Immunocytochemical and ultrastructural evidence of adrenal chromaffin cell subtypes in sea bass Dicentrarchus labrax (L.).

Histology demonstrated chromaffin cells in the head kidney and opisthonephros of the sea bass. Immunohistochemistry showed the catecholamine-synthesizing enzymes tyrosine hydroxylase and dopamine b-hydroxylase in these cells. Phenylethanolamine N-methyltransferase was detected in a fraction of the chromaffin cells in the head kidney (59%) and in the opisthonephros (54%). Distinct noradrenaline- and adrenaline-synthesizing cells are therefore suggested. Ultrastructural analysis confirmed the existence of two main chromaffin cell types, distinguished by different types of the secretory granules. Cells that contain vesicles with a round, electron-dense core were interpreted as noradrenaline cells, while cells with electron-lucent vesicles were identified as adrenaline cells. The ultrastructure of these chromaffin cell subtypes does not differ in the head kidney and opisthonephros. A minor population of chromaffin cells was identified, which typically show smaller vesicles with an electron-dense core. This population may account for a limited number of not fully differentiated chromaffin cells.