1962 Volume 33 Issue 1 Pages 38-46
Histological changes were observed in the hypothalamo-hypophysial system and the anterior hypophysis of the rabbit during pregnancy, parturition, and lactation, from the viewpoint of neurosecretion.
The results obtained are as follows.
1. During pregnancy, a comparatively large number of cells with enlarged nuclei and vacuoles were observed in both supraoptic and paraventricular nuclei. On the 25th day of pregnancy, reaccumulation of densely-packed or colloid-like granules was seen in the peripheral zone of neurosecretory (NS) cells. Granules was seen in the hyphothalamo-hypophysial tract (HHT) and the neurohypophysis increased in number on the 5th, 15th, and 20th days of pregnancy and decreased slightly on the 10th and 25th days, suggesting a cyclic fluctuation in the NS activity of the hypothalamus during pregnancy. Granules were transferred increasingly from within the HHT and the pars nervosa into the pars anterior on the 5th, 15th, and 20th days of pregnancy. The number of granules transferred decreased slightly on the 10th and 25th days, but it was still larger than that in the normal control. On the 5th, 15th, and 20th days of pregnancy, an increase of acidophils and degranulation of both acidophils and basophils were observed in the pars anterior.
2. At parturition, a large number of cells with enlarged nuclei and cytoplasmic vacuoles were observed in both supraotic and paraventricular nuclei. These cells had less granules. Granules decreased markedly in number in the pars nervosa. Degranulation was visible particularly in the peripheral zones of blood vessels, suggesting a release of the oxytocic principle into the blood stream. NS granules increased in number in the pars intermedia and the pars anterior. Similar stainable substance was seen in the pituitary cleft. Degranulation was observed in both acidophils and basophils of the pars anterior. Cytoplasmic vacuolization was strikingly apparent in the basophils.
3. During the period of lactation, pictures of both promoted granule-elaboration and vacuole-formation were observed in NS cells with functional nuclear enlargement. In the pars nervosa, degranulation was frequently observed in the peripheral zones of blood vessels, especially 5 minutes after suckling stimulus was given by young. In the lactating period, a comparatively large number of NS granules were seen in the pars intermedia and the pars anterior. Such granules increased markedly in number especially 5 minutes after suckling stimulus was given. A great amount of the same stainable substance was present in the pituitary cleft. In the animal exhibiting the pictures mentioned above, NS granules were clearly seen in the ventral part of the pars anterior. In the pars anterior, degranulation of both acidophils and basophils was usually observed, especially 5 minutes after suckling stimulus was given. Peripheral vacuoles were seen in a large number of bashphils. From the morphological evidence of lactating animals, it seems highly probable that tactile stimuli given to the mammary gland pass the afferent nerve pathways to activate the NS mechanism in the hypothalamus, which in turn excites the secretion of the oxytocic principle from the pars nervosa, and that this NS substance penetrates the pars anterior from within the HHT and the pars nervosa through the hypophysial portal vessels and the pars intermedia, and promotes the release of lactogenic hormone to the pars anterior.
From the results mentioned above, the penetration of NS granules into the adenohypophysis coincided, in time and lacation, with the increase of acidophils and the appearance of degranulation of basophils. Therefore, it was postulated that the stainable NS substance might be the neurohumor stimulating the release of anterior-pituitary hormone.
