Ultrastructure of neurosecretory cells at different stages of differentiation in the preoptic nucleus of immature sterlet.

Ultrastructure of neurosecretory cells of the preoptic nucleus in immature sterlet (Acipenser ruthenus L.) was studies for the first time. The dorsal zone of the preoptic nucleus houses light, dark, and pycnomorphic neurosecretory cells, which contain varying numbers of elementary secretory granules measuring 1995 plus or minus 32 A in diameter. Light cells containing numerous secretory granules with a diameter of 1707 plus or minus 27 A are predominant in the middle zone. Pycnomorphic cells are absent in this zone. The ventral zone contains only poorly differentiated cells with solitary elementary granules measuring 1100-1300 A in diameter. The neurosecretory cells also differ with respect to the number and structural characteristics of their organoids. Thus, neurosecretory cells in the preoptic nucleus are found in different morphofunctional states, a circumstance that reflects the sequence of their development in ontogenesis and different phases of the secretory cycle.