Ultrastructural Changes of the Pars Tuberalis and Median Eminence of Rats Following Hypophysectomy

The pars tuberalis of the hypophysis and the external layer of the median eminence were studied by electron microscopy using hypophysectomized rats. Twenty day-old and adult rats were hypophysectomized and examined at various intervals (from 10 to 150 days) afterwards. Several hypophysectomized adult rats were adrenalectomized and examined 3 days later.Ten days after hypophysectomy, the external layer of the median eminence indicated several neurosecretory axons containing large vesicles (1, 500-3, 000Å) with osmiophilic interior and aminergic axons with small cored vesicles (800-1, 200Å) and clear vesicles (300-500Å). Thereafter these axons steadily increased in number, especially the neurosecretory axons, and extended deeply into the pars tuberalis making contact with the surface of the glandular cells.In spite of the alterations mentioned above, the fine structures of the tuberalis cells showed no remarkable changes, while the anterior hypophysial cells in the remnant of the sectioned stalk changed remarkably in their cytoplasmic appearance.In the adrenalectomized adult rats, whose hypophysis had been removed 30 days earlier, the anterior hypophysial tissue in the remnant of the stalk sectioned indicated many active ACTH cells (KUROSUMI and KOBAYASHI, 1966), while the tuberalis cells did not show any alteration in their cytoplasmic details.These observations may suggest that the tuberalis cells, unlike the anterior hypophysis, are not under the neurohumoral control of the hypothalamus in spite of their topographical and embryological association.