The adrenal medulla is an important part of the sympathoadrenal system and plays a key role in its adaptation to stress. The rat adrenal gland is the object of many experimental studies, therefore, versatile fundamental knowledge about it, including the features of its morphology, is in great demand. At the same time, it is impossible to make a complete picture of the structure of an organ without understanding the principles of its spatial [volumetric, three-dimensional (3D)] organization, especially at the tissue level.

The main components of the adrenal medulla are chromaffin tissue, connective tissue stroma, blood vessels and nerve elements. In turn, it is generally accepted that the rat chromaffin tissue is formed by two main subpopulations of chromaffinocytes, adrenaline-storing cells (A-cells) and noradrenaline-storing cells (NA-cells). It is possible that a third type of chromaffin cells: small granule chromaffin cells (SGC-cells), is also present in the rat adrenal medulla. However, there is currently no consensus on whether these cells are chromaffinocytes, an intermediate form between neurons and chromaffinocytes, or variant of SIF (small intensely fluorescent) ganglion cells (Coupland and Tomlinson, 1989, Coupland et al., 1977, Coupland, 1989, Kobayashi, 1977, Tischler and DeLellis, 1988, Tomlinson et al., 1987).