Short photoperiod-induced ovarian regression is mediated by apoptosis in Siberian hamsters (Phodopus sungorus)

Effect of PACAP/PAC1R on Follicle Development of Djungarian Hamster (Phodopus sungorus) with the Variation of Ambient Temperatures

In Phodopus sungorus, the relationship between pituitary adenylate cyclase-activating polypeptide (PACAP) and its receptor (PAC1R), follicle-stimulating hormone (FSH), and follicle development remains unclear. In this study, we found that the development of growing follicles and antral follicles were inhibited at low (8 °C, 14 °C) and high (29 °C) temperatures. Meanwhile, PACAP/PAC1R expression and follicle-stimulating hormone (FSH) serum concentration significantly decreased during ambient temperatures of 8 °C, 14 °C and 29 °C compared to 21 °C. Thus, ambient temperature may influence the expression of PACAP/PAC1R and the synthesis of FSH for involvement in follicle development. Moreover, PACAP/PAC1R had major functional elements including PKA/PKG and PKC phosphorylation sites, which may involve in the pathway of FSH synthesis through cAMP-PKA and its downstream signal pathway. Moreover, there was a significant positive correlation between the expression levels of PACAP/PAC1R and the number of the growing and antral follicles, as well as the serum FSH concentration and the number of antral follicles. However, there was no significant correlation between the expression levels of PACAP/PAC1R and the serum FSH concentration, indicating a complicated pathway between PACAP/PAC1R and FSH. In conclusion, ambient temperature affects the expression of PACAP/PAC1R and the serum FSH concentration. The expression of PACAP/PAC1R and the serum FSH concentration are correlated with follicle development, which implies that they are involved in follicle development, which will ultimately influence the reproduction of Phodopus sungorus. This study can lay the foundation for future investigation on the regulation mechanism of reproduction in Phodopus sungorus.

The Photoperiod Regulates Granulosa Cell Apoptosis through the FSH-Nodal/ALK7 Signaling Pathway in Phodopus sungorus

The photoperiod regulates the seasonal reproduction of mammals by affecting the follicle development, for which the granulosa cells provide nutrition. However, the underlying mechanism remains unclear. Here, Djungarian hamsters (Phodopus sungorus) were raised under different photoperiods to study the ovarian status and explore the potential mechanism of the follicle development mediated by the FSH-Nodal/ALK7 signaling pathway. Compared with the moderate daylight (MD) group, the short daylight (SD) group exhibited a significant decrease in the ovarian weight and increase in the atretic follicle number and granulosa cell apoptosis, whereas the long daylight (LD) group showed an increase in the ovarian weight, the growing follicle number, and the antral follicle number, but a decrease in the granulosa cell apoptosis. Based on these findings, the key genes of the Nodal/ALK7 signaling pathway controlling the granulosa cell apoptosis were studied using the quantitative real-time polymerase chain reaction and western blotting. In the SD group, the follicle-stimulating hormone (FSH) concentration significantly decreased and the Nodal/ALK7/Smad signaling pathways were activated, while the phosphatidylinositol 3-kinase (PIK3)/Akt signaling pathway was inhibited. The BAX expression was significantly increased, while the Bcl-xL expression was significantly decreased, leading to an increase in the caspase-3 activity, the granulosa cell apoptosis, and ovarian degeneration. However, in the LD group, the FSH concentration significantly increased, the Nodal/ALK7/Smad signaling pathway was inhibited, and the PIK3/Akt signaling pathway was activated. Taken together, our results indicate that the photoperiod can regulate the apoptosis of the granulosa cells by regulating the concentration of FSH, activating or inhibiting the Nodal/ALK7 signaling pathway, thereby affecting the ovarian function. Our research provides an important theoretical basis for understanding the photoperiod-regulated mechanisms of the mammalian seasonal reproduction.

Short communication: Photoperiod impacts ovarian extracellular matrix and metabolic gene expression in Siberian hamsters

Ovarian cyclicity is variable in adult Siberian hamsters (Phodopus sungorus), who respond to long breeding season photoperiods with follicle development and ovulation, while short photoperiods typical of the non-breeding season induce gonadal atrophy. Recent RNAseq results identified ovarian matrix components and regulators of metabolism as differentially regulated by photoperiod; however, the impact of photoperiod across a full cycle of ovarian regression and recrudescence had not been explored for additional regulators of ovarian metabolism and extracellular matrix components. We hypothesized that matrix and metabolism-related genes would be expressed differentially across photoperiods that mimic breeding and non-breeding season daylengths. Hamsters were housed in one of four photoperiod groups: long day (16 h of light per day: 8 h of dark; LD, controls), short day regressed (8 L:16D; SD, regressed), and females exposed to SD then transferred to LD to stimulate return of ovarian function for 2 (early recrudescence), or 8 (late recrudescence) weeks. Plasma leptin concentrations along with expression of ovarian versican and liver-receptor homolog-1/Nr582 mRNA decreased in SD compared to LD and late recrudescence, while vimentin mRNA expression peaked in early and late recrudescence. Ovarian expression of fibronectin and extracellular matrix protein-1 was low in LD ovaries and increased in regressed and recrudescing groups. Expression of hyaluronidase-2, nectin-2, liver-X receptors-α and-β, and adiponectin mRNA peaked in late recrudescence, with no changes noted for adiponectin receptor-1 and -2. The results offer a first look at the parallels between expression of these genes and the dynamic remodeling that occurs during ovarian regression and recrudescence.

Seasonal reproduction and gonadal function: A focus on humans starting from animal studies

Photoperiod impacts reproduction in many species of mammals. Mating occurs at specific seasons to achieve reproductive advantages, such as optimization of offspring survival. Light is the main regulator of these changes during the photoperiod. Seasonally breeding mammals detect and transduce light signals through extraocular photoreceptor, regulating downstream melatonin-dependent peripheral circadian events. In rodents, hormonal reduction and gonadal atrophy occur quickly, and consensually with short-day periods. It remains unclear whether photoperiod influences human reproduction. Seasonal fluctuations of sex hormones have been described in humans, although they seem to not imply adaptative seasonal pattern in human gonads. This review discusses current knowledge about seasonal changes in the gonadal function of vertebrates, including humans. The photoperiod-dependent regulation of hypothalamic-pituitary-gonadal axis, as well as morphological and functional changes of the gonads are evaluated herein. Endocrine and morphological variations of reproductive functions, in response to photoperiod, are of interest as they may reflect the nature of past population selection for adaptative mechanisms that occurred during evolution.

Photoperiodic modulation of ovarian metabolic, survival, proliferation and gap junction markers in adult golden hamster, Mesocricetus auratus

Female reproductive physiology is greatly dependent on tight regulation of metabolic and survival factors. Photoperiod regulates female reproductive rhythms but very less information exists explaining whether photoperiod could modulate thyroid hormone homeostasis, metabolic/energy parameters along with survival, proliferation and gap junction proteins in the ovary of a long-day breeder, Mesocricetus auratus. Adult female hamsters were exposed to different photoperiodic regimes i.e., critical photoperiod (CP; 12.5L:11.5D), short photoperiod (SP; 8L:16D) and long photoperiod (LP; 16L:8D) for 12 weeks. LP upregulated thyroidal and gonadal activity as apparent by histoarchitecture, thyroid hormone profile [triiodothyronine (T3), thyroxin (T4) and thyroid stimulating hormone (TSH)], luteinizing hormone (LH), follicle stimulating hormone (FSH), estradiol (E2) and progesterone (P4) levels when compared with SP exposed hamsters. Further, LP increased thyroid hormone receptor-α/deiodinase-2 (TRα/Dio-2), estrogen receptor-α (ERα)/aromatase and insulin receptor/glucose transporter-4 (IR/GLUT-4) expressions in ovary. Interestingly, ovarian sirtuin-1 (SIRT-1) expression was also upregulated under LP condition along with cell proliferation (proliferating cell nuclear antigen or PCNA), survival (B cell lymphoma-2 or Bcl-2) and gap junction (connexin-43) markers when compared to SP exposed hamsters. We also noted elevated levels of circulatory leptin, insulin along with melatonin and its receptor (MT-1) in ovary under SP condition. Thus, we suggest that photoperiod plays a vital role in regulation of thyroid and reproductive hormone homeostasis along with key metabolic and survival markers in the ovary of adult golden hamsters, M. auratus providing further insight into the regulation of female reproductive seasonality in a long-day breeder.

Seasonal patterns of melatonin alter aggressive phenotypes of female Siberian hamsters

Many animal species exhibit year-round aggression, a behaviour that allows individuals to compete for limited resources in their environment (eg, food and mates). Interestingly, this high degree of territoriality persists during the non-breeding season, despite low levels of circulating gonadal steroids (ie, testosterone [T] and oestradiol [E₂ ]). Our previous work suggests that the pineal hormone melatonin mediates a 'seasonal switch' from gonadal to adrenal regulation of aggression in Siberian hamsters (Phodopus sungorus); solitary, seasonally breeding mammals that display increased aggression during the short, 'winter-like' days (SDs) of the non-breeding season. To test the hypothesis that melatonin elevates non-breeding aggression by increasing circulating and neural steroid metabolism, we housed female hamsters in long days (LDs) or SDs, administered them timed or mis-timed melatonin injections (mimic or do not mimic a SD-like signal, respectively), and measured aggression, circulating hormone profiles and aromatase (ARO) immunoreactivity in brain regions associated with aggressive or reproductive behaviours (paraventricular hypothalamic nucleus [PVN], periaqueductal gray [PAG] and ventral tegmental area [VTA]). Females that were responsive to SD photoperiods (SD-R) and LD females given timed melatonin injections (Mel-T) exhibited gonadal regression and reduced circulating E₂ , but increased aggression and circulating dehydroepiandrosterone (DHEA). Furthermore, aggressive challenges differentially altered circulating hormone profiles across seasonal phenotypes; reproductively inactive females (ie, SD-R and Mel-T females) reduced circulating DHEA and T, but increased E₂ after an aggressive interaction, whereas reproductively active females (ie, LD females, SD non-responder females and LD females given mis-timed melatonin injections) solely increased circulating E₂ . Although no differences in neural ARO abundance were observed, LD and SD-R females showed distinct associations between ARO cell density and aggressive behaviour in the PVN, PAG and VTA. Taken together, these results suggest that melatonin increases non-breeding aggression by elevating circulating steroid metabolism after an aggressive encounter and by regulating behaviourally relevant neural circuits in a region-specific manner.

Photoperiod Manipulation Affects Transcriptional Profile of Genes Related to Lipid Metabolism and Apoptosis in Zebrafish (Danio rerio) Larvae: Potential Roles of Gut Microbiota

Gut microbiota plays a fundamental role in maintaining host's health by controlling a wide range of physiological processes. Administration of probiotics and manipulation of photoperiod have been suggested as modulators of microbial composition and are currently undergoing an extensive research in aquaculture as a way to improve health and quality of harvested fish. However, our understanding regarding their effects on physiological processes is still limited. In the present study we investigated whether manipulation of photoperiod and/or probiotic administration was able to alter microbial composition in zebrafish larvae at hatching stage. Our findings show that probiotic does not elicit effects while photoperiod manipulation has a significant impact on microbiota composition. Moreover, we successfully predicted lipid biosynthesis and apoptosis to be modulated by microbial communities undergoing continuous darkness. Interestingly, expression levels of caspase 3 gene (casp3) and lipid-related genes (hnf4a, npc1l1, pparγ, srebf1, agpat4 and fitm2) were found to be significantly overexpressed in dark-exposed larvae, suggesting an increase in the occurrence of apoptotic processes and a lipid metabolism impairment, respectively (p < 0.05). Our results provide the evidence that microbial communities in zebrafish at early life stages are not modulated by a short administration of probiotics and highlight the significant effect that dark photoperiod elicits on zebrafish microbiota and potentially on health.

Transcriptome analysis during photostimulated recrudescence reveals distinct patterns of gene regulation in Siberian hamster ovaries†

In Siberian hamsters, exposure to short days (SDs, 8 h light:16 h dark) reduces reproductive function centrally by decreasing gonadotropin secretion, whereas subsequent transfer of photoinhibited hamsters to stimulatory long days (LDs, 16 L:8 D) promotes follicle stimulating hormone (FSH) release inducing ovarian recrudescence. Although differences between SD and LD ovaries have been investigated, a systematic investigation of the ovarian transcriptome across photoperiod groups to identify potentially novel factors that contribute to photostimulated restoration of ovarian function had not been conducted. Hamsters were assigned to one of four photoperiod groups: LD to maintain ovarian cyclicity, SD to induce ovarian regression, or post transfer (PT), where females housed in SD for 14-weeks were transferred to LD for 2-days or 1-week to reflect photostimulated ovaries prior to (PTd2) and following (PTw1) the return of systemic FSH. Ovarian RNA was extracted to create RNA-sequencing libraries and short-read sequencing Illumina assays that mapped and quantified the ovarian transcriptomes (n = 4/group). Ovarian and uterine masses, plasma FSH, and numbers of antral follicles and corpora lutea decreased in SD as compared to LD ovaries (P < 0.05). When reads were aligned to the mouse genome, 18 548 genes were sufficiently quantified. Most of the differentially expressed genes noted between functional LD ovaries and regressed SD ovaries; however, five main expression patterns were identified across photoperiod groups. These results, generally corroborated by select protein immunostaining, provide a map of photoregulated ovary function and identify novel genes that may contribute to the photostimulated resumption of ovarian activity.

Early-life sickness may predispose Siberian hamsters to behavioral changes following alterations of the gut microbiome in adulthood

Although it is well-established that the immune system plays an important role in the development of physiology and behavior, the gut microbiome has recently become of interest in the study of developmental origins of behavior. Studies suggest that the effects of early-life immune activation may not occur until a secondary stressor is introduced, though the precise nature and timing of the stressor may be critical in the response. Further, recent work suggests that the microbiome and the immune system develop in parallel, and therefore any perturbations to one of these systems early in life will likely affect the other. Here, we sought to determine whether early-life activation of the immune system had long-term consequences on how the gut microbiome responds to antibiotic treatment in adulthood and whether those changes influence adult same-sex social behavior. In order to test the hypothesis that an early-life immune challenge makes individuals more vulnerable to the effects of antibiotics, we mimicked an early-life infection by injecting pups at postnatal day 3 and 5 with lipopolysaccharide (LPS; cell wall component of gram-negative bacteria) or saline, and subsequently exposed the same animals to antibiotic treatment (known to influence microbial community composition and behavior) or water in adulthood. We tracked physiology across development, and paired males and females with a novel individual of the same age and sex in adulthood to score same-sex behavior (e.g., aggression, investigation, grooming) before antibiotic treatment, immediately following treatment, and after recovery from antibiotics. LPS-treated females exhibited impaired reproductive physiology and function in adulthood (e.g., smaller ovaries and abnormal estrous cycles), and female and male gut microbial communities were strongly affected by antibiotic treatment in adulthood, but only slightly affected by postnatal LPS alone. Interestingly, LPS-treated males exhibited more robust changes in their behavioral response following adult antibiotic treatment, including decreased investigation and increased grooming, suggestive of changes in anxiety-like behaviors. These data suggest that males may be more vulnerable than females to behavioral abnormalities after being predisposed to an immune challenge early in life. Collectively, these results provide novel evidence that some of the sex-specific behavioral consequences of an early-life immune challenge may not transpire until an individual is faced with a secondary challenge, and the context in which an individual is exposed can greatly influence the response.

Assessing recrudescence of photoregressed Siberian hamster ovaries using in vitro whole ovary culture

In vitro culture has been used to study different aspects of ovarian function; however, this technique has not been applied to study recrudescence, or the return of ovarian function in seasonally breeding species. In Siberian hamsters, exposure to inhibitory photoperiods induces declines in ovarian function, which are restored with photostimulation. Because these changes are mediated by changes in systemic gonadotropin (GT) secretion, we hypothesized that culturing photoregressed ovaries with GT would restore aspects of function and induce expression of key folliculogenic factors. Adult female Siberian hamsters were exposed to either long-day (LD; 16L:8D) or short-day (SD; 8L:16D) photoperiods for 14 weeks to maintain in vivo cyclicity or induce gonadal regression, respectively. Isolated ovaries were then cultured for 10 days with or without GT. Ovarian mass and messenger RNA (mRNA) expression of mitotic marker Pcna were increased in cultured SD ovaries (cSD) ovaries with GT as compared to without GT, with no changes noted among cultured LD (cLD) ovaries. Media estradiol and progesterone concentrations increased in both cLD and cSD ovaries cultured with GT as compared to without GT. No differences in follicle numbers or incidence of apoptosis were noted across groups. In addition, differential mRNA expression of folliculogenic growth factors ( Bmp-4, Ntf-3, Inh-α, Gdf-9, Igf-1, Has-2, and Cox-2) was observed in cSD treated with or without GT. Together, these results suggest that this in vitro model could be a useful tool to (a) study the return of function in photoregressed ovaries, and (b) to identify the specific roles folliculogenic factors play in ovarian recrudescence.

Effect of season on reproductive behaviors and fertilization success in cavies (Cavia aperea)

Finding the optimal timing for breeding is crucial for small mammals to ensure survival and maximize lifetime reproductive success. Species living in temperate regions therefore often restrict breeding to seasons with favorable food and weather conditions. Although caviomorph rodents such as guinea pigs are described as non-seasonal breeders, a series of recent publications has shown seasonal adaptations in litter size, offspring birth mass and maternal investment. Here, we aim to test if seasonal patterns of litter size variation found in earlier studies, are mediated by seasonal differences in female estrus length, fertilization rate and mating behavior. The female estrus period was longer in fall compared to all other seasons (p < 0.001), frequently lasting 7-9 days while estrus in spring usually lasted less than 2 days. In fall, females mated later during estrus (p < 0.001), resulting in reduced fertilization rates (p < 0.001). Fertilization rate was well above 95% in summer while it dropped to less than 85% in fall and winter. While none of the male mating characteristics such as number and duration of copulations differed across seasons, the number of mating bouts was reduced in fall (p = 0.04). Finally, the developmental stages of flushed embryos were more diverse in spring and summer compared to fall and winter. These results suggest that seasonal differences in fertilization rate and quality of implanted embryos are mediated by female estrus length and timing and intensity of mating behavior. Together, these effects contribute to the observed differences in litter size across seasons.

Folliculogenic factors in photoregressed ovaries: Differences in mRNA expression in early compared to late follicle development

The early stages of ovarian folliculogenesis generally progress independent of gonadotropins, whereas later stages require signaling initiated by FSH. In Siberian hamsters, cycles of folliculogenesis are mediated by changes in photoperiod which depress the hypothalamic pituitary gonadal axis. Reduced gonadotropins lead to decreases in mature follicle development and ovulation; however, early stages of folliculogenesis have not been explored in regressed ovaries. We hypothesized that intraovarian factors that contribute predominantly to later stages of folliculogenesis would react to changes in photoperiod, whereas factors contributing to earlier stages would not change. To probe if the early stages of folliculogenesis continue in the photoinhibited ovary while late stages decline, we measured the mRNA abundance of factors that interact with FSH signaling (Fshr, Igf1, Cox2) and factors that can function independently of FSH (c-Kit, Kitl, Foxo3, Figla, Nobox, Sohlh1, Lhx8). While plasma FSH, antral follicles, and corpora lutea numbers declined with exposure to inhibitory photoperiod, the numbers of primordial, primary, and secondary follicles did not change. Expression of factors that interact with FSH signaling changed with changes in photoperiod; however, expression of factors that do not interact with FSH were not significantly altered. These results suggest that the photoinhibited ovary is not completely quiescent, as factors important for follicle selection and early follicle growth are still expressed in regressed ovaries. Instead, the lack of gonadotropin support that characterizes the non-breeding season appears to inhibit only final stages of folliculogenesis in Siberian hamsters.

Sickness-induced changes in physiology do not affect fecundity or same-sex behavior

Previous work in our lab has shown that early-life infection affects female reproductive physiology and function (i.e., smaller ovaries, abnormal estrous cycles) and alters investigation and aggression towards male conspecifics in a reproductive context. Although many studies have investigated the effects of postnatal immune challenge on physiological and behavioral development, fewer studies have examined whether these changes have ultimate effects on reproduction. In the current study, we paired Siberian hamsters (Phodopus sungorus) and simulated a bacterial infection in early life by administering lipopolysaccharide (LPS) to male and female pups on pnd3 and pnd5. In adulthood, hamsters were paired with novel individuals of the same sex, and we scored an array of social behaviors (e.g., investigation, aggression). We then paired animals with individuals of the opposite sex for 5 consecutive nights, providing them with the opportunity to mate. We found that females exhibited impaired reproductive physiology and function in adulthood (i.e., smaller ovaries and abnormal estrous cycles), similar to our previous work. However, both LPS-treated males and females exhibited similar same-sex social behavior when compared with saline-treated controls, they successfully mated, and there were no significant changes in fecundity. These data suggest that the physiological changes in response to neonatal immune challenge may not have long-term effects on reproductive success in a controlled environment. Collectively, the results of this study are particularly important when investigating the relationships between physiology and behavior within an ultimate context. Animals exposed to early-life stress may in fact be capable of compensating for changes in physiology in order to survive and reproduce in some contexts.

Overcoming neonatal sickness: Sex-specific effects of sickness on physiology and social behavior

Early-life environmental stressors, including sickness, have the potential to disrupt development in ways that could severely impact fitness. Despite what is known about the effects of sickness on reproduction, the precise physiological mechanisms have not yet been determined. The goal of this study was to investigate the effects of a neonatal immune challenge on adult reproductive physiology and opposite-sex social behavior. Male and female Siberian hamster (Phodopus sungorus) pups were administered lipopolysaccharide ([LPS]; a cell wall component of gram-negative bacteria) or saline injections on postnatal days 3 and 5 and body mass, food intake, and measures of reproductive maturity were taken throughout development. In adulthood, hamsters were placed in staged mating pairs with reproductively mature individuals of the opposite sex, during which a series of behaviors were scored. We found that although males and females showed no change in food intake, body mass, or reproductive behaviors, LPS-treated females had abnormal estrous cycles and smaller ovaries. Females also showed increased investigation of and increased aggression towards males in a reproductive context. In contrast, LPS-treated males showed no change in any physiological measures, nor did they show any changes in behavior. The present findings demonstrate that females may be more robustly affected by neonatal sickness than males and that these effects could have potential impacts on reproductive success. Collectively, the results of this study can be used to expand upon what is already known about sickness and reproduction, specifically the importance of social behaviors involved in pre-copulation and information necessary to choose the appropriate mate.

Photoperiod-Induced Increases in Bone Mineral Apposition Rate in Siberian Hamsters and the Involvement of Seasonal Leptin Changes

The adipokine leptin regulates energy balance, appetite, and reproductive maturation. Leptin also acts on bone growth and remodeling, but both osteogenic and anti-osteogenic effects have been reported depending on experimental conditions. Siberian hamsters (Phodopus sungorus) have natural variation in circulating leptin concentrations, where serum leptin is significantly decreased during the short day (SD)-induced winter state. In summer long day (LD) photoperiods, appetite and body adiposity increase with associated central leptin insensitivity. This natural change in leptin secretion was exploited to investigate leptin's effect on bone growth. Hamsters were injected with calcium-chelating fluorescent dyes to measure bone mineral apposition rate (MAR). Measurements were initially obtained from 5-week and 6-month-old animals maintained in low leptin (SD) or high leptin (LD) states. A further study investigated effects of chronic administration of recombinant mouse leptin to hamsters housed in SD and LD conditions; growth plate thickness and bone density were also assessed. As expected, a reduction in body mass was seen in hamsters exposed to SD, confirming the phenotype change in all studies. Serum leptin concentrations were significantly reduced in SD animals in all studies. MAR was reproducibly and significantly increased in the femurs of SD animals in all studies. Vitamin D and growth plate thickness were significantly increased in SD animals at 6 months. No effect on bone density was observed in any study. Taken together these data suggest that bone growth is associated with the low leptin, winter, lean state. In leptin-treated animals, there was a significant interaction effect of leptin and photoperiod. In comparison to their vehicle counterparts, SD animals had decreased and LD animals had increased MAR, which was not apparent prior to leptin administration. In conclusion, increased MAR was associated with low serum leptin levels in early life and sustained over 6 months, implying that leptin has a negative effect on bone growth in this model. The unexpected finding that MAR increased after peripheral leptin administration in LD suggests that leptin exerts different effects on bone growth dependent on initial leptin status. This adds further weight to the hypothesis that leptin-treated LD animals display central leptin resistance.

Rapid changes in ovarian mRNA induced by brief photostimulation in Siberian hamsters (Phodopus sungorus)

This study sought to characterize the rapid intraovarian mRNA response of key folliculogenic factors that may contribute to the restoration of folliculogenesis during 2-10 days of photostimulation in Siberian hamsters. Adult hamsters were exposed to short photoperiod (8L:16D) for 14 weeks (SD). A subset were then transferred to long photoperiod (16L:8D) for 2 (PT day-2), 4 (PT day-4), or 10 days (PT day-10). Quantitative real-time PCR was used to measure intraovarian mRNA expression of: gonadotropin releasing hormone (GnRH), follicle stimulating hormone β-subunit (FSHβ-subunit), luteinizing hormone β-subunit (LHβ-subunit), FSH and LH receptors, estrogen receptors α and β (Esr1 and Esr2), matrix metalloproteinase (MMP)-2 and -9, anti-Müllerian hormone (AMH), inhibin-α subunit, fibroblast growth factor-2 (FGF-2) and proliferating cell nuclear antigen (PCNA). Compared to SD, plasma FSH concentrations increased on PT day-4 and the number of antral follicles and corpora lutea increased on PT day-10. FSHR and inhibin-α mRNA expression also increased on PT day-4, whereas LHR and proliferation marker PCNA both increased on PT day-10 as compared to SD. Esr1 mRNA increased on PT day-2 and remained significantly increased as compared to SD, whereas Esr1 mRNA increased only on PT day-2, similar to FGF-2 and MMP-2 results. No differences were observed in mRNA expression in ovarian GnRH, FSHβ- and LHβ-subunits, AMH, and MMP-9 mRNA with 2-10 days of photostimulation. Rapid increases in intraovarian FSHR and inhibin-α mRNA and antral follicle/corpora lutea numbers suggest that the ovary is primed to react quickly to the FSH released in response to brief periods of photostimulation.

Matrix metalloproteinase inhibition influences aspects of photoperiod stimulated ovarian recrudescence in Siberian hamsters

Blocking matrix metalloproteinase (MMP) activity in vivo with inhibitor GM6001 impedes photostimulated ovarian recrudescence in photoregressed Siberian hamsters. Since direct and indirect effects of MMPs influence a myriad of ovarian functions, we investigated the effect of in vivo MMP inhibition during recrudescence on ovarian mRNA expression of steroidogenic acute regulatory protein (StAR), 3β-hydroxysteroid dehydrogenase (3β-HSD), Cyp19a1 aromatase, epidermal growth factor receptor (EGFR), amphiregulin (Areg), estrogen receptors (Esr1 and Esr2), tissue inhibitors of MMPs (TIMP-1,-2,-3), proliferating cell nuclear antigen (PCNA), vascular endothelial growth factor A (VEGFA), its receptor VEGFR-2, and angiopoietin-2 (Ang-2). Female Siberian hamsters were randomly assigned to one of four photoperiod groups: stimulatory long (LD) or inhibitory short (SD) photoperiods, or transferred from SD to LD for 2 weeks (post-transfer, PT). Half of the PT hamsters were injected (ip) daily with GM6001 (PTG). SD exposure reduced ovarian StAR, 3β-HSD, Cyp19a1, Esr1, Esr2, TIMPs 2-3, PCNA, VEGFR-2 and Ang-2 mRNA expression (p<0.05), and 2 weeks of photostimulation restored mRNA expression of 3β-HSD and PCNA and increased Areg and VEGFA mRNA expression in the PT group. GM6001 treatment during photostimulation (PTG) increased TIMP-1, -2 and -3 and PCNA mRNA, but inhibited Areg mRNA expression compared to PT. Neither photoperiod nor GM6001 altered EGFR expression. Results of this study suggest that in vivo inhibition of MMP activity by GM6001 may impede ovarian recrudescence, particularly follicular growth, in two ways: (1) directly by partially inhibiting the release of EGFR ligands like Areg, thereby potentially affecting EGFR activation and its downstream pathway, and (2) indirectly by its effect on TIMPs which themselves can affect proliferation, angiogenesis and follicular growth.

Metabolic stressors and signals differentially affect energy allocation between reproduction and immune function

Most free-living animals have finite energy stores that they must allocate to different physiological and behavioral processes. In times of energetic stress, trade-offs in energy allocation among these processes may occur. The manifestation of trade-offs may depend on the source (e.g., glucose, lipids) and severity of energy limitation. In this study, we investigated energetic trade-offs between the reproductive and immune systems by experimentally limiting energy availability to female Siberian hamsters (Phodopus sungorus) with 2-deoxy-d-glucose, a compound that disrupts cellular utilization of glucose. We observed how glucoprivation at two levels of severity affected allocation to reproduction and immunity. Additionally, we treated a subset of these hamsters with leptin, an adipose hormone that provides a direct signal of available fat stores, in order to determine how increasing this signal of fat stores influences glucoprivation-induced trade-offs. We observed trade-offs between the reproductive and immune systems and that these trade-offs depended on the severity of energy limitation and exogenous leptin signaling. The majority of the animals experiencing mild glucoprivation entered anestrus, whereas leptin treatment restored estrous cycling in these animals. Surprisingly, virtually all animals experiencing more severe glucoprivation maintained normal estrous cycling throughout the experiment; however, exogenous leptin resulted in lower antibody production in this group. These data suggest that variation in these trade-offs may be mediated by shifts between glucose and fatty acid utilization. Collectively, the results of the present study highlight the context-dependent nature of these trade-offs, as trade-offs induced by the same metabolic stressor can manifest differently depending on its intensity.

Anti-Müllerian hormone (AMH), inhibin-α, growth differentiation factor 9 (GDF9), and bone morphogenic protein-15 (BMP15) mRNA and protein are influenced by photoperiod-induced ovarian regression and recrudescence in Siberian hamster ovaries

Exposure of Siberian hamsters to short photoperiod (SD) inhibits ovarian function, including folliculogenesis, whereas function is restored with their transfer to long photoperiods (LD). To investigate the mechanism of photo-stimulated recrudescence, we assessed key folliculogenic factors-anti-Müllerian hormone (AMH), inhibin-α, growth differentiation factor-9 (GDF9), and bone morphogenic protein-15 (BMP15)-across the estrus cycle and in photo-regressed and recrudescing ovaries. Adult hamsters were exposed to either LD or SD for 14 weeks, which respectively represent functional and regressed ovaries. Select regressed hamsters were transferred back to LD for 2 (post-transfer week 2; PTw2) or 8 weeks (PTw8). Ovaries were collected and fixed in formalin for immunohistochemistry or frozen in liquid nitrogen for real-time PCR. AMH, inhibin-α, GDF9, and BMP15 mRNA and protein were detected in all stages of the estrus cycle. Fourteen weeks of SD exposure increased (P < 0.05) ovarian AMH, GDF9, and BMP15, but not inhibin-α mRNA levels as compared to LD. Transfer of regressed hamsters to stimulatory long photoperiod for 8 weeks returned AMH and GDF9 mRNA levels to LD-treated levels, and further increased mRNA levels for inhibin-α and BMP15. Immunostaining for AMH, inhibin-α, GDF9, and BMP15 proteins was most intense in preantral/antral follicles and oocytes. The overall immunostaining extent for AMH and inhibin-α generally mirrored the mRNA data, though no changes were observed for GDF9 or BMP15 immunostaining. Shifts in mRNA and protein levels across photoperiod conditions suggest possible syncretic roles for these folliculogenic factors in photo-stimulated recrudescence via potential regulation of follicle recruitment, preservation, and development.

Photoperiod-gonadotropin mismatches induced by treatment with acyline or FSH in Siberian hamsters: impacts on ovarian structure and function

Many seasonal breeders time their reproductive efforts to specific times of the year to ensure adequate resources for the production and care of young. For long-day (LD) breeders, females born before the summer solstice (LDs) reach sexual maturity quickly and often breed that same year, whereas females born after the summer solstice (short days (SDs)) may delay reproductive development to the following spring when environmental conditions are favorable for reproduction. In Siberian hamsters, development in SD is associated with structural and functional differences in the ovary compared with females held in LD, including a greater number of primordial follicles and an abundance of hypertrophied granulosa cells (HGCs), which are immunoreactive for anti-Müllerian hormone. The goal of this study was to determine whether SD-induced gonadotropin suppression is responsible for these phenotypic differences. Gonadotropin levels were suppressed in LD hamsters using the GNRH antagonist acyline. Conversely, to determine whether the SD ovarian phenotype is completely reversed by gonadotropin stimulation, recombinant human FSH (rhFSH) was administered. Our treatments were successful in mimicking FSH concentrations of the opposite photoperiod, but they did not produce a comparable change in the ovarian phenotype. Most notable was the lack of HGCs in the ovaries of acyline-treated LD females. Similarly, HGCs were maintained in the ovaries of SD females treated with rhFSH. Our data suggest that gonadotropins alone do not account for the SD ovarian phenotype. Future studies will determine whether SD-induced changes in other factors underlie these phenotypic changes.

X-linked inhibitor of apoptosis protein and active caspase-3 expression patterns in antral follicles in the sheep ovary

X-linked inhibitor of apoptosis protein (XIAP) interacts with caspases to inhibit their activity, thereby providing a potential mechanism for regulation of granulosa cell apoptosis occurring during follicular atresia. The aim of this study was to determine the presence and localization of XIAP mRNA and protein content in the sheep ovary and compare these expression patterns with active caspase-3 protein in the same antral follicles. Romney ewe estrous cycles (n=25) were synchronized with 2–3 Estrumate injections and ovarian tissue collected during the luteal and follicular phases of the cycle. The presence ofXIAPmRNA was confirmed by RT-PCR using laser capture microdissected ovarian cell samples.XIAPmRNA was subsequently localized byin situhybridization histochemistry and XIAP and active caspase-3 protein visualized by immunohistochemistry. In antral follicles extensive XIAP localization was evident in both granulosa and thecal cells. In contrast, mRNA expression was widespread in granulosa cells and only detected in thecal tissue from a small proportion of antral follicles. Active caspase-3 and XIAP comparative expression analysis showed positiveXIAPmRNA expression in all late luteal phase (day 14) follicles, despite varying levels of active caspase-3 protein. A proportion of follicular phase (days 15 and 16) follicles, however, showed an inverse expression relationship at the protein and mRNA levels in both granulosa and thecal tissue, as did XIAP protein in day 14 follicles. These results suggest high XIAP may prevent activation of caspase-3, thereby regulating follicular atresia in antral follicles and could potentially be utilized as a marker of follicular health.

Intraovarian expression of GnRH-1 and gonadotropin mRNA and protein levels in Siberian hamsters during the estrus cycle and photoperiod induced regression/recrudescence

The hypothalamic-pituitary-gonadal (HPG) axis is the key reproductive regulator in vertebrates. While gonadotropin releasing hormone (GnRH), follicle stimulating (FSH), and luteinizing (LH) hormones are primarily produced in the hypothalamus and pituitary, they can be synthesized in the gonads, suggesting an intraovarian GnRH-gonadotropin axis. Because these hormones are critical for follicle maturation and steroidogenesis, we hypothesized that this intraovarian axis may be important in photoperiod-induced ovarian regression/recrudescence in seasonal breeders. Thus, we investigated GnRH-1 and gonadotropin mRNA and protein expression in Siberian hamster ovaries during (1) the estrous cycle; where ovaries from cycling long day hamsters (LD;16L:8D) were collected at proestrus, estrus, diestrus I, and diestrus II and (2) during photoperiod induced regression/recrudescence; where ovaries were collected from hamsters exposed to 14 weeks of LD, short days (SD;8L:16D), or 8 weeks post-transfer to LD after 14 weeks SD (PT). GnRH-1, LHβ, FSHβ, and common α subunit mRNA expression was observed in cycling ovaries. GnRH-1 expression peaked at diestrus I compared to other stages (p < 0.05). FSHβ and LHβ mRNA levels peaked at proestrus and diestrus I (p < 0.05), with no change in the α subunit across the cycle (p > 0.05). SD exposure decreased ovarian mass and plasma estradiol concentrations (p<0.05) and increased GnRH-1, LHβ, FSHβ, and α subunit mRNA expression as compared to LD and, except for LH, compared to PT (p < 0.05). GnRH and gonadotropin protein was also dynamically expressed across the estrous cycle and photoperiod exposure. The presence of cycling intraovarian GnRH-1 and gonadotropin mRNA suggests that these hormones may be locally involved in ovarian maintenance during SD regression and/or could potentially serve to prime ovaries for rapid recrudescence.

Inhibition of matrix metalloproteinases in Siberian hamsters impedes photostimulated recrudescence of ovaries

Exposure of Siberian hamsters to short photoperiod for 14 weeks induces ovarian regression. Subsequent transfer to long photoperiod restores ovarian function, and 2 weeks of photostimulation increases plasma estradiol (E(2)), antral follicles, and corpora lutea (CL). Because tissue remodeling involved with photostimulated ovarian recrudescence is associated with differential expression of matrix metalloproteinases (MMPs), we hypothesized that inhibiting MMP activity using a broad-spectrum in vivo MMP inhibitor, GM6001, would curtail recrudescence. One group of hamsters was placed in long days (LD; 16 h light:8 h darkness) for 16 weeks. Another group was placed in inhibitory short days (SD; 8 h light:16 h darkness) for 14 weeks. A third group was placed in SD for 14 weeks and transferred to LD for 2 weeks to stimulate recrudescence. During weeks 14-16, animals were either not treated or treated daily with i.p. injections of GM6001 (20 mg/kg) or vehicle (DMSO). GM6001 reduced gelatinase activity and decreased immunohistochemical staining for MMP1, MMP2, and MMP3 compared with vehicle. No differences between controls, vehicle, or GM6001 treatment were observed among LD animals, despite a trend toward reduction in CL and E(2) with GM6001. Although SD reduced ovarian function, photostimulation of transferred controls increased uterine mass, plasma E(2), appearance of antral follicles, and CL. With GM6001 treatment, photostimulation failed to increase uterine mass, plasma E(2), antral follicles, or CL. These data show, for the first time, that in vivo GM6001 administration inhibits MMP activity in hamster ovaries during photostimulation, and indicate that this inhibition may impede photostimulated recrudescence of ovaries. This study suggests an intriguing link between MMP activity and return to ovarian function during photostimulated recrudescence.

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

BACKGROUND

Matrix 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.

METHODS

MMP-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).

RESULTS

MMP-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.

CONCLUSIONS

Although 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.

Short photoperiod initiated during adulthood sustains reproductive function in older female siberian hamsters more effectively than short photoperiod initiated before puberty

Reproductive aging in female mammals is characterized by a progressive decline in fertility and fecundity. Many women delay their first full-term pregnancy until an age at which their reproductive potential has already declined. No treatment is presently available to delay the aging process. In a limited number of rodent species, caloric restriction sustained reproductive function in older females, and in most investigations, sexual maturation was delayed because caloric restriction was initiated at weaning. We have previously reported similar outcomes in female Siberian hamsters that were reared in short photoperiod (SP), which profoundly inhibits reproductive physiology. When compared to hamsters held in long photoperiod (LP), females reared in SP matured much later and had greater reproductive success at 9 mo of age. Herein, we determined if delayed onset of sexual maturation was necessary for SP to decelerate reproductive aging. We initiated a 6-mo period of SP before or after sexual maturation and measured the reproductive success of females at 12 mo of age. Maintenance of hamsters in SP beginning after puberty was associated with significantly greater litter success (77%) compared to imposition of SP before puberty (35%); the difference in weaning success was even greater (73% and 12%, respectively). Regardless of which SP regime was used, litter success of females exposed to SP was substantially greater than that of 12-mo-old females held continuously in LP (6%). The efficacy of SP in decelerating female reproductive aging is manifest at several life stages and is greater when treatment is initiated after rather than before puberty.

Use of Morphology and Endocrinology to Predict Sex in California Sheephead: Evidence of Altered Timing of Sex Change at Santa Catalina Island, California

To estimate the health of the California sheephead Semicossyphus pulcher fishery, a 2004 stock assessment used available biological data that were collected decades prior to an increase in fishing pressure. However, a recent study has found that sex ratios, growth rates, survivorship, and average sizes of females and males have changed in response to size-selective fishing in some California sheephead populations. To better understand the potential changes in protogynous California sheephead, this study sought to determine (1) whether external morphology was still an accurate method of predicting sex in sexually dimorphic California sheephead at Santa Catalina Island, California, and (2) whether nonlethal blood sampling and plasma hormone analysis could be used to predict sex for future stock assessments. Sex was determined using gonadal histology and compared with several specific external morphological characters. Estradiol and 11-ketotestosterone plasma concentrations were also compared across sexed individuals. The rate of error when using external morphology alone to predict sex was 58%. In contrast, sex steroid concentrations varied significantly across sexes; estradiol concentrations were significantly greater in females than in transitioning and male individuals during the breeding season, and 11-ketotestosterone concentrations were significantly lower among females. Gonadal histology showed that 21% of the fish caught during the breeding season were classified as transitional, in stark contrast to historical data. The inability to accurately predict sex using external morphology alone suggests that commonly used methods of surveying California sheephead populations (e.g., diver surveys) may be inaccurate. Nonlethal blood sampling and subsequent plasma hormone analysis may offer an alternative method for assessing sex in California sheephead. Because California sheephead are not reproductively functional during transition and because we found such a large proportion in transition during the breeding season at Santa Catalina Island, we believe there is a need for continued assessment of the reproductive potential in this population of California sheephead.

Differential ovarian expression of KiSS-1 and GPR-54 during the estrous cycle and photoperiod induced recrudescence in Siberian hamsters (Phodopus sungorus)

Kisspeptins, coded by the KiSS-1 gene, regulate aspects of the reproductive axis by stimulating GnRH release via the G protein coupled receptor, GPR54. Recent reports show that KiSS/GPR54 may be key mediators in photoperiod-controlled reproduction in seasonal breeders, and that KiSS-1/GPR54 are expressed in the hypothalamus, ovaries, placenta, and pancreas. This study examined the expression of KiSS-1/GPR54 mRNA and protein in ovaries of Siberian hamsters (Phodopus sungorus). Ovaries from cycling hamsters were collected during proestrus (P), estrus (E), diestrus I (DI), and diestrus II (DII). To examine KiSS-1/GPR54 during stimulated recrudescence, additional hamsters were maintained either in long day (LD 16L:8D, control) or short day (SD 8L:16D) for 14 weeks and then transferred to LD for 0-8 weeks. Staining of KiSS-1/GPR54 protein was detected by immunohistochemistry in steroidogenic cells of pre-antral and antral follicles, and corpora lutea. Immunostaining peaked in P and E, but decreased in the diestrus stages (P < 0.05). In recrudescing ovaries, KiSS-1/GPR54 immunostaining was low after 14 weeks of SD exposure (post-transfer [PT] week 0), and increased during the early weeks of recrudescence. Expression of KiSS-1/GPR54 mRNA was low with short day exposure, but increased during recrudescence and was higher at PT week 8 as compared to PT weeks 0 and 2 (P < 0.05). The elevated KiSS-1/GPR54 expression during P and E suggests a potential role in ovulation in Siberian hamsters. Transient increases in KiSS-1/GPR54 expression following LD stimulation are also suggestive of possible involvement in ovulation and/or restoration of ovarian function.

Gonadal Restructuring During Sex Transition in California Sheephead: a Reclassification Three Decades After Initial Studies

California Sheephead, Semicossyphus pulcher, is a monandric protogynous hermaphrodite and a commercially and recreationally valuable labrid. Gonadal functionality of Sheephead through sex change was reclassified into nine classes using current criteria for categorization. Female ovaries were classified as immature, early maturing, mature, and regressing/recovering classes. Transition from female to male and subsequent male development was divided into early, mid and late transitional, developing/active male and regressing/recovering male. Reproductive states in Sheephead were correlated with estradiol (E2) and 11-keto testosterone (11-KT) concentrations in the blood plasma. All sexes had low E2 concentrations in the fall /winter seasons; in transitional and male individuals, levels remained low throughout the year. In contrast, female E2 concentrations were elevated in spring and peaked in the summer. Concentrations of 11-KT were variable throughout the year; however, females had significantly lower levels in the summer. This study allows a better understanding of the current state of California Sheephead in a heavily fished area. Knowledge of a species' reproductive characteristics is important in evaluating the sustainability of a population as it can set a baseline for reproductive potential. This research takes a critical step in gathering and organizing reproductive data such that it may be used in future studies for comparing reproductive potential across the range of the California sheephead.

The effect of mifepristone on apoptosis and caspase-3 activation in human ovarian luteinized granulosa cells

OBJECTIVE

To investigate the effect of mifepristone, an oral contraceptive, on apoptosis in human ovarian luteinized granulosa cells.

STUDY DESIGN

Human ovarian luteinized granulosa cells were treated in vitro with 1.25, 2.5, 5.0, 10.0, or 20.0 microM of mifepristone. Nuclear morphology, apoptosis ratio, and level of caspase-3 expression were determined with immunofluorescence microscopy, the terminal deoxynucleotidyl transferase mediated nick end labeling (TUNEL) assay, and flow cytometry.

RESULTS

We found that mifepristone-treated cells contained single condensed chromatin with multiple nuclear fragments, which is morphologic evidence of apoptosis. A significant difference was observed in the TUNEL assay between mifepristone-treated cells and control cells (P<0.05). Consistent with the results of the TUNEL assay, the fluorescence intensity of caspase-3 in drug-treated cells was also significantly different (P<0.05) from control cells; specifically, the difference between cells treated with different doses of drugs was much smaller and negligible.

CONCLUSION

From these results, we propose that mifepristone induces human ovarian luteinized granulosa cells to undergo apoptosis by activating caspase-3.

Differential activity of matrix metalloproteinases (MMPs) during photoperiod induced uterine regression and recrudescence in Siberian hamsters (Phodopus sungorus)

Siberian hamsters adapt to seasonal changes by reducing their reproductive function during short days (SD). SD exposure reduces uterine mass and reproductive capacity, but underlying cellular mechanisms remain unknown. Because matrix metalloproteinases (MMPs) and their tissue inhibitors (TIMPs) are important in uterine development, parturition, and postpartum remodeling, their expression in uterine tissue from Siberian hamsters undergoing photoperiod-mediated reproductive regression and recrudescence was investigated. Female hamsters were exposed to long day (LD, 16L:8D, controls) or SD (8L:16D) for 3-12 weeks (regression); a second group was exposed to SD or LD for 14 weeks and then transferred to LD for 0-8 weeks (recrudescence). Hamsters were euthanized, uteri collected, and homogenates analyzed by gelatin zymography or Western blotting for MMP and TIMP protein levels. Uterine weight decreased (67-75%) at SD weeks 12-14 and increased post-LD transfer (PT) reaching LD values by PT week 2. MMP-2, but not MMP-9 activity was reduced by SD week 12 or 14 but increased to LD levels at PT week 2. MMP-3 expression increased at SD week 9 compared to other SD and LD groups. MMP-14 and -13 protein levels decreased at SD week 3 but returned to LD levels by SD week 6. During recrudescence, MMP-3 (PT weeks 0-2), MMP-13 (PT week 4), and MMP-14 (PT weeks 2, 4) protein levels were higher than LD. TIMP-1 and 2 were present at low levels. Significant and differential variations in uterine MMP activity/expression during photoperiod-induced regression and recrudescence were observed. These changes likely reflect increases in tissue remodeling during both the adaptation to SD and the restoration of reproductive function.

Photoperiod-dependent modulation of anti-Müllerian hormone in female Siberian hamsters, Phodopus sungorus

Fertility and fecundity decline with advancing age in female mammals, but reproductive aging was decelerated in Siberian hamsters (Phodopus sungorus) raised in a short-day (SD) photoperiod. Litter success was significantly improved in older hamsters when reared in SD and the number of primordial follicles was twice that of females held in long days (LD). Because anti-Müllerian hormone (AMH) appears to inhibit the recruitment of primordial follicles in mice, we sought to determine whether the expression patterns of AMH differ in the ovaries and serum of hamsters raised in SD versus LD. Ovaries of SD female hamsters are characterized by a paucity of follicular development beyond the secondary stage and are endowed with an abundance of large eosinophilic cells, which may derive from granulosa cells of oocyte-depleted follicles. In ovaries from 10-week-old SD hamsters, we found that the so-called 'hypertrophied granulosa cells' were immunoreactive for AMH, as were granulosa cells within healthy-appearing primary and secondary follicles. Conversely, ovaries from age-matched LD animals lack the highly eosinophilic cells present in SD ovaries. Therefore, AMH staining in LD was limited to primary and secondary follicles that are comparable in number to those found in SD ovaries. The substantially greater AMH expression in SD ovaries probably reflects the abundance of hypertrophied granulosa cells in SD ovaries and their relative absence in LD ovaries. The modulation of ovarian AMH by day length is a strong mechanistic candidate for the preservation of primordial follicles in female hamsters raised in a SD photoperiod.

Differential expression of matrix metalloproteinases during stimulated ovarian recrudescence in Siberian hamsters (Phodopus sungorus)

The matrix metalloproteinases (MMPs) are a family of extracellular matrix-cleaving enzymes involved in ovarian remodeling. In many non-tropical species, including Siberian hamsters, ovarian remodeling is necessary for the functional changes associated with seasonal reproduction. We evaluated MMPs and their endogenous inhibitors (TIMPs), during photoperiod-induced ovarian recrudescence in Siberian hamsters. Hamsters were transferred from long day (LD; 16:8) to short day (SD; 8:16) photoperiods for 14weeks, and then returned to LD for 0, 1, 2, 4, or 8weeks for collection of ovaries and plasma. Post-transfer (PT) LD exposure increased body and ovarian mass. Number of corpora lutea and antral, but not preantral follicles increased in PT groups. Plasma estradiol concentrations were lower in PT weeks 0-4, and returned to LD levels at PT week 8. No change was observed in relative MMP/TIMP mRNA levels at PT week 0 (SD week 14) as compared to LD. Photostimulation increased MMP-2 mRNA at PT week 8 as compared to PT weeks 0-1. MMP-14 mRNA expression peaked at PT weeks 1-2 as compared to LD levels, while MMP-13 expression was low during this time. TIMP-1 mRNA peaked at PT week 8 as compared to PT weeks 0-4. No changes were noted in MMP-9 and TIMP-2 mRNA expression. In general, MMP/TIMP protein immunodetection followed the same patterns with most staining occurring in granulosa cells of follicles and corpora lutea. Our data suggest that mRNA and protein for several members of the MMP/TIMP families are expressed in Siberian hamster ovaries during recrudescence. Because of the variation observed in expression patterns, MMPs and TIMPs may be differentially involved with photostimulated return to ovarian function.