Ruiyong Wu

Sexual or paternal experiences alter alloparental behavior and the central expression of ERα and OT in male mandarin voles (Microtus mandarinus)

Various hypotheses have been proposed to explain factors influencing male alloparental behavior in cooperatively breeding species. Mandarin voles (Microtus mandarinus) are ideal animal models to investigate these factors because they are highly social rodents and display biparental care and spontaneous parental care when exposed to foster pups. Here we test the idea that the sexual and paternal experience of males influences alloparental behavior toward novel pups, and that these experiences alter the expression of neuropeptide oxytocin (OT) and estrogen receptor alpha (ERalpha). Alloparental behavior and OT and ERalpha expression were compared between virgin males that had no prior sexual or reproductive experience, exposed males that with prior exposure to novel pups before the test, paired males that had been housed with a female, and new fathers having their first litter with a female. Our results show that prior exposure to novel pups and prior mating and paternal experience increased male alloparental behavior toward a novel pup. This experience also increased OT expression and affected the expression of ERalpha. This study reveals important initiation factors for male alloparental behavior and suggests a relationship between alloparental behavior and central OT expression in males.

Neonatal paternal deprivation impairs social recognition and alters levels of oxytocin and estrogen receptor α mRNA expression in the MeA and NAcc, and serum oxytocin in mandarin voles

Paternal care is necessary for the healthy development of social behavior in monogamous rodents and social recognition underpins social behavior in these animals. The effects of paternal care on the development of social recognition and underlying neuroendocrine mechanisms, especially the involvement of oxytocin and estrogen pathways, remain poorly understood. We investigated the effects of paternal deprivation (PD: father was removed from neonatal pups and mother alone raised the offspring) on social recognition in mandarin voles (Microtus mandarinus), a socially monogamous rodent. Paternal deprivation was found to inhibit the development of social recognition in female and male offspring according to a habituation-dishabituation paradigm. Paternal deprivation resulted in increased inactivity and reduced investigation during new encounters with other animals. Paternal deprivation reduced oxytocin receptor (OTR) and estrogen receptor α (ERα) mRNA expression in the medial amygdala and nucleus accumbens. Paternal deprivation reduced serum oxytocin (OT) concentration in females, but had no effect on males. Our results provide substantial evidence that paternal deprivation inhibits the development of social recognition in female and male mandarin voles and alters social behavior later in life. This is possibly the result of altered expression of central OTR and ERα and serum OT levels caused by paternal deprivation.

Effects of group housing on stress induced emotional and neuroendocrine alterations

Chronic restraint stress can induce depressive and anxiety-like behavior and neurophysiological disturbances. The social living shows the health-promoting and stress-protective effects on both human and animal. However, whether group housing exerts effects on development of depression and anxiety induced by chronic restraint treatments and its detailed neuroendocrine mechanism remain unclear. Following repeated restraint, the anxiety and depression-like behaviors of single and group housing mice were examined using the elevated plus-maze, open field test and forced swimming test. The levels of central oxytocin (OT) expression in the paraventricular nucleus (PVN), glucocorticoid receptors (GR) in the hippocampus and serum OT and corticosterone (CORT) were also measured using immunohistochemistry and ELISA methods. Our results show that chronic restraint significantly decreased time in open arm of elevated plus maze and increased immobility time in forced swimming test in single-housed mice. However, chronic restraint exerted no effects on these aspects in group-housed mice. Accompanying the changes of behaviors, chronic restraint up-regulated levels of serum CORT and reduced the hippocampus GR in single-housed animals, but did not change these measures in group-housed mice. Furthermore, repeated restraint had no effect on OT levels in these two housing conditions although group-housing significantly increased the PVN OT levels. Taken together, these results provide substantial evidence that group housing can reduce levels of anxiety and depression induced by chronic restraint stress in mice. The elevation of central GR and OT, and decrease of circulating CORT may possibly be involved in these buffering effects.

The effects of neonatal paternal deprivation on pair bonding, NAcc dopamine receptor mRNA expression and serum corticosterone in mandarin voles

High levels of paternal care are important for the development of social behavior in monogamous rodents. However, the effects of paternal care on the formation of pair bonding and underlying neuroendocrine mechanisms, especially the involvements of dopamine system and corticosterone, are not well understood. We investigated effects of paternal deprivation on pair bonding in mandarin voles (Microtus mandarinus), a socially monogamous rodent. Paternal deprivation was found to inhibit the formation of pair bonding in females according to partner preference tests (PPT). Paternal deprivation also reduced body contact behavior and increased aggression in males and females in PPT. During social interaction tests (SIT), paternal deprivation was found to reduce investigative and aggressive behaviors but increase body contact and self-grooming in females, and reduce staring, aggression, body contact and self-grooming in males when interacting with the opposite sex. Paternal deprivation reduced the expression of dopamine 1-type receptor (D1R) mRNA and dopamine 2-type receptor (D2R) mRNA in the nucleus accumbens of female offspring in later life, but enhanced mRNA expression of these two dopamine receptors in males. After three days of cohabitation the expression of D1R mRNA and D2R mRNA was negatively correlated for voles reared by two parents, but positively correlated in paternally deprived animals. Paternal deprivation reduced serum corticosterone levels in females but had the opposite effect in males. Three days of cohabitation did not alter corticosterone levels of PD females, but reduced it in PC females. Our results provide substantial evidence that paternal deprivation inhibits the formation of pair bonding in female mandarin voles and alters social behavior later in life. These behavioral variations were possibly associated with sex-specific alterations in the expression of two types of dopamine receptors and serum corticosterone levels induced by paternal deprivation.

Pubertal exposure to bisphenol A disrupts behavior in adult C57BL/6J mice.

Bisphenol A (BPA) is a widespread endocrine disrupting chemical that influences adult physiology and behavior after perinatal exposure. However, it is not clear if pubertal exposure to BPA exerts hormone dependent effects on behaviors. Using C57BL/6J mice, we sought to determine how pubertal exposure to BPA affects locomotion, exploration, anxiety and sociability in adulthood. Compared to controls, pubertal exposure to BPA or E(2) (17β-estradiol) significantly altered female exploratory and anxiety behavior. Moreover, BPA and E(2)-treated female mice displayed increased levels of affiliation to female stimulus mice and decreased levels of affiliation to male stimulus mice; while our control males showed affiliation preference to female stimulus. These results indicate that pubertal exposure to BPA or E(2) may masculinize female social and emotional behavior.

Comparison of sociability, parental care and central estrogen receptor alpha expression between two populations of mandarin voles (Microtus mandarinus)

The socially monogamous mandarin vole (Microtus mandarinus) shows significant behavioral plasticity. We examined whether levels of sociability, parental care and central expression of estrogen receptor alpha differed between two populations with different ecologies. Our results show that males from the Chengcun population display significantly more amicable and less aggressive behaviors towards novel same-sex individuals compared to males from the second population of Xinzheng. Chengcun voles directed more licking behavior towards neonatal pups than did Xinzheng voles. Differences were also found in the number of estrogen receptor alpha-immunoreactive neurons. For example, Xinzheng males displayed significantly higher immunoreactivity than Chengcun males in the medial amygdala, medial preoptic area and ventromedial nucleus of the hypothalamus. Xinzheng females expressed higher levels of estrogen receptor alpha-immunoreactivity than Chengcun females in the medial preoptic area. Chengcun females exhibited significantly more estrogen receptor alpha expression than Xinzheng females in the bed nucleus of the stria terminalis. Our results indicate that mandarin voles from the Chengcun site possess monogamous traits, and animals from Xinzheng possess polygamous traits. It also appears that different social behavior and levels of parental care in these two populations may be associated with differences in estrogen receptor alpha-immunoreactive neurons.

Sociality and oxytocin and vasopressin in the brain of male and female dominant and subordinate mandarin voles.

The dominant–subordinate hierarchy in animals often needs to be established via agonistic encounters and consequently affects reproduction and survival. Differences in brain neuropeptides and sociality among dominant and subordinate males and females remain poorly understood. Here we explore neuropeptide levels and sociality during agonistic encounter tests in mandarin voles. We found that dominant mandarin voles engaged in higher levels of approaching, investigating, self-grooming and exploring behavior than subordinates. Dominant males habituated better to a stimulus vole than dominant females. Dominant males displayed significantly less oxytocin-immunoreactive neurons in the paraventricular nuclei and more vasopressin-immunoreactive neurons in the paraventricular nuclei, supraoptic nuclei, and the lateral and anterior hypothalamus than subordinates. Dominant females displayed significantly more vasopressin-immunoreactive neurons in the lateral hypothalamus and anterior hypothalamus than subordinates. Sex differences were found in the level of oxytocin and vasopressin. These results indicate that distinct parameters related to central nervous oxytocin and vasopressin are associated with behaviors during agonistic encounters in a sex-specific manner in mandarin voles.

Early social deprivation impairs pair bonding and alters serum corticosterone and the NAcc dopamine system in mandarin voles.

Early life stress has a long-term negative impact on emotion, learning, memory and adult sexual behavior, and these deficits most likely impair pair bonding. Here, we investigated whether early social deprivation (ED) affects the formation of pair bonds in socially monogamous mandarin voles (Microtus mandarinus). In a partner preference test (PPT), ED-reared adult females and males did not show a preference for their partner, spent more time exploring the cage of an unfamiliar animal and directed high levels of aggression toward unfamiliar animals. In social interaction test, ED increased exploring behavior only in females, but increased movement around the partner and reduced inactivity in both males and females. Three days of cohabitation did not alter serum corticosterone levels in ED-reared males, but increased corticosterone levels in males that received bi-parental care (PC). Interestingly, serum corticosterone levels in ED- and PC-reared females declined after cohabitation. ED significantly increased basal serum corticosterone levels in males, but had no effect on females. ED significantly up-regulated the levels of dopamine and the mRNA expression of dopamine 1-type receptor (D1R) in the nucleus accumbens (NAcc) in females and males. ED suppressed dopamine 2-type receptor mRNA (D2R) expression in females, but increased this in males. After three days of cohabitation, levels of D1R mRNA and D2R mRNA expression changed in opposite directions in PC-reared voles, but in the same direction in ED-reared males, and only the expression of D2R mRNA increased in ED-reared females. Our results indicate that early social deprivation inhibits pair bonding at adulthood. This inhibition is possibly associated with sex-specific alterations in serum corticosterone, levels of dopamine and mRNA expression of two types of dopamine receptors in the NAcc.

The effects of repeated early deprivation on ultrasonic vocalizations and ontogenetic development in mandarin vole pups

Early deprivation is popularly used in rodent models as an early life social stress to investigate and determine the factors that affect the development of the brain and behavior. Ultrasonic calls made by pups play an important role in parental-pup interactions during the neonatal period. However, whether repeated early deprivation affects the properties of ultrasonic vocalizations (USVs) produced by mandarin vole (Microtus mandarinus) pups, and whether ontogenetic development is subsequently affected, remains unclear. Here we measured USVs and developmental parameters in mandarin vole pups deprived of their parents and littermates for 3h per day (ED, which is significantly different from 5 min isolation used to induce USVs) and another pup group developed under normal nest conditions (PC). Repeated measures analysis indicated that the number of USVs from ED pups was significantly lower than those from PC pups during the postnatal period (p<0.05). The pulse durations of ED pups were longer than those of PC pups at two (p<0.001) and five days of age (p<0.05), but shorter at 14 days of age (p<0.001). Compared with PC pups, the frequency range of the ED pups was wider at 18-45 kHZ, variable during the first week, smaller and narrower at 18-30 kHZ at eight and 11 days of age, and became stable similar to PC pups at 25 kHZ after 14 days of age. ED also reduced pup body weight significantly and resulted in earlier eye opening compared with PC pups (p<0.001). A positive relationship was also found between USV emissions and levels of parental care received by pups. It appears that pup USVs are an important age-dependent behavioral phenotype and an effective communicative method between parents and offspring. Prolonged parental and littermate deprivation (ED) may alter USVs emitted by pups and then ontogenetic development and parental care. Mandarin voles show USV properties similar to socially monogamous rodents and this add further support to the hypothesis that species with different social systems produce different patterns of ultrasonic vocalizations. USVs, ontogenetic development and parental care are closely associated.

Behavioral responses to pups in males with different reproductive experiences are associated with changes in central OT, TH and OTR, D1R, D2R mRNA expression in mandarin voles

Male rodents behave differently toward pups because of different sexual and/or paternal experiences; however, the mechanisms underlying these responses are not well understood. Using socially monogamous mandarin voles (Microtus mandarinus) we investigated the behavioral responses of males with different reproductive experiences (virgin males, paired males and new fathers) to new born pups. Central levels of neuropeptide oxytocin (OT), tyrosine hydroxylase (TH), as well as oxytocin receptor (OTR), dopamine 1-type receptor (D1R) and dopamine 2-type receptor (D2R) mRNA expression in the nucleus accumbens and medial amygdala were also measured in these males. Our data showed that new fathers exhibited more approaching behavior and contained more OT-immunoreactive and TH-immunoreactive neurons. In addition to increased OTR mRNA expression in the nucleus accumbens and medial amygdala, new fathers had higher D1R and D2R mRNA expression in the nucleus accumbens, and less D1R and D2R mRNA expression in the medial amygdala than paired males. These results demonstrate that males with different reproductive experiences display different behavioral responses to pups and that these differences are associated with altered OT and dopamine, and their receptors in specific brain regions.