ABSTRACT
Estrogen receptor (ER) agonists rapidly affect neural plasticity within 1 h, suggesting they play a functional role in learning and memory. However, behavioral learning experiments on such a rapid time scale are lacking. Therefore we investigated whether the ERα agonist propyl pyrazole triol (PPT) and ERß agonist diarylpropionitrile (DPN) could affect social recognition, object recognition, or object placement learning within 40 min of drug administration. At the same time, we examined their effects on CA1 hippocampal dendritic spines. Ovariectomized female CD1 mice were administered a range of PPT or DPN doses (0, 30, 50, 75, or 150 µg/mouse). PPT at the middle doses improved social recognition, facilitated object recognition and placement at a dose of 75 µg, and increased dendritic spine density in the stratum radiatum and lacunosum-moleculare. In contrast, DPN impaired social recognition at higher doses, did not affect object recognition, but slightly facilitated object placement learning at the 75-µg dose. DPN did not affect spines in the stratum radiatum but decreased spine density and increased spine length in the lacunosum-moleculare. This suggests that rapid estrogen-mediated learning enhancements may predominantly be mediated through ERα, while the effects of DPN are weaker and may depend on the learning paradigm. The role of ERα and ERß in learning and memory may vary depending on the timing of drug administration, as genomic studies often implicate ERß in enhancing effects on learning and memory. To our knowledge, this is the first report of estrogens' effects on learning within such a short time frame.
