The renin-angiotensin system (RAS) is critical for the control of blood pressure (BP) and salt balance in mammals. Studies reveal that local RAS are present in the rat brain and renin is the first effector of the brain RAS for generating angiotensin II (Ang II) which exerts diverse physiological actions in both peripheral and central nervous system. The existence of renin within the brain has now been demonstrated by numerous studies. Previous studies suggest that renin may go through angiotensin-dependent and independent pathway to influence vascular tone, by Ang II type 1 receptor (AT1R) and renin specific (pro)renin receptor (PRR), respectively. Studies also indicate that AT1R and PRR are highly expressed in the nucleus tractus solitarii (NTS), which is important for central feedback regulation of BP. Further studies have shown that Ang II contributes to the release of NO, which plays an important role in cardiovascular regulation in the NTS. These results indicate that renin plays cardiovascular modulatory role in the NTS. However, the mechanisms how renin modulate cardiovascular functions in the NTS remained unclear. In the present study, I investigated the molecular mechanisms of renin-induced cardiovascular effects in the NTS. Unilateral microinjection of renin into the NTS of WKY rats produced prominent depressor and bradycardic effects. Pretreatment with a non-selective NOS inhibitor L-NAME, eNOS specific inhibitor L-NIO, Akt inhibitor IV, and PI3K inhibitor LY294002 significantly attenuated the cardiovascular response evoked by renin, whereas nNOS specific inhibitor Vinyl-L-NIO and MEK inhibitor PD98059 did not cause significant changes. Western blot studies showed renin increased eNOSS1177 and AktS473 phosphorylation instead of nNOSS1416 and ERK1/2T202/Y204 phosphorylation, and pretreatment with LY294002 blocked renin-induced eNOSS1177 and AktS473 phosphorylation. These results indicated that renin might go through PI3K-Akt-eNOS pathway to increase eNOS activity and ultimately result in NO release. The cardiovascular effects of renin were also attenuated by renin specific inhibitor aliskiren, angiotensin converting enzyme inhibitor lisinopril, AT1R antagonist losartan, and intracellular Ca2+ chelator, BAPTA-AM instead of G protein £]£^ subunit inhibitor gallein, PLC inhibitor U73122, calmodulin inhibitor (W-7) and (pro)renin receptor blocker, handle region peptide. These results indicated that renin mainly through AT1R to regulate BP. Therefore, my results indicated that the modulation of cardiovascular effects of renin in the NTS involves AT1R-PI3K-Akt pathway to activate eNOS activation.

Autophagy is an important cellular process in maintenance of protein homeostasis. Emerging evidence indicates differential roles of autophagy in cellular function under different pathophysiologic conditions. In some circumstance, autophagy results in cell survival, wheras in other situations it results in cell death. Endotoxin affects neurons in the nucleus tractus solitarii (NTS), baroreceptor afferent terminal site in the brain stem, resulting in cardiovascular depression. The aim of this study was to examine whether modulation of autophagic activity in NTS and other brain regions subserving cardiovascular regulation are associated with cardiovascular depression during experimental endotoxemia. Adult male Sprague-Dawley rats received continuously intraperitoneal infusion via osmotic minipump of lipopolysaccharide (LPS, 2.5 mg/kg/day) or normal saline (NS). Body weight (BW) and systolic blood pressure (SBP) were recorded in animals on days 1, 2, 3, 5, 7, 10, and 14 after LPS treatment. Western bolotting was used to assess the expression of autophagic activity marker, microtubule-associated protein 1 light chain 3 (LC3). Rapamycin (0.55 mg/Kg/day), chemical reported to activate autophagy, was infused continuously into the lateral ventricle of the endotoxemic rats for 7 days via osmotic minipump. Both BW and SBP of rats were decreased in the initial 5 days, followed by a gradual return to baseline after LPS treatment. There was a trend in the decrease in autophagic activity (using the ratio of LC3-¢º/LC3-I as an experimental index) at NTS. However, there is no apparent association between the change in autophagic activity at NTS and the LPS-induced cardiovascular depression. In addition, there was no obvious change in the autophagic activity at RVLM, hypothalamus and hippocampus. Intracranial infusion of rapamycin, a mTOR inhibitor that maintains cellular autophagic activity, resulted in a further enhancement of cardiovascular depression induced by LPS. These results suggest that continuously intraperitoneal infusion via osmotic minipump of LPS result in decreases of body weight and systolic blood pressure. However, the present study provides no direct evidence to support for a cause-and-effect role of autophage at NTS, RVLM, hypothalamus as well as hippocampus in the LPS-induced cardiovascular depression during experimental endotoxemia.

Insulin resistance was thought as the major etiology of hypertension of the metabolic syndrome. Both human and animal studies revealed sympathetic overactivity were present in the metabolic syndrome. Nowadays, most of the studies that examined the etiologies of hypertension of metabolic syndrome were focused on the pathophysiologic effects of insulin resistance on the peripheral vessels. However, there was no study ever examined the insulin resistance in cardiovascular regulatory centers of central nervous system or the pathogenesis of sympathetic overactivity in metabolic syndrome. Our previous study demonstrated that insulin plays a cardiovascular regulatory role in the nucleus tractus solitarii (NTS), one of the cardiovascular regulatory centers in the brain stem. We also demonstrated that the cardiovascular regulatory effects of insulin in the NTS were accomplished through activating PI3K-PKB/Akt-NO signaling pathways. Recently, increases in oxidative stress could raise the incidence rate of diabetes mellitus and cardiovascular diseases had been reported. Besides, it has been reported that there were marked increases in reactive oxidative species (ROS) in various hypertension animal models. It was also reported that elevation of ROS in various tissues may activate the mitogen-activated protein kinase (MAPK) superfamily. Activated MAPKs may phosphorylate insulin receptor substrate 1 (IRS1) on the serine 307 residue. It has been reported that IRS1S307 phosphorylation would inhibit normal insulin signal transduction. The aims of this thesis were to investigate whether the neuronal cells in the NTS would develop insulin resistance in the metabolic syndrome rats, whether development of insulin resistance in the NTS cause hypertension in the metabolic syndrome rats, which signaling molecule in insulin signaling pathway is the key molecule that cause insulin resistance in the NTS, and what the pathogenesis of insulin resistance is in the NTS of metabolic syndrome rats. In the pioneer study, Wistar-Kyoto (WKY) rats were fed with 10% fructose water as their drinking water for 8 weeks. Another group of fructose-fed WKY rats were fed with insulin sensitizer, rosiglitazone, since the 5th week. Blood pressure was measured by tail vein sphygmomanometer every week and venous blood were draw to measure blood sugar and insulin level every other week. Thereafter, all the rats enrolled in this study were fed with 10% fructose water with/without rosiglitazone for 2-3 weeks. My results demonstrated the blood pressure of fructose-fed WKY rats was significantly elevated after 2-week fructose feeding. But at the same time, HOMA-IR did not elevated, which indicated the insulin resistance in the peripheral did not develop yet. Interestingly, at the same time, endogenous insulin in the NTS was significantly elevated in the fructose-fed group. The cardiovascular responses of insulin in the NTS were diminished in the fructose-fed group. While in the rosiglitazone-treated group, the blood pressure and endogenous insulin in the NTS were decreased the baseline level. The cardiovascular responses of insulin in the NTS were restored in the rosiglitazone-treated group. These results indicated insulin resistance do develop in the NTS of fructose-fed rats, and the neuronal insulin resistance in the NTS can induce hypertension. The immunoblotting results demonstrated the phosphorylation of IRS1S307 was significantly elevated in the fructose-fed rats. While the phosphorylation of its downstream molecules, such as AktS473 and eNOSS1177, were significantly decreased as compared with the control group. In the NTS of rosiglitazone-treated group, the phosphorylation of IRS1S307 was decreased, and the phosphorylation of AktS473 and eNOSS1177 were restored. These results indicated that the underline pathogenesis of insulin resistance in the NTS was phosphorylation on the inhibitory serine residue of IRS1, which interfered with the normal insulin signal transduction in the NTS. Increases in ROS in the NTS of fructose-fed rats were demonstrated in the DHE histostaining. Phosphorylation of p38MAPK in the NTS of fructose-fed rats was also detected by immunoblotting. In the NTS of Tempol-treated fructose-fed rats, the phosphorylation of p38MAPK reduced and the nitric oxide production elevated to the basal level. Blood pressure decreased significantly when p38MAPK inhibitor, SB203680, was microinjected into the NTS of fructose-fed rats. These results indicated the pathogenesis of insulin resistance in the NTS is increases in ROS in the NTS, which activate p38MAPK and then phosphorylate IRS1S307. In conclusion, the neuronal cells in the NTS may develop insulin resistance in fructose-fed rats, and the neuronal insulin resistance in the NTS contributes to the hypertension of metabolic syndrome. The mechanism of insulin resistance in the NTS is phosphorylation on the serine 307 residue of IRS1, which interfere with insulin signaling and subsequent NO production in the NTS. The pathogenesis of IRS1S307 phosphorylation is activated p38MAPK which in turn is activated by ROS in the NTS.

Carbon monoxide (CO) has been identified as an endogenous biological messenger in the brain. Heme oxygenase (HO) catalyzes the metabolism of heme to CO and biliverdin. CO has been shown to act as a neurotransmitter and neuronal messenger in the brain. We reported recently that CO was involved in central cardiovascular regulation, modulated the baroreflex, may affect glutamatergic neurotransmission, and metabotropic glutamate receptors (mGluRs) may be coupled to the activation of HO in the nucleus tractus solitarii (NTS) of rats. We also reported previously that adenosine can increase the release of glutamate in the NTS. The present study was designed to investigate the possible interaction of CO, adenosine, and mGluRs groups in the NTS. Male Sprague-Dawley rats were anesthetized with urethane, and blood pressure were monitored intra-arterially. Unilateral microinjection of ascending doses of hemin (0.01 to 3.3 nmol), a heme molecule cleaved by HO to yield CO, produced decreases in blood pressure and heart rate dose-dependently. In addition, similar cardiovascular effects were observed in adenosine (2.3 nmol) and several agonists for mGluRs groups such as DHPG (group ¢¹) (0.03 nmol), APDC (group ¢º) (0.3 nmol)and L-AP4 (group ¢») (0.3 nmol). These cardiovascular effects of hemin were attenuatd by prior administration of the adenosine receptor antagonist DPSPX (0.92 nmol). Similarly, pre-treatment of HO inhibitor ZnPP¢Á or ZnDPBG (1 nmol) also attenuated the depressor and bradycadic effects of adenosine. Among the mGluRs agonists, prior administration of ZnPP¢Á (1 nmol), an inhibitor of HO activity, significantly attenuated the cardiovascular effects of APDC and L-AP4, and failed to prevent the cardiovascular responses of DHPG. These results indicated an interaction between CO and adenosine, and group ¢º and ¢» mGluRs may be coupled to the activation of HO in central cardiovascular regulation.

Insulin resistance plays an intricate role in the development of cardiovascular diseases, hypertension is associated with insulin-resistant states such as diabetes and obesity. However, the underlying mechanism to explain the associations between hypertension and insulin resistance is unknown. The insulin exerts various biological effects in different type of cells. Clinical studies have reported that insulin has been shown to stimulate the protein kinase Akt via activation of PI3K in endothelial cells. Furthermore, insulin stimulated production of nitric oxide (NO) is inhibited by wortmannin in human umbilical vein endothelial cells (HUVECs). We also reported previously that NO contributes to the regulation of blood pressure in central nervous system. The aim of this study was to elucidate the potential mechanisms linking hypertension with insulin resistance and whether insulin signaling may involved in cardiovascular regulation in rat NTS neurons, we investigated the cardiovascular effects of insulin in the nucleus tractus solitarii (NTS) of urethane-anesthetized male spontaneous hypertensive rat (SHR) and normotensive Wistar-kyoto rats (WKY). Unilateral microinjection of insulin (100 IU/ml) into the NTS produced prominent depressor and bradycardic effects in 8/16 week-old WKY. However, no significant cardiovascular effects were found in adult SHR (16 week-old) after insulin injection. Furthermore, young SHR (8 week-old) with normal blood pressure showed depressor and bradycardic effects after insulin injection. Pretreatment with PI3K inhibitor LY294002 and NO synthase inhibitor L-NAME into the NTS attenuated the cardiovascular response evoked by insulin in WKY and young SHR but not in adult SHR. Furthermore, insulin induced Akt phosphorylation in-situ in WKY and SHR rats. Thus, these results indicated that insulin-PI3K-Akt-NOS sensitive mechanisms were involved in WKY and young SHR (normotensive) but not in adult SHR (hypertensive). The results also suggested the possible defective insulin signaling may resulted in the development of hypertension in adult SHR.

The caudal nucleus tractus solitarius (cNTS) is the key recipient of the primary afferents from visceral sensory neurons and also an important site that processes and integrates gastrointestinal, cardiovascular and respiratory functions. Glutamate and gamma-aminobutyric acid are the major neurotransmitters within the NTS, but studies have suggested that nicotinic acetylcholine receptors (nAChRs) and transient receptor potential (TRP) channels can modulate excitatory/inhibitory neurotransmission. I have designed studies to understand the role of nAChRs and TRP channels in the modulation of neurotransmission in the cNTS. In the first aim, experiments were designed to test the hypothesis that the cNTS contains function-specific subsets of neurons whose responsiveness to nicotine correlates with the target of their axonal projections. cNTS neurons send axonal projections to brain regions such as parabrachial nucleus (PBN), hypothalamic paraventricular nucleus (PVN), nucleus ambiguous (NA), dorsal motor nucleus of the vagus (DMV) and the caudal ventrolateral medulla (CVLM) and are involved in integrating autonomic and neuroendocrine functions. Presynaptic/postsynaptic modulation by nAChRs differ in the axonal projections of cNTS neurons, studying of which would provide better understanding of this complex integration. In vivo fluorescent tracing combined with in vitro slice patch-clamp electrophysiological recordings from anatomically identified caudal NTS neurons were used to study the expression and function of nAChRs (mainly á3â4 containing nAChRs) in the cNTS. Results from these studies demonstrate that presynaptic and postsynaptic responsiveness of caudal NTS neurons to nicotine correlates with the areas the neurons project to in the following order of prevalence: DMV>PVN>NA>CVLM>PBN (for presynaptic responses) and DMV>CVLM>PBN>NA>PVN (for postsynaptic responses). In the second aim, experiments were designed to test the hypothesis that nociceptive TRP channels TRPV1 (vanilloid) and TRPA1 (ankyrin) modulate synaptic transmission in the NTS. As a result of this modulation, the efferent functions that control autonomic and visceral functions will be regulated and account for the changes in autonomic neuropathy as patients with diabetes develop significant alterations in blood pressure and heart rate as well as silent myocardial ischemia as a result of blunted pain carrying ability. Results obtained from these studies demonstrated that TRPV1 and TRPA1 mRNA were detected in the dorsal root ganglion (DRG), but not in the NTS. Immunofluorescence studies revealed that TRPV1 and TRPA1 were expressed in the solitary tract central sensory terminals inputs to NTS but not in NTS neurons. This suggests that TRPV1 and TRPA1 are expressed only in solitary tract. Administration of capsaicin (TRPV1 agonist) and allyl isothiocyanate (AITC, TRPA1 agonist) both increased the frequency of s/mEPSCs without affecting spontaneous and miniature inhibitory postsynaptic currents (s/mIPSCs). Next, the modulation of TRPV1- and TRPA1-induced responses by utilizing a PKC activator (PDBu) was examined. Incubation of slices with PDBu synergistically increased the mEPSC frequency following capsaicin application suggesting an increased receptor affinity; however following application of AITC there was no significant change, suggesting that activation by covalent modification does not enhance binding affinity. Finally, the specificity of TRPV1 and TRPA1 effect on synaptic transmission by ablating TRPV1 and TRPA1were tested. There was no modulation of synaptic transmission in these animals, further confirming that capsaicin- and AITC-mediated modulation of synaptic transmission are specifically mediated by TRPV1 and TRPA1, respectively. Furthermore, animals with painful diabetic peripheral neuropthy exhibited enhanced synaptic activity at the NTS, suggesting a role in nociception and other visceral functions. In summary, nAChRs, TRPV1 and TRPA1 are expressed in the NTS and activation of which modulate excitatory synaptic transmission. The results obtained from these studies and their interpretation may provide a better understanding of the central mechanism of modulation on efferent functions from NTS that regulate cardiovascular, respiratory and gastrointestinal functions.

The 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) are unequivocally useful for lowering cholesterol levels in patients with dyslipidemias. In addition to cholesterol lowering properties, statins exert a number of pleiotropic, vascular-protective effects include improvement of endothelial function, increased nitric oxide (NO) bioavailability, antioxidant properties. Since endothelial dysfunction and reactive oxygen species (ROS) are important pathophysiological determinants of essential hypertension, these actions of statins raise the possibility that statin therapy may be useful for simultaneously clinical hypertension management. However, the signaling mechanisms of statins that improve hypertension remain unclear. Our previous study showed, in the NTS, insulin may decrease blood pressure and heart rates through PI3K-Akt-eNOS pathway, and NTS integrates convergent information from peripheral baroreceptors and central cardiovascular regulatory center. Statins also prevent the synthesis of other important isoprenoid intermediates of the cholesterol biosynthetic pathway, members of the Ras and Rac1 GTPase family are major substrates for posttranslational modification by isoprenylation and may be important targets for inhibition by statins. Statins could inhibit Rac1 isoprenylation and Rac1-mediated nicotinamide adenine dinucleotide phosphate oxidase activity attenuates reactive oxygen species production. The aim of this study was to investigate the possible signaling pathways involved in simvastatin-mediated blood pressure regulation in the nucleus tractus solitarii (NTS). Male 20-week-old spontaneously hypertensive rats (SHR) were divided into two groups: control group and intracerebroventricular injection with simvastatin group for three days. We found that systolic blood pressure measured with tail-cuff method of the simvastatin-treated rats decreased significantly, and the NO level in the NTS was significantly increased. In addition, we observed that simvastatin could lower the ROS level and increase Ras GTPase activity in the NTS. Immunoblotting and immunohistochemistry analysis further showed that simvastatin increased the phosphorylation ratio of ERK1/2, Akt, and endothelial nitric oxide synthase (eNOS) in the NTS. Taken together, these results suggest that eNOS signaling in the NTS may play an important role in simvastatin-induced blood pressure lowering effects. Keywords: statins, nucleus tractus solitarii, nitric oxide, oxidative stress, central cardiovascular regulatory, isoprenylation

Recent studies demonstrated that fructose intake can increase blood pressure in experimental animals. Oxidative stress has emerged as an important pathogenic factor in the development of hypertension. It has been reported that increased superoxide production in fructose-fed rat mediated through nicotinamide adenine dinucleotide phosphate NAD(P)H oxidase. Superoxide dismutase (SOD) is one of the most important enzymes against oxidative stress. However, the signaling mechanisms of fructose which induce hypertension through superoxide remain unclear. Nucleus tractus solitarii (NTS) is the integrative center for baroreflex. Our previous study had revealed that accumulation of superoxide in the NTS can induce hypertension. As an important antioxidant in red wine, resveratrol is likely to contribute to the potential of red wine to prevent cardiovascular disease. At pharmacological doses, resveratrol increases vascular nitric oxide (NO) levels and improves NO bioavailability in animal models. Resveratrol is a potent activator of AMPK in neuronal cell lines, primary neurons, and the brain. Recent reports have indicated that metformin targets AMPK which activates nNOS and eNOS. Therefore, we hypothesized that resveratrol causes blood pressure decrease through regulating nitric oxide and superoxide production in the NTS of fructose-fed rats. There were three specific aims: 1. To investigate whether fructose induce superoxide production and causes hypertension in the NTS. 2. To investigate which signaling pathway is involved in fructose-induced hypertension. 3. To investigate which signaling pathway is involved in resveratrol modulates blood pressure. Male Wistar Kyoto rats (WKY) were divided into two groups: control group and fed with 10% fructose water group for 1 week. After one-week treatment, the systolic blood pressure and superoxide production increased significantly and the nitrate level in the NTS was significantly decreased. Immunoblotting showed that administration of fructose significantly increased NADPH oxidase subunits p22-phox, p67-phox activity, RAGE activity and reduce SOD2 activity in the NTS. Based on our previous studies, male Wistar-Kyoto rats (WKY) were divided into five groups: Group I: Control group; Group II: fructose-fed rats (FFR) fed with 10% fructose for 4 weeks; Group III: Control + resveratrol (R) rats received a gavage of resveratrol; Group IV: FFR+ resveratrol (FR) fed with 10% fructose and resveratrol ; Group V: FFR + 2weeks resveratrol (F2R) fed with 10% fructose and received a gavage of resveratrol 2 weeks. We found that systolic blood pressure measured by tail-cuff method in F group rats and F2R group rats revealed a significantly increased than C group rats continuously through week 0 to week 2 but R group rats and FR group rats were no difference with C group. However, received a gavage of resveratrol (10 mg/kg/d) 2 weeks, F2R group revealed a significantly decrease in SBP than the F group continuously through week 2 to week 4. Fructose-induced hypertension increased NADPH oxidase activity and SOD2 activity related to inhibit the production of NO in the regulation of blood pressure. These results suggest that in the NTS, intake of fructose induces NADPH oxidase activity and reduces SOD2 activity to increase blood pressure. Resveratrol can not only reverse fructose-induced hypertension but also prevent fructose-induced hypertension.

Angiotensin II (Ang II) exerts diverse physiological actions in both peripheral and central nervous system. It has been demonstrated to implicate in central mechanisms leading to hypertension in the nucleus tractus solitarii (NTS) of rats, and mediated by the type-1 receptors (AT1R). Our previous studies already suggested that inhibition of NO synthesis in the NTS causes sustained hypertension. It was reported that the activity of Ang II was higher in the NTS of spontaneously hypertensive rat (SHR) and AT1R are colocalized in the neurons of the NTS, providing the local reactive oxygen species (ROS) production by Ang II. However, the signaling mechanisms of Ang II that induce hypertension remain uncertain. In the present study, we investigated the possible signal pathways involved in the cardiovascular regulation of Ang II in the NTS. Male SHR was treated with AT1R blocker, losartan (30 mg/kg/day) or superoxide dismutase (SOD) mimetic, tempol (1 mM/kg/day) for two weeks, systolic blood pressure was decreased significantly in losartan- or tempol-treated SHR. The NTS was excised for dihydroethidium (DHE) staining, NO analysis, immunoblotting and immunohistochemistry. Our results demonstrated that DHE staining revealed of ROS was much more in the NTS of SHR than in the NTS of wistar-Kyoto (WKY) rat. The ROS in the NTS of SHR was reduced by losartan. The NO content in the NTS of SHR was lower than WKY, while losartan and tempol could increase NO in the NTS of SHR. Immunoblotting and immunohistochemistry studies demonstrated that Ang II-induced hypertension inhibited neuronal NO synthase (nNOS), ERK and RSK phosphorylation levels in the NTS of SHR. These results suggest that Ang II induces ROS production in the NTS of SHR. In addition, the cardiovascular modulatory effects of Ang II in the NTS are accomplished by downregulation of ERK1/2-RSK phosphorylation levels and then nNOS level.

O núcleo do trato solitário é uma área integrativa do sistema nervoso central (CNS) envolvida no controle autonômico e respiratório. Estudos da literatura sugerem que o óxido nítrico (NO) exerce um importante papel na modulação dos reflexos cardiovasculares e ventilatórios no NTS. Além disso, evidências da literatura indicam uma possível interação entre o NO e o ATP no SNC. Fundamentados nessas evidências, no presente estudo, avaliamos a possível participação do NO na modulação dos parâmetros cardiorespiratórios basais e no processamento das respostas cardiovasculares e respiratórias à ativação do quimiorreflexo no NTS caudal de ratos não-anestesiados. Além disso, o possível papel do NO produzido pela óxido nítrico sintase neuronal (nNOS) nas respostas cardiovasculares e respiratórias à microinjeção unilateral de ATP no NTS caudal também foi avaliado. Para tanto, os animais foram submetidos ao implante de cânulas guia em direção ao NTS caudal e à canulação da artéria e veia femoral. Os parâmetros ventilatórios foram avaliados pelo método de pletismografia de corpo inteiro. A análise dos resultados monstrou que as microinjeções bilaterais do L-NAME, um inibidor nãoseletivo da NOS, no NTS caudal, promoveram um aumento significativo na pressão arterial basal dos animais, sugerindo um papel modulatório do NO sobre os neurônios envolvidos com as vias neurais do barorreflexo. No entanto, as microinjeções bilaterais do N-PLA, um inibidor seletivo da nNOS, no NTS caudal, não promoveram alterações significativas na pressão arterial basal, sugerindo que a produção do NO envolvido no controle autonômico basal no NTS caudal não é dependente da atividade da nNOS. Com relação às respostas do quimiorreflexo, as microinjeções bilaterais do L-NAME ou do N-PLA, no NTS caudal de ratos nãoanestesiados, promoveram um atenuação significativa no aumento da freqüência respiratória (fR) à ativação do quimiorreflexo, sugerindo a participação do NO Resumo xii produzido pela nNOS na modulação do componente respiratório do quimiorreflexo no NTS caudal. No entanto, as respostas pressora e bradicárdicas decorrentes da ativação do quimiorreflexo não foram alteradas pelas microinjeções bilaterais do LNAME ou N-PLA no NTS caudal, sugerindo que o NO não está envolvido na modulação das respostas cardiovasculares decorrentes da ativação deste reflexo. No que diz respeito às respostas decorrentes da microinjeção de ATP no NTS caudal, a análise dos resultados demonstrou que as respostas de aumento na pressão arterial, fR e ventilação minuto produzidas pela microinjeção unilateral de ATP no NTS caudal de ratos não-anestesiados foram significativamente atenuadas após a microinjeção do N-PLA no mesmo sítio, sugerindo a participação do NO produzido pela nNOS na modulação de tais respostas. Neste contexto, os achados do presente trabalho sugerem que no NTS caudal: 1) o NO, provavelmente produzido pela NOS endotelial, exerce um importante papel modulatório nas vias neurais do barorreflexo; 2) a neurotransmissão do aumento da fR decorrente da ativação do quimiorreflexo envolve a formação de NO produzido pela nNOS; 3) a neurotransmissão das respostas cardiovasculares decorrentes da ativação do quimiorreflexo não envolve a formação de NO; 4) a neurotransmissão das respostas cardiovascualres e respiratórias decorrentes da microinjeção unilateral de ATP envolve a formação de NO produzido pela nNOS. / The nucleus tractus solitarius (NTS) is an integrative area in the central nervous system (CNS) involved with the ventilatory and autonomic control. Several studies suggest that nitric oxide (NO) in the NTS plays an important role in the modulation of the cardiovascular and ventilatory reflexes. In addition, there is evidence indicating a possible interaction of NO and ATP in the CNS. Considering these findings, in the present study, we evaluated the possible role of NO on the modulation of the basal cardiorespiratory parameters as well as on the processing of the cardiovascular and ventilatory responses elicited by chemoreflex activation in the caudal NTS of awake rats. In addition, the possible role of NO produced by neuronal nitric oxide sintase (nNOS) on the cardiovascular and respiratory responses produced by unilateral microinjection of ATP into the caudal NTS was also evaluated. For this purpose, rats received bilateral guide cannulae in direction of the caudal NTS and femoral artery and vein were cannulated. The ventilatory measurements were obtained by whole-body pletismograph method. Our data showed that bilateral microinjections of L-NAME, a non-selective NOS inhibitor, into the caudal NTS, produced a significant increase in basaline mean arterial pressure, suggesting a modulatory role of NO in the neural pathways of the baroreflex. However, bilateral microinjections of N-PLA, a selective nNOS inhibitor, into the caudal NTS, produced no significant changes in the baseline mean arterial pressure, suggesting that NO produced by nNOS is not involved in the basal autonomic control in the caudal NTS. With respect to chemoreflex responses, bilateral microinjections of L-NAME or NPLA, into the caudal, produced a significant attenuation in the increase in respiratory frequency (fR) produced by chemoreflex activation, suggesting that NO produced by nNOS is involved in the modulation of the respiratory component of the chemoreflex. However, the pressor and bradicardic responses elicited by chemoreflex actiovation Abstract xv were not affected by microinjections of L-NAME or N-PLA, suggesting that NO is not involved in the modulation of the cardiovascular responses. With respect to ATP microinjection responses, the data showed that unilateral microinjection of ATP into the caudal NTS produced increase in arterial pressure, fR and minute ventilation, which were significantly attenuated by N-PLA, suggesting that NO produced by nNOS is involved in the modulation of the cardiovascular and ventilatory responses to ATP microinjection into the caudal NTS. In conclusion, the data of present study indicate that in the caudal NTS: 1) NO, produced probably by endothelial NOS, plays an important modulatory role on the neural pathways of the baroreflex; 2) the neurotransmission of the increase in respiratory frequency to chemoreflex activation involve NO production by nNOS. 3) NO is not involved in modulation of the autonomic components of chemoreflex; 4) the cardiovascular and ventillatory responses produced by ATP micronjection are, at least in part, mediated by NO produced by nNOS.