Variations of nNOS and its mRNA in the neurons of the hypothalamic supraoptic nucleus in response to stress by immobilization

[EN]Using rats subjected to immobilization stress, the aim of the present study was to investigate the expression of neuronal nitric oxide synthase and of its mRNA in the magnocellular neurons of the supraoptic nucleus of the hypothalamus, which does not have parvocellular neurons or direct neurohaemal connections with the anterior lobe of the hypophysis. nNOS expression was studied with immunohistochemistry using sheep antinNOS serum, and the intraneural detection of nNOS mRNA was accomplished using a nonisotopic in situ hybridization technique, employing a specific biotinylated probe. The acute stress elicited by restraint induced an increase in the overall size of the supraoptic nucleus, together with an increase in the number of magnocellular neurons expressing nNOS immunoreaction. The optical densitometry values of the nNOS immunoreaction, the nuclear areas of the immunoreactive neurons, and the density of neurons showing nNOS mRNA hybrids were higher in the supraoptic nucleus of the stress-treated animals than in the controls, suggesting that nitric oxide of nNOS origin plays an active role in the magnocellular neurons of the hypophyseal-hypothalamic system and the involvement of this system in the stress axis.