Ultrasonic calls of bank vole pups isolated and exposed to cold or to nest odor.

Bank vole pups produce ultrasounds when isolated from the nest, as other rodents do. The present study was intended to elucidate the possible interaction between the social stress of isolation from the mother and the physical stress of low ambient temperature during the nesting period. Although bank vole pups removed from nests and monitored at nest temperature vocalized at high frequency, the number and duration of signals increased at lower ambient temperature. In the tested voles it appears that exposure to cold was the most important stimulus of vocalization during the preweaning period. This effect can be enhanced by prolonged isolation from the mother, manifested as longer duration of calls. Moreover, vocalization was reduced not only by the odor from the home nest, but also by exposure to bedding of an alien lactating bank vole or even a lactating mouse fed the same diet. This suggests that the olfactory signals affecting the ultrasonic vocalization of bank vole pups probably are a mixture of volatile metabolites related to the physiological status and diet of rodent females. The reported experiments provide convincing evidence that the vocalization of bank vole pups is affected by isolation from the mother, by ambient temperature, and by olfactory signals released by lactating rodent females.

Sociogenic stress and rodent reproduction.

Social stress, which is a part of the interaction between animals, can be defined as the set of physical stresses caused specifically by the presence and actions of certain conspecifics. Dense populations are characterized by considerably increased intermale and interfemale aggressive behavior. This establishes a hierarchy which influences reproduction of the animals. Aggression of adults toward unrelated juveniles harms the physiological development of attacked young. Stress from crowding during pregnancy can affect reproductive activity even through the second generation. During postnatal development, sexual maturation of juveniles can be delayed by the presence of group-living adults. In adult females, disturbance of homeostasis after fertilization can evoke untimely termination of pregnancy. In monogamous rodents, removal of the male partner reduces the number of parturitions. In several species, recently inseminated females exposed to a strange male will lose developing embryos. Thus, sociogenic stressors are among the most important factors affecting fecundity in animals.

Removal of the olfactory system modifies male bank vole behaviour in the presence of females.

The role of the olfactory and vomeronasal systems of male bank voles in behavioural interaction with females was investigated. Bulbectomy (OBX), but not vomeronasalectomy (VNX), resulted in a decrease of female-stimulated ultrasonic calling by males, manifested as longer latency to the first call and fewer calls by OBX males in comparison to VNX or sham-operated (SHAM) animals. OBX males showed significantly fewer non-aggressive approaches but more attacks toward females. Females were less aggressive toward OBX males than toward VNX or SHAM animals, manifested as longer latency to the first attack and fewer attacks toward OBX males during 10 min encounters. The report may be regarded as the first evidence that bulbectomy of the male can evoke a behavioural reaction which in turn alters the activity of a female partner.

Home bedding modifies ultrasonic vocalization of infant bank voles.

Bank vole,Clethrionomys glareolus, pups, similar to many other infant rodents, emit ultrasonic vocalizations when they are removed from the nest and cooled. Infants exposed to bedding from their home cage produced fewer and shorter calls than infants tested without bedding. Sound frequencies were significantly higher in infants exposed to home bedding than in other experimental groups. These results provide evidence that infant bank voles are able to identify the presence of home bedding, probably on the basis of odor. This appears to be the first report of shifts in frequency of pup ultrasonic calls in response to olfactory cues.

Suppression of estrus in female mice by the presence of conspecifics or by foot shock.

The reaction of reproductive system of outbred female mice to crowded conditions or electric foot shock was investigated. Both experimental factors inhibited estrous cycle, and decidual cell reaction (DCR) was observed after traumatization of uterine horns in tested animals. Further investigations showed that corpora lutea in females subjected to social stress were significantly larger than those in mice stressed by classical stressor. Also, plasma progesterone level increased only in females exposed to grouped females. These results indicate that social interaction among female mice lead to the development of typical pseudopregnancy, whereas inhibition of ovulation and DCR in females subjected to electric foot shock are not related to the increase of activity of corpora lutea.

Acute increase in plasma corticosterone level in female mice evoked by pheromones.

Exposure of a singly reared estrous female to grouped females or their bedding during 20 min resulted in an increase in the plasma corticosterone level during the first 10 min. The reaction of the adrenal glands was similar to the excitation evoked by stress connected with moving females from their own cage to a new, clean cage. The highest level of the adrenal hormone was present in estrous females after exposure to male bedding during 10 min. This was followed by a dramatic decrease during the next 90 min. It is suggested that male pheromones, through activation of the pituitary-adrenal system and acute release of corticosterone, participate in the stimulation of sexual behavior in receptive female mice.

Salivary glands and preputial glands of males as source of estrus-stimulating pheromone in female mice.

Male mice produce pheromones that induce estrus in adult female mice. The synthesis of these chemosignals is controlled by testosterone. Male tissues abundant in testosterone-binding receptors were tested for their ability to stimulate estrus in grouped females. The percentage of females that showed estrus during two days following exposure to male tissues was used as the indicator of biological activity of tested samples. Homogenates of salivary glands and preputial glands induced estrus; other tested organs (liver, testes, coagulation and vesicular glands or kidneys) did not stimulate estrus in female mice. These results indicate that estrus-stimulating pheromone has multiple sources.

Puberty delay of bank vole females in a high-density population.

The onset of puberty in bank vole females was studied, with uterine weight, ovarian weight, and the number of large ovarian follicles used as indicators of gonadal activity. Maturation of females born at the beginning of the reproductive season was suppressed by the presence of other females. Puberty of animals born at the end of season was primarily influenced by climatic variation.

Adrenal-mediated endogenous metabolites inhibit puberty in female mice.

While assessing a potential role of adrenal glands in the production of the hitherto unidentified puberty-delaying pheromone of female mice, the urinary volatile profiles of normal and adrenalectomized animals were quantitatively compared. Six components, whose concentrations were depressed after adrenalectomy, were identified: 2-heptanone, trans-5-hepten-2-one, trans-4-hepten-2-one, n-pentyl acetate, cis-2-penten-1-yl acetate, and 2,5-dimethylpyrazine. When these laboratory-synthesized chemicals were added (in their natural concentrations) to either previously inactive urine from adrenalectomized females or plain water, the biological activity was fully restored.

Androgen-dependent proteins in the urine of bank voles (Clethrionomys glareolus).

The concentration of proteins in the urine of adult bank vole males was higher than that in urine of immature males and females. After separation of the urine by polyacrylamide gel electrophoresis in the presence of SDS, the principal urinary protein had a slightly lower mobility than cytochrome C. Urine from females or castrated males contained only trace amounts of this protein. Injection of testosterone into castrated males increased this protein band. We suggest that bank vole males, like those of rats and mice, synthesize and release in their urine an androgen-dependent protein fraction.

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.

Influence of the male on provoked ovulation in immature female mice.

Acceleration of ovulation in juvenile females by exposure to the male and injection of gonadotrophins was investigated. The male-induced ovulation in CBA/kw and outbred females was observed only after injection of PMSG. Exposure to the male and injection of HCG did not evoke this effect. Our results indicated that the presence of a male stimulates LH release from the pituitary of juvenile females. Pheromonal reaction of the females was affected by the age and body weight of the tested animals. Most sensitive were females of CBA/kw strain 21-day-old, outbred 21-day-old, 10.0-12.0 g and 24-day-old, 7.5-9.5 g.

Pregnancy block elicited by male urinary peptides in mice.

After fractionation of the urine of male mice on Sephadex G-75 followed by thin-layer electrophoresis pheromonal activity (i.e. pregnancy blocking) was found in the peptide fraction. The pregnancy-blocking pheromone is therefore a peptide or a substance bound with the peptide fraction.

Male-pheromone effect on the efficiency of pregnancy in female mice.

Outbred female mice were exposed during 3 oestrous cycles and mated to outbred or C57BL/kw males. Although ovulation number (CL and flushed eggs) was similar in all females, there were significantly fewer (P < 0.01) fertilized eggs and implantations in females exposed and mated to C57BL/kw males. Exposure to outbred males and mating with C57BL/kw males led to some improvement but the best results were obtained with females mated to outbred males. The activity of uterine dehydrogenases on Day 4 of pregnancy was also greatest in females mated to outbred males. It is concluded that the pheromonal stimulation leads to hormone concentration differences which affect implantation.