Comparison of social interaction and neural activation in the main olfactory bulb and the accessory olfactory bulb between Microtus mandarinus and Microtus fortis

To gain insight into the function of AOB and MOB during different social interaction and in different vole species,the behaviors and neural activation of the olfactory bulbs in social interactions of mandarin voles Microtus mandarinus and reed voles Microtus fortis were compared in the present research.Mandarin voles spent significantly more time attacking and sniffing their opponents and sniffing sawdust than reed voles.During same sex encounters,mandarin voles attacked their opponents for a significantly longer time and sniffed its opponent for shorter time compared with male-female interactions.However,no significant behavioral differences were found during encounters of two individual reed voles,regardless of gender composition of the pair.Using c-Fos as an indicator of neural activation,we observed that neural activation was significantly higher in almost all sub-regions of the main olfactory bulb(MOB)and the accessory olfactory bulb(AOB)of mandarin voles compared with reed voles.Numbers of c-Fos-ir neurons in almost all sub-regions of the AOB and the MOB during male-female interactions were also higher than those in interactions of the same sex.Anterior-posterior ratios of Fos-ir neurons in the AOBM(AOBMR)and the AOBG(AOBGR)in male-female interaction were significantly higher than those in interaction of the same sex.The AOBMR of male mandarin voles and reed voles were larger than those of females in male-female interactions.Behavioral patterns are consistent with cellular activity patterns.Consistent level of neural activation in MOB and AOB suggests important roles of both the main olfactory bulb and the accessory olfactory bulb in social interaction in two species.

Effects of reproductive experience on paternal behavior,levels of testosterone,prolactin in serum and dendritic spines in medial prefrontal cortex of mandarin voles

Maternal behaviors and brains change dramatically with pregnancy,parturition and other mothering experiences.However,whether paternal behavior,brain plasticity and levels of relevant hormones also change along with fathering experience and pups’age remains unclear.Using socially monogamous mandarin voles(Micro-tus mandarinus),we found that experienced fathers exhibited more active paternal behaviors,such as licking,retrievals and nest building,but less paternal care,such as huddling,than new fathers.The high levels of licking and nest building appeared in the earlier days of their mate’s lactation.Experienced fathers retrieved 9–13-day-old pups more frequently.However,these paternal behaviors did not show significant changes with age of pups in new fathers.In addition,experienced fathers had dramatically higher prolactin levels than new fathers but had similar concentrations of testosterone to new fathers.New fathers had lower levels of testosterone but higher levels of prolactin than new paired males.The fathers had higher prolactin levels in the earlier days of their mate’s lactation.The new and experienced fathers had similar dendritic length and spine density on pyramidal neurons in the medial prefrontal cortex but displayed higher levels than new paired males.Taken together,these results indicate that reduction of testosterone levels and increase of prolactin levels may be associated with initiation of paternal care.Fathering experience significantly affects levels of parental care and paternal behaviors toward different aged pups,and brain plasticity can also be enhanced by transition to fatherhood.