Increasing hypothalamic arcuate nucleus glial peroxidase activity in aging female rats is reduced by an antiestrogen and a gonadotropin-releasing hormone agonist

Progressive arcuate glial peroxidase activity is associated with reproductive aging of the female rat. We tested the hypothesis that age-related increase of glial peroxidase activity within the arcuate nucleus and posterior periventricular area is due to endogenous estrogen and could be reduced by an antiestrogen, keoxiphene, or a gonadotropin-releasing hormone super agonist, goserelin acetate (Zoladex), or both. At 3 months of age, 4-5-day regularly cycling female rats were divided into four groups. One group served as a baseline 3-month-old control and was killed by perfusion-fixation followed by serial sectioning of the hypothalamus and staining with 3,3′-diaminobenzidine tetrahydrochloride (DAB). Other groups consisted of animals receiving keoxiphene, goserelin acetate depot (Zoladex), or sham implants for 6 months. Two months after removal of the implants, at 11.25 months of age, the animals were killed by perfusion-fixation, and serial hypothalamic sections were stained with DAB. Sections from each of the four groups were examined in a fixed-size standard test area using a computerized image analyzer to assess the surface density of the DAB reaction. Overall, periventricular peroxidase reaction of the 11.25-month keoxiphene group showed a 63.5% increase in surface density of DAB reaction over the 3-month control group (5,834.6 ± 101.0 [μm²versus 3,566.2 ± 173.6 μm²), whereas the 11.25-month Zoladex group showed a 42.4% increase in surface density of DAB reaction over the 3-month control group (5,078.5 ± 114.6 μm²versus 3,566.2 ± 173.6 μm²). This was in sharp contrast to the 11.25 month sham control group, which showed a 94% increase over the 3-month control group (6,926.6 ± 121.3 (μm²versus 3,566.2 ± 173.6 μm²), p < 0.0001. The differences in increase of the surface density of DAB in zone of reaction in keoxiphene-treated and Zoladex-treated rats were not equally distributed throughout the periventricular brain: The greatest difference was noted in the anterior arcuate (p<0.0001), followed by the posterior arcuate (p<0.001), with no difference noted in the posterior periventricular area. These results demonstrate than an antiestrogen and functional hypogonadotropic hypogonadism induced by a gonadotropin-releasing hormone agonist reduce the increase in hypothalamic glial peroxidase activity in the arcuate nucleus of maturing (aging) female rats but not in the posterior periventricular area. They support the hypothesis that estrogen secreted during the ovarian cycle contributes causally to hypothalamic aging in the female rat and indicate the presence of an estrogen-sensitive anterior region and an estrogen-insensitive posterior periventricular zone of age-dependent glial reaction. The failure of blockade by Zoladex further indicates that hypothalamic aging in the posterior periventricular area may be indifferent to the presence of the ovary.