| Paternal behavior is one kind of parental care including retrieving, licking and crouching behavior to pups expressed by father during neonatal period. Fathers play an important role in the survival and development of offspring in many mammalian species In humans, paternal behaviors have a strong influence on the emotional and social development of children. Fathers, more frequently than mothers, leave the family nucleus, or become abusive, leading to offspring that are more likely to grow under stressful conditions and greater susceptibility to abnormal health and social outcomes. In spite of this, because the occurrence of mammalian paternal care is relatively rare, literature on parental behaviors, human or animal, has primarily focused on the interactions between mothers and offspring, with little research directed at understanding paternal behavior. In most of the mammals (including humans), the basic mechanism understanding of parental behavior mainly from the maternal behavior, so the basic mechanisms of paternal behavior in the mammalian are not well understood, and the neural circuitry controlling paternal behavior remain unclear. However, the work from human, some studies reveal commonalities in parental behaviors and their underlying neural circuits, these highlight the possibility that paternal behavior has components that are strictly masculine with unique neurobiological mechanisms. Therefore, the neuroendocrine mechanisms of paternal cares need further exploration.The neuropeptides oxytocin (OT). and vasopressin (AVP) are important modulators for the parental behavior, especially, in the regulation of the affiliation behavior. Estrogen receptor alpha (ERa) also plays an important role in the regulation of male behavior, decrease of ERa expression can reduce the polygamous male behavioral phenotypes. To assess further the specific mechanisms of paternal behavior, the present study used method of behavior and immunocytochemistry to detect behavioral response of father to pups’ exposure, and the brain areas activated by pups and the expression and distribution of central OT、AVP or ERa in Mandarin voles. Male mandarin voles were separated from their female mate and their litter for3h and then exposed to their own pups, alien pups or a control object (a marble with the approximate size and oblong shape of a newborn pup) for15min. The behavioral responses to different stimulus were observed and recorded. The numbers of Fos-ir neurons in several brain regions and numbers of central OT. AVP. ERa neurons were also compared among the three groups. This research could identify brain areas involved in paternal behavior in the male mandarin vole. Moreover, it helped to elucidate the association between paternal behavior and central OT, AVP, ERa expression. This study can provide insights into neuroendocrine mechanisms of paternal behavior. The main results include the following points:1. Through behavioral observation, all males receiving their own pups or alien pups exposure showed strong paternal responses, such as retrieving, licking, crouching, whereas males exposed to a pebble contacted it only occasionally. These results showed that the stimulus from their pups induced male express more paternal behavior than a pebble stimulus. Exposure to their own pups induced more sniffing behavior than exposure to alien pups.2. More interestingly, male parents exposed to their own pups demonstrated more Fos-ir neurons in the anterior cingulate cortex (ACd), medial preoptic area (MPOA), bed nucleus of stria terminalis (BNST). medial amygdaloid nucleus (MeA), lateral septum(LS), hypothalamic paraventricular nucleus (PVN), lateral habenular nucleus (LHb), piriform cortex (PCp) and the nucleus accumbens (NAcc) areas than those exposed to a pebble, and it demonstrates that these brain regions are involved in paternal behavior. In addition, exposure to their own pups produced more Fos-ir neurons in the anterior cingulate cortex (ACd), piriform cortex (PCp), lateral septum (LS) than exposure to alien pups, it suggests that these brain regions play a role in determining the differences between male parental behavior and alloparental behavior. Finally, exposure to alien pups induced more Fos-ir neurons in the anterior cingulate cortex (ACd). medial preoptic area (MPOA). bed nucleus of stria terminalis (BNST). medial amygdaloid nucleus (MeA), nucleus accumbens (NAcc) and piriform cortex (PCp) than a pebble stimulus. These findings also showed that exposure to their own pups, alien pups and a pebble induced site-specific neural activation in fathers.3. Importantly, fathers exposed to their own pups demonstrated more neuropeptide oxytocin (OT) immunoreactive neurons in the hypothalamic paraventricular nucleus (PVN) than those exposed to alien pups and a pebble. Fathers exposed to alien pups or a pebble did not showed significant differences. In addition. OT-ir neurons in the supraoptic nucleus of the hypothalamus (SON), did not showed significant differences between three groups. In addition, we did not find OT-ir neurons in other brain regions. These results mean that OT in the PVN is also involved in the regulation of paternal behavior.4. Moreover, exposure to their own pups induced AVP immunoreactive neurons expression in the hypothalamic paraventricular nucleus (PVN) and the supraoptic nucleus of the hypothalamus (SON) than exposure to alien pups and pebble. In addition, there was no significant difference in other brain regions. These results showed that AVP in the PVN and SON may also be involved in the paternal behavior.5. Fathers exposed to their own pups demonstrated more ERa-ir neurons in the ventromedial hypothalamic nucleus (VMH) and the central amygdaloid nucleus (CeA), but less ERa-ir neurons in the bed nucleus of stria terminalis (BNST) and medial amygdaloid nucleus (MeA) than exposure to pebble. These results suggest that ERa in VMH, CeA, BNST and MeA may be involved in paternal behavior. In addition, exposure to their own pups produced more ERa-ir neurons in the ventromedial hypothalamic nucleus (VMH) and the central amygdaloid nucleus (CeA) than exposure to alien pups, it suggests that ERa in these brain regions plays a role in determining the differences between male parental behavior and alloparental behavior.From the above results, this research concludes that the male mandarin voles whether exposed to their own pups or alien pups showed high levels of paternal care, such as retrieving, licking, crouching. However, father spent more time in sniffing their own pups than alien and pebble. In addition, the anterior cingulate cortex (ACd), medial preoptic area (MPOA). bed nucleus of the stria terminalis (BNST), the medial amygdaloid nucleus (MeA), lateral septum (LS), hypothalamic paraventricular nucleus (PVN). the lateral habenular nucleus (LHb). piriform cortex (PC) and the nucleus accumbens (NAcc) areas are involved in paternal care. The ACd. PCp and LS may be involved in social investigation and discrimination. Furthermore, the neuropeptides OT. AVP and ERa in certain brain areas also play a role in regulating paternal behavior. |
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