The sequence of morphological differentiation of Müller cells in the chick retina was investigated in relation to the differentiation of the retinal neurons using the Golgi method. From the beginning of differentiation, the Müller cell develops spurs and lateral processes. Some of these glial processes become transformed into accessory prolongations of the Müller cell. From the 17th or 18th day of incubation, the morphology of the Müller cells is similar to that of the adult retina. On the basis of their inner prolongation, two types of Müller cells were identified. The first type, with diffuse and abundant descending processes, is identical to that described classically. The second type is a cell characterized by sparse and scanty inner ramifications. This report also describes electron microscopic observations of Müller cells and their enwrapping relationship with the axons of the optic nerve fiber layer.

The adrenal gland plays a pivotal role in the stress response since this response involves the hypothalamic-pituitary-adrenal axis (HPAA) and the sympatho-adrenomedullary system (SAMS) as its two principal components. An important relation between the immune system and the other stress response systems is also centered on the adrenal gland. It is well known that the cortex secretes glucocorticoids while the medulla secretes epinephrine, two of the major effects of the stress response. Some other aspects, however, also deserve special consideration: The paracrine effects of the cortical secretion on the medullary cells through the special irrigation system of the gland and reciprocally the influence of the medulla upon the cortex, either by direct close contact or by local innervation. The influence of vascular events also needs to be considered as well as the existence of some local hormonal axis such as those resulting from the local production of renin or CRH in adrenal cells. Some other cells such as mast cells, macrophages and endothelial cells seem to play a role in the regulation of the adrenal cortex and hence in the tuning of the stress response. Stressors stimulate the release of CRH from the hypothalamic paraventricular nucleus inducing the secretion of ACTH from the pituitary and that of corticosteroids from the adrenal cortex. Through the activation of the sympathetic system the adrenal can be stimulated even before adequate levels of ACTH are reached. In conditions of chronic stress the adrenal cortex undergoes an adaptation that allows the hypersecretion of glucocorticoids to occur even without the increment of ACTH.

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A morphological and autoradiographic study was made of the adrenal gland of adult male rats after autotransplantation. The simple technique involved placement of pieces of the adrenal gland in a dorsal plane between the skin and muscle. Animals for morphological studies were sacrificed at 2, 3, 4, 7, 15, 30, 90, and 180 days after autotransplantation. Those for autoradiographic studies were sacrificed at 2, 3, 7, and 15 days after autotransplantation, with 3H-thymidine being administered intraperitoneally 2 h before sacrifice. Sham-operated animals were used as controls. The majority of glandular adrenal cells suffered necrosis in the first days (2 and 3) after autotransplantation. Up until 15 days and after revascularization, morphological features of the cells were compatible with protein synthesis exhibiting a developed RER, scarce SER, and mitochondria with tubular and lamellar cristae. These data may correspond to a proliferative phase of glandular cells. At day 15, cells showed morphological signs of steroidogenic activity (mitochondria with vesicular cristae, increase of SER), and at day 30, an increased number of microvilli were seen. Between 30 and 90 days zonation of the adrenal was evident with glomerulosa, fasciculata, and reticular zones readily apparent. The quantitative analysis showed a significant increase of the volumetric density of mitochondria and microvilli between the days 7 and 30. Autoradiographic studies showed an intense labelling of fibroblast-like cells at days 2 and 3 and of glandular cells at days 7 and 15, which was confirmed by the quantitative studies. Corticosterone in autotransplanted animals decreased during the first 15 days, but after 30 days the values were similar to controls. The model reported here seems to be good for study of the regeneration of the adrenal gland and can be a simple, useful, and reproducible method for adrenal transplantation.