Differential effects on visual and spatial recognition memory of a novel hormone therapy regimen of estrogen alone or combined with progesterone in older surgically menopausal monkeys.

Building upon our initial studies in young adult surgically menopausal monkeys, this study examined the effects of a novel schedule of administration of estradiol therapy alone, or in combination with progesterone, on visual and spatial recognition memory in older monkeys. Monkeys were preoperatively trained on a delayed matching-to-sample task and a delayed response task. At the time of ovariectomy, monkeys began their hormonal treatments and were cognitively assessed at 2, 12 and 24 weeks following treatment initiation. A schedule of hormone administration was used that closely modeled the normal fluctuations of hormones during the course of a normal primate menstrual cycle. Monkeys receiving placebo had lower levels of accuracy than monkeys receiving estrogen therapies on the delayed matching-to-sample task that were not apparent until 12 weeks following initiation of therapy and were no longer detected at the 24-week assessment. There was no effect of hormone therapy on accuracy in the delayed response task at any of the postoperative assessments. In both tasks, monkeys treated with estrogen plus progesterone had longer choice response latencies, especially on trials in which they made errors; however these effects did not influence accuracy measures in these animals. Our findings indicate that visual recognition ability may be more sensitive than spatial recognition memory to this novel hormone therapy regimen, that treatment with estradiol plus progesterone was equivalent to that of estradiol alone, and that neither therapy had significant negative impact on memory profiles.