ABSTRACT
In invertebrates and lower vertebrates, the adrenal medulla is not a discrete organ but rather is represented by dispersed chromaffin cells. Ghosh reviewed the gross and light-microscopic morphology of the avian adrenal glands. A detailed histochemical and immunohistochemical study of the adrenal gland of the bullfrog was performed by Kuramoto. Using a combination of techniques, he identified three types of chromaffin cells in the adrenal gland: cells with epinephrine and serotonin; cells with norepinephrine and serotonin; and cells with epinephrine, enkephalin, and serotonin. The development of adrenal medulla in the opossum was described at the light and electron microscopic levels. Rosenheck and Plattner characterized vesicles made from plasma membranes of adrenal chromaffin cells and examined their interaction with chromaffin vesicles. Morphologic signs of increasing activity were observed in all layers of the cortex and the medulla. Bezrukov and Shaposhnikov studied the ultrastructure of the adrenal glands of mature and old rats after electrical stimulation of the hypothalamic ventral medial nuclei.
