Abstract
Effects of exposure to sea water on the hormone content and on the fine structure of the hypothalamo-neurohypophysial system of the rainbow trout ( Salmo irideus) were investigated. After 2 hours in sea water the arginine-vasotocin content of the pituitary fell by 50%; the ichthyotocin content did not change appreciably. The neurohypophysial hormone content in the glands of the fish after 4 and 8 hours in sea water was similar to that of the fresh water controls. Depletion of the osmiophilic material from the elementary granules of some nerve swellings was seen in the neurohypophysis of trout kept in sea water for 2 hours. An increased abundance of elementary granules in the preoptic neurones of the same fish was evident. The electron microscopic appearance of the neurohypophysis of trout kept in sea water for 4–8 hours did not differ from the fresh-water controls. In the preoptic neurones of the fish exposed to sea water for 4–8 hours the number and distribution of elementary granules was comparable to that of the control trout. However, in common with the “2-hour fish,” changes were seen in the perikarya of the preoptic neurones of all sea-water-treated fish, namely, diminished number of mitochondria, fewer large granules in the Golgi area, and an increased vacuolation of the cytoplasm. Elementary granules of two size ranges (one 1320–2370 Å, mean diameter 1850 ± 69 Å; the other 1180–1710 Å, mean diameter 1380 ± 49 Å) and multilamellar bodies were seen in nerve fiber swellings of the trout neurohypophysis. The physiological function of the hypothalamo-neurohypophysial system in osmoregulation of teleosts is discussed.
Published Version
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