Effects of long-term estradiol exposure on the hypothalamic neuron number

Neuron density, volume of the area and total neuron number were measured in the medial preoptic area, anterior hypothalamic area and arcuate nucleus of the hypothalamus of young (6-month-old), middle age (14-month-old) and old (22-month-old) male and female rats. Intact male rats did not show neuron loss even in old age, while intact female rats manifested neuron loss in the medial preoptic area, anterior hypothalamic area and arcuate nucleus in old age. Long-term administration of estradiol benzoate to castrated male rats induced neuron loss in the anterior hypothalamic area and arcuate nucleus of the middle age group and in all three areas of the old age group. However, long-term ovariectomy could not prevent neuron loss in these hypothalamic areas in old age. The results suggested that estradiol can have a cumulative impact on the degree of neuron damage and simulate female-type age-related neuron loss in male rats and that there may be the possibility of an intrinsic aging process inducing neuron loss in female rats.