Elsevier

Hormones and Behavior

Volume 52, Issue 2, August 2007, Pages 237-243
Hormones and Behavior

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

https://doi.org/10.1016/j.yhbeh.2007.04.010Get rights and content

Abstract

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 1 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.

Section snippets

Subjects

Forty female Long–Evans hooded rats, approximately 2 months of age, were purchased from Harlan Sprague–Dawley (Indianapolis, IN). Animal care was in accordance with guidelines set by the National Institutes of Health Guide for the Care and Use of Laboratory Animals and all procedures were approved by the Institutional Animal Care and Use Committee of Tulane University. Rats were housed individually in a temperature controlled vivarium under a 12-h light/dark cycle (lights on at 7:00 a.m.). One

Results

Data from one rat (E–SH) were excluded from all analyses due to a hormone implant lost during the acquisition trials. Data from a second rat (E–IH) were excluded from the delay-trial analyses due to a hormone implant lost during delay trials.

Discussion

The primary finding of the present study is that the enhancing effects of estradiol on working memory were obscured in rats that received 2 min of increased daily handling in addition to the standard handling that was involved in the experimental procedures and routine care. An effect of increased handling was maintained throughout the length of the experiment, which included weeks of behavioral testing. These results indicate that a minimal difference in the amount of handling that animals

Acknowledgments

This work was supported by National Science Foundation Grant 0423331 (J.M.D). We thank Amanda Bearl and Caroline Greene for their assistance in collection of behavioral data.

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