Anna Marchlewska-Koj

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.

Stimulation of Estrus in Female Mice by Male Urinary Proteins

Stimulation of estrus in adult female mice was obtained with major urinary proteins (MUPs) with the natural volatile ligands bound. The MUP threshold concentration for this effect was about 1.8 mg/ml. MUPs without the ligands bound, as purified by organic extraction of hydrophobic compounds, stimulated estrus in mice only when dissolved in carrier urine of juvenile or castrated adult male mouse or ovariectomized female mouse. They did not stimulate estrus when dissolved in water. Mice that had the vomeronasal organ removed were insensitive to MUPs. It is concluded that MUPs are an integral part of the mouse male pheromones that stimulate hormonal activity in females and that the vomeronasal system is involved in the estrus-stimulating effect of the major urinary proteins.

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.

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.

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.

Prenatal stress modifies behavior in offspring of bank voles (Clethrionomys glareolus)

The aim of the present study was to investigate the effect of prenatal stress on behavior of adult bank vole males and females. Pregnant females were submitted to stress by short encounters of two females at the same stage of pregnancy, to crowded condition by transfer to a cage with four to five nonpregnant females, or stressed by immobilization. The stressors were applied on Days 13, 14, and 15 of pregnancy. The results indicate that prenatal stress influenced adult offspring behavior tested in the presence of the same sex, as compared to controls. Females and males differ in their reactions to stress. Prenatal stress decreased the nonaggressive behavior of females but males did not change their amicable approaches toward males. In bank vole males, prenatal social or immobilization stress increased aggression, but females made more attacks only after prenatal stressing by immobilization. This indicates that in bank vole females classical stressor involved different mediators from those associated with prenatal social stresses. Our results indicate that prenatal stress in bank voles decreases the social activity of female offspring and increases aggression in male offspring. Social stress applied to females in late pregnancy may increase the number of aggressive males in a population.

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.

ULTRASONIC RESPONSE OF CBA NEWBORN MICE TO BEDDING ODOUR

A drop in ambient temperature which increases thermogenesis is the fundamental factor stimulating ultrasonic vocalization in newborn rodents. Neonatal mice modify ultrasonic calling in response to olfactory cues. When removed from the nest and cooled, CBA-strain mouse pups produced ultrasonic calls on the 3rd, 5th and 7th days of life. The presence of conspecific bedding affected their ultrasonic vocalization. The number and duration of calls were higher in 3-day-old CBA pups exposed to bedding of C57BL lactating females than in newborns tested in the presence of bedding from CBA lactating females. This indicates that CBA pups discriminate between the odours of the two genotypes. The influence of postnatal experiences on the ability to differentiate odours was investigated. Three-day-old CBA mice nursed by their own mothers vocalized at higher frequencies than did newborns fostered by C57BL lactating females. It is suggested that ultrasonic vocalization in CBA pups is affected by genetic factors and postnatal environmental conditions.

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.

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.