels are disassociated from adipose tissue when fattening is of evolutionary advantage to survive coming periods of low food availability. Studying a species that has to survive a dry season with low food availability, we tested the ecological leptin hypothesis, predicting low leptin levels when food availability and thus adiposity is high promoting foraging and fattening, but high leptin levels in the seasons of low food availability, reducing energetic costs due to foraging. We measured leptin levels in 154 samples of free living African striped mice (Rhabdomys pumilio). Striped mice gain significant body mass during the moist season to survive the following dry season with low food availability. We found a strong seasonal effect, with higher leptin levels in the dry season with low food availability, which was in contrast to the hypothesis deriving from studies on laboratory rodents, but in agreement with ecological leptin hypothesis: leptin levels remained low in the period of high food availability, allowing fattening, but increased during periods of low food availability, possibly suppressing energetically costly foraging in an environment where foraging success would have been very low. Leptin correlated significantly and negatively with testosterone levels, and high testosterone levels in the moist season could explain why leptin levels were low even though food availability was high. However, analysing samples from an experimental laboratory study where testosterone levels were increased via implants found no support for a suppressive role of testosterone on leptin. In sum, our study indicates that in a species with seasonal fattening, leptin levels might be uncoupled from the amount of adipose tissue.

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.

Seasonal changes of body mass and energy budget in striped hamsters: the role of leptin

Proper adjustments of physiology and behavior are required for small mammals to cope with seasonal climate change. The aim of this study was to examine the role of leptin in the regulation of body mass and energy budget in striped hamsters. We first investigated seasonal changes in body mass, energy budget, and serum leptin levels in hamsters acclimated to outdoor natural daylight and ambient temperature. Then we assessed the effect of leptin administration on energy budget, serum lipoprotein lipase (LPL) and hepatic lipase (HL) activities, and gene expression of uncoupling protein 1 (UCP1) in brown adipose tissue and of hypothalamic neuropeptides associated with the regulation of energy balance in hamsters maintained at 21° and 5°C. Hamsters showed constant body mass throughout the four seasons but significantly increased food intake and thermogenesis in winter, compared to summer. Minimum body fat was observed in winter, and minimum serum leptin was found in autumn. Hamsters housed at 5°C showed higher energy intake, upregulated gene expression of UCP1 and hormone-sensitive lipase, and lower fat content and LPL and HL activity than the animals maintained at 21°C. Leptin administration had no effect on energy intake but increased maximal thermogenic capacity, as indicated by upregulated UCP1 gene expression at both 21° and 5°C. Body fat and activity of LPL and HL were decreased in hamsters treated with leptin. The results suggest that leptin plays an important role in the seasonal regulation of thermogenic capacity and body composition in striped hamsters. Leptin may be involved in increasing maximal thermogenesis in the cold rather than acting as a starvation signal to increase energy intake.