Secretory surface phenomena in freeze-etched preparations of the adenohypophysial cells and neurosecretory fibers

The freeze-fractured median eminence. II. Developmental changes in the neurohemal contact zone of the median eminence of the rat

The neurohemal contact area of the median eminence was examined in adult, young, neonatal, and fetal rats in freeze-fracture preparations. While no specializations of the membranes of axonic terminals abutting on the perivascular space was observed, adjacent areas of the same membranes are rich in signs of hormone release. Signs of exocytosis are defined in the manner of Theodosis et al. (1978). Exocytotic pits with a single dense granule as a core are identified on P-faces along with mounds on corresponding E faces. These features appear near the time of birth, are especially numerous at 3 days, 3 weeks, and 5 weeks, and continue in lesser numbers into adulthood. Even more numerous and appearing even earlier, by the last day of fetal life, were P-face clusters of large particles usually in a pit, and pits without particles. These fall into 2 significantly different categories distinguished by the size of the pit. E face counterparts are large and small protuberances, respectively. Fenestrae of adult size and distribution are observed along the endothelium of portal vessels from the 20th day of fetal life on. Their frequency correlates well with other structural manifestations of a median eminence ready for the onset of functional activity at about the time of birth (Monroe and Paull 1974).

Secretory phenomenon of the adenohypophyseal cells viewed with the scanning electron microscope

Exocytosis from rat adenohypophyseal cells, probably somatotrophic, was studied in the scanning electron microscope after freeze fracturation of the glands. This technique permitted the distinguishing of a clearly delimited exoplasm interrupted by the passage of the secretory granules. It was postulated that the exoplasm could be involved in the control of the release of secretory granules in the endocrine cells studied. At the basal cell surface a simultaneous discharge of several secretory granules has been detected.

Development of the adrenal medullary cells in rats with reference to synaptogenesis

The adrenal medullae of rats were studied electron microscopically from day 13.5 of gestation. Synapses with thickening of pre-and post-synaptic membranes were first evidenced on the medullary cells of 15.5-day-old fetuses. They increased gradually in number with advancing age. In the medullary cells, a few membrane-limited granules were recognized on day 13.5 of gestation, and thereafter they increased in number. The appearance of the granules was not uniform; some of the granular contents consisted of fine or coarse particles and others contained homogeneous material of varying electron-densities. The population of these granules in the cytoplasm was different from cell to cell. Thus, the discrimination of cell types (NA-and A-cells) was not possible in the prenatal period. Granular discharge of the cells was totally absent in the normal untreated fetuses. However upon the intraperitoneal administration of insulin to the fetus on day 16.5, 18.5, or 21.5 of gestation, discharge by reverse pinocytosis was first evidenced in the medullary cells of the 21.5-day-old fetus.