[Plastisity of secreteory neurons of hypothalamic supraoptic and paraventricular nuclei during light exposure].

Changes of secreteory neurons of hypothalamic supraoptic (SON) and paraventricular nuclei (PVN) were analyzed using light and electron microscopy in 100 adult male rats from the first minutes up to 180 days after their round-the-clock 48 hours-long exposure to bright light. At the early stages after the exposure, SON and PVN cellular formula was changed in favor of functionally active neurons containing few secretory granules, large nucleus and nucleoli, low RNA content, sparse complexes of rough endoplasmic reticulum, vacuoles and lysosomes in their perikarya. After 24 hours in both SON and PVN and after 10 days in SON the number of cells accumulating secretion was greater than that in control group. Normalization of the cellular formula and of the structural organization of protein-synthesis apparatus in PVN secretory neurons took place at days 10-30, while those ones in SON--at days 30-180. The results obtained suggest that the range of plasticity in PVN neurons in animals exposed to continuous bright light is larger than that in SON neurons.