Increased daily handling of ovariectomized rats enhances performance on a radial-maze task and obscures effects of estradiol replacement

Estrogen impacts performance on tasks of learning and memory, although there are inconsistencies in the direction and magnitude of the reported effects. Contributory factors to the inconsistencies may be methodological differences associated with different regimens of treatment. The goal of the present experiment was to assess the effect of increased handling, such as that commonly associated with pharmacological or other experimental manipulations, on the ability of estrogen to influence working memory performance. Young adult rats were ovariectomized and implanted with capsules containing either cholesterol or 25% estradiol diluted in cholesterol. Half of each hormone treatment group received standard handling, which consisted of handling required to carry out experimental procedures and half received increased handling, which consisted of standard handling as well as 2 min of additional daily handling by the experimenter. Animals were trained daily on a working memory task on an eight-arm radial maze for 24 days of acquisition and for eight additional daily trials in which delays of either I min or 3 h were imposed between the fourth and fifth arm choices. Animals that received increased handling exhibited significantly enhanced performance during acquisition and delay trials compared to those that received standard handling. Estradiol significantly enhanced performance during delay trials in animals that received standard handling but had no effect in animals that received increased handling. These results suggest that the amount of handling that animals receive as part of experimental procedures may obscure the memory enhancing effects of estradiol replacement on certain tasks of cognition. (c) 2007 Elsevier Inc. All rights reserved.