Aging leads to sex-dependent effects on pair bonding and increased number of oxytocin-producing neurons in monogamous prairie voles.

Pair bonds powerfully modulate health, which becomes particularly important when facing the detrimental effects of aging. To examine the impact of aging on relationship formation and response to loss, we examined behavior in naive 6-, 12-, and 18-month male and female prairie voles, a monogamous species that forms mating-based pair bonds. We found that older males (18-months) bonded quicker than younger voles, while similarly aged female voles increased partner directed affiliative behaviors. Supporting sex differences in bonding behaviors, we found that males were more likely to sample both partner and stranger voles while females were more likely to display partner preference during the initial 20 min of the test. We also found that male voles of all ages show enduring bonding behavior despite four weeks of partner separation while females show an overall decrease in partner-directed affiliation, including an erosion of partner preference in 12-month females. Finally, we found that the number of oxytocin, but not vasopressin, cells in the paraventricular hypothalamus increased at 18 months of age. These results establish prairie voles as a novel model to study the effects of normal and abnormal aging on pair bonding.