| The formation of enduring pair bonds is an integral and critical aspect of social relationship in mammals including human. It not only play important roles in survival and reproduction of animals, but also has been implicated in both physical and psychological health. These studies may not only contribute to the understanding of pair bonding in our own species, but may also offer insight into the underlying mechanism of social deficits noted in several mental health disorders. They also guide us optimal parental care at right time to guarantee formation of normal physiological and behavioral phynotypes for offspring. However, due to the inherent complexity of these bonds and the relative rarity with which they are formed in other mammalian species, we know surprisingly little about their underlying neurobiology. Previous studies establish that the voles with different mating systems exhibit significantly different levels of parental care. In addition, levels of maternal care can transfer from one generation to next generation through epigenetic mechanism. Early social experiences often determine the offspring behavioral phyenotype. The following questiones can be raised:whether alterations in levels and pattern of paretnal care via early social or paternal deprivation can affect partner preference and levels of paternal care? What pathway through which these effects are produced? Whether neuroendocrine properties associated with mating system and paternal care can be altered by these early manipulatios? All these questions need to be answered. In present study, using monogamous mandarin voles (Microtus mandarinus) as model, we investigated the effects of early life environment on the parental behaviors and pups’ ultrasonic vocalizations (USVs), the offspring pair bonding and paternal behaviors in adulthood.The underlying neuroendocrine mechanisms of these behaviors were also investigated.(1) The ultrasonic sound emmited by pups play important roles in parents-pups interaction. In order to identify whether the effects of early deprivation on offspring behaviors were caused by alteration in ultrasonic sound, the effect of early social deprivation on USVs and development in mandarin vole pups were investigated. Here we measured USVs and developmental parameters in vole pups deprived of their parents and littermates for3h per day (ED, which is significantly different from5min 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. The pulse durations of ED pups were longer than those of PC pups at two and five days of age, but shorter at14days of age. Compared with PC pups, the frequency range of the ED pups was wider at18-45kHZ, variable during the first week, smaller and narrower at18-30kHZ at eight and11days of age, and became stable similar to PC pups at25kHZ after14days of age. ED also reduced pup body weight significantly and resulted in earlier eye opening compared with PC pups. 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.(2) In order to test the hypothesis that pups separation (PS) affects their behavioral development via alteration in their parents’ care behavior leaded by changes in their ultrasonic sounds, the effects of pups’ deprivatin on parental care of mothers and fathers. Biparental huddling behavior in intact parents of control group peaked at10days of age, and exploring behavior peaked at17days of age in control voles, however these behaviors had no peak in PS voles. At postnatal3days of age, the levels of biparental huddling behavior in PS group was more than those in control group, but less than those in control group at10days postnatal. Levels of nesting behavior from control and PS groups peaked at17days of age. PS reduced significantly the licking and grooming behaviors, and the nesting behavior in both mothers and fathers. At postnatal3days of age, PS increased huddling behavior, exploring and eating behaviors in mothers; PS decreased licking and grooming behavior in fathers. At postnatal10days, mothers in PS group exhibited higher levels of retrieving behavior, but displayed low levels of licking and grooming behavior, nesting and eating behaviors; PS decreased retrieving and nesting behaviors in fathers. At postnatal17days, PS increased retrieving behavior, but decreased nesting behavior in mothers; PS decreased retrieving, licking and grooming, nesting behaviors in fathers. It appears that PS may affect the parental care behavior, and the variations were sexually dimorphic, and these complex behaviors are associated with. US Vs emitted by pups.(3) The effect of patenal deprivation on offspring pair bonding and underlying mechanism:Here, we investigated the pair bonding in mandarin voles deprived of their male parent during postnatal24hours (PD) and another group developed under normal nest conditions (PC). PD was found to inhibit the formation of pair bonding in females according to partner preference tests (PPT). PD also reduced body contact behavior and increased aggression in males and females in PPT. During social interaction tests (SIT), PD 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. PD reduced the expression of dopamine1-type receptor (D1R) mRNA and dopamine2-type receptor (D2R) mRNA in the nucleus accumbens (NAcc) 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. PD 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.(4) The effect of early social deprivation on offspring pair bonding and underlying mechanism:Here, we investigated the pair bonding in mandarin voles deprived of their parents and littermates for3h per day (ED) and another group developed under normal nest conditions (PC). In the partner preference test (PPT), ED-reared female and male offspring at adult did not display significant partner preference, and spent more time for exploring stranger cage rather than partner cage, although they showed high levels of aggressive behavior to the stranger. Three days of cohabitation did not alter serum corticosterone levels in ED-reared males, but increased corticosterone levels in males reared by bi-parental care (PC). Interestingly, serum corticosterone levels in both ED-reared females and the PC-reared females were decreased after the cohabitation. Although ED significantly increased basal serum corticosterone levels in males, but have no effect in females. Three days of cohabitation increased the number of TH-IR neurons in VTA and SN in both PC and ED voles. ED significantly up-regulated dopamine release and levels of dopamine1-type receptor (D1R) expression in the nucleus accumbens (NAcc) in both females and males. ED suppressed the2-type receptor mRNA(D2R) expression in females, but increased it in males. After three days of cohabitation the levels of D1R mRNA and D2R mRNA expression changed in opposite direction in PC-reared voles, but in same direction in ED-reared males and only the expression of D2R mRNA increased in ED-reared females. In all, our results establish that early social deprivation inhibits the pair bonding at adulthood. This inhibition is possibly associated with sex-specific alterations in levels of serum corticosterone, the levels of dopamine and mRNA expression of two types of dopamine receptors in NAcc induced by early social deprivation.(5) The effect of early social environment on offspring paternal behavior and underlying mechanism:Here, we investigated the paternal behavior in ED-reared, PD-reared and PC-reared mandarin voles. PD significantly increased self-grooming behavior, while reduced retrieve behavior. ED increased inactive behavior, while reduced huddling behavior. ED significantly increased serum CORT concentrations. These early life adversities have a significant effect on the D1R mRNA expression, but no effect on D2R and OTR mRNA expression in the NAcc; and have a significant effect on the ERa mRNA expression and OTR mRNA expression in the MPOA. ED significantly increased the levels of D1R mRNA expression in the NAcc, but decreased the levels of OTR mRNA expression in the MPOA. Furthermore, both PD and ED decreased the mRNA expression of ERa in the MPOA. Our results provide substantial evidence that early life stress affect the offspring paternal behavior at adult. These behavioral variations were possibly associated with expression of dopamine type Ⅰ receptors in NAcc and the expression of the EαR and OTR in the MPOA, and serum corticosterone levels induced by early life stress.In all, Mandarin voles show USVs properties similar to socially monogamous rodents and ED alter the pattern of USVs emitted by pups, simultaneously, alter the maternal and paternal care. Early life stress such as ED or PD can affect the offspring pair bonding and paternal behaviors at adulthood. And these variations are closely implicated with the dopamine system in NAcc and the expression of the EaR and OTR in the MPOA, and serum corticosterone levels. |
PDF Full Text Request