RESUMEN
KEY POINTS: Neurons from the brainstem nucleus of the tractus solitarius (NTS) participate in the counter-regulatory mechanisms in response to hypoglycaemia. ATP-sensitive potassium (KATP ) channels are expressed in NTS neurons, and are partially open at rest in normoglycaemic 5 mM glucose. In normoglycaemic conditions, most NTS neurons depolarize in response to low external glucose (0.5 mM), via a voltage-dependent mechanism. Conversely, most NTS neurons incubated in hyperglycaemic 10 mM glucose do not respond to low glucose due to a more positive resting membrane potential caused by the closure of KATP channels following increased intracellular metabolic ATP. Our findings show that in hyperglycaemic conditions, NTS neurons failed to sense rapid changes in external glucose, which could be related to hypoglycaemia-associated autonomic failure. ABSTRACT: The nucleus of the tractus solitarius (NTS) is an integrative centre for autonomic counter-regulatory responses to hypoglycaemia. KATP channels link the metabolic status of the neuron to its excitability. Here we investigated the influence of KATP channels on the membrane potential of NTS neurons in normo- and hyperglycaemic external glucose concentrations, and after switching to a hypoglycaemic concentration, using in vitro electrophysiological recordings in brainstem slices. We found that in normoglycaemic (5 mM) glucose, tolbutamide, a KATP channel antagonist, depolarized the membrane of most neurons, and this effect was observed in more hyperpolarized neurons. All neurons hyperpolarized after pharmacological activation of KATP channels. Most NTS neurons depolarized in the presence of low glucose (0.5 mM), and this effect was only seen in hyperpolarized neurons. The effect of glucose was caused by a cationic current with a reversal potential around -50 mV. In the presence of hyperglycaemic glucose (10 mM), neurons were more depolarized, and fewer neurons responded to KATP blockage. Application of 0.5 mM glucose solution to these neurons depolarized the membrane only in more hyperpolarized neurons. We conclude that NTS neurons present with KATP channels open at rest in normoglycaemic conditions, and their membrane potential is affected by extracellular glucose. Moreover, NTS neurons depolarize the membrane in response to the application of a low glucose solution, but this effect is occluded by membrane depolarization triggered by KATP blockage. Our data suggest a homeostatic regulation of the membrane potential by external glucose, and a possible mechanism related to the hypoglycaemia-associated autonomic failure.
Asunto(s)
Potenciales de Acción , Glucosa/metabolismo , Canales KATP/metabolismo , Neuronas/metabolismo , Núcleo Solitario/fisiología , Animales , Glucosa/farmacología , Masculino , Neuronas/efectos de los fármacos , Neuronas/fisiología , Ratas , Ratas Wistar , Núcleo Solitario/citología , Núcleo Solitario/metabolismoRESUMEN
The application of sodium cyanide (NaCN) to the carotid body receptors (CBR) (CBR stimulation) induces rapid blood hyperglycemia and an increase in brain glucose retention. The commissural nucleus tractus solitarius (cNTS) is an essential relay nucleus in this hyperglycemic reflex; it receives glutamatergic afferents (that also release brain derived neurotrophic factor, BDNF) from the nodose-petrosal ganglia that relays CBR information. Previous work showed that AMPA in NTS blocks hyperglycemia and brain glucose retention after CBR stimulation. In contrast, BDNF, which attenuates glutamatergic AMPA currents in NTS, enhances these glycemic responses. Here we investigated the combined effects of BDNF and AMPA (and their antagonists) in NTS on the glycemic responses to CBR stimulation. Microinjections of BDNF plus AMPA into the cNTS before CBR stimulation in anesthetized rats, induced blood hyperglycemia and an increase in brain arteriovenous (a-v) of blood glucose concentration difference, which we infer is due to increased brain glucose retention. By contrast, the microinjection of the TrkB antagonist K252a plus AMPA abolished the glycemic responses to CBR stimulation similar to what is observed after AMPA pretreatments. In BDNF plus AMPA microinjections preceding CBR stimulation, the number of c-fos immunoreactive cNTS neurons increased. In contrast, in the rats microinjected with K252a plus AMPA in NTS, before CBR stimulation, c-fos expression in cNTS decreased. The expression of AMPA receptors GluR2/3 did not change in any of the studied groups. These results indicate that BDNF in cNTS plays a key role in the modulation of the hyperglycemic reflex initiated by CBR stimulation.
Asunto(s)
Factor Neurotrófico Derivado del Encéfalo/metabolismo , Cuerpo Carotídeo/efectos de los fármacos , Cuerpo Carotídeo/metabolismo , Hiperglucemia/metabolismo , Núcleo Solitario/metabolismo , Ácido alfa-Amino-3-hidroxi-5-metil-4-isoxazol Propiónico/metabolismo , Animales , Factor Neurotrófico Derivado del Encéfalo/administración & dosificación , Ensayo de Inmunoadsorción Enzimática , Glucosa/metabolismo , Hiperglucemia/inducido químicamente , Hiperglucemia/patología , Inmunohistoquímica , Masculino , Microinyecciones , Neurotransmisores/farmacología , Proteínas Proto-Oncogénicas c-fos/metabolismo , Distribución Aleatoria , Ratas Wistar , Receptor trkB/agonistas , Receptor trkB/antagonistas & inhibidores , Receptor trkB/metabolismo , Receptores AMPA/agonistas , Receptores AMPA/antagonistas & inhibidores , Receptores AMPA/metabolismo , Cianuro de Sodio/farmacología , Núcleo Solitario/citología , Núcleo Solitario/efectos de los fármacos , Ácido alfa-Amino-3-hidroxi-5-metil-4-isoxazol Propiónico/administración & dosificaciónRESUMEN
A single exposure to amphetamine induces neurochemical sensitization in striatal areas. The neuropeptide angiotensin II, through AT1 receptors (AT1-R) activation, is involved in these responses. However, amphetamine-induced alterations can be extended to extra-striatal areas involved in blood pressure control and their physiological outcomes. Our aim for the present study was to analyze the possible role for AT1-R in these events using a two-injection protocol and to further characterize the proposed AT1-R antagonism protocol. Central effect of orally administered AT1-R blocker (Candesartan, 3mg/kg p.o.×5days) in male Wistar rats was analyzed by spontaneous activity of neurons within locus coeruleus. In another group of animals pretreated with the AT1-R blocker or vehicle, sensitization was achieved by a single administration of amphetamine (5mg/kg i.p. - day 6) followed by a 3-week period off drug. On day 27, after receiving an amphetamine challenge (0.5mg/kg i.p.), we evaluated: (1) the sensitized c-Fos expression in locus coeruleus (LC), nucleus of the solitary tract (NTS), caudal ventrolateral medulla (A1) and central amygdala (CeAmy); and (2) the blood pressure response. AT1-R blockade decreased LC neurons' spontaneous firing rate. Moreover, sensitized c-Fos immunoreactivity in TH+neurons was found in LC and NTS; and both responses were blunted by the AT1-R blocker pretreatment. Meanwhile, no differences were found neither in CeAmy nor A1. Sensitized blood pressure response was observed as sustained changes in mean arterial pressure and was effectively prevented by AT1-R blockade. Our results extend AT1-R role in amphetamine-induced sensitization over noradrenergic nuclei and their cardiovascular output.
Asunto(s)
Anfetamina/farmacología , Presión Sanguínea/efectos de los fármacos , Neuronas/efectos de los fármacos , Receptor de Angiotensina Tipo 1/metabolismo , Simpatomiméticos/farmacología , Potenciales de Acción/efectos de los fármacos , Potenciales de Acción/fisiología , Bloqueadores del Receptor Tipo 1 de Angiotensina II/farmacología , Animales , Presión Sanguínea/fisiología , Núcleo Amigdalino Central/citología , Núcleo Amigdalino Central/efectos de los fármacos , Núcleo Amigdalino Central/metabolismo , Locus Coeruleus/citología , Locus Coeruleus/efectos de los fármacos , Locus Coeruleus/metabolismo , Masculino , Bulbo Raquídeo/citología , Bulbo Raquídeo/efectos de los fármacos , Bulbo Raquídeo/metabolismo , Neuronas/citología , Neuronas/metabolismo , Proteínas Proto-Oncogénicas c-fos/metabolismo , Distribución Aleatoria , Ratas Wistar , Núcleo Solitario/citología , Núcleo Solitario/efectos de los fármacos , Núcleo Solitario/metabolismoRESUMEN
This study was designed to investigate brain connections among chemosensitive areas in newborn rats. Rhodamine beads were injected unilaterally into the locus coeruleus (LC) or into the caudal part of the nucleus tractus solitarius (cNTS) in Sprague-Dawley rat pups (P7-P10). Rhodamine-labeled neurons were patched in brainstem slices to study their electrophysiological responses to hypercapnia and to determine if chemosensitive neurons are communicating between LC and cNTS regions. After 7-10 days, retrograde labeling was observed in numerous areas of the brainstem, including many chemosensitive regions, such as the contralateral LC, cNTS and medullary raphe. Whole-cell patch clamp was done in cNTS. In 4 of 5 retrogradely labeled cNTS neurons that projected to the LC, firing rate increased in response to hypercapnic acidosis (15% CO2), even in synaptic blockade medium (SNB) (high Mg(2+)/low Ca(2+)). In contrast, 2 of 3 retrogradely labeled LC neurons that projected to cNTS had reduced firing rate in response to hypercapnic acidosis, both in the presence and absence of SNB. Extensive anatomical connections among chemosensitive brainstem regions in newborn rats were found and at least for the LC and cNTS, the connections involve some CO2-sensitive neurons. Such anatomical and functional coupling suggests a complex central respiratory control network, such as seen in adult rats, is already largely present in neonatal rats by at least day P7-P10. Since the NTS and the LC play a major role in memory consolidation, our results may also contribute to the understanding of the development of memory consolidation.
Asunto(s)
Locus Coeruleus/citología , Locus Coeruleus/fisiología , Neuronas/citología , Neuronas/fisiología , Núcleo Solitario/citología , Núcleo Solitario/fisiopatología , Potenciales de Acción/fisiología , Animales , Animales Recién Nacidos , Dióxido de Carbono/metabolismo , Recuento de Células , Femenino , Locus Coeruleus/crecimiento & desarrollo , Masculino , Memoria , Microscopía Confocal , Vías Nerviosas/citología , Vías Nerviosas/crecimiento & desarrollo , Vías Nerviosas/fisiología , Técnicas de Trazados de Vías Neuroanatómicas , Técnicas de Placa-Clamp , Ratas Sprague-Dawley , Respiración , Núcleo Solitario/crecimiento & desarrollo , Técnicas de Cultivo de TejidosRESUMEN
OBJECTIVE: The current study considers changes of the postnatal brainstem cell number and angiotensin receptors by maternal protein restriction (LP) and LP taurine supplementation (LPT), and its impact on arterial hypertension development in adult life. METHODS AND RESULTS: The brain tissue studies were performed by immunoblotting, immunohistochemistry, and isotropic fractionator analysis. The current study shows that elevated blood pressure associated with decreased fractional urinary sodium excretion (FENa) in adult LP offspring was reverted by diet taurine supplementation. Also, that 12-day-old LP pups present a reduction of 21% of brainstem neuron counts, and, immunohistochemistry demonstrates a decreased expression of type 1 angiotensin II receptors (AT1R) in the entire medial solitary tract nuclei (nTS) of 16-week-old LP rats compared to age-matched NP and LPT offspring. Conversely, the immunostained type 2 AngII (AT2R) receptors in 16-week-old LP nTS were unchanged. CONCLUSION: The present investigation shows a decreased FENa that occurs despite unchanged creatinine clearance. It is plausible to hypothesize an association of decreased postnatal nTS cell number, AT1R/AT2R ratio and FENa with the higher blood pressure levels found in taurine-deficient progeny (LP) compared with age-matched NP and LPT offspring.
Asunto(s)
Presión Sanguínea/efectos de los fármacos , Dieta con Restricción de Proteínas , Riñón/metabolismo , Receptores de Angiotensina/biosíntesis , Sodio/orina , Núcleo Solitario/citología , Taurina/farmacología , Animales , Recuento de Células , Creatinina/sangre , Femenino , Litio/metabolismo , Masculino , Bulbo Raquídeo/citología , Bulbo Raquídeo/efectos de los fármacos , Potasio/orina , Embarazo , Ratas , Núcleo Solitario/efectos de los fármacos , Urodinámica/efectos de los fármacosRESUMEN
The rostral ventrolateral medulla (RVLM) contains the presympathetic neurons involved in cardiovascular regulation that has been implicated as one of the most important central sites for the antihypertensive action of moxonidine (an α2-adrenergic and imidazoline agonist). Here, we sought to evaluate the cardiovascular effects produced by moxonidine injected into another important brainstem site, the commissural nucleus of the solitary tract (commNTS). Mean arterial pressure (MAP), heart rate (HR), splanchnic sympathetic nerve activity (sSNA) and activity of putative sympathoexcitatory vasomotor neurons of the RVLM were recorded in conscious or urethane-anesthetized, and artificial ventilated male Wistar rats. In conscious or anesthetized rats, moxonidine (2.5 and 5 nmol/50 nl) injected into the commNTS reduced MAP, HR and sSNA. The injection of moxonidine into the commNTS also elicited a reduction of 28% in the activity of sympathoexcitatory vasomotor neurons of the RVLM. To further assess the notion that moxonidine could act in another brainstem area to elicit the antihypertensive effects, a group with electrolytic lesions of the commNTS or sham and with stainless steel guide-cannulas implanted into the 4th V were used. In the sham group, moxonidine (20 nmol/1 µl) injected into 4th V decreased MAP and HR. The hypotension but not the bradycardia produced by moxonidine into the 4th V was reduced in acute (1 day) commNTS-lesioned rats. These data suggest that moxonidine can certainly act in other brainstem regions, such as commNTS to produce its beneficial therapeutic effects, such as hypotension and reduction in sympathetic nerve activity.
Asunto(s)
Antihipertensivos/farmacología , Imidazoles/farmacología , Núcleo Solitario/efectos de los fármacos , Núcleo Solitario/fisiología , Antagonistas Adrenérgicos alfa/farmacología , Anestesia , Animales , Antihipertensivos/administración & dosificación , Presión Sanguínea/efectos de los fármacos , Estado de Conciencia/fisiología , Cuarto Ventrículo/citología , Cuarto Ventrículo/efectos de los fármacos , Cuarto Ventrículo/fisiología , Frecuencia Cardíaca/efectos de los fármacos , Idazoxan/análogos & derivados , Idazoxan/farmacología , Imidazoles/administración & dosificación , Inyecciones , Inyecciones Intraventriculares , Masculino , Neuronas/efectos de los fármacos , Ratas , Ratas Endogámicas SHR , Ratas Wistar , Núcleo Solitario/citología , Técnicas Estereotáxicas , Yohimbina/farmacologíaRESUMEN
The parapyramidal (ppy) region targets primarily the intermediolateral cell column and is probably involved in breathing and thermoregulation. In the present study, we tested whether ppy serotonergic neurons respond to activation of central and peripheral chemoreceptors. Bulbospinal ppy neurons (n=30) were recorded extracellularly along with the phrenic nerve activity in urethane/α-chloralose-anesthetized, paralyzed, intact (n=7) or carotid body denervated (n=6) male Wistar rats. In intact animals, most of the ppy neurons were inhibited by hypoxia (n=14 of 19) (8% O2, 30s) (1.5 ± 0.03 vs. control: 2.4 ± 0.2 Hz) or hypercapnia (n=15 of 19) (10% CO2) (1.7 ± 0.1 vs. control: 2.2 ± 0.2 Hz), although some neurons were insensitive to hypoxia (n=3 of 19) or hypercapnia (n=4 of 19). Very few neurons (n=2 of 19) were activated after hypoxia, but not after hypercapnia. In carotid body denervated rats, all the 5HT-ppy neurons (n=11) were insensitive to hypercapnia (2.1 ± 0.1 vs. control: 2.3 ± 0.09 Hz). Biotinamide-labeled cells that were recovered after histochemistry were located in the ppy region. Most labeled cells (90%) showed strong tryptophan hydroxylase immunocytochemical reactivity, indicating that they were serotonergic. The present data reveal that peripheral chemoreceptors reduce the activity of the serotonergic premotor neurons located in the ppy region. It is plausible that the serotonergic neurons of the ppy region could conceivably regulate breathing automaticity and be involved in autonomic regulation.
Asunto(s)
Células Quimiorreceptoras/fisiología , Inhibición Neural/fisiología , Nervio Frénico/citología , Neuronas Serotoninérgicas/fisiología , Núcleo Solitario/citología , Potenciales de Acción/efectos de los fármacos , Potenciales de Acción/fisiología , Vías Aferentes/efectos de los fármacos , Vías Aferentes/fisiología , Animales , Presión Arterial/efectos de los fármacos , Presión Arterial/fisiología , Biotina/análogos & derivados , Biotina/metabolismo , Dióxido de Carbono/farmacología , Recuento de Células , Células Quimiorreceptoras/efectos de los fármacos , Estimulación Eléctrica , Hipercapnia/fisiopatología , Hipoxia/fisiopatología , Masculino , Microscopía Electrónica de Transmisión , Inhibición Neural/efectos de los fármacos , Nervio Frénico/fisiología , Ratas , Ratas Wistar , Triptófano/análogos & derivados , Triptófano/metabolismoRESUMEN
The glomus cells in the carotid bodies (CB) detect alterations in pH and pCO2 and low pO2 level in arterial blood. The carotid sinus nerve conveys the information related to the oxygen level to 2nd-order neurons in the nucleus tractus solitarius (NTS) via tractus solitarius (TS), which is part of the chemoreflex pathways. It has been demonstrated that in 2nd-order NTS neurons receiving inputs from the aortic depressor nerve (ADN), the TS stimulation presents high temporal fidelity. However, the temporal properties of synaptic activity in NTS neurons receiving inputs from CB were not yet fully investigated. Herein using patch-clamp recordings in NTS brainstem slices, we studied TS-evoked excitatory postsynaptic currents (TS-eEPSCs) on morphologically identified 2nd-order NTS neurons that receive afferent inputs from the CB and compared with 2nd-order ADN-NTS neurons recorded in the same experimental conditions. The amplitudes of TS-eEPSCs were similar in both groups, but the latencies and standard deviation (SD) of latency were significantly higher in the CB-NTS neurons (latency: 4±0.2 ms, SD: 0.49±0.03 ms) than in ADN-NTS neurons (latency: 3.3±0.3 ms, SD: 0.19±0.02 ms; P=0.049 for latency and P<0.001 for SD of latency). In a series of double-labeling experiments, we confirmed that some CB-NTS 2nd-order neurons send direct projections to the rostral ventrolateral medulla (RVLM). We conclude that: (a) CB-NTS 2nd-order neurons present temporally distinct postsynaptic currents when compared with ADN-NTS 2nd-order neurons; (b) low SD of latency of TS-eEPSCs is not necessarily a characteristic of all 2nd-order neurons in the NTS; and (c) the presence of direct connections between these 2nd-order neurons in the NTS and RVLM is indicative that these synaptic properties of CB-NTS neurons are relevant for the processing of respiratory and autonomic responses to chemoreflex activation.
Asunto(s)
Vías Nerviosas/citología , Vías Nerviosas/metabolismo , Neuronas/metabolismo , Núcleo Solitario/citología , Núcleo Solitario/metabolismo , Transmisión Sináptica/fisiología , Animales , Cuerpo Carotídeo/metabolismo , Masculino , Técnicas de Cultivo de Órganos , Técnicas de Placa-Clamp , Ratas , Ratas WistarRESUMEN
The commissural nucleus of the solitary tract (commNTS) is a main area that receives afferent signals involved in the cardiovascular and respiratory control like those related to chemoreceptor activation, however, the importance of the commNTS for the cardiorespiratory responses to chemoreceptor activation is still controversial. In the present study, we investigated the cardiorespiratory responses to hypoxia or hypercapnia in anesthetized and conscious rats treated with injections of the GABA-A agonist muscimol into the caudal portion of the commNTS. Male Holtzman rats (280-300 g) were used. In conscious rats that had a stainless steel cannula previously implanted into the commNTS, the injection of muscimol (2 mM) into the commNTS reduced the pressor response (16±2 mmHg, vs. saline: 36±3 mmHg) and the increase in ventilation (250±17 ml/min/kg, vs. saline: 641±28 ml/min/kg) produced by hypoxia (8-10% O(2)). In urethane anesthetized rats, the injection of muscimol into the commNTS eliminated the pressor response (5±2 mmHg, vs. saline: 26±5 mmHg) and the increase in phrenic nerve discharge (PND) (20±6%, vs. saline: 149±15%) and reduced the increase in splanchnic sympathetic nerve discharge (sSND) (93±15%, vs. saline: 283±19% of baseline) produced by hypoxia. However, muscimol injected into the commNTS did not change hypercapnia (8-10% CO(2)) induced pressor response or the increase in the sSND or PND in urethane anesthetized rats or the increase in ventilation in conscious rats. The present results suggest that the cardiorespiratory responses to hypoxia are strongly dependent on the caudal portion of the commNTS, however, this area is not involved in the responses to hypercapnia.
Asunto(s)
Células Quimiorreceptoras/fisiología , Hipercapnia/fisiopatología , Hipoxia/fisiopatología , Fenómenos Fisiológicos Respiratorios , Núcleo Solitario/fisiología , Animales , Células Quimiorreceptoras/citología , Células Quimiorreceptoras/efectos de los fármacos , Agonistas de Receptores de GABA-A/farmacología , Masculino , Muscimol/farmacología , Ratas , Ratas Sprague-Dawley , Fenómenos Fisiológicos Respiratorios/efectos de los fármacos , Núcleo Solitario/citología , Núcleo Solitario/efectos de los fármacosRESUMEN
Prominent Fos expression in the nucleus of the solitary tract (NTS) related to feeding has been reported in the brainstem of adult animals. In this study, we used a Fos-guided immunohistochemical approach to determine the brainstem areas activated specifically in response to milk ingestion in rat pups at two different ages. Rats at 9 or 18 days postpartum were isolated from the mother for a 6-h period, after which they were returned to the mother for a suckling period of either 5 or 90 min and then perfused at 90 min after the beginning of suckling. Control groups were sacrificed before or after the 6-h-deprivation period and showed little or no Fos-ir. In contrast, a 90-min-suckling episode after 6 h of deprivation induced strong Fos-ir in the caudal regions of the NTS and in the spinal nucleus of the trigeminal (SPV). Moderate expression was observed in the rostral NTS and in the nucleus raphé obscurus. In rat pups that suckled for only 5 min, the main area activated was the SPV. Fos immunostaining was detected in only 1% of the catecholaminergic neurons from the NTS after milk ingestion. The experimental design employed here allowed us to distinguish brainstem areas activated by milk ingestion from those activated by suckling action in rat pups. In contrast to adult rats, catecholaminergic neurons from the caudal NTS seem to contribute little to the regulation of feeding at this age.
Asunto(s)
Tronco Encefálico/metabolismo , Ingestión de Alimentos/fisiología , Conducta Alimentaria/fisiología , Lactancia/fisiología , Leche/metabolismo , Proteínas Proto-Oncogénicas c-fos/metabolismo , Envejecimiento/fisiología , Animales , Animales Lactantes , Biomarcadores/análisis , Biomarcadores/metabolismo , Mapeo Encefálico , Tronco Encefálico/citología , Catecolaminas/metabolismo , Femenino , Inmunohistoquímica , Neuronas/citología , Neuronas/metabolismo , Proteínas Proto-Oncogénicas c-fos/análisis , Núcleos del Rafe/citología , Núcleos del Rafe/metabolismo , Ratas , Ratas Wistar , Núcleo Solitario/citología , Núcleo Solitario/metabolismo , Núcleo Espinal del Trigémino/citología , Núcleo Espinal del Trigémino/metabolismoRESUMEN
Microinjection of acetylcholine chloride (ACh) in the nucleus of the solitary tract (NTS) of awake rats caused a transient and dose-dependent hypotension and bradycardia. Because it is known that cardiovascular reflexes are affected by nitric oxide (NO) produced in the NTS, we investigated whether these ACh-induced responses depend on NO in the NTS. Responses to ACh (500 pmol in 100 nl) were strongly reduced by ipsilateral microinjection of the NOS inhibitor NG-nitro-L-arginine methyl ester (L-NAME; 10 nmol in 100 nl) in the NTS: mean arterial pressure (MAP) fell by 50 +/- 5 mmHg before L-NAME to 9 +/- 4 mmHg, 10 min after L-NAME, and HR fell by 100 +/- 26 bpm before L-NAME to 20 +/- 10 bpm, 10 min after L-NAME (both P < 0.05). Microinjection of the selective inhibitor of neuronal nitric oxide synthase (nNOS), 1-(2-trifluoromethylphenyl) imidazole (TRIM; 13.3 nmol in 100 nl), in the NTS also reduced responses to ACh: MAP fell from 42 +/- 3 mmHg before TRIM to 27 +/- 6 mmHg, 10 min after TRIM (P < 0.05). TRIM also tended to reduce ACh-induced bradycardia, but this effect was not statistically significant. ACh-induced hypotension and bradycardia returned to control levels 30-45 min after NOS inhibition. Control injections with D-NAME and saline did not affect resting values or the response to ACh. In conclusion, injection of ACh into the NTS of conscious rats induces hypotension and bradycardia, and these effects may be mediated at least partly by NO produced in NTS neurons.
Asunto(s)
Acetilcolina/metabolismo , Presión Sanguínea , Sistema Cardiovascular/inervación , Fibras Colinérgicas/metabolismo , Frecuencia Cardíaca , Neuronas Nitrérgicas/metabolismo , Óxido Nítrico/metabolismo , Núcleo Solitario/metabolismo , Acetilcolina/administración & dosificación , Animales , Presión Sanguínea/efectos de los fármacos , Bradicardia/metabolismo , Bradicardia/fisiopatología , Fibras Colinérgicas/efectos de los fármacos , Fibras Colinérgicas/enzimología , Inhibidores Enzimáticos/farmacología , Frecuencia Cardíaca/efectos de los fármacos , Hipotensión/metabolismo , Hipotensión/fisiopatología , Imidazoles/farmacología , Masculino , Microinyecciones , NG-Nitroarginina Metil Éster/farmacología , Neuronas Nitrérgicas/efectos de los fármacos , Neuronas Nitrérgicas/enzimología , Óxido Nítrico Sintasa/antagonistas & inhibidores , Óxido Nítrico Sintasa/metabolismo , Óxido Nítrico Sintasa de Tipo I , Ratas , Ratas Wistar , Núcleo Solitario/citología , Núcleo Solitario/efectos de los fármacos , Factores de Tiempo , VigiliaRESUMEN
This study shows the distribution and density of adenosine A1 receptor (A1R) within the nucleus tractus solitarii (NTS) of Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR) from birth to adulthood (1, 15, 30 and 90 days old). The NTS shows heterogeneous distribution of A1R in dorsomedial/dorsolateral, subpostremal and medial/intermediate subnuclei. A1R decrease from rostral to caudal within dorsomedial/dorsolateral subnucleus in 15-, 30- and 90-day-old WKY and SHR. A1R increase from rostral to caudal subpostremal subnucleus in 30- and 90-day-old WKY, and in 15-, 30- and 90-day-old SHR. Furthermore, A1Rs are increased in SHR as compared with WKY within dorsomedial/dorsolateral in 30- and 90-day-old and within subpostremal of 15-, 30- and 90-day-old rats. Finally, A1Rs increase from 1- to 30-day-old rats. Medial/intermediate did not show any changes in A1R from rostral to caudal levels, age or strain. In summary, our result highlights the importance of A1 adenosine system regarding the neural control of blood pressure and the development of hypertension.
Asunto(s)
Envejecimiento/metabolismo , Hipertensión/metabolismo , Receptor de Adenosina A1/metabolismo , Núcleo Solitario/crecimiento & desarrollo , Núcleo Solitario/metabolismo , Animales , Autorradiografía , Presión Sanguínea/fisiología , Interpretación Estadística de Datos , Hipertensión/genética , Modelos Lineales , Masculino , Ratas , Ratas Endogámicas SHR , Ratas Endogámicas WKY , Núcleo Solitario/citologíaRESUMEN
Glutamatergic transmission through metabotropic and ionotropic receptors, including kainate receptors, plays an important role in the nucleus of the solitary tract (NTS) functions. Glutamate system may interact with several other neurotransmitter systems which might also be influenced by steroid hormones. In the present study we analyzed the ability of systemic kainate to stimulate rat NTS neurons, which was evaluated by c-Fos as a marker of neuronal activation, and also to change the levels of NTS neurotransmitters such as GABA, NPY, CGRP, GAL, NT and NO by means of quantitative immunohistichemistry combined with image analysis. The analysis was also performed in adrenalectomized and kainate stimulated rats in order to evaluate a possible role of adrenal hormones on NTS neurotransmission. Male Wistar rats (3 month-old) were used in the present study. A group of 15 rats was submitted either to bilateral adrenalectomy or sham operation. Forty-eight hours after the surgeries, adrenalectomized rats received a single intraperitoneal injection of kainate (12 mg/kg) and the sham-operated rats were injected either with saline or kainate and sacrificed 8 hours later. The same experimental design was applied in a group of rats in order to register the arterial blood pressure. Systemic kainate decreased the basal values of mean arterial blood pressure (35%) and heart rate (22%) of sham-operated rats, reduction that were maintained in adrenalectomized rats. Kainate triggered a marked elevation of c-Fos positive neurons in the NTS which was 54% counteracted by adrenalectomy. The kainate activated NTS showed changes in the immunoreactive levels of GABA (143% of elevation) and NPY (36% of decrease), which were not modified by previous ablation of adrenal glands. Modulation in the levels of CGRP, GAL and NT immunoreactivities were only observed after kainate in the adrenalectomized rats. Treatments did not alter NOS labeling. It is possible that modulatory function among neurotransmitter systems in the NTS might be influenced by steroid hormones and the implications for central regulation of blood pressure or other visceral regulatory mechanisms control should be further investigated.
Asunto(s)
Adrenalectomía , Presión Sanguínea/efectos de los fármacos , Ácido Kaínico/farmacología , Neurotransmisores/metabolismo , Núcleo Solitario/efectos de los fármacos , Animales , Péptido Relacionado con Gen de Calcitonina/metabolismo , Galanina/metabolismo , Frecuencia Cardíaca/efectos de los fármacos , Masculino , Neuronas/citología , Neuronas/efectos de los fármacos , Neuronas/enzimología , Neuropéptido Y/metabolismo , Neurotensina/metabolismo , Óxido Nítrico Sintasa/metabolismo , Proteínas Proto-Oncogénicas c-fos/metabolismo , Ratas , Ratas Wistar , Núcleo Solitario/citología , Núcleo Solitario/enzimología , Ácido gamma-Aminobutírico/metabolismoRESUMEN
Peripheral chemoreflex activation with potassium cyanide (KCN) in awake rats or in the working heart-brainstem preparation (WHBP) produces: (a) a sympathoexcitatory/pressor response; (b) bradycardia; and (c) an increase in the frequency of breathing. Our main aim was to evaluate neurotransmitters involved in mediating the sympathoexcitatory component of the chemoreflex within the nucleus tractus solitarii (NTS). In previous studies in conscious rats, the reflex bradycardia, but not the pressor response, was reduced by antagonism of either ionotropic glutamate or purinergic P2 receptors within the NTS. In the present study we evaluated a possible dual role of both P2 and NMDA receptors in the NTS for processing the sympathoexcitatory component (pressor response) of the chemoreflex in awake rats as well as in the WHBP. Simultaneous blockade of ionotropic glutamate receptors and P2 receptors by sequential microinjections of kynurenic acid (KYN, 2 nmol (50 nl)(-1)) and pyridoxalphosphate-6-azophenyl-2',4'-disulphonate (PPADS, 0.25 nmol (50 nl)(-1)) into the commissural NTS in awake rats produced a significant reduction in both the pressor (+38+/-3 versus +8+/-3 mmHg) and bradycardic responses (-172+/-18 versus -16+/-13 beats min(-1); n=13), but no significant changes in the tachypnoea measured using plethysmography (270+/-30 versus 240+/-21 cycles min(-1), n=7) following chemoreflex activation in awake rats. Control microinjections of saline produced no significant changes in these reflex responses. In WHBP, microinjection of KYN (2 nmol (20 nl)(-1)) and PPADS (1.6 nmol (20 nl)(-1)) into the commissural NTS attenuated significantly both the increase in thoracic sympathetic activity (+52+/-2% versus +17+/-1%) and the bradycardic response (-151+/-17 versus -21+/-3 beats min(-1)) but produced no significant changes in the increase of the frequency of phrenic nerve discharge (+0.24+/-0.02 versus +0.20+/-0.02 Hz). The data indicate that combined microinjections of PPADS and KYN into the commissural NTS in both awake rats and the WHBP are required to produce a significant reduction in the sympathoexcitatory response (pressor response) to peripheral chemoreflex activation. We conclude that glutamatergic and purinergic mechanisms are part of the complex neurotransmission system of the sympathoexcitatory component of the chemoreflex at the level of the commissural NTS.
Asunto(s)
Adenosina Trifosfato/metabolismo , Tronco Encefálico/metabolismo , Células Quimiorreceptoras/metabolismo , Ácido Glutámico/metabolismo , Corazón/inervación , Reflejo , Núcleo Solitario/metabolismo , Sistema Nervioso Simpático/metabolismo , Adenosina Trifosfato/análogos & derivados , Adenosina Trifosfato/farmacología , Animales , Antihipertensivos/farmacología , Presión Sanguínea , Tronco Encefálico/citología , Tronco Encefálico/efectos de los fármacos , Células Quimiorreceptoras/efectos de los fármacos , Antagonistas de Aminoácidos Excitadores/farmacología , Corazón/efectos de los fármacos , Frecuencia Cardíaca , Ácido Quinurénico/farmacología , Masculino , Neuronas Aferentes/metabolismo , Nitroprusiato/farmacología , Cianuro de Potasio/farmacología , Fosfato de Piridoxal/análogos & derivados , Fosfato de Piridoxal/farmacología , Ratas , Ratas Wistar , Receptores de Glutamato/metabolismo , Receptores Purinérgicos P2/metabolismo , Reflejo/efectos de los fármacos , Mecánica Respiratoria , Núcleo Solitario/citología , Núcleo Solitario/efectos de los fármacos , Sistema Nervioso Simpático/citología , Sistema Nervioso Simpático/efectos de los fármacos , VigiliaRESUMEN
The nucleus of the solitary tract (NTS) receives primary afferents involved in cardiovascular regulation. We investigated the role of NK(1)-receptor bearing neurons in the NTS on cardiovascular reflexes in awake rats fitted with chronic venous and arterial cannulae. These neurons were lesioned selectively with saporin conjugated with substance P (SP-SAP, 2 microM, bilateral injections of 20 nL in the subpostremal NTS, or 200 nL in both the subpostremal and the commissural NTS). Before, and 7 and 14 days after injection of SP-SAP, we measured changes in blood pressure and heart rate induced by i.v. injection of phenylephrine and nitroprusside (baroreceptor reflex), cyanide (arterial chemoreceptor reflex), and phenylbiguanide (Bezold-Jarisch reflex). The smaller injections with SP-SAP completely abolished NK1 receptor staining in the subpostremal NTS. The larger injections abolished NK1 receptor immunoreactivity in an area that extended from the commissural NTS to the rostral end of the subpostremal NTS. The lesions seemed to affect only a limited number of neurons, since neutral red stained sections did not show any obvious reduction in cell number. The smaller lesions reduced the gain of baroreflex bradycardia and the hypotension induced by phenylbiguanide. The larger lesions completely abolished the response to phenylbiguanide, blocked the baroreflex bradycardia induced by phenylephrine, severely blunted the baroreflex tachycardia, and blocked the bradycardia and reduced the hypertension induced by cyanide. Thus, these responses depend critically on NK(1)-receptor bearing neurons in the NTS.
Asunto(s)
Fenómenos Fisiológicos Cardiovasculares , Corazón/inervación , Neuronas Aferentes/metabolismo , Receptores de Neuroquinina-1/metabolismo , Núcleo Solitario/metabolismo , Aferentes Viscerales/metabolismo , Animales , Barorreflejo/efectos de los fármacos , Barorreflejo/fisiología , Biguanidas/farmacología , Presión Sanguínea/efectos de los fármacos , Presión Sanguínea/fisiología , Bradicardia/inducido químicamente , Bradicardia/fisiopatología , Células Quimiorreceptoras/efectos de los fármacos , Células Quimiorreceptoras/fisiología , Corazón/fisiología , Frecuencia Cardíaca/efectos de los fármacos , Frecuencia Cardíaca/fisiología , Hipotensión/inducido químicamente , Hipotensión/fisiopatología , Masculino , Degeneración Nerviosa/inducido químicamente , Degeneración Nerviosa/fisiopatología , Neuronas Aferentes/citología , Neurotoxinas , Parasimpatectomía , Cianuro de Potasio/farmacología , Ratas , Ratas Wistar , Proteínas Inactivadoras de Ribosomas Tipo 1 , Saporinas , Agonistas de Receptores de Serotonina/farmacología , Núcleo Solitario/citología , Sustancia P/análogos & derivados , Aferentes Viscerales/citología , Vigilia/fisiologíaRESUMEN
The nucleus of the tractus solitarius (NTS) plays an important role in the control of several autonomic reflex functions and has glutamate and GABA as main neurotransmitters. In this work, we used patch-clamp recordings in transverse slice preparations from rats to study whether the glycine binding site of the N-methyl-D-aspartate (NMDA) receptor is saturated or not in neurons of the subpostremal NTS. Except at hyperpolarized voltages and close to the reversal potential, glycine potentiated the NMDA responses in a concentration-dependent manner. The total charge transferred by glutamatergic currents was enhanced by glycine (500 microM; from 28 +/- 13 to 42 +/- 18 pC at +50 mV, n = 7, P < 0.05). Glycine increased the conductance of the postsynaptic membrane, without altering its reversal potential, both in the presence (from 2.4 +/- 0.06 to 3.4 +/- 0.09 nS; n = 7) and absence (from 3.1 +/- 0.06 to 4.4 +/- 0.10 nS; n = 8) of Mg2+ in the bathing solution. d-serine, in the presence of strychnine, also increased the amplitude of the NMDA component (by 68 +/- 19%, P < 0.05, n = 5). The membrane potential was hyperpolarized (16 +/- 6 mV, n = 8) by glycine, suggesting the presence of inhibitory glycinergic receptors. Our results indicate that the glycine site of the NMDA receptor in neurons of the subpostremal NTS is not saturated and that glycine may act as a modulator of the NMDA transmission in this nucleus.
Asunto(s)
Glicina/metabolismo , Neuronas/metabolismo , Receptores de N-Metil-D-Aspartato/metabolismo , Núcleo Solitario/citología , Sinapsis/fisiología , Aminoquinolinas/farmacología , Animales , Animales Recién Nacidos , Sitios de Unión/efectos de los fármacos , Sitios de Unión/fisiología , Relación Dosis-Respuesta a Droga , Estimulación Eléctrica/métodos , Agonistas de Aminoácidos Excitadores/farmacología , Antagonistas de Aminoácidos Excitadores/farmacología , Potenciales Postsinápticos Excitadores/efectos de los fármacos , Potenciales Postsinápticos Excitadores/fisiología , Potenciales Postsinápticos Excitadores/efectos de la radiación , Glicinérgicos/farmacología , Técnicas In Vitro , Potenciales de la Membrana/efectos de los fármacos , Potenciales de la Membrana/fisiología , Potenciales de la Membrana/efectos de la radiación , N-Metilaspartato/farmacología , Neuronas/efectos de los fármacos , Técnicas de Placa-Clamp/métodos , Ratas , Ratas Wistar , Serina/farmacología , Estricnina/farmacología , Sinapsis/efectos de los fármacosRESUMEN
The nucleus tractus solitarius (NTS) plays an important role in the control of autonomic reflex functions. Glutamate, acting on N-methyl-D-aspartate (NMDA) and non-NMDA ionotropic receptors, is the major neurotransmitter in this nucleus, and the relative contribution of each receptor to signal transmission is unclear. We have examined NMDA excitatory postsynaptic currents (NMDA-EPSCs) in the subpostremal NTS using the whole cell patch clamp technique on a transverse brainstem slice preparation. The NMDA-EPSCs were evoked by stimulation of the solitary tract over a range of membrane potentials. The NMDA-EPSCs, isolated pharmacologically, presented the characteristic outward rectification and were completely blocked by 50 æM DL-2-amino-5-phosphonopentanoic acid. The I-V relationship of the NMDA response shows that current, with a mean (± SEM) amplitude of -41.2 ± 5.5 pA, is present even at a holding potential of -60 mV, suggesting that the NMDA receptors are weakly blocked by extracellular Mg2+ at near resting membrane potentials. This weak block can also be inferred from the value of 0.67 ± 0.17 for parameter delta obtained from a fit of the Woodhull equation to the I-V relationship. The maximal inward current measured on the I-V relationship was at -38.7 ± 4.2 mV. The decay phase of the NMDA currents was fitted with one exponential function with a decay time constant of 239 ± 51 and 418 ± 80 ms at a holding potential of -60 and +50 mV, respectively, which became slower with depolarization (e-fold per 145 mV). The biophysical properties of the NMDA receptors observed in the present study suggest that these receptors in the NTS contain NR2C subunits and may contribute to the synaptic signal integration.
Asunto(s)
Animales , Masculino , Femenino , Ratas , Neuronas/química , Receptores de N-Metil-D-Aspartato/análisis , Núcleo Solitario/citología , Sinapsis/fisiología , Transmisión Sináptica/fisiología , Electrofisiología , Potenciales de la Membrana/fisiología , Neuronas/fisiología , Técnicas de Placa-Clamp , Ratas Wistar , Núcleo Solitario/fisiologíaRESUMEN
Calcitonin gene-related peptide (alpha CGRP) and galanin (GAL) are peptides known to participate in central mechanisms of blood pressure control. Nonetheless, variations in the synthesis of the peptides in response to a hypertensive challenge are not well described, specially using a model, which allows acute and chronic analyses. In this study, we have employed in situ hybridization to analyse changes in mRNA expression of alpha CGRP and GAL in the nucleus tractus solitarii (NTS), hypothalamic paraventricular nucleus (PVN) as well as petrosal and nodose ganglia after aortic coarctation-induced hypertension in rats. Acute (2h) and chronic (3 and 7 days) analyses were performed in order to evaluate the involvement of both peptides in different periods of hypertension. The analysis of relative mRNA levels showed significant differences between sham-operated and aortic coarcted hypertensive rats. alpha CGRP mRNA expression was decreased 2h (40%) and 3 days (42%) in nodose and petrosal ganglia, respectively, after coarctation. No changes in CGRP mRNA signal were seen in the NTS and PVN in the analysed periods. GAL mRNA expression was decreased in the NTS (19%) and PVN (55%), 3 and 7 days, respectively, after coarctation-induced hypertension. No changes in GAL mRNA expression were observed in petrosal and nodose ganglia following aortic coarctation. Data suggest that alpha CGRP and GAL may participate in the mechanisms involved in the establishment/maintenance of hypertension induced by aortic coarctation. Acute changes might be involved with the adaptation to the hypertensive state, while changes at the chronic phase might be related to counteraction of hypertension.
Asunto(s)
Péptido Relacionado con Gen de Calcitonina/metabolismo , Galanina/metabolismo , Hipertensión/metabolismo , Neuronas/metabolismo , Nervios Periféricos/citología , Animales , Presión Sanguínea/fisiología , Péptido Relacionado con Gen de Calcitonina/genética , Galanina/genética , Hipertensión/fisiopatología , Hibridación in Situ/métodos , Masculino , Ganglio Nudoso/metabolismo , Núcleo Hipotalámico Paraventricular/citología , ARN Mensajero/metabolismo , Ratas , Ratas Endogámicas WKY , Núcleo Solitario/citología , Factores de TiempoRESUMEN
Prolactin-releasing peptide (PrRP) was originally thought to participate in the control of adenohypophyseal prolactin secretion, but its predominant expression in a subset of medullary noradrenergic neurons is more in line with roles in interoceptive and/or somatosensory information processing. To better define functional contexts for this peptide system, immuno- and hybridization histochemical methods were used to monitor the capacity of PrRP neurons to display activational responses to lactation, suckling, acute footshock or hypotensive hemorrhage. PrRP mRNA signal was reduced in the medulla of lactating dams, relative to both male and diestrus female controls, with cell counts revealing 42% and 43% reductions in the number of positively hybridized cells in the nucleus of the solitary tract (NTS) and ventrolateral medulla, respectively. Lactating mothers killed after a 90 min suckling episode (following 4 h pup removal) failed to show induced Fos expression in identified medullary PrRP neurons, despite the fact that responsive neurons were detected in other aspects of the caudal NTS. By contrast, acute exposure to hypotensive (25%) hemorrhage or footshock each activated substantial complements of medullary neurons expressing PrRP mRNA. A substantially greater fraction of the total medullary PrRP population exhibited sensitivity to footshock than hemorrhage (71 versus 39%, respectively). These results suggest that medullary PrRP neurons are negatively regulated by (presumably hormonal) changes in lactation, and are not recruited to activation by suckling stimuli. These populations exhibit differential sensitivity to distinct acute stressors, and may participate in the modulation of adaptive neuroendocrine and autonomic responses to each.
Asunto(s)
Hormonas Hipotalámicas/metabolismo , Lactancia/metabolismo , Neuronas/metabolismo , Neuropéptidos/metabolismo , Núcleo Solitario/metabolismo , Estrés Fisiológico/metabolismo , Animales , Animales Recién Nacidos , Animales Lactantes/metabolismo , Conducta Animal , Química Encefálica , Recuento de Células , Diestro/metabolismo , Electrochoque/efectos adversos , Femenino , Hemorragia/metabolismo , Humanos , Hormonas Hipotalámicas/genética , Inmunohistoquímica , Hibridación in Situ , Masculino , Neuropéptidos/genética , Embarazo , Hormona Liberadora de Prolactina , Proteínas Proto-Oncogénicas c-fos/metabolismo , ARN Complementario/metabolismo , Ratas , Ratas Sprague-Dawley , Núcleo Solitario/citologíaRESUMEN
Previous work demonstrated that oxytocinergic projections to the solitary vagal complex are involved in the restraint of exercise-induced tachycardia (2). In the present study, we tested the idea that oxytocin (OT) terminals in the solitary vagal complex [nucleus of the solitary tract (NTS)/dorsal motor nucleus of the vagus (DMV)] are involved in baroreceptor reflex control of heart rate (HR). Studies were conducted in male rats instrumented for chronic cardiovascular monitoring with a cannula in the NTS/DMV for brain injections. Basal mean arterial pressure and HR and reflex HR responses during loading and unloading of the baroreceptors (phenylephrine/sodium nitroprusside intravenously) were recorded after administration of a selective OT antagonist (OT(ant)) or OT into the NTS/DMV. The NTS/DMV was selected for study because this region contains such a specific and dense concentration of OT-immunoreactive terminals. Vehicle injections served as a control. OT and OT(ant) changed baroreflex control of HR in opposite directions. OT (20 pmol) increased the maximal bradycardic response (from -56 +/- 9 to -75 +/- 11 beats/min), whereas receptor blockade decreased the bradycardia (from -61 +/- 13 to -35 +/- 2 beats/min). OT(ant) also reduced the operating range of the reflex, thus decreasing baroreflex gain (from -5.68 +/- 1.62 to -2.83 +/- 1.05 beats x min(-1) x mmHg(-1)). OT injected into the NTS/DMV of atenolol-treated rats still potentiated the bradycardic responses to pressor challenges, whereas OT injections had no effect in atropine-treated rats. The brain stem effect was specific because neither vehicle administration nor injection of OT or OT(ant) into the fourth cerebral ventricle had any effect. Our data suggest that OT terminals in the solitary vagal complex modulate reflex control of the heart, acting to facilitate vagal outflow and the slowdown of the heart.