Pregnant Voles Research Articles

Effects of predator-induced stress during pregnancy on reproductive output and offspring quality in Brandt’s voles (Lasiopodomys brandtii)

Animals may use different reproductive strategies depending on environmental conditions. This study investigated the effects of maternal stress induced by exposure to predator odors on reproductive output and adult offspring quality in pregnant Brandt’s voles (Lasiopodomys brandtii). We exposed pregnant Brandt’s voles to cat urine, rabbit urine, or distilled water for 18 days (1 h/day). Our results indicated that pregnant voles in the cat odor-exposed group tended to produce more offspring and the number of viable female offspring was larger. However, we did not observe any differences in the sex ratios of vole offspring among the three treatment groups. Compared with the control (distilled water) group, female offspring of voles in the cat odor-exposed group had lower body weights, lengths, and smaller body weights in relation to body length, whereas they had larger ovaries in relation to body weight. Furthermore, the female offspring of the voles exposed to the cat odor had higher concentrations of serum estradiol and higher levels of gonadotropin-releasing hormone mRNA in the hypothalamus compared with the female offspring of the voles in the control group. However, we observed no differences among the male offspring in the three treatment groups. Our findings suggest that pregnant Brandt’s voles suffering from chronic exposure to predator odors will produce greater numbers of low-weight female offspring that probably possess higher breeding potential to improve the fitness via regulation of the hypothalamic-pituitary-gonadal axis.

Effects of maternal stress induced by predator odors during gestation on behavioral and physiological responses of offspring in Brandt's vole (Lasiopodomys brandtii).

Maternal effects play a crucial role in regulating populations of small mammals and anti-predator behaviors of offspring. The present study investigated the effects of maternal stress induced by exposure to predator odors during gestation on the behavioral and physiological responses of offspring in Brandt's vole (Lasiopodomys brandtii). Effects included changes in growth, behaviors, hormone levels in serum, and fosB/ΔfosB mRNA and FosB/ΔFosB protein expression in the hypothalamus. Our results showed that when pregnant voles were exposed to cat and rabbit urine odors for 18 days (1 h/day), the weight of the female offspring decreased; however, the thymus and ovary indices increased, compared with the control group. Male offspring of voles exposed to cat odor spent more time exploring and foraging, and showed a decrease in corticosterone (CORT) compared with voles in the control group. Both fosB/ΔfosB mRNA and FosB/ΔFosB protein expressions were downregulated in the hypothalamus of male offspring in the cat odor-exposed group compared to that in offspring in the control group. However, the mRNA levels of fosB/ΔfosB in the hypothalamus of female offspring did not decrease in response to cat urine odor. Our findings suggested that maternal stress induced by predator odors during gestation restrained the growth of female offspring and increased the duration of exploring and foraging behaviors of male offspring by regulating the HPA axis, which, in turn, reduced the sensitivity of offspring to unfamiliar environments and increased their probability of becoming prey.

Cold exposure does not decrease serum leptin concentration, but increases energy intake and thermogenic capacity in pregnant Brandt's voles ( Lasiopodomys brandtii)

In most mammals, maternal body mass and fat mass increase during pregnancy due to hyperphagia. These physiological changes provide the fetus with energy and nutrients and prepare the mother for the high energetic demands of lactation. In the present study, metabolic changes in response to cold and pregnancy were examined in female Brandt's voles ( Lasiopodomys brandtii). At 23±1 °C, the voles increased body mass and deposited body fat during pregnancy. However, at 5±1 °C pregnant voles did not deposit body fat even though energy intake increased above the level in the warm. Serum leptin concentration increased during pregnancy and was not influenced by cold exposure. Thermogenic capacity, as indicated by uncoupling protein 1 (UCP1) content in brown adipose tissue (BAT), increased in cold-exposed pregnant voles. The number and mass of fetuses were not affected by cold exposure. Our data may indicate the importance of an increased serum leptin concentration for a successful outcome of the pregnancy and also the independence of leptin secretion from body fat in pregnant voles. It also implies the need to develop central leptin resistance with respect to control of energy balance for pregnant voles.

Hypothalamic Suppressor‐of‐Cytokine‐Signalling 3 mRNA is Elevated and Pro‐Opiomelanocortin mRNA is Reduced During Pregnancy in Brandt’s Voles (Lasiopodomys brandtii )

Leptin acts within the hypothalamus to diminish food intake. In Brandt's voles (Lasiopodomys brandtii), both circulating leptin levels and food intake are elevated during pregnancy, suggesting an ineffectiveness of leptin to reduce food intake. Diminished hypothalamic leptin receptors and impaired leptin signal transduction are characteristic of central leptin resistance. The present study aimed to determine whether these characteristic modulations of leptin sensitivity occurred in pregnant Brandt's voles. The mRNA expression of the long form of the leptin receptor (Ob-Rb), suppressor-of-cytokine-signalling 3 (SOCS3), neuropeptide Y (NPY), agouti-related protein (AgRP), pro-opiomelanocortin (POMC) and cocaine- and amphetamine-regulated transcript (CART) in the hypothalamus were examined on dioestrous, day 5, day 10 and day 18 of pregnancy. Compared to controls, there was no significant change in hypothalamic Ob-Rb mRNA during the pregnancy. SOCS3 mRNA was increased significantly by 68% on day 10% and 93% on day 18 of pregnancy compared to controls. Despite elevated leptin levels, POMC mRNA was decreased significantly by 60% on day 18 of pregnancy, whereas no differences were found in the mRNA expression of NPY, AgRP and CART in pregnant voles compared to controls. The elevation of SOCS3 mRNA together with disrupted leptin regulation of neuropeptides in the hypothalamus suggests that leptin resistance may develop in pregnant Brandt's voles.

Different physiological roles of serum leptin in the regulation of energy intake and thermogenesis between pregnancy and lactation in primiparous Brandt's voles ( Lasiopodomys brandtii)

Reproduction, especially lactation, is associated with major metabolic adaptive changes. In this study, we investigated the metabolic changes and the roles of leptin during different periods of reproduction in primiparous Brandt's voles ( Lasiopodomys brandtii). Energy intake, thermogenic capacity and serum leptin levels were examined in non-reproductive, mid pregnant, late pregnant, early lactating and peak lactating voles. Voles increased body mass by nearly 70% during late pregnancy compared to the non-breeding controls. The increase in body mass was mainly due to the increase in body fat mass which increased by 56%, and the growth of the reproductive tissues and digestive organs. Lactating voles decreased body fat by nearly 27% at peak lactation compared to the controls, and 53% compared to late pregnant voles. At the same time they increased food intake significantly. Uncoupling protein 1 (UCP1) content in brown adipose tissue (BAT) decreased significantly at peak lactation. Serum leptin increased significantly in the mid pregnancy, at a time when there was no increase in body fat, and remained at this high level in late pregnancy. Leptin levels decreased after parturition and reached a nadir at peak lactation. Serum leptin was negatively correlated with energy intake during lactation, but not during pregnancy. These data suggest that Brandt's voles adjust energy intake, thermogenic capacity and body reserves to match the high energy demands for reproduction. Hyperleptinemia, without decreased energy intake suggests a state of leptin resistance during pregnancy, and hypoleptinemia during lactation might act as a signal to stimulate energy intake.

ENERGY REQUIREMENTS DURING REPRODUCTION IN FEMALE BRANDT'S VOLES (MICROTUS BRANDTII)

We compared energy intake of reproductive and nonreproductive female Brandt’s voles (Microtus brandtii). Daily energy intake of pregnant voles was significantly higher than that of nonreproductive voles. Metabolizable energy intake increased after parturition and reached a maximum at the end of lactation (334.23 kJ/day), 323% of typical nonreproductive requirements. Moreover, pregnant females had significantly higher lipid mass than controls. During lactation lipid contents were lower than in controls. Over the course of lactation females decreased by 17.6% in body mass, suggesting that females have depleted their body reserve. Use of energy reserves and maximum metabolizable energy intake both were dependent on litter size. Our results indicate that Brandt’s voles meet most of their energy demands for lactation by increasing food intake but also supplement that energy by using body reserves even before food intake is maximized.

6-Methoxy-2-benzoxazolinone and photoperiod: prenatal and postnatal influences on reproductive development in prairie voles (Microtus ochrogaster ochrogaster)

The effects of photoperiod and 6-methoxy-2-benzoxazolinone (6-MBOA) on the gonadal development of prairie voles was studied when this plant compound was available to pups in utero, during nursing, or postweaning. In part 1, pregnant voles exposed to long or short day lengths were fed food in which 6-MBOA was present (50 μg of 6-MBOA/g food) or absent prior to the birth of their young; all of these dams received a diet that lacked 6-MBOA after the pups were born. Other females were fed food without 6-MBOA throughout pregnancy, but received one of the diets during lactation. Short days inhibited reproductive development in male offspring, affected pup survival, and enhanced pelage development. Postnatal exposure to 6-MBOA did not affect the reproductive function of males. In contrast, prenatal exposure to 6-MBOA accelerated reproductive development among short-day males. Prenatal exposure to 6-MBOA did not affect survival of short-day males, but reduced survival of long-day pups. Prenatal 6-MBOA treatment affected the sex ratio of pups that survived until weaning (13:21; male:female) and of pups that died prior to weaning (26:5). In contrast, photoperiod did not affect reproductive function in female voles. Although reproductive function appears to be uncoupled from photoperiodic regulation, female prairie voles processed photoperiodic information; pelage development was enhanced among short-day females. In part II, breeding pairs were exposed to long or short days and fed food devoid of 6-MBOA prior to the birth of the young. On the day of birth, and for the following 3 weeks, either 6-MBOA-free or 6-MBOA-enriehed food was provided. After weaning, pups received their parents type of food until autopsy 3 or 7 weeks later. Again, photoperiod affected male, but not female, reproductive function. No consistent pattern of results from postnatal exposure to 6-MBOA was discerned for either males or females. Acceleration of reproductive function among short-day males because of prenatal influences may, be involved in the rapid rate of sexual maturation observed prior to peak population densities of microtine rodents. Because males of this species induce females into estrus, male prairie voles may depend on environmental cues to regulate reproductive function, while females may respond only to males. The physiological and ecological implications of these data are discussed.

Adrenal response in a wild Microtus population: seasonal aspects

Adrenal response was determined during a 13-month period in a population of southern Manitoba meadow voles (Microtus pennsylvanicus) as a preliminary part of a study to determine the effects of chronic ionizing radiation on free-living mammals. Livetrapped voles were subjected to behavioral tests, killed, and their isolated adrenals superfused and stimulated with ACTH. Superfusates were assayed fluorometrically for corticosterone. Peaks of adrenal response occurred during spring in both adult males and females, followed by a significant decline into early summer. Subadult males exhibited a peak response in early summer. Corticosterone levels of adults were generally higher than those of juveniles in the same season. Levels of nonpregnant adult females were higher than those of pregnant voles. Observed differences over the annual cycle were attributed to the behavioral and hormonal states of various age and sexual components of the population.

Pesticide fate in terrestrial laboratory ecosystems

The disposition and effects of pesticides are being investigated in eight terrestrial microcosm chambers (TMC) containing a variety of plants and animals. Each TMC (1 m. x 0.75 m. x .60 m) has 40 cm. of aerial space and 20 cm. of soil, an air trapping system and “spring” and “rain” systems. Total mass balance of pesticide fate is followed with a combination of chromatographic and radiometric techniques. Pregnant voles (Microtus canicaudus) rear pups to weaning during the 30–45 day functional lives of the TMC's.

THE GROWTH OF THE ADRENAL GLAND OF LABORATORY AND FIELD VOLES, AND CHANGES IN IT DURING PREGNANCY

In laboratory-bred voles of either sex which weigh more than 22 g, adrenal gland weight remains constant as body weight increases. Females have larger adrenals than males, this difference becoming accentuated after animals have become sexually mature. Adrenals of pregnant voles are larger than those of nulliparous animals, but do not increase in weight with increase in body weight. However, adrenals of field males and pregnant field females increase in weight with increase in body weight.Difference in weight between adrenals of male and female laboratory voles could be due to a reduction in size of the X zone of the adrenal cortex in males, brought about by androgens. But since, in the field, adrenal weight increases with body weight, it is supposed that further factors (e.g. effects of social interactions) are influencing the adrenal cortex of field animals.The increase in size of the adrenals of voles in their first pregnancy is associated with an increase in the size of the X zone. This enlargement itself increases as pregnancy proceeds and could be caused by a rising level of L.H. and (or) a decreasing titer of androgens.