Female meadow voles housed in long and short daylengths respond to exogenous estrogen with similar mating latencies.

After weaning, adult female meadow voles were maintained for 7 weeks in either long (LD, 14 h light/day) or short photoperiods (SD, 10 h light/day). They were then ovariectomized and implanted with 3-week, timed-release estrogen pellets (0.0, 0.001, 0.05, or 0.5 mg/pellet of 17-beta-estradiol). An additional group received a sham ovariectomy (intact) and a 0.0-mg/pellet control (no estrogen) pellet. One week after surgery, females were paired with an LD sexually experienced male. Each pair was videotaped continuously until the first intromission or for 2 weeks. LD sham animals mated significantly earlier than did SD sham animals (P=.05). However, there were no differences in mating latencies between LD and SD control groups or between any of the LD and SD groups receiving estrogen replacement (P>.05). In addition, no ovariectomized animals receiving either the control or the 0.001-mg/pellet estrogen dosage mated within the 2-week time period, while all shams and all animals receiving either the 0.05- or 0.5-mg/pellet doses mated. The results indicate that there is some minimal amount of estrogen that is necessary for meadow voles to enter behavioral estrus and that LD and SD females do not differ in their sensitivity to estrogen, since animals in both photoperiods mate with similar latencies as long as enough estrogen is present.

Effects of stress during pregnancy on maternal behavior in mice.

The effects of stress experienced during pregnancy and raising stressed offspring on maternal behavior were investigated in Swiss-Webster mice. Dams were either stressed or not stressed during pregnancy, and raised either prenatally stressed or nonstressed cross-fostered pups. Maternal behaviors such as grooming, nursing, pup retrieval and maternal aggression were assessed during the first 4 days after birth. Nonstressed dams raising stressed pups and stressed dams raising nonstressed pups groomed and nursed their pups significantly less than did control dams (stressed dams raising stressed pups and nonstressed dams raising nonstressed pups). Nonstressed dams raising stressed pups were also the slowest to retrieve both the first and last pup in retrieval tests. Nonstressed dams raising nonstressed pups were significantly less aggressive than other dams. In contrast, stressed dams raising stressed pups exhibited high levels of nursing and grooming, retrieved their pups rapidly and were very aggressive towards an intruder. These results indicate that raising stressed pups, or experiencing stress during a pregnancy can have significant effects on maternal behaviors. Stressed dams raising stressed pups exhibit maternal care comparable to that of nonstressed dams raising nonstressed pups at least for nesting/nurturing behaviors, and show increased levels of aggression and pup retrieval.

Sexual and reproductive behaviors.

The procedures described in this unit include testing procedures for male and female reproductive behaviors, gonadectomy, and hormonal treatments appropriate for inducing male and female reproductive behaviors. Because reproductive behaviors are social behaviors, and therefore require the presence of stimulus animals, the protocols in this unit also provide information on the preparation of stimulus animals. The protocols are written for use with laboratory rats, although a discussion of issues related to species differences in the study of reproductive behaviors is included.

Effects of prenatal stress on development in mice: maturation and learning.

Female CD-1 mice were stressed during the final week of gestation. Beginning 3 days after birth, until weaning, their pups were examined for eye opening, startle response, tooth eruption, surface righting, ability to cling to and climb an incline, tail pull reflex, rotation, linear movement and exploration. At 3 months of age, they were tested in a Morris Water Maze. Stressed animals were significantly lighter and shorter than non-stressed animals the first week after birth. By 3 days after birth, significantly fewer stressed animals could rotate or right themselves. By 6 days after birth, significantly fewer stressed animals could cling to or climb an inclined screen, or show the tail pull reflex. By 9 days of age, significantly fewer stressed animals had teeth. In contrast, by day 12 of age, significantly more stressed animals demonstrated exploratory behavior than did non-stressed animals. There were no sex differences in the ability of animals to perform these tasks at the same age. Stressed animals were significantly slower than non-stressed animals to reach the hidden platform in the water maze on all trials, and this difference was due to stressed females being slower to find the platform than non-stressed females, with no main effect of stress on males. This study supports and expands previous findings in rodents that prenatal stress can cause deficiencies in some early indices of physical maturation and also that these deficiencies can be continued into adulthood.

Actions of testosterone in prepubertal and postpubertal male hamsters: dissociation of effects on reproductive behavior and brain androgen receptor immunoreactivity.

This study was conducted to determine whether there is a increase in responsiveness to the activating effects of testosterone on male reproductive behavior during puberty in male golden hamsters and whether responsiveness to behavioral actions of testosterone is correlated with the ability of testosterone to upregulate brain androgen receptor immunoreactivity (AR-ir). Sexually naive male hamsters were castrated at 21 or 42 days of age and implanted subcutaneously with a pellet containing 0, 2.5, or 5 mg of testosterone. One week later, males were given a 10-min mating test with a receptive female. Animals were euthanized 1 hr after the behavioral test, and blood samples and brains were collected. Plasma testosterone levels were equivalent in prepubertal and adult males that had been administered the same dose of testosterone. However, adult males exhibited more mounts, intromissions, and ejaculations than prepubertal males, demonstrating that postpubertal males are more responsive than prepubertal males to the effects of testosterone on sexual behavior. In both age groups, testosterone increased the number of AR-ir cells per unit area in several brain regions involved in male sexual behavior, including the medial preoptic nucleus (MPN), medial amygdala, posteromedial bed nucleus of the stria terminalis, and magnocellular preoptic nucleus (MPNmag). Surprisingly, testosterone increased AR-ir in the latter three regions to a greater extent in prepubertal males than in adults. Thus, prepubertal males are more responsive to the effects of testosterone on AR-ir in these regions. In a separate experiment, a pubertal increase in the number of AR-ir cells per unit area was found in both the MPN and MPNmag of intact male hamsters. These results indicate that a testosterone-dependent increase in brain AR during puberty may be necessary, but is not sufficient, to induce an increase in behavioral responsiveness to testosterone.

Interaction of maternal photoperiod history and food type on growth and reproductive development of laboratory meadow voles (Microtus pennsylvanicus).

The interaction of maternal photoperiod history and four diets were tested by measuring body growth, reproductive development, and pelage development in 9-week-old juvenile meadow voles. Meadow vole dams were housed in long daylengths (LD; 14 h light/day), short daylengths for 2 weeks (SD; 10 h light/day), or short daylengths for 26 weeks (PR; photorefractory) prior to mating. Immediately following parturition, one of four diets was available to dams and pups; (a) a control diet containing no 6-methoxy-2-benzoxazolinone (6-MBOA); (b) the control diet plus sprouted wheat (which contains 6-MBOA); (c) the control diet plus alfalfa harvested in spring (no 6-MBOA); and (d) the control diet plus alfalfa harvested in autumn (no 6-MBOA). By 9 weeks of age, juvenile meadow voles born to photorefractory dams and fed either spring or fall alfalfa or sprouted wheat were significantly larger and more had achieved puberty than juveniles fed only the control diet. Juveniles born to LD dams demonstrated a smaller increase in developmental rate than photorefractory juveniles when fed alfalfa and spring wheat, and juveniles of SD dams showed the smallest effect of alfalfa and sprouted wheat on development. Supplements of spring wheat and both forms of alfalfa had similar positive effects on growth and reproduction. The authors suggest that juvenile meadow voles rely on the interaction of maternal photoperiod history and the availability of nutrient-rich food such as sprouted wheat and alfalfa to time the onset of growth and puberty.

Luteinizing hormone and prolactin in mated female meadow voles housed in long and short day lengths.

Fertility differs dramatically between female meadow voles (Microtus pennsylvanicus) housed in long (LD; 14 h light/day) and short (SD; 10 h light/day) day lengths. All mated LD females ovulate, and 75-100% produce litters. In contrast, 40% of SD females that mate only after long contact with a male do not ovulate, and fertility for SD females is much lower (30-40% produce litters overall). Because copulation causes the surge in LH required for ovulation and the increase in prolactin (PRL) needed to maintain corpora lutea, we hypothesized that SD females might have lower ovulation rates and litter production because of inadequate hormonal responses. Serum LH was measured 24 h before, and 30, 60, 90, 120, and 180 min after, mating. Prolactin was measured before, and 24 and 48 h after, copulation. LD and SD females that ovulated demonstrated a sharp increase in LH levels at 30 and 60 min post mating, but LH in non-ovulating females was approximately 50% lower than that of ovulating females at 30 and 60 min post mating. PRL in LD females was double baseline levels at 24 and 48 h after mating. PRL in SD females increased at 24 h, but declined to pre-mating levels by 48 h post mating. These data suggest that reduced fertility in short day lengths in female voles may be related to two separate problems: 1) The rise in LH following copulation is insufficient in some females to cause ovulation. 2) PRL may not remain elevated long enough to support functional corpora lutea in some females that ovulate.

Effect of vomeronasal organ removal on behavioral estrus and mating latency in female meadow voles (Microtus pennsylvanicus).

The vomeronasal organ (VNO) mediates the induction of behavioral estrus in prairie voles by male chemosignals; however, the importance of this system for the initiation of estrus in meadow voles, a species in which spontaneous estrus has been postulated, is unknown. This experiment was designed to investigate the influence of VNO-mediated chemosensory information on behavioral estrus in meadow voles housed in photoperiods simulating summer (long photoperiods; 14L:10D) and winter (short photoperiods; 10L:14D). The VNO was removed from nulliparous female meadow voles, and the percentage of animals mating after removal and the timing of mating onset were assessed. Removal of the organ did not suppress mating or change the timing of mating onset in females housed in short photoperiods. In animals housed in long photoperiods, in contrast, removal of the organ significantly increased the percentage of females mating and the percentage of females mating rapidly after pairing. The results indicate that chemosensory information mediated via the VNO is not necessary for the induction of behavioral estrus in meadow voles and lends support to the hypothesis that meadow voles have a spontaneous estrus. We postulate that polygynous, solitary meadow voles reproduce more effectively with spontaneous estrus than with the induced estrus described for monogamous, group-living prairie voles.

Female meadow voles have a preferred mating pattern predicted by photoperiod, which influences fertility.

In a previous study, Meek and Lee found that female meadow voles mated within three distinct time periods after pairing with a male, and fertility was influenced by the time of mating and photoperiod. In the present studies, we tested the hypothesis that different patterns of mating would correlate with high and low fertility. We found two very different patterns of mating were correlated with high fertility. Females housed in long daylengths (long day; 14 h light/day) and mating within 48 h of pairing with a male, received few mounts, intromissions, and intromissions per ejaculatory series, with very short interintromission intervals. All long-day females utilizing this mating pattern ovulated, and 86-100% produced litters. We suggest this pattern of mating is associated with spontaneous estrus. In contrast to long-day females mating within 48 h, females housed in short daylengths (short day; 10 h light/day) and mating between 14-48 h after pairing with a male, received significantly more short mounts and intromissions, with longer interintromission intervals. These short day females all ovulated and 86% produced litters. We suggest that this pattern of mating is associated with an induced estrus. Short-day females that did not exhibit this pattern of mating (66%) produced far fewer litters. We discuss two mechanisms by which fertility may be inhibited in most short-day females.

Prediction of fertility by mating latency and photoperiod in nulliparous and primiparous meadow voles (Microtus pennsylvanicus).

Mating behavior and litter production of female meadow voles (Microtus pennsylvanicus) housed in long (14 h light: 10 h dark; long day; LD) or short (10 h light: 14 h dark; short day; SD) photoperiods were monitored to determine whether the reduced birthrate of SD females resulted from a lack of copulation. All females mated, but fewer SD females gave birth. LD and SD females fell into three distinct groups based on mating latency. The rapid onset group (RO) mated between 7 min and 9 h after pairing, the intermediate onset group (IO) mated between 16-44 h and the late onset group (LO) mated after 58-262 h of male contact. Sixty-seven per cent of LD females were assigned to group RO, 27% to IO, and 6% to LO. In contrast, 30% of SD females were assigned to group RO, 35% to IO and 35% to LO. Fertility was predicted by mating latency. Sixty-nine per cent of RO, 93% of IO and 33% of LO animals gave birth. In a further experiment, a small-mouthed cup was added to the environment to serve as an escape for females wishing to avoid mating. Although females did not use the cup to escape male approaches, mating occurred in only 66% of SD females, but was observed in all LD females. In a final experiment, mating latency and litter production were recorded in primiparous LD and SD females initially observed in the first experiment. Group LO was eliminated in parous females; all primiparous LD and SD females mated within 48 h.(ABSTRACT TRUNCATED AT 250 WORDS)