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Menopause. 2003 Sep-Oct;10(5):406-11.

Onset of estrogen replacement has a critical effect on synaptic density of CA1 hippocampus in ovariectomized adult rats.

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1
Department of Gynecology, Universidade Federal de São Paulo, Brazil.

Abstract

OBJECTIVES:

The aim of this study was to evaluate differences between estrogen replacement therapy initiated either 4 or 12 days after ovariectomy on the synaptic density of the hippocampal CA1 field in rats.

DESIGN:

Female, adult, Wistar rats were ovariectomized bilaterally under ether anesthesia and divided among the following groups: 1) estrogen (conjugated equine estrogen 50 microg in 0.5 mL of propylene glycol, daily, p.o. gavage, for 60 days), starting 4 days after ovariectomy (n = 5); 2) propylene glycol (0.5 mL daily, p.o. gavage, for 60 days), starting 4 days after ovariectomy (n = 4); 3) estrogen (conjugated equine estrogen 50 microg in 0.5 mL of propylene glycol, daily, p.o. gavage, for 45 days), starting 12 days after ovariectomy (n = 3); 4) propylene glycol (0.5 mL daily, p.o. gavage, for 45 days), starting 12 days after ovariectomy (n = 3). At the end of the treatment, the rats were processed for electron microscopy and light analysis.

RESULTS:

Synaptic density in all of the CA1 strata subjected to evaluation was significantly higher in animals in which estrogen replacement was initiated 4 days after ovariectomy as compared with controls. In contrast, initiation of treatment after a 12-day interval did not result in recovery of synaptic density in any of the CA1 strata and was significantly lower than that of the animals subjected to hormone replacement after a 4-day delay (P < 0.01).

CONCLUSION:

The delay for hormone replacement therapy might have critical implications for modulating synaptic density.

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