RESUMO
Rodents rely heavily on odor detection, discrimination, and memory to locate food, find mates, care for pups, and avoid predators. Estrogens have been shown to increase memory retention in rodents performing spatial memory and object placement tasks. Here we evaluate the extent to which 17ß-estradiol modulates memory formation and duration in the olfactory system. Adult CD-1 mice were gonadectomized and given either systemic 17ß-estradiol replacement, local 17ß-estradiol in the main olfactory bulb, or no replacement. Before performing the behavioral task the mice were given saline or PHTPP (an estrogen receptor ß [ER-ß] antagonist) via bilateral infusion into the main olfactory bulb. As the beta-type estrogen receptor (ER-ß) is more abundant than the alpha-type estrogen receptor in the murine main olfactory bulb, the current study focuses on 17ß-estradiol and its interactions with ERß. Habituation, a simple, nonassociative learning task in which an animal is exposed to the same odor over successive presentations, was used to evaluate the animals' ability to detect odors and form an olfactory memory. To evaluate memory duration, we added a final trial of intertrial interval time (30 or 60 min) in which we presented the habituated odor. Neither surgical nor drug manipulation affected the ability of mice to detect or habituate to an odor. After habituation, gonadectomized 17ß-estradiol-treated mice retained memory of an odor for 30 min, whereas non-estradiol-treated, 17ß-estradiol+ERß antagonist (PHTPP), and untreated male mice did not remember an odor 30 min after habituation. The results show that both systemic and local bulbar infusions of 17ß-estradiol enhance odor memory duration in mice.
