Abstract
Summary
The effect of estrogen-tipped steel tubes has previously been studied with permanent implant methods. An improved technique makes it possible to place and remove 27-gauge estrogen-tipped tubes through a short 22-gauge “guide barrel” permanently implanted in the calvarium. The “guide barrel” is implanted and the animal allowed to recover from the effects of surgery prior to placement of the estrogen tube. Three experiments are described demonstrating the value of this technique: (i) Castrated female rats with estrogen tubes placed in the preoptic-suprachiasmatic region of the anterior hypothalamus exhibited behavioral lordosis and mating in less time than that previously described for rats with permanent tube implants. (ii) Estrogen tubes placed in the estrogen-sensitive center of the posterior hypothalamus of intact, normally cycling female rats for 7 days suppressed the return of normal vaginal cycles for 16-37 days after the tubes were removed. In previous reports with permanently implanted tubes it was not possible to examine the delay in return to normal vaginal cycling following estrogen application to this hypothalamic center influencing gonadotropin release. (iii) Intact female rats with estrogen tubes placed in the anterior estrogen-sensitive center of the hypothalamus showed only temporary interference with normal vaginal cycling.
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