Intermittent stimulation and acceleration of puberty by urinary chemosignals in female mice (Mus musculus domesticus)

A sequence of 17 experiments was used to test the effects of intermittent stimulation with urinary chemosignals on the age of puberty in young female mice. The three chemosignals tested all accelerate the age of sexual maturation: urine from adult males, urine from females in estrus, and urine from females that are pregnant or lactating. The basic technique involved presenting the prepubertal females with 'Nestlets' on which the urine was placed. The 'Nestlets' were placed in the cages of the test females for a 15-min period, removed for a variable period, and then replaced in the cage for 15 min. In this manner it was possible to vary the number of exposures, the total length of exposure, and the total time period over which the exposures occurred. Control procedures, involving exposures of young females to cotton squares with water rather than urine placed upon them, resulted in no alterations in puberty relative to untreated females. For mice exposed to the urine-treated cotton squares, acceleration of puberty occurred with less total stimulus-exposure time when the stimulus was presented in short exposures over a number of hours than in previous investigations when the exposure to the urinary chemosignal occurred in a single block of time of one or two hours. For each of the three acceleratory chemosignals, there was a diminution of acceleratory effect when the ratio of total stimulus-exposure time to total exposure time grew smaller. This diminution was more pronounced for urine from pregnant or lactating females than for urine from males or from females in estrus.(ABSTRACT TRUNCATED AT 250 WORDS)     

Role of photoperiod and temperature in production of the oestrus-inducing pheromone in male wild mice

Ninety adult males divided in six equal groups were exposed to different photoperiods for 21 days. Exposures included natural light (ca 11 hr), long photoperiod (16L:8D) and short photoperiod (8L:16D). The first three groups received these exposures at room temperature (13-20 degrees C) while the remaining three at raised temperature (36-38 degrees C). Soiled bedding of the above males was introduced in the cages of unisexually housed noncyclic females and their potentiality to induce oestrus was assessed. It was noticed that the bedding of all the males proved to be a stimulus inducing oestrus in the majority of the females during the 7 day exposure. There was no significant difference in the number of females returning to oestrus following exposure to soiled bedding of different males. These results elucidate that environmental factors, especially light and temperature do not influence the production/release of the oestrus-inducing pheromone in wild mice.     

Acceleration and delay of first vaginal oestrus in female mice by urinary chemosignals: Dose levels and mixing urine treatment sources

The effects of varying dose levels and mixing of urine from various types of donor mice on the age of sexual maturation in female mice were tested. Over the range from 0.001 ml/day to 0.01 ml/day, there was no difference in the effectiveness of male urine in producing acceleration of puberty, nor was there any difference over the same dose range for urine from grouped females bringing about a delay of puberty. Urine from pregnant and lactating females brought about earlier puberty when applied in the higher dose amounts but was not effective in altering the age of first oestrus relative to untreated controls at lower doses. These findings concerning dose levels are important for a full understanding of the behavioural consequences of urinary chemosignals. When urine from different sources was mixed, all treatments which involved urine from grouped females produced delays in first oestrus. The second finding has important consequences for a feedback model for population regulation in house mice involving urinary chemosignals that accelerate or delay sexual maturation and thus shorten or lengthen generation time by affecting reproductive behaviour.     

Role of the vomeronasal organ and prolactin in the acceleration of puberty in female mice

Young female mice were grouped on Day 21 after birth and subjected to removal of the vomeronasal organ. Soiled bedding from intact adult males failed to advance the onset of first oestrus in these lesioned mice compared to the various control groups. Vomeronasal organ lesions of prepubertal females also prevented increases in uterine weight following exposure to soiled bedding for 48 h on Day 23 when compared to controls. Lowering prolactin by injections of bromocriptine for 48 h on Day 26, but not Day 23, advanced the onset of puberty in intact and vomeronasal organ-lesioned females. Elevating prolactin by injections of domperidone were without effect on the early onset of oestrus when compared to sham-injected controls. It is concluded that marked similarities exist in both the receptor system and neuroendocrine mechanism of male pheromone action observed in prepubertal females and that seen in the adult.     

Effects of donor age on urinary chemosignals that influence the timing of first oestrus in young female house mice, Mus domesticus

The effects of donor age on the effectiveness of puberty-influencing urinary chemosignals in wild house mice was tested in a series of 3 experiments. The chemosignal from male mice that accelerates puberty was present in the urine from about the time of puberty and throughout the normal lifespan, but declined about 1 year of age. Oestrous females released a substance in their urine that accelerates puberty in young females. This substance remained effective from first oestrus until over 1 year of age, although older females were in oestrus less frequently than younger mice. Females that are pregnant or lactating released a puberty-accelerating substance in their urine regardless of age. Production and release of the puberty-delaying chemosignal by grouped females was initiated before puberty and continued throughout the lifespan of the mouse.     

Puberty in pine voles, Microtus pinetorum, and the influence of chemosignals on female reproduction

We investigated the reproductive biology of an induced ovulator, the pine vole (Microtus pinetorum). Male puberty, measured as age at first impregnation, was found to occur as early as 44 days of age. Female puberty measured as age at first conception, was found to occur as early as 32 days of age, considerably earlier than previously reported. Females paired with stud males exhibited a doubling of uterine weight within 12 h, and vaginal sperm were present after 48 h. This indicates that although behavioral responses to males--including mating--require prolonged contact, physiological responses to males occur rapidly. Chemosignals from males slightly increased uterine and ovarian weights of females, but chemosignals from other females did not. Young females paired with stud males for 48 h in the presence of soiled bedding from the female's family had significantly smaller increases in ovarian and uterine weights than similar females paired on clean bedding. Suppression of reproduction in female offspring while they remain with the extended family unit is discussed as a life-history tactic and as a possible mechanism for inbreeding avoidance.     

Peripubertal exposure to male odors influences female puberty and adult expression of male-directed odor preference in mice

Testosterone-dependent olfactory signals emitted by male are well known to accelerate female puberty in mice (Vandenbergh effect). However, it remains unclear whether these chemosignals also influence adult expression of male-directed odor preference. Therefore, we exposed female mice to intact or castrated male bedding (vs clean bedding as control) during the peripubertal period (postnatal day (PD) 21–38) and measured male-directed odor preference in adulthood. At PD45 or PD60, females exposed to intact male odors, and thus showing puberty acceleration, preferred to investigate odors from intact males over females or castrated males. Females exposed to castrated male odors did not show puberty acceleration but preferred male (intact or castrated) over female odors. Finally, control females did not show any odor preference when tested at PD45, although a preference for male odors emerged later (PD60). In a second experiment, females that were exposed to intact male odors after pubertal transition (PD36–53) also preferred intact male over castrated male odors. In conclusion, our results indicate that peripubertal exposure to male odors induced early expression of male-directed odor preference regardless of puberty-accelerating effect and that induction of male-directed odor preference is not specific to the peripubertal period.     

Antimutagenic effect of chemosignals from isolated female house mouse on male germ cells (Mus musculus L.)

The influence of chemosignals from isolated mature females of the CBA strain on level of spontaneous and radiation-induced meiotic disturbances in spermatocytes I of males of the same strain was studied. Using an ana-telophase method, 24-hour exposure of males to soiled bedding containing isolated females’ chemosignals was shown to lead to a significantly lower frequency of chromosomal aberrations and other meiotic disturbances in spermatocytes I as compared to males kept on clean bedding. The same effect of female chemosignals was found in the germ cells of irradiated males (4 Gr). The mechanisms and importance of the revealed antimutagenic effect of mouse female chemosignals on the male reproductive cells in the reproduction process are discussed.     

Chemosignals from isolated females have antimutagenic effect in dividing the cells of bone marrow from male mice of the CBA strain

A level of X-ray induced mitotic disturbances in the cells of the bone marrow of male mice was studied under the modifying influence of chemosignals from isolated adult female mice of the CBA strain. It has been shown that the frequency of chromosomal aberrations in irradiated (4 Gr) males after exposing them for 24 hours on bedding soiled with female chemosignals is lower than in irradiated males in cages with clean bedding. The mechanisms and importance of the antimutagenic effect of female house mouse chemosignals are discussed.     

Male-induced puberty acceleration in young female wild mice: hormonal regulation and source of pheromonal cue

Experiments were designed to examine the influence of adult males on the rate of sexual maturation in young female wild mice. In one experiment, young females were raised in presence of adult males, adult females and in absence of any individual, while in another, they were exposed to urines of: (1) castrated males, (2) spayed females, (3) castrated and TP-treated males, (4) castrated and placebo-injected males. Female maturation as measured by age at vaginal opening and first vaginal oestrus was accelerated by presence of adult males, whereas presence of adult females considerably delayed the vaginal opening and the appearance of first oestrus in young females. In the other set of the experiments, urine from castrated or castrated and placebo-injected males was ineffective in inducing early puberty while urine from spayed females highly delayed the sexual maturation. By contrast, urine from castrated and TP-treated males accelerated the puberty more or less like normal males. The results indicate that male's chemosignal accelerating puberty in young females is present in urine and its production is under the control of androgens. However, the female-originating urinary pheromone which delays the puberty in young females is not regulated by ovarian hormones.     

Reliability of soiled bedding transfer for detection of mouse parvovirus and mouse hepatitis virus

Serologic monitoring of sentinel mice exposed to soiled bedding is a common method of detecting viral infections in mice. Because bedding transfer protocols vary, the sensitivity of this method has not been documented sufficiently. We examined the reliability of bedding transfer during various stages of infection with mouse parvovirus (MPV) and mouse hepatitis virus (MHV). Most mice exposed to bedding contaminated with MPV 0, 3, or 7 d previously seroconverted, whereas only mice exposed to bedding contaminated with MHV 4 h previously seroconverted, thus confirming the differing stabilities of these viruses. Index mice were inoculated with 30 times the infectious dose 50 (ID50) of MPV or 300 ID50 of MHV. At 3 d, 1 wk, and 2 wk postinoculation (PI), we transferred 25, 50, or 100 ml of bedding to cages of sentinel mice. Viral infection and shedding by index mice was confirmed by serology and fecal polymerase chain reaction assay. Transfer of soiled bedding between mice in static cages induced seroconversion of sentinel mice most reliably during peak viral shedding (1 wk PI for MPV and 3 d PI for MHV). Soiled bedding transfer between mice in individually ventilated cages induced a higher prevalence of sentinel seroconversion to MPV and MHV than that after transfer between mice in static cages. Our findings indicate that although soiled bedding transfer is an effective method for detecting MHV and MPV under optimal conditions, the method is less than 100% reliable under many conditions in contemporary mouse facilities.     

Social influences on reproductive development and fertility in female Djungarian hamsters (Phodopus campbelli).

Social influences on the sexual maturation of female Djungarian hamsters were investigated in two experiments. In the first experiment females were housed from weaning with an adult male, by themselves, or with a weanling sister. Maturation was accelerated in females housed with males as indicated by younger age at first ovulation, increased rates of ovarian and uterine growth, and lower LH levels at some ages. Maturation was delayed in females housed with sisters compared to those housed alone as measured by time of first ovulation and by lower estradiol levels at some ages. The most marked differences between groups occurred 8 to 12 days after weaning, suggesting that events during this period are particularly important in the social mediation of sexual maturation. In the second experiment the effects of reproductive suppression (caused by living with a sister) on the subsequent fertility of females housed with males were examined. If male-female pairs were housed in clean cages, no effects were observed; however, pairs housed in cages previously soiled by the female and her sister had fewer young surviving until 1 week of age despite no differences in the age of pregnancy onset or in the initial litter size. Thus, even cues present in unrenewed soiled bedding may have subtle but long lasting effects on reproductive function.     

Effects of urine from females in oestrus on puberty in female mice

A series of 9 experiments was conducted to examine various characteristics of the urinary chemosignal found in the urine of oestrous female mice that accelerates the sexual development of conspecific females. This urinary chemosignal was effective in doses as small as 0.001 ml/day, was present in excreted and bladder urine, required 3 days of treatment starting before Day 29 of age to effect an acceleration of puberty, required a minimum daily exposure of 2 h, and was relatively nonvolatile. In addition the chemosignal from oestrous females was effective in summer but not in winter months, was significantly more effective when collected at the middle or end of the dark portion of the daily cycle than at the beginning of the dark phase or middle of the light phase, and was not affected by food deprivation or shortened photoperiod. Simultaneous treatment of test subjects with urine from oestrous females and grouped females resulted in delays in puberty and simultaneous treatment with urine from oestrous females and urine from males or pregnant or lactating females did not result in any enhanced acceleration of puberty.     

Pheromone-induced reproductive inhibition in young female Peromyscus leucopus

Soiled bedding and urine from adult female white-footed mice (Peromyscus leucopus) were tested for their capacity to inhibit reproduction of young females. Test animals were given either physical or airborne contact with soiled bedding from adult females, adult female urine, clean bedding, or water from 21 to 150 days of age. Results indicate that reproductive inhibition is due to an airborne pheromone emitted by the adult females as a component of their urine. In the second experiment, young female mice were exposed to an adult female for 0, 1, 3, 6, 12, 18, or 24 h/day from 21 to 150 days of age. Results from this experiment show that exposure to adult females of as little as 3 h/day was sufficient to cause reproductive inhibition to occur. This phenomenon has important implications in terms of both female-female reproductive competition and socially mediated population regulation.     

The effectiveness of a microisolator cage system and sentinel mice for controlling and detecting MHV and Sendai virus infections

Experiments were conducted to determine (a) whether BALB/c mice housed on soiled bedding can be used as sentinels for the detection of Sendai virus and MHV from infected mice housed in microisolators, and (b) whether the microisolator caging system protects mice against Sendai virus and MHV infections. Sentinel mice were housed in microisolator cages, exposed continuously to soiled bedding and bled at 21 and 42 days for serology. All sentinel mice were seropositive for MHV by 42 days; however, sentinel mice exposed to soiled bedding were seronegative for Sendai virus at 21 and 42 days. These results suggest that sentinels housed on soiled bedding may not detect all infectious murine viruses. This study also showed that the microisolator caging system provided an effective barrier against MHV infection at the cage level and suggests that the microisolators should protect mice against other infectious agents.     

Long-term effects of accelerated or delayed sexual maturation on reproductive output in wild female house mice (Mus musculus)

The effects of acceleration and delay of puberty in female house mice on survival and reproduction were tested using 6 experimental groups: (1) control females mated at the time of first oestrus, (2) females mated at weaning, (3) females treated with male urine starting at weaning and mated at first oestrus, (4) females housed in groups and mated at first oestrus, (5) females housed alone, treated with urine from grouped females and mated at first oestrus, and (6) females housed alone and mated at 68 days of age. Females caged with males at weaning or treated with male urine and mated at puberty had lower rates of survival to 180 days of age, but did not differ in rates of fertility from mice in the other four treatments. Those females that were housed with males from weaning or treated with male urine also had smaller total numbers of litters, fewer total young, and smaller average litter sizes than did females for which the age of mating was delayed, by grouping or treatment with urine from grouped females, or by being held until age 68 days before mating. Control females mated at first oestrus generally were intermediate or did not differ from the male treatments on these dependent variables. There were no differences in the average number of female young/litter across the 6 treatments. However, females that were delayed in age of first mating had significantly more male young/litter than did females that were accelerated in their sexual development or control females.(ABSTRACT TRUNCATED AT 250 WORDS)     

Social environment and reproduction in female pouched mice, Saccostomus campestris

Pouched mice were kept under controlled conditions of illumination (10D:14L) and temperature (22 +/- 2 degrees C). Age at vaginal opening, first oestrus and first conception did not differ significantly between juvenile females raised singly, in single-sex groups of 5, or with an adult male. After the introduction of a male, sterile cycles and/or matings before first conception were experienced by all females whether they were raised singly or in single-sex groups. Of 10 females raised with a male, 4 conceived at their first mating. Onset of puberty in juvenile females raised with an adult female was delayed, while in juvenile females raised with their families (mother, father and litter mates) only vaginal opening was delayed. However, when raised in family groups without the father, vaginal opening as well as first oestrus were delayed. Grouping of females after weaning, with or without a male, did not change the oestrous cycle pattern. Females in these groups cycled independently of each other and the females grouped with a male also mated and conceived independently of each other. Pregnancy was blocked in 7 of 8 females when the stud male was removed and a strange male was introduced. In females exposed to a succession of males, pregnancy was blocked up to 4 times.     

Effect of conspecifics on sexual maturation in female European pine voles (Pitymys subterraneus)

Using the number of large ovarian follicles (Type 8) as an indicator of sexual maturation we found that urinary compounds released by adult males accelerated puberty while urine from females suppressed hormonal activity in juvenile female European pine voles. The release of chemosignals that delayed puberty of juvenile females was not influenced by ovarian hormones; urine from ovariectomized females was as effective as urine from unoperated animals.     

Social cues influence growth and sexual maturation of the male musk shrew (Suncus murinus)

Musk shrews were maintained from weaning (20 days of age) for 20 or 40 days in one of several social conditions. In Exp. 1, young males housed with adult females gained more weight and had heavier sex accessory organs than did young males housed with an adult male or reared alone. In Exp. 2 this same pattern of accelerated growth and sexual maturation was found when males were reared directly with an adult female or in a split cage where a wire barrier served to separate the male and his adult female cagemate. In Exp. 3, males were reared in cages containing clean or soiled bedding: soiled bedding was taken once every 5 days from the cage of an adult male, or a female. Under these conditions differences in the weights of reproductive tissues showed minimal variation with housing condition after 20 days of treatment. At that time males reared in soiled bedding taken from the cage of an adult female had accelerated development compared with control males. In Exp. 4, males were housed alone or in a split cage with an adult female which was separated by a wire mesh or a solid, opaque barrier. Males separated by a solid barrier from their female cagemates for 40 days had reproductive tissue weights equivalent to those measured in males reared alone. Taken together these results suggest that the presence of an adult female has dramatic effects on body growth and development of reproductive target tissues in young male musk shrews. Male-female social interactions could play an important role in the timing of puberty in this opportunistically breeding tropical mammal.     

Microbiological monitoring of laboratory mice and biocontainment in individually ventilated cages: a field study

Over recent years, the use of individually ventilated cage (IVC) rack systems in laboratory rodent facilities has increased. Since every cage in an IVC rack may be assumed to be a separate microbiological unit, comprehensive microbiological monitoring of animals kept in IVCs has become a challenging task, which may be addressed by the appropriate use of sentinel mice. Traditionally, these sentinels have been exposed to soiled bedding but more recently, the concept of exposure to exhaust air has been considered. The work reported here was aimed firstly at testing the efficiency of a sentinel-based microbiological monitoring programme under field conditions in a quarantine unit and in a multi-user unit with frequent imports of mouse colonies from various sources. Secondly, it was aimed at determining biocontainment of naturally infected mice kept in an IVC rack, which included breeding of the mice. Sentinels were exposed both to soiled bedding and to exhaust air. The mice which were used in the study carried prevalent infectious agents encountered in research animal facilities including mouse hepatitis virus (MHV), mouse parvovirus (MPV), intestinal flagellates and pinworms. Our data indicate that the sentinel-based health monitoring programme allowed rapid detection of MHV, intestinal flagellates and pinworms investigated by a combination of soiled bedding and exhaust air exposure. MHV was also detected by exposure to exhaust air only. The IVC rack used in this study provided biocontainment when infected mice were kept together with non-infected mice in separate cages in the same IVC rack.