RESUMEN
Parkinson's disease (PD) involves the degeneration of dopaminergic neurons in the substantia nigra (SNpc) and manifests with both classic and non-classic motor symptoms, including respiratory failure. Our study aims to investigate the involvement of the commissural and intermediate nucleus of the solitary tract (cNTS and iNTS) in the attenuated respiratory response to hypoxia in PD. Using a PD rat model induced by bilateral injection of 6-hydroxydopamine (6-OHDA) into the striatum of male Wistar rats, we explored potential alterations in the population of Phox2b neurons or hypoxia-activated neurons in the NTS projecting to the retrotrapezoid nucleus (RTN). Additionally, we explored neuronal connectivity between SNpc and cNTS. Projections pathways were assessed using unilateral injection of the retrograde tracer Fluorogold (FG) in the cNTS and RTN. Neuronal activation was evaluated by analyzing fos expression in rats exposed to hypoxia. In the PD model, the ventilatory response, measured through whole-body plethysmography, was impaired at both baseline and in response to hypoxia. A reduction in Phox2b-expressing neurons or hypoxia-activated neurons projecting to the RTN was observed. Additionally, we identified an indirect pathway linking the SNpc and cNTS, which passes through the periaqueductal gray (PAG). In conclusion, our findings suggest impairment in the SNpc-PAG-cNTS pathway in the PD model, explaining the loss of Phox2b-expressing neurons or hypoxia-activated neurons in the cNTS and subsequent respiratory impairment during hypoxic stimulation. We propose that the reduced population of Phox2b-expressing neurons in the NTS may include the same neurons activated by hypoxia and projecting to the RTN.
Asunto(s)
Hipoxia , Oxidopamina , Ratas Wistar , Núcleo Solitario , Animales , Masculino , Ratas , Núcleo Solitario/patología , Hipoxia/patología , Oxidopamina/toxicidad , Proteínas de Homeodominio/metabolismo , Modelos Animales de Enfermedad , Degeneración Nerviosa/patología , Neuronas/patología , Trastornos Parkinsonianos/patología , Trastornos Parkinsonianos/inducido químicamente , Trastornos Parkinsonianos/fisiopatología , Factores de Transcripción/metabolismoRESUMEN
The rodent renovascular hypertension model has been used to investigate the mechanisms promoting hypertension. The importance of the carotid body for renovascular hypertension has been demonstrated. As the commissural NTS (cNTS) is the first synaptic site in the central nervous system that receives information from carotid body chemoreceptors, we evaluated the contribution of cNTS to renovascular hypertension in the present study. Normotensive male Holtzman rats were implanted with a silver clip around the left renal artery to induce two-kidney, one-clip (2K1C) hypertension. Six weeks later, isoguvacine (a GABAA agonist) or losartan (an AT1 antagonist) was injected into the cNTS, and the effects were compared with carotid body removal. Immunohistochemistry for Iba-1 and GFAP to label microglia and astrocytes, respectively, and RT-PCR for components of the renin-angiotensin system and cytokines in the NTS were also performed 6 weeks after renal surgery. The inhibition of cNTS with isoguvacine or the blockade of AT1 receptors with losartan in the cNTS decreased the blood pressure and heart rate of 2K1C rats even more than carotid body removal did. The mRNA expression of NOX2, TNF-α and IL-6, microglia, and astrocytes also increased in the cNTS of 2K1C rats compared to that of normotensive rats. These results indicate that tonically active neurons within the cNTS are essential for the maintenance of hypertension in 2K1C rats. In addition to signals from the carotid body, the present results suggest that angiotensin II directly activates the cNTS and may also induce microgliosis and astrogliosis within the NTS, which, in turn, cause oxidative stress and neuroinflammation.
Asunto(s)
Hipertensión Renovascular/etiología , Núcleo Solitario/metabolismo , Bloqueadores del Receptor Tipo 1 de Angiotensina II , Animales , Cuerpo Carotídeo/cirugía , Hipertensión Renovascular/patología , Hipertensión Renovascular/cirugía , Masculino , Ratas Sprague-Dawley , Núcleo Solitario/patologíaRESUMEN
Humans ascending to high altitudes are submitted to sustained hypoxia (SH), activating peripheral chemoreflex with several autonomic and respiratory responses. Here we analyzed the effect of short-term SH (24 h, FIO210%) on the processing of cardiovascular and respiratory reflexes using an in situ preparation of rats. SH increased both the sympatho-inhibitory and bradycardiac components of baroreflex and the sympathetic and respiratory responses of peripheral chemoreflex. Electrophysiological properties and synaptic transmission in the nucleus tractus solitarius (NTS) neurons, the first synaptic station of afferents of baroreflexes and chemoreflexes, were evaluated using brainstem slices and whole-cell patch-clamp. The second-order NTS neurons were identified by previous application of fluorescent tracer onto carotid body for chemoreceptor afferents or onto aortic depressor nerve for baroreceptor afferents. SH increased the intrinsic excitability of NTS neurons. Delayed excitation, caused by A-type potassium current (IKA), was observed in most of NTS neurons from control rats. The IKA amplitude was higher in identified second-order NTS neurons from control than in SH rats. SH also blunted the astrocytic inhibition of IKA in NTS neurons and increased the synaptic transmission in response to afferent fibers stimulation. The frequency of spontaneous excitatory currents was also increased in neurons from SH rats, indicating that SH increased the neurotransmission by presynaptic mechanisms. Therefore, short-term SH changed the glia-neuron interaction, increasing the excitability and excitatory transmission of NTS neurons, which may contribute to the observed increase in the reflex sensitivity of baroreflex and chemoreflex in in situ preparation.
Asunto(s)
Potenciales de Acción/fisiología , Células Quimiorreceptoras/fisiología , Hipoxia/patología , Neuroglía/fisiología , Núcleo Solitario/patología , 4-Aminopiridina/farmacología , Vías Aferentes/fisiología , Aminoácidos , Animales , Barorreflejo/efectos de los fármacos , Bicuculina/farmacología , Antagonistas de Receptores de GABA-A/farmacología , Frecuencia Cardíaca/fisiología , Técnicas In Vitro , Masculino , Bloqueadores de los Canales de Potasio/farmacología , Presorreceptores/efectos de los fármacos , Ratas , Ratas Wistar , Sistema Nervioso Simpático/fisiopatologíaRESUMEN
In the present study, we investigated the effects of lesions of A2 neurons of the commissural nucleus of the solitary tract (cNTS) alone or combined with the blockade of angiotensinergic mechanisms on the recovery of arterial pressure (AP) to hemorrhage in conscious rats. Male Holtzman rats (280-320g) received an injection of anti-dopamine-beta-hydroxylase-saporin (12.6ng/60nl; cNTS/A2-lesion, n=28) or immunoglobulin G (IgG)-saporin (12.6ng/60nl, sham, n=24) into the cNTS and 15-21days later had a stainless steel cannula implanted in the lateral ventricle. After 6days, rats were submitted to hemorrhage (four blood withdrawals, 2ml/300g of body weight every 10min). Both cNTS/A2-lesioned and sham rats had similar hypotension to hemorrhage (-62±7 and -73±7mmHg, respectively), however cNTS/A2-lesioned rats rapidly recovered from hypotension (-5±3mmHg at 30min), whereas sham rats did not completely recover until the end of the recording (-20±3mmHg at 60min). Losartan (angiotensin type 1 receptor antagonist) injected intracerebroventricularly (100µg/1µl) or intravenously (i.v.) (10mg/kg of body weight) impaired the recovery of AP in cNTS/A2-lesioned rats (-24±6 and -35±7mmHg at 30min, respectively). In sham rats, only i.v. losartan affected the recovery of AP (-39±6mmHg at 60min). The results suggest that lesion of the A2 neurons in the cNTS facilitates the activation of the angiotensinergic pressor mechanisms in response to hemorrhage.
Asunto(s)
Neuronas Adrenérgicas/metabolismo , Angiotensina II/metabolismo , Hemorragia/metabolismo , Núcleo Solitario/patología , Neuronas Adrenérgicas/patología , Animales , Hemorragia/patología , Masculino , Ratas , Ratas Sprague-Dawley , Núcleo Solitario/metabolismoRESUMEN
Recent studies suggest that neuron-glia interactions are involved in multiple aspects of neuronal activity regulation. In the nucleus tractus solitarius (NTS) neuron-glia interactions are thought to participate in the integration of autonomic responses to physiological challenges. However, it remains to be shown whether NTS glial cells might influence breathing and cardiovascular control, and also if they could be integral to the autonomic and respiratory responses to hypoxic challenges. Here, we investigated whether NTS glia play a tonic role in the modulation of central respiratory and sympathetic activities as well as in the changes in respiratory-sympathetic coupling induced by exposure to chronic intermittent hypoxia (CIH), a model of central autonomic and respiratory plasticity. We show that bilateral microinjections of fluorocitrate (FCt), a glial cell inhibitor, into the caudal and intermediate subnuclei of the NTS did not alter baseline respiratory and sympathetic parameters in in situ preparations of juvenile rats. Similar results were observed in rats previously exposed to CIH. Likewise, CIH-induced changes in respiratory-sympathetic coupling were unaffected by FCt-mediated inhibition. However, microinjection of FCt into the ventral medulla produced changes in respiratory frequency. Our results show that acute glial inhibition in the NTS does not affect baseline respiratory and sympathetic control. Additionally, we conclude that NTS glial cells may not be necessary for the continuous manifestation of sympathetic and respiratory adaptations to CIH. Our work provides evidence that neuron-glia interactions in the NTS do not participate in baseline respiratory and sympathetic control.
Asunto(s)
Hipoxia/patología , Neuroglía/fisiología , Respiración , Núcleo Solitario/patología , Sistema Nervioso Simpático/fisiopatología , Potenciales de Acción/efectos de los fármacos , Análisis de Varianza , Animales , Animales Recién Nacidos , Enfermedad Crónica , Citratos/farmacología , Modelos Animales de Enfermedad , Hipoxia/tratamiento farmacológico , Bulbo Raquídeo/efectos de los fármacos , Bulbo Raquídeo/fisiología , Neuroglía/efectos de los fármacos , Ratas , Ratas Wistar , Respiración/efectos de los fármacos , Sistema Nervioso Simpático/efectos de los fármacosRESUMEN
Ample animal studies demonstrate that neuropeptides NPY and α-MSH expressed in Arcuate Nucleus and Nucleus of the Tractus Solitarius, modulate glucose homeostasis and food intake. In contrast is the absence of data validating these observations for human disease. Here we compare the post mortem immunoreactivity of the metabolic neuropeptides NPY, αMSH and VGF in the infundibular nucleus, and brainstem of 11 type-2 diabetic and 11 non-diabetic individuals. α-MSH, NPY and tyrosine hydroxylase in human brain are localized in the same areas as in rodent brain. The similar distribution of NPY, α-MSH and VGF indicated that these neurons in the human brain may share similar functionality as in the rodent brain. The number of NPY and VGF immuno positive cells was increased in the infundibular nucleus of diabetic subjects in comparison to non-diabetic controls. In contrast, NPY and VGF were down regulated in the Nucleus of the Tractus Solitarius of diabetic patients. These results suggest an activation of NPY producing neurons in the arcuate nucleus, which, according to animal experimental studies, is related to a catabolic state and might be the basis for increased hepatic glucose production in type-2 diabetes.
Asunto(s)
Núcleo Arqueado del Hipotálamo/metabolismo , Diabetes Mellitus Tipo 2/genética , Factores de Crecimiento Nervioso/genética , Neuronas/metabolismo , Neuropéptido Y/genética , Núcleo Solitario/metabolismo , Adulto , Anciano , Núcleo Arqueado del Hipotálamo/patología , Autopsia , Estudios de Casos y Controles , Diabetes Mellitus Tipo 2/metabolismo , Diabetes Mellitus Tipo 2/patología , Femenino , Regulación de la Expresión Génica , Humanos , Inmunohistoquímica , Masculino , Persona de Mediana Edad , Factores de Crecimiento Nervioso/metabolismo , Neuronas/patología , Neuropéptido Y/metabolismo , Núcleo Solitario/patología , alfa-MSH/genética , alfa-MSH/metabolismoRESUMEN
Electrolytic lesions of the commissural nucleus of the solitary tract (commNTS) in rats enhance the pressor response to bilateral carotid occlusion or to intravenous infusion of hypertonic NaCl without changing baroreflex responses. In an opposite direction, commNTS lesions abolish the pressor responses to peripheral chemoreflex activation. These opposite effects of commNTS lesions apparently result from an impairment of sympathetic activation in one case and in a facilitation of vasopressin secretion in the others. In the present study, we investigated the effects of the electrolytic lesions of the commNTS in the pressor responses that depend on sympathetic activation and vasopressin secretion produced by central cholinergic or adrenergic activation with intracerebroventricular (i.c.v.) injections of carbachol or noradrenaline, respectively, in unanesthetized rats. Male Holtzman rats (280-320 g, n=8-15/group) with acute (1 day) or chronic (21 days) sham or commNTS lesions (1 mA×10 s) and a stainless steel cannula implanted in the lateral ventricle were used. Acute commNTS lesions increased the pressor response to i.c.v. injection of carbachol (0.5 nmol/1µ1) (52 ± 2, vs. sham: 37 ± 2mm Hg) or noradrenaline (80 nmol/1µl) (45 ± 6, vs. sham: 30 ± 3 mm Hg), whereas chronic commNTS lesions did not affect the pressor responses to the same treatments. Lesions of the commNTS impaired chemoreflex responses produced by intravenous KCN, without changing baroreflex responses. The results suggest that commNTS-dependent inhibitory signals are involved in the modulation of the pressor responses to central cholinergic and adrenergic activation, probably limiting vasopressin secretion.
Asunto(s)
Agonistas alfa-Adrenérgicos/farmacología , Carbacol/farmacología , Agonistas Colinérgicos/farmacología , Norepinefrina/farmacología , Núcleo Solitario/fisiopatología , Animales , Barorreflejo , Células Quimiorreceptoras/fisiología , Electrólisis , Inyecciones Intraventriculares , Masculino , Ratas , Ratas Sprague-Dawley , Núcleo Solitario/patología , Vasopresinas/metabolismoRESUMEN
Commissural nucleus of the solitary tract (commNTS) lesions transitorily (first 5 days) reduce mean arterial pressure (MAP) in spontaneously hypertensive rats (SHR), and lesions of the tissue surrounding the anteroventral third ventricle (AV3V region) chronically reduce MAP in other models of hypertension. In the present study, we investigated the effects of combined AV3V+commNTS electrolytic lesions on MAP and heart rate (HR) in conscious SHR. Baseline MAP and HR were recorded in male SHR before and for the next 40 days after sham or AV3V lesions combined with sham or commNTS lesions. The AV3V lesions produced no change in MAP in SHR, while commNTS lesions reduced MAP acutely (121 +/- 2 to 127 +/- 3 mmHg in the 1st and 5th days, respectively, vs. prelesion: 192 +/- 4 mmHg) but not chronically (from 10 to 40 days). However, combined AV3V+commNTS lesions reduced MAP of SHR chronically (119 +/- 2 to 161 +/- 4 mmHg, in the 1st and 40th day, respectively, vs. prelesion levels: 186 +/- 4 mmHg) or sham-lesioned SHR (187 +/- 4 to 191 +/- 6 mmHg). Sympathetic and angiotensinergic blockade produced less reduction in MAP in SHR with AV3V+commNTS-lesions, and there was no relationship between changes on water and food intake, body weight, or urinary excretion produced by AV3V+commNTS lesions with the changes in MAP. The present findings suggest that in the absence of the commNTS, the AV3V region contributes to the hypertension observed in SHR by mechanisms that appear to involve enhanced angiotensinergic and sympathetic activity.
Asunto(s)
Presión Sanguínea , Frecuencia Cardíaca , Hipertensión/prevención & control , Núcleo Solitario/cirugía , Tercer Ventrículo/cirugía , Bloqueadores del Receptor Tipo 1 de Angiotensina II/farmacología , Animales , Antihipertensivos/farmacología , Barorreflejo , Presión Sanguínea/efectos de los fármacos , Peso Corporal , Modelos Animales de Enfermedad , Ingestión de Líquidos , Ingestión de Alimentos , Electrólisis , Bloqueadores Ganglionares/farmacología , Frecuencia Cardíaca/efectos de los fármacos , Hexametonio/farmacología , Hipertensión/patología , Hipertensión/fisiopatología , Losartán/farmacología , Masculino , Ratas , Ratas Endogámicas SHR , Ratas Sprague-Dawley , Sistema Renina-Angiotensina , Núcleo Solitario/patología , Núcleo Solitario/fisiopatología , Sistema Nervioso Simpático/fisiopatología , Tercer Ventrículo/patología , Tercer Ventrículo/fisiopatología , Factores de Tiempo , Equilibrio HidroelectrolíticoRESUMEN
Exposure to chronic intermittent hypoxia (CIH) leads to significant autonomic and respiratory changes, similar to those observed in obstructive sleep apnea. The hypertension associated with CIH is due to sympathoexcitation triggered by long-term exposure to intermittent hypoxia. However, the mechanisms underlying these effects are unknown. Changes in central regulation of sympathetic activity may underlie CIH-induced hypertension. Since NO appears to be mainly sympathoinhibitory in the nucleus of the solitary tract (NTS), we hypothesized that CIH augments sympathetic activity, in part by reducing neuronal nitric oxide synthase (nNOS) expression and consequently nitric oxide (NO) production in this brain region. To test our hypothesis, juvenile male Wistar rats were exposed to CIH for 8 h/day for 10 days and sections of perfused brainstem were either stained to reveal nNOS-immunoreactivity or loaded with DAF 2-DA to label neurons containing NO. CIH rats showed a significant increase in mean arterial pressure and heart rate compared to controls. However, there was no significant difference in the distribution, staining intensity or numbers of nNOS-immunoreactive neurons in the NTS between experimental and control rats. We also found no significant change in NO content in the DAF 2-DA-loaded sections of NTS from CIH rats. Our data show that NO is not altered in the NTS of juvenile CIH rats, suggesting that nitrergic mechanisms, at least in the NTS, are unlikely to be involved in the sympathetic excitation that generates the hypertension observed after 10 days of CIH.
Asunto(s)
Hipoxia/patología , Neuronas/enzimología , Óxido Nítrico Sintasa de Tipo I/metabolismo , Óxido Nítrico/metabolismo , Núcleo Solitario/enzimología , Núcleo Solitario/patología , Animales , Presión Sanguínea/efectos de los fármacos , Presión Sanguínea/fisiología , Modelos Animales de Enfermedad , Fluoresceína/metabolismo , Regulación de la Expresión Génica/fisiología , Frecuencia Cardíaca/efectos de los fármacos , Frecuencia Cardíaca/fisiología , Indicadores y Reactivos/metabolismo , Masculino , Microscopía Confocal/métodos , Ratas , Ratas WistarRESUMEN
Knowing that exercise training reduces arterial pressure in hypertensive individuals and that pressure fall is accompanied by blockade of brain renin-angiotensin system, we sought to investigate whether training (T) affects central renin-angiotensin system. Spontaneously hypertensive rats (SHRs) and normotensive Wistar-Kyoto controls (WKY) were submitted to training or kept sedentary (S) for 3 months. After functional recordings, brain was removed and processed for autoradiography (brain stem sequential slices hybridized with (35)S-oligodeoxynucleotide probes for angiotensinogen [Aogen] and angiotensin II type 1 [AT(1A)] receptors). Resting arterial pressure and heart rate were higher in SHR(S) (177+/-2 mm Hg, 357+/-12 bpm versus 121+/-1 mm Hg, 320+/-9 bpm in WKY(S); P<0.05). Training was equally effective to enhance treadmill performance and to cause resting bradycardia (-10%) in both groups. Training-induced blood pressure fall (-6.3%) was observed only in SHR(T). In SHR(S) (versus WKY(S)) AT(1A) and Aogen mRNA expression were significantly increased within the NTS and area postrema (average of +67% and +41% for AT(1A) and Aogen, respectively; P<0.05) but unchanged in the gracilis nucleus. Training did not change AT(1A) expression but reduced NTS and area postrema Aogen mRNA densities specifically in SHR(T) (P<0.05 versus SHR(S), with values within the range of WKY groups). In SHRs, NTS Aogen mRNA expression was correlated with resting pressure (y=5.95x +41; r=0.55; P<0.05), with no significant correlation in the WKY group. Concurrent training-induced reductions of both Aogen mRNA expression in brain stem cardiovascular-controlling areas and mean arterial pressure only in SHRs suggest that training is as efficient as the renin-angiotensin blockers to reduce brain renin-angiotensin system overactivity and to decrease arterial pressure.
Asunto(s)
Angiotensinógeno/metabolismo , Presión Sanguínea/fisiología , Hipertensión/fisiopatología , Condicionamiento Físico Animal/fisiología , ARN Mensajero/metabolismo , Núcleo Solitario/metabolismo , Animales , Frecuencia Cardíaca/fisiología , Hipertensión/patología , Masculino , ARN Mensajero/genética , Ratas , Ratas Endogámicas SHR , Ratas Endogámicas WKY , Receptor de Angiotensina Tipo 1/metabolismo , Sistema Renina-Angiotensina/fisiología , Núcleo Solitario/patologíaRESUMEN
Acute electrolytic lesions of the commissural nucleus of the solitary tract (commNTS) reduce blood pressure (BP) in SHR but not in normotensive Wistar-Kyoto and Wistar rats and abolish the pressor response to intravenous injection of potassium cyanide. We investigated the chronic effect of commNTS lesions on mean arterial pressure (MAP), and on baroreceptor and chemoreceptor reflex responses in SHR. The contribution of the sympathetic nervous system and the hormones vasopressin and angiotensin II to maintenance of BP in lesioned SHR was also investigated. MAP fell to normotensive levels the day after lesioning the commNTS but returned to the hypertensive level 9 days later. The reflex tachycardia evoked by sodium nitroprusside remained attenuated for 10 days after commNTS lesions but became enhanced 30 days after commNTS lesions. The pressor component of the chemoreflex elicited by potassium cyanide remained blocked for 30 days after lesions. Vasopressin antagonist or ACE blocker did not change MAP in sham or commNTS-lesioned SHR. Ganglionic blockade with hexamethonium elicited similar reductions in MAP in sham and commNTS-lesioned SHR. Results demonstrated that commNTS lesions in SHR produce a transient fall in BP and a long-lasting inhibition of the pressor response of the chemoreflex. Therefore, the blockade of the pressor response to peripheral chemoreflex activation is not sufficient to chronically reduce MAP in SHR. In the chronic absence of the commNTS, other subnuclei of the NTS or other brain stem nuclei may reorganize to replace the function of commNTS neurons, restoring sympathetic activity and high BP in SHR.
Asunto(s)
Arginina Vasopresina/análogos & derivados , Presión Sanguínea , Hipertensión/fisiopatología , Núcleo Solitario/fisiopatología , Inhibidores de la Enzima Convertidora de Angiotensina/farmacología , Animales , Antagonistas de los Receptores de Hormonas Antidiuréticas , Arginina Vasopresina/farmacología , Barorreflejo , Presión Sanguínea/efectos de los fármacos , Captopril/farmacología , Células Quimiorreceptoras/metabolismo , Estimulación Eléctrica , Bloqueadores Ganglionares/farmacología , Frecuencia Cardíaca/efectos de los fármacos , Hexametonio/farmacología , Hipertensión/patología , Cinética , Masculino , Ratas , Ratas Endogámicas SHR , Núcleo Solitario/patologíaRESUMEN
It has been suggested that increased sympathetic activity and arterial chemoreceptors are important for the high blood pressure in spontaneously hypertensive rats (SHR). Electrolytic lesions of the commissural nucleus of the solitary tract (commNTS) abolish (1) the cardiovascular responses to chemoreflex activation with potassium cyanide (KCN) in normotensive rats and (2) the hypertension that follows acute aortic baroreceptor denervation in rats. Therefore, in this study we investigated the effects of electrolytic lesions of the commNTS on basal mean arterial pressure (MAP), baroreflex, and chemoreflex in SHR and in normotensive control Wistar-Kyoto (WKY) and Wistar rats. CommNTS lesions elicited a dramatic fall in MAP to normal levels during the period of study (from the first to fourth day following lesions) in SHR and almost no changes in WKY and Wistar rats. The pressor responses to chemoreflex activation with KCN tested in the days 1 and 4 after commNTS lesions were abolished in SHR and in normotensive strains. The reflex tachycardia induced by sodium nitroprusside was also attenuated in days 1 and 4 after commNTS lesions in SHR, WKY, and Wistar rats. The data suggest that the integrity of commNTS is important for the maintenance of high blood pressure in SHR and for the reflex responses dependent on sympathetic activation either in SHR or in normotensive strains.