SOCIAL REGULATION OF ADULT NEUROGENESIS IN A EUSOCIAL MAMMAL

The present study examined the effects of social status on adult neurogenesis in an extreme cooperative breeder: the naked mole rat. These animals live in large colonies of up to 300 individuals, with a strict reproductive dominance hierarchy; one female and one to three males breed, and all other members are socially subordinate and reproductively suppressed. We examined the effects of social and gonadal cues on doublecortin (DCX; a marker for immature neurons) immunoreactivity in the dentate gyrus (DG), piriform cortex (PCx) and basolateral amygdala (BLA) by comparing dominant breeding animals to non-breeding subordinates from intact colonies. We also examined DCX expression in subordinate animals that had been removed from their colony and paired with an opposite-or same-sex conspecific for 6 months. Compared to subordinates, dominant breeders had significantly reduced DCX immunoreactivity in all brain areas, with BLA effects confined to females. By contrast, the effects of same- versus opposite-sex housing were region-specific. In the DG and PCx, more DCX immunoreactivity was observed for opposite- than same-sex-paired subordinates. Conversely, same-sex-paired females had more DCX immunoreactivity than opposite-sex-paired females in the BLA. Gonadectomy did not affect DCX expression in opposite-sex-paired animals, and no significant relationships between gonadal steroids and DCX immunoreactivity were detected, suggesting that group differences in neurogenesis are independent of gonadal hormones. The apparent lower neurogenic capacity displayed by breeders contrasts previous reports on neurogenesis and social rank, challenging the conventional view that subordination is stressful and impairs neurogenesis. Future work will clarify whether the present findings can be attributed to status-dependent differences in stress, behavioral plasticity, or life stage. (C) 2014 IBRO. Published by Elsevier Ltd. All rights reserved.