5-HYDROXYTRYPTAMINE IN HYPOTHALAMONEUROHYPOPHYSEAL SYSTEM AFTER ISCHEMIA - AN ULTRASTRUCTURAL IMMUNOGOLD STUDY ON THE RAT

We have examined the significance of serotonergic system in the regula tion of hypothalamo-neurohypophysial system after ischemia. Stimulator y effect of ischemia on the 5-HT system was observed. Recently, 5-HT-l ike immunoreactivity had been demonstrated in presynaptic terminals ma king synaptic contacts with a few neurosecretory neurons of paraventri cular nucleus (PV). A marked and rapid change in the level of this neu rotransmitter after ischemia was observed. This finding suggests that 5-HT plays a role in the neuroendocrine cell regulation of some specia l neurons (containing probably CRF) and also acts as a neuromodulator to control the secretion of anterior pituitary hormone through the hyp ophysial portal system. 5-HT-like immunoreactive axon terminals were n ot found to make synaptic contacts with the neurons of nucleus supraop tic and with the majority of neurons of PV. Neurohypophysis was immuno negative, too. These results indicate that serotonin does not directly control the synthesis and the release of the neurohypophysial hormone . The role of serotonine toxicity after ischemia is discussed.