[Preoptic-hypophyseal neurosecretory system of the Baikal salmon, Coregonus autumnalis migratorius, during the prespawning period].

It has been shown that functional condition of the preoptic-hypophyseal neurosecretory system (PHNS) in the fish studied is associated with the activity of population. During early spring, when the fish are not yet completely active after winter, the PHNS is characterized by a low level of activity (accumulation of the neurosecretory substance and neurohypophysis, as well as moderate extrusion of the neurosecretory material along the axons beyond the preoptic nucleus). In July, some activation of synthesis and extrusion of the neurosecretory substance from cells of the preoptic nucleus and significant accumulation of the substance in the neurohypophysis are observed. In August and especially in September, during spawning migration, the rate of extrusion of the neurosecret from the preoptic nucleus and the extrusion of the neurohormones from neurohypophysis into the blood flow significantly increase. Neurosecretory cells of the preoptic nucleus remain highly active. During the same period, infiltration of the preoptic nucleus by leucocytes and neuronal hydroencephalokrynia are observed. During spawning migration, females (in contrast to males) exhibit more, significant decrease in the bulk of neurosecretory substance in the neurohypophysis, which is presumably associated with higher energy expenditures for the completion of ovogenesis.