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

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

Kisspeptin stimulates oocyte maturation,and food deprivation modulates the abundance of kisspeptin system in zebrafish gonads

Kisspeptin is a hormone involved in the neuroendocrine control of reproduction in fish.We hypothesized that kisspeptin stimulates oocyte maturation and modulates other reproductive hormones in zebrafish;and the gonadal kisspeptin system in zebrafish is affected during energy unavailability.The main goals of this research were to test in vitro effects of kisspeptin on oocyte maturation and mRNA abundance in zebrafish ovarian follicles and determine how short-term feed restriction affects kisspeptin and its receptors in zebrafish testis and ovary.This study demonstrates the presence of kisspeptin and its receptors in zebrafish(Danio rerio)gonads and its direct action on ovarian follicles in vitro.Kisspeptin(10 ng/mL)induced oocyte maturation,as indicated by germinal vesicle break down at 18-and 24-hours post-treatment.Kisspeptin significantly increased the abundance of mRNAs encoding reproductive hormones and its receptors in zebrafish oocytes.This suggests that kisspeptin-10 affects ovarian functions by modulating other hormones.Reproduction is a process that requires energy.Therefore,whether energy availability affects the kisspeptin system in zebrafish gonads was determined.Food deprivation modulated kisspeptin expression differently in zebrafish testis and ovary.Kiss2 and kiss1ra were upregulated while kiss1rb was downregulated in the testis post-food deprivation.Meanwhile,no changes in kiss in the ovary were found after food deprivation.However,kiss1rb was downregulated in unfed fish at 3-and 7-days post-food deprivation.Overall,our results suggest sex-and tissue-specific changes in the gonadal abundance of the kisspeptin system in zebrafish.The fine tuning of reproduction during energy fluctuations in fish is likely mediated via changes in hormones,including kisspeptin as shown in this research.

Many-lined Sun Skinks(Mabuya multifasciata) Shift Their Thermal Preferences Downwards When Fasted

We maintained adult many-lined sun skinks(Mabuya multifasciata; 12 females and 12 males) collected from Hainan(southern China) in September 2006 in two outdoor enclosures to examine the effect of feeding condition on selected body temperature(Tsel).Skinks shifted their thermal preferences when fasted.Temporal variation in Tsel was not found within each sex feeding condition combination,and neither in fed nor in fasted skinks did the mean values for Tsel differ between sexes.Body temperatures selected by fed skinks fell within the range from 30.2 to 33.9 C,and those selected by fasted skinks within the range from 25.1 to 31.8 C.Body temperatures(31.8 0.3 C) selected by fed skinks were on average 4.0 C higher than those(27.8 0.4 C) selected by fasted skinks.Fasted skinks had no difficulty in attaining higher body temperatures,but they voluntarily shift their thermal preferences downwards to save energy.This finding suggests an adaptive mechanism adopted by many-lined sun skinks to enhance their fitness during the periods when food availability is low.

3D imaging of the mitochondrial redox state of rathearts under normal and fasting conditions

The heart requires continuous ATP availability that is generated in the mitochondria.Althoughstudies using the cell culture and perfiused organ models have been carried out to investigate thebiochemistry in the mitochondria in response to a change in substrate supply,mitochondrialbioenergetics of heart under normal feed or fasting conditions has not been studied at the tissuelevel with a sub-millimeter spatial resolution either in vivo or er vivo.Oxidation of many food-derived metabolites to generate ATP in the mitochondria is realized through the NADH/NAD+couple acting as a central electron carrier.We employed the Chance redox scanner thelow-temperat ure fluorescence scanner to image the three-dimensional(3D)spatial distribution of themitochondrial redox states in heart tissues of rats under normai feeding or an overnight star-vation for 14.5 h.Multiple consecutive sections of each heart were imaged to map three redoxindices,i.e,NADH,oxidized favoproteins Fp,including flavin adenine dinucleotide(FAD)andthe redox ratio NADH/Fp.The imaging results revealed the micro-heterogeneity and the spatial distribution of these redox indices.The quantitative analysis showed that in the fasted hearts thestandard deviation of both NADH and Fp,ie.,SD NADH and SDFp,significantly decreasedwith a p value of 0.032 and 0.045,respectively,indicating that the hearts become relatively morehomogeneous after fasting.The fasted hearts contained 28.6%less NADH(p=0.038).No sig.nificant change in Fp was foumnd(p=0.4).The NADH/Fp ratio decreased with a marginalP value(0.076).The decreased NADH im the fasted hearts is consistent with the cardiac celsreliance of fatty acids consumption for energy metabolism when glucose becomes scarce.Theexperimental o bservation of N ADH decrease induced by dietary restriction in the heart at tissuelevel has not been reported to our best knowledge.The Chance redox scanner demonstrated thefeasibility of 3D imaging of the mitochondrial redox st ate in the heart and provides a usefil toolto study heart metabolism and fiunction under normal,dietary-change and pathological con-ditions at tisue level. We would like to thank Dr.Joseph Baur for thehelpful discussion and Dr.Hui Qiao for animalpreparation and organ harvesting.

Variation of food availability affects male striped hamsters(Cricetulus barabensis)with different levels of metabolic rate

In the present study,we examined metabolic,morphological and neurochemical changes in male striped hamsters(Cricetulus barabensis)in response to variations in food availability.Males with low and high levels of metabolic rate(MR:L-MR and H-MR,respectively),defined by their activity MR,were compared.In Experiment 1,36-h food deprivation was found to significantly decrease MR levels,body fat content,mass of small and large intestines,and leptin gene expression in the white adipose tissues in male hamsters.Interestingly,L-MR males displayed decreased MR during both the day and night phases of circadian cycles,whereas H-MR males only showed a decrease in MR during the day(resting phase).These data indicate that individual differences in physical activity were associated with animals’different metabolic responses to food deprivation.In Experiment 2,both groups of males went through a 4-week fasting and re-feeding(re)paradigm.H-re males showed a persistent high level of MR,with decreased body fat content and a trending decrease in leptin mRNA expression,compared to L-re males.Together,our data indicate that male striped hamsters with different levels of physical activity display altered,adaptive changes in response to variations in food availability.The neurochemical involvement of such adaptive changes needs to be further studied.

Larval feeding status regulates the transcript levels of genes encoding PTTH and allatoregulatory peptides in silkworm Bombyx mori

In Bombyx mori,two dorsolateral neurosecretory cells(NSCs)in each of thetwo brain lobes have been identified as prothoracicotropic hormone(PTTH)producingcells.This neuropeptide in insects stimulates the prothoracic gland for the synthesis andrelease of ecdysone,responsible for the molting events.Allatotropin(AT)and allatostatin(AST)are allatoregulatory neuropeptides that regulate juvenile hormone biosynthesis.Here,by using RT-qPCR,we showed that in B.mori,nutritional stress modulates themRNA expression of AT and AST-C(allatostain type C)in the central nervous systemconsisting of the brain lobes and all the associated ganglia.Using whole-mount in situhybridization,we showed that the feeding status of Bombyx larvae also influences the ex-pression of PTTH in the NSCs of the brain.Food deprivation significantly decreased themRNA expression levels of PTTH in larvae at active or terminal growth period.Further,we showed that insulin modulates the expression level of PTTH.However,its action wasdependent on the feeding status of the larvae.At feeding,the insulin decreased the PTTHexpression level,while at food deprivation,the insulin increased the PTTH expressionlevel.The data thus indicates that larval feeding status plays an important role in alteringthe mRNA expression levels of allatoregulatory peptide genes and PTTH.