| The development of animals is a various and changeable process, which can be influenced by living environment. The plasticity of gene and behavior is higher in early period of development. During this period, social environment has profound effects on brain development and subsequent expression of social behavior. The studies on the effect of early social environment on social behaviors and related neuroendocrine mechanisms have been investigated largely, but most of them primarily focused on the influence of maternal care on offspring, with little research directed at understanding the effect of paternal behavior on offspring. However, in monogamous mammal, fathers also exhibit high levels of parental care as mothers. Thus, paternal deprivation is a perfect paradigm of investigating the effect of paternal care on offspring, some aspects of which has been studied deeply by our laboratory. However, the longer lasting effects of PD on social recognition in monogamous rodents are known little. All social relationships are dependent on the ability to remember and recognize conspecifics, social recognition is therefore critical for reproduction, territorial defense, and the establishment of dominance hierarchies in a natural context. Some studies have shown that early social environment has profound influence on social recognition, thus we predict that the lack of paternal care can also affect social recognition.Previous studies found that the neuropeptide oxytocin (OT) is an important modulator for social recognition, furthermore, oxytocin receptors (OTR) and estrogen receptors alpha (ERa) also plays important roles in social recognition. Likewise, the reduction of OTR and ERa expression impairs social recognition abilities. Based on the above reports, the present research used mandarin vole(Microtus mandarinus), which is a socially monogamous rodent, as animal model to answer the following questions:1) Using habituation-dishabituation paradigm to investigate the effects of paternal deprivation on social recognition memory;2) paternal deprivation affects the social recognition possibly via alteration in serum OT release induced by this treatment;3) paternal deprivation possibly alter OTR and ERa mRNA expression in the MeA and Nacc and subsequently affects social recognition. Thus, in this study, we used mandarin voles, which has complex social behaviors, as animal model and established two social environments including biparental care (PC) and paternal deprivation (PD) in present research. We study the developmental influences of different social environments on subsequent social recognition, and try to explore the neural mechanism through which paternal deprivation regulates the development of social recognition. The main results include the following points:1. We used habituation-dishabituation paradigm to test the social recognition of mandarin voles at approximately postnatal day45. Through behavioral observation, both female and male mandarin voles from PC group showed a significant decrease in the amount of time spent investigating the stimulus across four repeated5-min presentations throughout, while mandarin voles both in female and male that experienced PD show no significant reduction. When presented with a novel vole in fifth trial, PC-reared including females and males showed a significant increase of social investigation compared with the fourth meeting with familiar voles, whereas PD-reared including females and males show no change in social investigation.2. PC mandarin voles both in female and male showed a significant habituation curve such that at T4they investigated the intruder less than at T1, At T5, the novel stimulus voles induced a significant increased social investigation in PC groups, which showed a significant dishabituation response. However, unlike mandarin voles from PC, PD did not show a normal habituation and dishabituation response.3. PD reduced investigative behavior but increased inactive behavior in both female and male voles during first interactions with a stranger in social recognition test. However, there were no difference of other behaviors including self-grooming, exploration, approaching behavior between PC and PD groups in both female and male voles, which indicated that paternal deprivation impaired social recognition through the reduced level of exploratory, locomotor activity and sociality.4. The serum concentration of OT was measured using Elisa. Our results showed that PC-reared females had significantly greater serum OT levels than PD-reared females. However, PC and PD males showed no statistical difference on serum OT levels groups, which indicated that the reduction of OT levels in female voles, but not in male voles, might be induced by paternal deprivation. As the results of previous studies, serum OT levels in female voles were much higher than male voles.5. OTR and ERa expression in the MeA was measured using RT-PCR. Our results showed that the expression of OTR and ERa mRNA in the MeA of PD groups significantly decreased compared with PC groups both in females and males, which indicated that paternal deprivation reduced the expression of OTR and ERa mRNA in the MeA.6. OTR expression in the Nacc was measured using RT-PCR. Our results showed that the expression of OTR mRNA in the Nacc of PD groups significantly decreased compared with PC groups both in females and males, which indicated that paternal deprivation reduced the expression of OTR mRNA in the Nacc.From the above results, the present study concluded that paternal deprivation had long-term effects on social recognition, which were possibly associated with the changes in OT release and decreases in ERa and OTR expression in specific brain regions. Thus, it is concluded that paternal deprivation influence the development of social behavior possibly through the alteration in neuroendocrine system. |
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