Phodopus Sungorus Research Articles

Ovarian matrix metalloproteinases are differentially regulated during the estrous cycle but not during short photoperiod induced regression in Siberian hamsters (Phodopus sungorus)

BackgroundMatrix metalloproteinases (MMPs) are implicated as mediators for ovarian remodeling events, and are involved with ovarian recrudescence during seasonal breeding cycles in Siberian hamsters. However, involvement of these proteases as the photoinhibited ovary undergoes atrophy and regression had not been assessed. We hypothesized that 1) MMPs and their tissue inhibitors, the TIMPs would be present and differentially regulated during the normal estrous cycle in Siberian hamsters, and that 2) MMP/TIMP mRNA and protein levels would increase as inhibitory photoperiod induced ovarian degeneration.MethodsMMP-2, -9, -14 and TIMP-1 and -2 mRNA and protein were examined in the stages of estrous (proestrus [P], estrus [E], diestrus I [DI], and diestrus II [DII]) in Siberian hamsters, as well as after exposure to 3, 6, 9, and 12 weeks of inhibitory short photoperiod (SD).ResultsMMP-9 exhibited a 1.6-1.8 fold decrease in mRNA expression in DII (p < 0.05), while all other MMPs and TIMPs tested showed no significant difference in mRNA expression in the estrous cycle. Extent of immunostaining for MMP-2 and -9 peaked in P and E then significantly declined in DI and DII (p < 0.05). Extent of immunostaining for MMP-14, TIMP-1, and TIMP-2 was significantly more abundant in P, E, and DI than in DII (p < 0.05). Localization of the MMPs and TIMPs had subtle differences, but immunostaining was predominant in granulosa and theca cells, with significant differences noted in staining intensity between preantral follicles, antral follicles, corpora lutea, and stroma classifications. No significant changes were observed in MMP and TIMP mRNA or extent of protein immunostaining with exposure to 3, 6, 9, or 12 weeks of SD, however protein was present and was localized to follicular and luteal steroidogenic cells.ConclusionsAlthough MMPs appear to be involved in the normal ovarian estrus cycle at the protein level in hamsters, those examined in the present study are unlikely to be key players in the slow atrophy of tissue as seen in Siberian hamster ovarian regression.

Complete Ablation of Vertical Auditive Conduct and Ear Pinna in a Dwarf Hamster ( Phodopus sungorus) with an Aural Spontaneous Squamous Cell Carcinoma

Abstract A 1-year-old male dwarf hamster ( Phodopus sungorus) with an inflammation of 7 days' duration in the right ear was examined. Abnormalities noted on physical examination were limited to the right ear and an anal mass. The right ear showed swollen skin and a yellowish secretion. The pinna presented scabs and ulcers, probably secondary to the scratching. Cytological examination of the secretion revealed rod-shaped bacteria and neutrophils. The anal mass was a freely movable nodule 1 mm in diameter attached to the anal skin. Initial treatment consisted of antibiotics and antiinflammatory drugs. After an incomplete response to the treatment, surgery was proposed. The surgical procedures consisted of right ear pinna and vertical canal ablation, and excision of the anal mass. The animal recovered uneventfully. All the samples were submitted for histologic examination. The diagnosis was aural squamous cell carcinoma (SCC) and anal papilloma. Although many neoplasias have been described in laboratory rodents, cutaneous SCC is underreported in rodents kept as pets, especially in hamsters. The case here describes an aural SCC that caused a nonresponsive otitis externa in a dwarf hamster. The tumor was successfully removed and the otitis resolved completely. To the authors' knowledge, this is the first report of ear SCC resolved after surgery in a dwarf hamster.

A Case of Cheek Pouch Prolapse in a Djungarian Hamster and its Excision Using an Ultrasonic Surgical Apparatus (SonoSurg, Olympus)

7ヵ月齢の雄のハムスターが、口腔から腫瘤が飛び出したため受診した。臨床所見から、左の頬袋が反転した頬袋脱と診断した。ハムスターは前肢で頬袋を掴むようにして取り除こうとする動作を繰り返していた。頬袋は浮腫により腫大していたため、還納することは困難であった。吸入麻酔を施し、超音波手術装置のショートシザーズで脱出した頬袋の基部を挟み、20～30秒の操作で頬袋を切除することができた。麻酔開始から手術終了までの時間はわずか5分で、術後、速やかに飲食ができるようになった。本例は、超音波手術装置を用いてハムスターの頬袋脱の手術を行った最初の報告である。

Short Day Lengths Skew Prenatal Sex Ratios toward Males in Siberian Hamsters

For decades, researchers have documented significant skews in the production of male versus female offspring in many species. Because males and females are differentially susceptible to environmental challenges and also represent different fitness benefits, it may be beneficial to exert control over the offspring sex ratio when environmental conditions become challenging. Some of the most dramatic environmental challenges occur on a seasonal basis. Indeed, seasonal variation in offspring sex ratios has been documented in both mammalian and nonmammalian species. The seasonal environmental factor (or factors) that drives the skews in sex ratios is unknown; however, it is essential that such a cue be predictable and reliable and that it does not vary from year to year. We hypothesized that photoperiod, a stable cue of seasonal changes in temperature and resource availability, may underlie seasonal variation in offspring sex ratios of mammals. We predicted that short day lengths in particular, which signal impending winter conditions and related energetic demands, would stimulate an anticipatory skew in the offspring sex ratio. We used Siberian hamsters as models because they are phenotypically responsive to photoperiod but up to 60% of females continue to breed during the winter. The sexes of weanling hamsters conceived and raised in short, winter like day lengths were significantly skewed toward males. Furthermore, these skews occurred before birth; embryos collected from pregnant females maintained in short-day conditions were also significantly male biased. Thus, photoperiod functions as an effective seasonal cue, stimulating sex ratio skews toward males when day lengths are short.

Cholecystokinin-33 acutely attenuates food foraging, hoarding and intake in Siberian hamsters

Neurochemicals that stimulate food foraging and hoarding in Siberian hamsters are becoming more apparent, but we do not know if cessation of these behaviors is due to waning of excitatory stimuli and/or the advent of inhibitory factors. Cholecystokinin (CCK) may be such an inhibitory factor as it is the prototypic gastrointestinal satiety peptide and is physiologically important in decreasing food intake in several species including Siberian hamsters. Systemic injection of CCK-33 in laboratory rats decreases food intake, doing so to a greater extent than CCK-8. We found minimal effects of CCK-8 on food foraging and hoarding previously in Siberian hamsters, but have not tested CCK-33. Therefore, we asked: Does CCK-33 decrease normal levels or food deprivation-induced increases in food foraging, hoarding and intake? Hamsters were housed in a wheel running-based foraging system with simulated burrows to test the effects of peripheral injections of CCK-33 (13.2, 26.4, or 52.8 μg/kg body mass), with or without a preceding 56 h food deprivation. The highest dose of CCK-33 caused large baseline reductions in all three behaviors for the 1st hour post-injection compared with saline; in addition, the intermediate CCK-33 dose was sufficient to curtail food intake and foraging during the 1st hour. In food-deprived hamsters, we used a 52.8 μg/kg body mass dose of CCK-33 which decreased food intake, hoarding, and foraging almost completely compared with saline controls for 1 h. Therefore, CCK-33 appears to be a potent inhibitor of food intake, hoarding, and foraging in Siberian hamsters.

MT1 Melatonin Receptors Mediate Somatic, Behavioral, and Reproductive Neuroendocrine Responses to Photoperiod and Melatonin in Siberian Hamsters (Phodopus sungorus)

Environmental day length drives nocturnal pineal melatonin secretion, which in turn generates or entrains seasonal cycles of physiology, reproduction, and behavior. In mammals, melatonin (MEL) binds to a number of receptor subtypes including high-affinity (MT1 and MT2) and low-affinity (MT3, nuclear orphan receptors) binding sites, which are distributed throughout the central nervous system and periphery. The MEL receptors that mediate photoperiodic reproductive and behavioral responses to MEL have not been identified in a reproductively photoperiodic species. Here I tested the hypothesis that MT1 receptors are necessary and sufficient to engage photoperiodic responses by challenging male Siberian hamsters (Phodopus sungorus), a species that does not express functional MT2 receptors, with ramelteon (RAM), a specific MT1/MT2 receptor agonist. In hamsters housed in a long-day photoperiod, late-afternoon RAM treatment inhibited gonadotropin secretion, induced gonadal regression, and suppressed food intake and body mass, mimicking effects of MEL. In addition, chronic (24 h/d) RAM infusions were sufficient to obscure endogenous MEL signaling, and these treatments attenuated gonadal regression in short days. Together, the outcomes indicate that signaling at the MT1 receptor is sufficient and necessary to mediate the effects of photoperiod-driven changes in MEL on behavior and reproductive function in a reproductively photoperiodic mammal.

Possible mechanisms of weight loss of Siberian hamsters (Phodopus sungorus sungorus) exposed to short photoperiod

Several weeks of short day photoperiod (SD) exposure promote a dramatic decrease of white adipose tissue (WAT) mass in Siberian hamsters(Phodopus sungorus sungorus). This slimming effect is accompanied by changes in the adipocyte responsiveness to adrenergic stimulation that are still under debate. We investigated whether possible changes in the antilipolytic responses, and/or lipogenic activities could be involved in such lipid deposition/mobilisation imbalance. Male Siberian hamsters were exposed for 11 weeks to SD or long day photoperiod and basal or stimulated lipolytic and lipogenic activities were measured on white adipocytes. As expected, the body mass of SD-animals was decreased. Besides a slight reduction in the basal lipolysis and in the maximal response to dibutyryl-cAMP, the responses to adrenergic and non-adrenergic lipolytic agents (forskolin, adenosine deaminase) were similar in both groups. Fat mass loss was likely not resulting from changes in the lipolytic responses of adipocytes to biogenic amines (e.g. octopamine), which were unaltered, or to a direct lipolytic stimulation by melatonin or histamine, which were inactive. Antilipolytic responses to insulin or tyramine were slightly decreased in SD-adipocytes. Basal or insulin-stimulated lipid accumulation in WAT, measured by glucose incorporation into lipids, did not change after SD-exposure. However, a significant decrease in the lipoprotein lipase activity was observed in the WAT of SDanimals. Despite the observed changes, the weight loss of SD-exposed Siberian hamsters was likely not resulting only from impaired antilipolytic orde novo lipogenic activities in white adipocytes, but either from other dramatic changes occurring during seasonal photoperiod-sensitive body weight regulation.

Photoperiod History Differentially Impacts Reproduction and Immune Function in Adult Siberian Hamsters

Seasonal changes in numerous aspects of mammalian immune function arise as a result of the annual variation in environmental day length (photoperiod), but it is not known if absolute photoperiod or relative change in photoperiod drives these changes. This experiment tested the hypothesis that an individual's history of exposure to day length determines immune responses to ambiguous, intermediate-duration day lengths. Immunological (blood leukocytes, delayed-type hypersensitivity reactions [DTH]), reproductive, and adrenocortical responses were assessed in adult Siberian hamsters (Phodopus sungorus) that had been raised initially in categorically long (15-h light/day; 15L) or short (9L) photoperiods and were subsequently transferred to 1 of 7 cardinal experimental photoperiods between 9L and 15L, inclusive. Initial photoperiod history interacted with contemporary experimental photoperiods to determine reproductive responses: 11L, 12L, and 13L caused gonadal regression in hamsters previously exposed to 15L, but elicited growth in hamsters previously in 9L. In hamsters with a 15L photoperiod history, photoperiods < or = 11L elicited sustained enhancement of DTH responses, whereas in hamsters with a 9L photoperiod history, DTH responses were largely unaffected by increases in day length. Enhancement and suppression of blood leukocyte concentrations occurred at 13L in hamsters with photoperiod histories of 15L and 9L, respectively; however, prior exposure to 9L imparted marked hysteresis effects, which suppressed baseline leukocyte concentrations. Cortisol concentrations were only enhanced in 15L hamsters transferred to 9L and, in common with DTH, were unaffected by photoperiod treatments in hamsters with a 9L photoperiod history. Photoperiod history acquired in adulthood impacts immune responses to photoperiod, but manifests in a markedly dissimilar fashion as compared to the reproductive system. Prior photoperiod exposure has an enduring impact on the ability of the immune system to respond to subsequent changes in day length.

Forensic hair analysis to identify animal species on a case of pet animal abuse

As part of an investigation of a case of pet animal abuse, we attempted to identify small mammalian species by morphological analysis and single-nucleotide polymorphism (SNP) typing of the cytochrome b gene using guard hairs as an analytical material. Guard hair samples from several species were measured for length, width, medulla formation, and cuticle scale pattern under a light microscope or scanning electron microscope. These samples were also analyzed for SNPs in the cytochrome b gene using a multiplex single-base primer extension reaction. Morphological analysis of cuticle scale pattern and medulla formation was able to discriminate ferret hairs from other hair samples that included rabbit, gerbil, degu, and Djungarian hamster. However, this also revealed a similarity of the guard hairs of the ferret (Mustela putorius furo) and Japanese weasel (Mustela itatsi). Although at three sites, the nucleotide color signals of SNPs in the cytochrome b gene could be used to discriminate completely among human, dog, and gerbil, the signals for cat, ferret, and Japanese weasel occurred at the same nucleotide sites. Unfortunately, no signals were obtained from degu, Djungarian hamster, and rabbit hairs. Although the discriminated hair samples were 100% identical to those of the ferret, there was only a 5% difference from Japanese weasel in the partial sequence of the cytochrome b gene. Construction of a database of mammalian hairs would be useful not only in forensic science, but also for investigating smuggling of endangered species in contravention of the Washington Convention.

Photic and Nonphotic Seasonal Cues Differentially Engage Hypothalamic Kisspeptin and RFamide‐Related Peptide mRNA Expression in Siberian Hamsters

Seasonally breeding animals use a combination of photic (i.e. day length) and nonphotic (e.g. food availability, temperature) cues to regulate their reproduction. How these environmental cues are integrated is not understood. To assess the potential role of two candidate neuropeptides, kisspeptin and RFamide-related peptide-3 (RFRP), we monitored regional changes in their gene expression in a seasonally breeding mammal exposed to moderate changes in photoperiod and food availability. Adult male Siberian hamsters (Phodopus sungorus) were housed under a long (16 h light/day; 16 L) or intermediate (13.5 L) photoperiod and fed ad lib. or a progressive food restriction schedule (FR; reduced to 80% of ad lib.) for 11 weeks. Gonadal regression occurred only in FR hamsters housed under 13.5 L. Immunohistochemistry was used to identify diencephalic populations of kisspeptin- and RFRP-immunoreactive cells, and quantitative PCR was used to measure gene expression in adjacent coronal brain sections. Photoperiod, but not food availability, altered RFRP mRNA expression in the dorsomedial sections, whereas food availability but not photoperiod altered Kiss1 expression in the arcuate sections; intermediate photoperiods elevated RFRP expression, and food restriction suppressed Kiss1 expression. Regional- and neuropeptide-specific activity of RFamides may provide a mechanism for integration of multi-modal environmental information in the seasonal control of reproduction.

Torpor and ultradian rhythms require an intact signalling of the sympathetic nervous system

During entrance into torpor heart and respiration rates are greatly reduced in parallel with the reduction of metabolic rate, suggesting an involvement of parasympathetic control. We compared the effect of parasympathetic inhibition with the effect of sympathetic inhibition on spontaneous torpor behaviour in the Djungarian hamster. Hamsters were acclimated to short photoperiod and displayed their standard torpor pattern as observed from T b records. Parasympathetic inhibition was achieved by a subcutaneous implant of 21-day release pellets with Atropine and the sympathetic noradrenergic pathway was inhibited with a single injection of 6-Hydroxydopamine. Atropine treatment did not affect the occurrence and quality of spontaneous daily torpor at all. However, the reversible sympathetic inhibition by 6-Hydroxydopamine injection resulted in a complete disappearance of torpor for about 6 days. These results conclude that the onset of daily torpor requires an intact noradrenergic signalling of the sympathetic nervous system. We further observed that parasympathetic as well as sympathetic blockade resulted in an immediate abolishment of ultradian rhythms of body temperature. This suggests that the expression of ultradian oscillations in body temperature require a continued interaction of sympathetic and parasympathetic activity.

The bed nucleus of the stria terminalis in the Syrian hamster ( Mesocricetus auratus): absence of vasopressin expression in standard and wild-derived hamsters and galanin regulation by seasonal changes in circulating sex steroids

The bed nucleus of the stria terminalis (BNST) is a nucleus of the forebrain highly sensitive to sex steroids and containing vasopressin neurons implicated in several social- and reproduction-related behaviours such as scent-marking, aggression, pair bonding and parental behaviour. Sexually dimorphic vasopressin expression in BNST neurons has been reported in almost all rodents, with the notable exception of the Syrian hamster. In this species, vasopressin expression is completely absent in the BNST. Because almost all Syrian hamsters used in research are derived from a very small breeding stock captured in 1930, we compared commercially available Syrian hamsters with a recently captured, wild-derived breeding stock. We checked for vasopressin expression using in situ hybridization and immunohistochemistry. Vasopressin expression in BNST neurons was completely absent in both breeding stocks, confirming the absence of BNST vasopressin expression in Mesocricetus auratus and ruling out a breeding artefact. Because vasopressin expression in BNST neurons appears to be strictly dependent on circulating sex steroids, the absence of vasopressin expression in Syrian hamster BNST neurons might be due to an insensitivity of these neurons to sex steroids. BNST vasopressin neurons also express galanin. Although galanin expression in the BNST is not sexually dimorphic in the Syrian hamster, it appears to be regulated by sex steroids. In the Djungarian hamster, photoperiodically driven seasonal variations of circulating sex steroids result in a seasonal rhythm of galanin expression in BNST neurons. We analysed the sex steroid dependence of galanin expression in the Syrian hamster. Castration and short photoperiod-induced sexual quiescence both resulted in downregulation of galanin mRNA in cell bodies (BNST) and immunoreactivity in the fibres (lateral septum). Testosterone supplementation of short photoperiod-adapted animals was able to restore galanin expression. Thus Syrian hamster BNST neurons respond to circulating sex steroids and their seasonal variations as observed in other rodent species.

In vivo but not in vitro leptin enhances lymphocyte proliferation in Siberian hamsters ( Phodopus sungorus)

Mounting an immune response requires a relatively substantial investment of energy and marked reductions in energy availability can suppress immune function and presumably increase disease susceptibility. We have previously demonstrated that a moderate reduction in energy stores by partial surgical lipectomy impairs humoral immunity of Siberian hamsters ( Phodopus sungorus) and is mediated, in part, by changes in the adipose tissue hormone leptin. The goals of the present study were to assess the role of leptin in cell-mediated immunity and to determine if the potential effects of leptin on immunity are via the direct actions of this hormone on lymphocytes, or indirect, via the sympathetic nervous system (SNS). In Experiment 1, hamsters received osmotic minipumps containing either murine leptin (0.5 μl/h) or vehicle alone for 10 days and splenocyte proliferation in response to the T-cell mitogen Concanavalin A (Con A) was determined. In Experiment 2, Con A-induced splenocyte proliferation was tested in the presence or absence of leptin in vitro. In Experiment 3, exogenous leptin was administered to intact or sympathetically denervated hamsters. Hamsters treated with in vivo leptin displayed increased splenocyte proliferation compared with control hamsters receiving vehicle. In contrast, in vitro leptin had no effect on splenocyte proliferation. Sympathetic denervation attenuated, but did not block, leptin-induced increases in immunity. Taken together, these results are consistent with the idea that leptin can enhance cell-mediated immunity; the SNS appears to contribute, least in part, to leptin-induced increases in immunity. Importantly, these findings confirm previous studies that leptin serves as an important endocrine link between energy balance and immunity.

Photoperiodic regulation of cellular retinoic acid-binding protein 1, GPR50 and nestin in tanycytes of the third ventricle ependymal layer of the Siberian hamster

Photoperiodic regulation of cellular retinoic acid-binding protein 1, GPR50 and nestin in tanycytes of the third ventricle ependymal layer of the Siberian hamster

Corrigendum

CorrigendaCorrigendumPublished Online:01 Nov 2009https://doi.org/10.1152/ajpregu.zh6-7009-corr.2009Original articleMoreSectionsPDF (529 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInEmailWeChat Volume 65, May 2009Herwig A, Wilson D, Logie TJ, Boelen A, Morgan PJ, Mercer JG, Barrett P. Photoperiod and acute energy deficits interact on components of the thyroid hormone system in hypothalamic tanycytes of the Siberian hamster. Am J Physiol Regul Integr Comp Physiol 296: , 2009. First published March 18, 2009; doi:10.1152/ajpregu.90755.2008 (http://ajpregu.physiology.org/cgi/content/full/296/5/R1307).In the original Figure 1A, the lower left panel was mistakenly a copy of the one on the lower right. The corrected figure appears below with its original legend.Fig. 1.Quantification of type II (D2) and III (D3) deiodinase (Dio2 and Dio3) mRNA expression in the 3rd ventricular tanycyte layer of Siberian hamster in long-day (LD) or short-day (SD) photoperiod with or without 48 h of starvation. A and C: representative autoradiographs of coronal brain sections from each of the 4 treatment conditions hybridized with a probe for Dio2 and Dio3. B and D: quantification of autoradiograph signals for Dio2 and Dio3 mRNA expression. Expression was normalized to the highest value obtained for each probe. Solid bars, ad libitum-fed hamsters; gray bars, fold-restricted (48-h-starved) animals. *P < 0.05; ***P < 0.001 by 2-way ANOVA and Tukey's post hoc test for Dio2 and by t-test for Dio3.Download figureDownload PowerPointIn the original Figure 4E, the panel on the upper right was mistakenly a copy of the panel on the upper left side. The corrected figure appears below with its original legend.Fig. 4.Quantification of VGF, neuropeptide Y (NPY), and thyrotropin-releasing hormone (TRH) mRNA expression in the hypothalamus of the Siberian hamster. A: representative autoradiographs of coronal brain sections from each of the treatment conditions hybridized with a probe for VGF. B: quantification of VGF mRNA expression in the dorsal region of the medial posterior area of the arcuate nucleus (dmpARC) of hamsters in the SD photoperiod (no expression in LD) with and without 48 h of starvation. C: autoradiographs of coronal brain sections from each of the treatment conditions hybridized with a probe for NPY. D: quantification of NPY expression in the arcuate nucleus of hamsters held in LD and SD photoperiods with and without 48 h of starvation. E: autoradiographs of coronal brain sections from each of the treatment conditions hybridized with a probe for TRH. F: quantification of TRH mRNA expression in the paraventricular nucleus. Expression was normalized to the highest value for each probe. Solid bars, ad libitum-fed hamsters; gray bars, starved hamsters. *P < 0.05; ***P < 0.001 by 2-way ANOVA and Tukey's post hoc test.Download figureDownload PowerPointThis article has no references to display. Download PDF Previous Back to Top FiguresReferencesRelatedInformationRelated ArticlesPhotoperiod and acute energy deficits interact on components of the thyroid hormone system in hypothalamic tanycytes of the Siberian hamster 01 May 2009American Journal of Physiology-Regulatory, Integrative and Comparative Physiology More from this issue > Volume 297Issue 5November 2009Pages R1624-R1624 Copyright & PermissionsCopyright © 2009 American Physiological Societyhttps://doi.org/10.1152/ajpregu.zh6-7009-corr.2009History Published online 1 November 2009 Published in print 1 November 2009 Metrics

Photoperiod-induced differences in uterine growth in Phodopus sungorus are evident at an early age when serum estradiol and uterine estrogen receptor levels are not different

Sexual development is inhibited in Siberian hamsters ( Phodopus sungorus) in short days (SD), and a small uterus is an obvious indicator of photo-inhibition. The small uterus in SD is presumably due to the delayed onset of estrous cycles. However, in an earlier study, the investigators reported that serum estradiol (E2) concentration was significantly higher in young females raised in SD than in long days (LD), with the highest concentrations measured in SD at 4 weeks of age. These seemingly contradictory findings were investigated in the present study. First, uterine mass and body mass were measured in SD- and LD-reared hamsters from 1 to 12 weeks of age. Uterine mass was significantly greater in LD than in SD by 3 weeks of age and onward. Thereafter, our investigation focused on 4-week-old hamsters. Serum E2 concentrations in LD and in SD were not significantly different and there were no significant LD–SD differences in uterine estrogen receptors (ER), as measured by immunohistochemistry and quantitative real-time RT-PCR. Therefore, alternative explanations for the photoperiodic difference in uterine size in young Siberian hamsters are considered.

Physiological Models of Leptin Resistance

In common forms of obesity, animals and humans become leptin resistant associated with impaired regulation of energy homeostasis. Over the last decade, significant advances in delineating the underlying mechanisms have been achieved. As well as the obvious scientific progress obtained by novel transgenic animals, natural and physiological models of leptin resistance such as the Siberian hamster (Phodoups sungorus), the field vole (Microtus agrestis) or the rat during pregnancy have also provided invaluable insight into the dynamic long-term control of energy homeostasis. Seasonal (in the hamster) and pregnancy-induced leptin resistance are characterised by a modulation of the leptin signalling cascade downstream of its receptor in the hypothalamus. In this state, leptin-induced phosphorylation of the important transcription factor, signal transducer and activator of transcription 3 (STAT3), is impaired in the arcuate nucleus and the ventromedial hypothalamus (only during pregnancy). This is accompanied by elevated levels of leptin signalling inhibitors such as the suppressor of cytokine signalling (SOCS3) and the protein tyrosine phosphatase 1B (PTP1B). The janus kinase 2 (JAK2)-STAT3 signalling pathway might be modulated by a dual function of the tyrosine residue Tyr(985) in the intracellular domain of the leptin receptor. In seasonal animals, SOCS3, most importantly seems to act as a 'molecular switch' enabling a photoperiod-induced alteration in leptin signalling and subsequent adjustments in energy homeostasis to allow attainment of a new body weight set-point. These physiological models show that animals can exhibit leptin resistance as an adaptive response to meet new physiological or environmental challenges, promoting the survival of the species during times of increased metabolic demand. The molecular mechanisms mediating physiological and/or pathological leptin resistance, like during diet induced obesity, might be very similar involving hypothalamic SOCS3. Investigation of these models might further provide new insight into the dynamic complexity of energy homeostasis.

The glutamate agonist NMDA blocks gonadal regression and enhances antibody response to an immune challenge in Siberian hamsters (Phodopus sungorus)

Seasonal variation in behavior and physiology, including changes in immune function, are common. This variability is elicited by changes in photoperiod and often covaries with fluctuations in both energy reserves and reproductive state. It is unclear, however, whether changes in either variable alone drive seasonal changes in immunity. We investigated the relative contributions of reproduction and energy balance to changes in immune function. To accomplish this, we uncoupled seasonal changes in reproduction from those related to energy balance via daily injections of N-methyl-D: -aspartate (NMDA) in Siberian hamsters (Phodopus sungorus). NMDA is a glutamatergic agonist that blocks short day-induced gonadal regression, while leaving short-day declines in body mass unaffected. In Experiment 1, we examined the effect of differing doses of NMDA on testosterone production as a proxy for NMDA effects on reproduction; a dose-dependent rise in testosterone was observed. In Experiment 2, animals were maintained on long or short days and received daily injections of NMDA. After 8 weeks, all animals underwent a humoral immune challenge. Short-day animals receiving daily injections of NMDA maintained long day-like gonads; however, contrary to our predictions, no trade-off between reproduction or energy balance and immune function was observed. Unexpectedly, NMDA treatment increased immunoglobulin levels in all groups, suggesting that NMDA may provide an immunomodulatory signal, presumably through actions on peripheral glutamate receptors. These results support a previous finding that NMDA blocks reproductive regression. In addition, these findings demonstrate a general immunoenhancing effect of NMDA that appears independent of changes in reproductive or energetic state of the animal.

Cryptosporidium spp. in Wild, Laboratory, and Pet Rodents in China: Prevalence and Molecular Characterization

To understand the prevalence of Cryptosporidium infection in rodents in China and to assess the potential role of rodents as a source for human cryptosporidiosis, 723 specimens from 18 rodent species were collected from four provinces of China and examined between August 2007 and December 2008 by microscopy after using Sheather's sugar flotation and modified acid-fast staining. Cryptosporidium oocysts were detected in 83 specimens, with an overall prevalence of 11.5%. Phodopus sungorus, Phodopus campbelli, and Rattus tanezumi were new reported hosts of Cryptosporidium. The genotypes and subtypes of Cryptosporidium strains in microscopy-positive specimens were further identified by PCR and sequence analysis of the small subunit rRNA and the 60-kDa glycoprotein (gp60) genes. In addition to Cryptosporidium parvum, C. muris, C. andersoni, C. wrairi, ferret genotype, and mouse genotype I, four new Cryptosporidium genotypes were identified, including the hamster genotype, chipmunk genotype III, and rat genotypes II and III. Mixed Cryptosporidium species/genotypes were found in 10.8% of Cryptosporidium-positive specimens. Sequence analysis of the gp60 gene showed that C. parvum strains in pet Siberian chipmunks and hamsters were all of the subtype IIdA15G1, which was found previously in a human isolate in The Netherlands and lambs in Spain. The gp60 sequences of C. wrairi and the Cryptosporidium ferret genotype and mouse genotype I were also obtained. These findings suggest that pet rodents may be potential reservoirs of zoonotic Cryptosporidium species and subtypes.

Photoperiod and food restriction differentially affect reproductive and immune responses in Siberian hamsters Phodopus sungorus

Summary 1. Organisms must contend with seasonal fluctuations in energy availability. To maintain a positive energy balance year‐round, a number of adaptations have evolved including seasonal changes in reproduction, energetics and immunity. Photoperiod is the primary environmental signal most animals use to predict seasonal events. Despite the established link between energetics and immune function, little is known regarding how changes in energy availability affect immunity. 2. The goal of the present study was to determine the effects of food restriction on photoperiodic changes in reproduction and immune function in the Siberian hamster (Phodopus sungorus). Adult hamsters were housed in long or short days and were food restricted or fed ad libitum. Immune responses were quantified by measuring specific antibody production and bacterial killing capacity. 3. Food restriction decreased body and relative reproductive masses in long‐day animals. Antibody responses, but not bacterial killing ability, were enhanced in food restricted short‐day animals as compared with ad libitum fed controls. We also found differential effects of body fat on immune responses depending on the immune measure. 4. The effects of food restriction on immune function appear to vary based on the restriction regimen, the response measured, and the physiological state of the organism including energy balance, metabolic rate and reproductive status. 5. In conclusion, these results suggest that a wide range of factors can differentially affect immune function. In addition, these effects may vary based on the specific response examined. Future studies should include a variety of measurements to provide a more integrative and accurate picture of reproductive, energetic, and photoperiodic effects on immune function.