Effects of oestrogen on hypothalamic beta-endorphin in ovariectomized and old rats

Immunocytochemical beta-endorphin (beta-EP) staining and ultrastructural observations in the hypothalamus were compared in normal mature female rats, ovariectomized rats, and aged female rats. The effects of oestradiol benzoate (EB) on the hypothalamus were studied. The female Wistar rats were divided into seven groups, as follows: 40-day-old rats (Mature), 54-day-old rats ovariectomized at 40 days (Ovx), rats ovariectomized at 40 days and injected with 0.1 mg EB daily for 7 days (Ovx + e) rats ovariectomized and injected with one dose of 1 mg EB (Ovx + E), 500-day-old (Old), old rats injected with 0.1 mg EB daily for 7 days (Old + e), and old rats injected with 1 mg EB (Old + E). In the Ovx and Old groups, beta-EP-positive cells in the arcuate nucleus were rarely seen, as compared with the Mature group. The staining of beta-EP-positive cells in Ovx + e was slightly recovered and that in Ovx + E was almost completely recovered. However, no recovery of beta-EP-positive cells was seen in the Old + e or Old + E groups. The number of nerve fibers in the median eminence were reduced in both the Ovx and Old groups, as compared with the Mature group. There was no relationship between changes in these numbers and oestrogen replacement in the Old group, but in the Ovx group oestrogen replacement brought about recovery of these numbers. The number of glial cells increased after oestrogen replacement in both the Ovx and Old groups. The frequency of giant mitochondria in the neurons in the arcuate nucleus decreased after oestrogen replacement in the Old group.