Degeneration and possible renewal processes related to the interrenal cells in the head kidney of the stickleback Gasterosteus aculeatus

The ultrastructural aspect of degeneration and recovery processes involving the steroidogenic interrenal cells of the stickleback was studied. Together with the adrenergic cells, the interrenals constitute the adrenal homolog in teleosts. From our study it appears that a process of massive cell death may lead to temporary disappearance of the gland. Moreover, our E.M. observations suggest two main ways, each leading to morphological dedifferentiation of the cells, no longer recognizable as interrenals: the first way involves elimination of organelles and recovery of the nucleus surrounded by a thin rim of cytoplasm; the second involves fragmentation of the cytoplasm by other pyknotic star-shaped interrenals, together with autophagocytosis processes. Our E.M. observations also suggest that the subsequent reconstitution of the tissue can occur in two ways. In the first, the interrenals appear mainly to differentiate from mesenchymatic-like electron-light cells, while in the second, the new interrenals appear mainly raising from some macrophagic electron-dense cells. Some data obtained with Mallory's trichrome staining of histological sections, and localization of the enzyme 3P hydroxysteroid dehydrogenase in thin sections, support the above-mentioned results. A hypothesis is advanced on the origin of the electron-dense differentiating interrenals, and a possible role of dedifferentiated cells in restoration of the interrenal gland is also discussed. (C) 2007 Elsevier Ltd. All rights reserved.