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Psychostimulant abuse is associated with a variety of impairments in social functioning, including an increased frequency of depression and aggression and deficits in social cognition. Psychostimulants reduce social investigation in rats and mice; however, it is less clear how other forms of social behavior (e.g., prosocial behavior) are affected. Females are also generally more sensitive to the effects of psychostimulants on locomotion and stereotyped behavior, which suggests that females might also display greater disruption of prosocial behavior. In order to test the hypothesis that psychostimulants reduce prosocial behavior and that females are more vulnerable, we treated adult male and female prairie voles with methamphetamine for three days (0, 0.2 or 2.0mg/kg, i.p.) and examined effects on locomotion and alloparental behavior. The lower methamphetamine dose increased activity in the open field in males and reduced locomotion in females. Methamphetamine-treated males took longer to enter the pup chamber, but both sexes displayed reduced pup contact following treatment with the lower methamphetamine dose. The methamphetamine-induced reduction in prosocial behavior was not associated with changes in pup-directed aggression in males or females. In order to investigate potential mechanisms underlying these changes in behavior, we measured adrenal weights as a proxy for activation of the hypothalamic-pituitary-adrenal (HPA) axis. The higher methamphetamine dose increased adrenal weights. Collectively, these data demonstrate that methamphetamine administration reduces alloparental behavior in both sexes and that females are more sensitive to some of the effects of this drug (e.g., locomotion/stereotyped behavior and possibly stimulation of the HPA axis)., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Oxytocin (OT) modulates adult mammalian sexual behavior, sperm production and transport, and steroidogenesis; however, the consequences of developmental manipulations of oxytocin have received little attention. The purpose of this experiment was to determine whether neonatal exposure to OT, an oxytocin antagonist (OTA), saline (SAL), or handling (HAN)-only would have long-term effects on reproductive potential in male prairie voles (Microtus ochrogaster). Adult males were observed for 24 h with a sexually receptive female and sexual behavior was recorded. Females were subsequently lavaged and smears were examined for sperm. Reproductive parameters including motility of epididymal sperm, testis weight, and plasma androgen levels were in the normal range. OT-treated males that did not mate within the first 30 min did not mate at all, and in comparison to controls, a higher proportion of those OT-treated and OTA-treated males that did mate did not transfer sperm to the females. OTA-treated males also had significantly higher testicular sperm concentrations than HAN-only males, and significantly lower epididymal sperm concentrations. These differences suggest that in males, developmental manipulations of OT may have the potential to influence the subsequent expression of sexual behavior and sperm transport.

Neonatal exposure to exogenous oxytocin (OT) can have long-term effects on the subsequent expression of adult behavior and physiology. Here, we test the prediction that early postnatal exposure to OT can affect the timing of sexual maturation in females, as indicated by the age of vaginal opening and the onset of first estrus. To test this hypothesis, female Sprague-Dawley rats received one of four treatments beginning on the day of birth and continuing for the next 6 days. Three groups received an intraperitoneal injection of one of the following: OT (1 mug/g), an OT antagonist (OTA, 0.1 mug/g) or isotonic saline (vehicle control). The fourth group was handled but not injected. Females were then examined to determine the day of vaginal opening and first estrus. The potential effects of OT on body weight were also measured, with females being weighed on postnatal days 1-7, 70, 91 and 136. Treatment with OT significantly delayed the age of vaginal opening and the onset of first estrus. There was no effect on weight. Results indicate that early exposure to OT can affect the timing and development of female sexual maturation.

Both exogenous and endogenous oxytocin (OT) are associated with an attenuated stress response. Increased levels of OT in the early postnatal period have been shown to affect behavior and physiology in rodents, and these effects last into adulthood, suggesting an organizational role for OT during development. We investigated the effects of neonatal exposure to OT on the development of the stress response in male and female prairie voles (Microtus ochrogaster). OT or an OT antagonist (OTA) was administered either on postnatal day 1 (single, D1) or days 1-7 (repeated, D1-7) and then on day 8 the response to social isolation was assessed by quantifying ultrasonic vocalizations (USVs) and measuring plasma corticosterone (CORT). Treatment effects were observed only in females. A single treatment with OTA was associated with a decrease in vocalizations, while repeated treatment produced an increase in vocalizations. A single treatment with either saline or OTA increased basal CORT. The results suggest that endogenous OT may be involved in the development of the stress response in females.

Although patterns of aggression and affiliation may play a major role in social organization, the mechanisms underlying these behaviors are not well understood. The purpose of this study was to examine the effects of social and hormonal experience on female-female aggression and affiliation in prairie voles, Microtus ochrogaster. Prairie voles exhibit the traits of social monogamy and tend to live in communal families structured around a male-female pair. It is rare for two unrelated females within a family to successfully reproduce. In this study, the social and/or hormonal experiences of female prairie voles were varied and female-female aggression and affiliation were measured during dyadic encounters with unfamiliar, nonaggressive females. An increase in aggression and decline in affiliative behaviors toward a stimulus female was observed during pregnancy and following male-cohabitation, with or without mating. Pairing with another female did not result in changes in either aggressive or affiliative behaviors toward the stimulus female. Female-female aggression increased and affiliative behaviors declined, with a maximal effect following approximately 8-12 days of male cohabitation. Similar patterns of change were seen in both ovariectomized and gonadally intact females, and treatment with estradiol and subsequent sexual experience did not significantly alter the tendency of females to show aggression or affiliative contact. Social experiences associated with prolonged cohabitation with a male facilitate the induction of female-female aggression; however, ovarian hormones, pregnancy or mating are not essential to induce aggression.

Prairie voles (Microtus ochrogaster) are monogamous New World rodents which show geographic variation in social behavior. In this study, parameters of female reproduction which might be related to mating system were compared in prairie voles from eastern Kansas (KAN) versus central Illinois (ILL). KAN females showed a more rapid onset of natural estrus following exposure to a male and were more likely to respond to injections of a low dose (0.5 microg) of exogenous estradiol benzoate than ILL females. Neither mating duration nor pregnancy success after mate removal differed in KAN versus ILL females. These results suggest that ILL voles are less sensitive than KAN voles to the estrus-inducing effects of either endogenous or exogenous estrogen, supporting the hypothesis that variations in reproductive strategy occur among geographically discrete populations of prairie voles.

Female prairie voles undergo induced estrus, and require both physical contact with males and exposure to male urine to become reproductively active. This study attempted to determine if physical contact with males enhanced female response to estradiol. Two groups of sexually naive females were tested. One was reared without any exposure to males after weaning, and the other was reared with sibling males to 60 days of age. Sibling males were used because females avoid direct contact with the urine of related males, allowing for the establishment of a group of females that experienced physical contact in the relative absence of exposure to male pheromones associated with urine. Females were then subcutaneously injected with 0.5 microg estradiol benzoate once a day for 7 days. Sexual receptivity was tested with novel adult males 48 h and 168 h after the first injection. There was a significant difference between the treatment groups, with 10% of sexually naive females reared without sibling males displaying lordosis compared to 70% of females raised with sibling males. The results indicate that exposure to sibling males significantly increased a female's behavioral response to estradiol.

This study examined the effects of estradiol on sexual receptivity and vaginal estrus in experienced and virgin female prairie voles, and running wheel activity in virgin females. Because prairie voles undergo induced ovulation, we predicted that exogenous estradiol would not affect activity patterns nor stimulate lordosis in virgins. Females were SC injected with estradiol benzoate (ED) and placed with males, and sexual receptivity was monitored. In experienced females 0.5 micrograms of EB resulted in 100% of the females displaying lordosis after 48 h. In contrast, only 20% of the females receiving 0.05 micrograms displayed lordosis. Less than 20% of virgin females receiving EB displayed lordosis. Virgins displayed no change in wheel-running activity after EB treatments, indicating that behaviors that are influenced by estradiol and regulated by the brain may require previous exposure to males to develop. Although all females receiving the 0.5 micrograms of EB displayed vaginal estrus, virgin females achieved vaginal estrus later than experienced females, suggesting that exposure to males has a priming effect resulting in a reduced period to vaginal estrus.

We predicted that female prairie voles (Microtus ochrogaster) would not increase in locomotor activity during "induced" proestrus. We developed and tested two alternative a priori hypotheses to explain this predicted lack of activity. The Non-Response Hypothesis in which voles cannot, physiologically, increase activity in response to estradiol and, the Threshold Effect Hypothesis in which a minimal concentration of estradiol is necessary to achieve estrus, while higher concentrations influence other behavioral parameters. The non-response hypothesis predicts that hormone concentration will not affect locomotor activity, while the threshold effects hypothesis predicts that voles achieve estrus at low concentrations, while higher concentrations should trigger increasing locomotor activity. Initial results using running wheels indicated that females decreased activity during induced proestrus. Radioimmunoassay revealed that induced proestrus was achieved at relatively low concentrations of estradiol. Results from a dose response experiment allowed for rejection of the nonresponse hypothesis and supported the threshold effects hypothesis as females decreased activity at low concentrations of estradiol, showed no relative change at moderate concentrations, and increased activity at higher concentrations.