Functional morphologic study on NO (nitric oxide) -containing neurons.

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Nitric oxide (NO) , agasous radical molecule which affects the environment, has been discovered to be synthesized in certain living cells of vertebrates. This molecule has mutifunctional physiological activities in various organs of the body. The nervous system, in particular, is under the influence of NO with various roles on, for example, neurotransmission, synaptic plasticity, neurotoxicity and neuronal aging. The multiplicity of NO appears to be dynamically regulated by its synthesizing enzyme, nitric oxide-synthase (NOS). In addition to the constitutive NOS (cNOS) which is present in the normal brain, inducible NOS (iNOS) has been known to be expressed in response to injury or inflammation. It is therefore evident that the brain function is associated with the production of NO synthesized by both types of NOS.In the present study, we studeid the ontogenetic aspect of NO-containing neurons in developing brains of the rat by using immunohistochemical and NADPH-diaphorase histochemical methods. Two prominent NO-containing neuronal cell groups were found, one in the pons and the other in the hypothalamus. As embryos grow, NO-containing neurons were distributed widely throughout various brain regions. The details of such patterns of distribution of No-neurons were mapped at embryonic day 15 and day 19.The origin and the pattern of projection of NO-containing nerve fibers from the pterygopalatine ganglion to brain arteries were also examined by the NADPH-diaphorase histochemical method combined with axonal tracing methods. The result provided the neuroanatomical basis for differential pharmacologic and physiologic activities of NO in different parts of brain vessels.In addition, these data were presented in an international symposium organized by the head investigator on July, 1995 at Otsu, as a satellite symposium of the meeting of The International Brain Research Organization.