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The myth of nitric oxide in central cardiovascular control by the nucleus tractus solitarii

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      Considerable evidence suggests that nitroxidergic mechanisms in the nucleus tractus solitarii (NTS) participate in cardiovascular reflex control. Much of that evidence, being based on responses to nitric oxide precursors or inhibitors of nitric oxide synthesis, has been indirect and circumstantial. We sought to directly determine cardiovascular responses to nitric oxide donors microinjected into the NTS and to determine if traditional receptor mechanisms might account for responses to certain of these donors in the central nervous system. Anesthetized adult Sprague Dawley rats that were instrumented for recording arterial pressure and heart rate were used in the physiological studies. Microinjection of nitric oxide itself into the NTS did not produce any cardiovascular responses and injection of sodium nitroprusside elicited minimal depressor responses. The S-nitrosothiols, S-nitrosoglutathione (GSNO), S-nitrosoacetylpenicillamine (SNAP), and S-nitroso-D-cysteine (D-SNC) produced no significant cardiovascular responses while injection of S-nitroso-L-cysteine (L-SNC) elicited brisk, dose-dependent depressor and bradycardic responses. In contrast, injection of glyceryl trinitrate elicited minimal pressor responses without associated changes in heart rate. It is unlikely that the responses to L-SNC were dependent on release of nitric oxide in that 1) the responses were not affected by injection of oxyhemoglobin or an inhibitor of nitric oxide synthesis prior to injection of L-SNC and 2) L- and D-SNC released identical amounts of nitric oxide when exposed to brain tissue homogenates. Although GSNO did not independently affect blood pressure, its injection attenuated responses to subsequent injection of L-SNC. Furthermore, radioligand binding studies suggested that in rat brain synaptosomes there is a saturable binding site for GSNO that is displaced from that site by L-SNC. The studies suggest that S-nitrosocysteine, not nitric oxide, may be an interneuronal messenger for cardiovascular neurons in the NTS

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        A novel neuronal messenger molecule in brain: the free radical, nitric oxide.

        Understanding of the organization and function of a newly identified neuronal messenger molecule, nitric oxide, has progressed rapidly. Nitric oxide synthase has been purified and molecularly cloned from brain. Its localization is exclusively neuronal and endothelial. The catalytic activity of nitric oxide synthase accounts for the NADPH diaphorase staining of neurons that are uniquely resistant to toxic insults and neurodegenerative disorders. Nitric oxide has diverse functions. In platelets it inhibits their aggregation, in macrophages it mediates cytotoxicity, and in blood vessels it acts as a vasodilator. In the nervous system nitric oxide may be the retrograde transmitter in long-term potentiation. It is the "neurotransmitter" of cerebral vasodilator nerves and the inhibitory "neurotransmitter" of the motor neurons of the intestines. Nitric oxide in situations of excessive production may function as a neurotoxin, suggesting a role for nitric oxide in neurodegenerative disorders.
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          Effect of nitric oxide production on the redox modulatory site of the NMDA receptor-channel complex.

          Nitric oxide (NO) is an important messenger both systemically and in the CNS. In digital Ca2+ imaging and patch-clamp experiments, clinically available nitroso compounds that generate NO are shown to inhibit responses mediated by the NMDA subtype of the glutamate receptor on rat cortical neurons in vitro. A mechanism of action for this effect was investigated by using the specific NO-generating agent S-nitrosocysteine. We propose that free sulfhydryl groups on the NMDA receptor-channel complex react to form one or more S-nitrosothiols in the presence of NO. If vicinal thiol groups react in this manner, they can form a disulfide bond(s), which is thought to constitute the redox modulatory site of the receptor, resulting in a relatively persistent blockade of NMDA responses. These reactions with NO can afford protection from NMDA receptor-mediated neurotoxicity. Our results demonstrate a new pathway for NO regulation of physiological function that is not via cGMP, but instead involves reactions with membrane-bound thiol groups on the NMDA receptor-channel complex.

            Author and article information

            Role: ND
            Brazilian Journal of Medical and Biological Research
            Braz J Med Biol Res
            Associação Brasileira de Divulgação Científica (Ribeirão Preto )
            April 1997
            : 30
            : 4
            : 515-520
            S0100-879X1997000400013 10.1590/S0100-879X1997000400013


            Product Information: SciELO Brazil


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