Social modulation of behavioral reproductive senescence in female rats.

During aging, the lordosis reflex of female rats changes from a state of cyclic lordosis, when the lordosis reflex can be elicited by manual palpation only on proestrus, to a state of constant lordosis (CL), when it can be elicited daily. Social signals from other females altered this pattern of behavioral senescence. Group living decreased the lordosis reflex intensity in both old and young rats and delayed the onset of CL. Long-term group living delayed CL until late in the life span, while temporary group living delayed it only until rats returned to isolation. Long-term group living also changed the temporal relationship between CL and the acyclic, anovulatory state of estrus. Finally, the lordosis reflex intensity, measured by manual palpation, predicted the old rats' receptivity to a male, indicating that constant lordosis is a biomarker for other aspects of behavioral reproductive senescence.