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Development of the adrenal medullary cells in rats with reference to synaptogenesis
Insights
This study reveals that rat fetal adrenal medullae develop synapses by 15.5 days of gestation. Insulin administration induces granular discharge via reverse pinocytosis in 21.5-day-old fetuses.
Area of Science:
- Developmental biology
- Neuroendocrinology
- Cell biology
Background:
- The adrenal medulla is crucial for stress response, producing catecholamines.
- Understanding its prenatal development is key to comprehending its function.
- Early differentiation and functional maturation remain areas of active research.
Purpose of the Study:
- To investigate the electron microscopic development of rat adrenal medullae during gestation.
- To identify the emergence of synaptic structures and granular content.
- To examine the effect of insulin on granular discharge in fetal adrenal medullae.
Main Methods:
- Electron microscopy was used to examine rat adrenal medullae from day 13.5 of gestation.
- Fetal rats received intraperitoneal insulin injections at specific gestational ages.
- Ultrastructural analysis focused on synaptic formation, granule morphology, and exocytosis.
Main Results:
- Synapses first appeared on medullary cells by 15.5 days of gestation and increased with age.
- Membrane-limited granules were observed from 13.5 days, with varied content and distribution.
- Cellular differentiation into specific catecholamine-producing cells was not discernible prenatally.
- Insulin administration induced granular discharge via reverse pinocytosis in 21.5-day-old fetuses.
Conclusions:
- Rat adrenal medullae exhibit progressive structural development during late gestation.
- Synaptogenesis and granule formation precede the ability for insulin-induced catecholamine release.
- The prenatal adrenal medulla shows potential for regulated secretion, demonstrated by insulin's effect.
Abstract:
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.