[Electron microscopic characteristics of neurosecretory cells in the preoptic nucleus of sturgeon fry].

In the sturgeon fry nucleus preopticus (Npo), light and weakly differentiated neurosecretory cells (NSC) as well as differentiated (i-cells) were revealed. Among these types of cells, there were the transitional forms. No "picnomorphic" cells were found in any Npo zone. NSC contained different amounts of elementary secretory granules 110-270 nm in diameter. The distribution of organelles was evaluated statistically, their number increasing from i-cells to the NSC. These data suggest that growth and differentiation of the NSC take place during this stage of ontogeny. The results are discussed in terms of specific functioning and maturity of the NSC.