RESUMO
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.
Assuntos
Vias Neurais/citologia , Vias Neurais/metabolismo , Neurônios/metabolismo , Núcleo Solitário/citologia , Núcleo Solitário/metabolismo , Transmissão Sináptica/fisiologia , Animais , Corpo Carotídeo/metabolismo , Masculino , Técnicas de Cultura de Órgãos , Técnicas de Patch-Clamp , Ratos , Ratos WistarRESUMO
Despite the well-established sympathoexcitation evoked by chemoreflex activation, the specific sub-regions of the CNS underlying such sympathetic responses remain to be fully characterized. In the present study we examined the effects of intermittent chemoreflex activation in awake rats on Fos-immunoreactivity (Fos-ir) in various subnuclei of the paraventricular nucleus of the hypothalamus (PVN), as well as in identified neurosecretory preautonomic PVN neurons. In response to intermittent chemoreflex activation, a significant increase in the number of Fos-ir cells was found in autonomic-related PVN subnuclei, including the posterior parvocellular, ventromedial parvocellular and dorsal-cap, but not in the neurosecretory magnocellular-containing lateral magnocellular subnucleus. No changes in Fos-ir following chemoreflex activation were observed in the anterior PVN subnucleus. Experiments combining Fos immunohistochemistry and neuronal tract tracing techniques showed a significant increase in Fos-ir in rostral ventrolateral medulla (RVLM)-projecting (PVN-RVLM), but not in nucleus of solitarii tract (NTS)-projecting PVN neurons. In summary, our results support the involvement of the PVN in the central neuronal circuitry activated in response to chemoreflex activation, and indicate that PVN-RVLM neurons constitute a neuronal substrate contributing to the sympathoexcitatory component of the chemoreflex.
Assuntos
Bulbo/fisiologia , Neurônios/metabolismo , Proteínas Oncogênicas v-fos/metabolismo , Núcleo Hipotalâmico Paraventricular/citologia , Vigília , Vias Aferentes/efeitos dos fármacos , Vias Aferentes/fisiologia , Análise de Variância , Animais , Pressão Sanguínea/efeitos dos fármacos , Pressão Sanguínea/fisiologia , Frequência Cardíaca/efeitos dos fármacos , Frequência Cardíaca/fisiologia , Masculino , Bulbo/efeitos dos fármacos , Neurônios/efeitos dos fármacos , Núcleo Hipotalâmico Paraventricular/efeitos dos fármacos , Cianeto de Potássio/farmacologia , Ratos , Ratos WistarRESUMO
Chemoreflex activation with potassium cyanide (KCN, i.v.) produces pressor and bradycardic responses in awake rats in addition to the tachypneic response. In the present study we evaluated the role of the paraventricular nucleus of the hypothalamus (PVN) in the cardiovascular responses to chemoreflex activation in awake rats. Bilateral electrolytic lesion of the PVN was performed 1 day before chemoreflex activation and the results were compared to those obtained with sham-lesioned rats. Bilateral electrolytic lesion of the PVN (n=6) produced a significant reduction in both the magnitude (+51+/-5 vs. +22+/-2 mmHg) and duration (+26+/-5 vs. +6+/-2 s) of the pressor response to chemoreflex activation when compared to sham-lesioned rats (n=10). The bradycardic response to chemoreflex activation in rats with bilateral lesion of the PVN was not significantly different from the response of sham-lesioned rats (-229+/-20 vs. -88+/-76 bpm). Unilateral or partial bilateral lesion of the PVN (n=10) produced no significant changes in the pressor response (+51+/-5 vs. +49+/-3 mmHg), in the duration of the response (+26+/-5 vs. +18+/-3 s) or in the bradycardic response (-229+/-20 vs. -230+/-27 bpm) compared to sham-lesioned rats. The data show that effective bilateral lesion of the PVN produced a significant reduction in the magnitude and duration of the pressor response, indicating that the PVN plays a key role in the processing of the sympathoexcitatory component of the chemoreflex.
Assuntos
Pressão Sanguínea/fisiologia , Células Quimiorreceptoras/fisiologia , Neurônios/fisiologia , Núcleo Hipotalâmico Paraventricular/fisiologia , Reflexo/fisiologia , Sistema Nervoso Simpático/fisiologia , Vigília/fisiologia , Animais , Pressão Sanguínea/efeitos dos fármacos , Células Quimiorreceptoras/efeitos dos fármacos , Inibidores Enzimáticos/farmacologia , Frequência Cardíaca/efeitos dos fármacos , Frequência Cardíaca/fisiologia , Masculino , Núcleo Hipotalâmico Paraventricular/citologia , Cianeto de Potássio/farmacologia , Ratos , Ratos Wistar , Reflexo/efeitos dos fármacos , Sistema Nervoso Simpático/citologiaRESUMO
In the present study we investigated the effects of bilateral microinjection into the lateral commissural nucleus tractus solitarius (NTS) of 2-methyl-5-HT, a 5-HT3 receptor agonist, on the bradycardic response of the von Bezold-Jarisch reflex of awake rats. We evaluated mainly the bradycardic response because in previous studies we documented that the hypotensive response of the von-Bezold-Jarisch reflex in awake rats is secondary to the intense bradycardic response. The Bezold-Jarisch reflex was activated by intravenous injection of serotonin (8 microg/kg) in awake rats before and 1, 3, 10, 20 and 60 min after bilateral microinjection of 2-methyl-5-HT (5 nmol/50 nl, n = 8) into the NTS. Microinjections of 2-methyl-5-HT into the NTS produced a significant increase in basal mean arterial pressure [(MAP), 97 +/- 4 vs. 114 +/- 4 mmHg), no changes in basal heart rate and a significant reduction in bradycardic (-78 +/- 19; -94 +/- 24 and -107 +/- 21 bpm) and hypotensive (-16 +/- 4; -10 +/- 5 and -17 +/- 4 mmHg) responses to activation of the von Bezold-Jarisch reflex at 3, 10 and 20 min, respectively, when compared with the control value (-231 +/- 13 bpm and -43 +/- 4 mmHg). The data of the present study suggest that serotonin acting on 5-HT3 receptors in the NTS may play an important inhibitory neuromodulatory role in the bradycardic response to activation of the von Bezold-Jarisch reflex.
Assuntos
Bradicardia/fisiopatologia , Receptores de Serotonina/fisiologia , Reflexo Anormal/efeitos dos fármacos , Agonistas do Receptor de Serotonina/farmacologia , Serotonina/farmacologia , Núcleo Solitário/efeitos dos fármacos , Análise de Variância , Animais , Nível de Alerta , Pressão Sanguínea/efeitos dos fármacos , Bradicardia/induzido quimicamente , Frequência Cardíaca/efeitos dos fármacos , Masculino , Microinjeções , Fibras Nervosas/efeitos dos fármacos , Fibras Nervosas/fisiologia , Inibição Neural/efeitos dos fármacos , Sistema Nervoso Parassimpático/citologia , Sistema Nervoso Parassimpático/efeitos dos fármacos , Sistema Nervoso Parassimpático/fisiologia , Ratos , Ratos Wistar , Receptores 5-HT3 de Serotonina , Serotonina/análogos & derivados , Núcleo Solitário/citologia , Núcleo Solitário/fisiologia , Sistema Nervoso Simpático/citologia , Sistema Nervoso Simpático/efeitos dos fármacos , Sistema Nervoso Simpático/fisiologia , Transmissão Sináptica/efeitos dos fármacosRESUMO
In the present study we evaluated the effects of bilateral microinjection of muscimol (a GABA(A) receptor agonist) and baclofen (a GABA(B) receptor agonist) into the lateral commissural nucleus tractus solitarii (NTS) of awake rats on the gain of the baroreflex (BG) activated by a short duration (10-15 s) infusion of phenylephrine (Phe, 2.5 microg/0.05 ml, i.v.). Microinjection of muscimol (50 pmol/50 nl, n=8) into the NTS produced a significant increase in baseline mean arterial pressure ((MAP) 122+/-6 vs. 101+/-2 mmHg), no changes in baseline heart rate (HR) and a reduction in BG (-1.59+/-0. 1 vs. -0.69+/-0.1 beats/mmHg). Microinjection of baclofen (6.25 pmol/50 nl, n=6) into the NTS also produced a significant increase in baseline MAP (138+/-5 vs. 103+/-2 mmHg), no changes in baseline HR and a reduction in BG (-1.54+/-0.3 vs. -0.53+/-0.2 beats/mmHg). Considering that the reduction in BG could be secondary to the increase in MAP in response to microinjection of muscimol (n=6) or baclofen (n=7) into the NTS, in these two groups of rats we brought the MAP back to baseline by infusion of sodium nitroprusside (NP, 3.0 microg/0.05 ml, i.v.). Under these conditions, we verified that the BG remained significantly reduced after muscimol (-1.49+/-0.2 vs. -0.35+/-0.2 beats/mmHg) and after baclofen (-1.72+/-0.2 vs. -0.33+/-0.2 beats/mmHg) when compared to control. Reflex tachycardia was observed during the normalization of MAP by NP infusion and, in order to prevent the autonomic imbalance from affecting BG, we used another group of rats treated with atenolol (5 mg/kg, i.v.), a beta1 receptor antagonist. In rats previously treated with atenolol and submitted to NP infusion, we verified that BG remained reduced after microinjection of muscimol or baclofen into the NTS. The data show that activation of GABA(A) and GABA(B) receptors, independently of the changes in the baseline MAP or HR, inhibited the neurons of the NTS involved in the parasympathetic component of the baroreflex.
Assuntos
Barorreflexo/fisiologia , Pressão Sanguínea/fisiologia , Bradicardia , Frequência Cardíaca/fisiologia , Receptores de GABA-A/fisiologia , Receptores de GABA-B/fisiologia , Núcleo Solitário/fisiologia , Animais , Anti-Hipertensivos/farmacologia , Baclofeno/farmacologia , Barorreflexo/efeitos dos fármacos , Pressão Sanguínea/efeitos dos fármacos , Bradicardia/induzido quimicamente , Cardiotônicos , Agonistas GABAérgicos/farmacologia , Frequência Cardíaca/efeitos dos fármacos , Masculino , Muscimol/farmacologia , Nitroprussiato/farmacologia , Fenilefrina , Ratos , Ratos Wistar , Receptores de GABA-A/efeitos dos fármacos , Receptores de GABA-B/efeitos dos fármacos , Núcleo Solitário/efeitos dos fármacosRESUMO
The neurotransmission of the chemoreflex in the nucleus tractus solitarii (NTS), particularly of the sympatho-excitatory component, is not completely understood. There is evidence that substance P may play a role in the neurotransmission of the chemoreflex in the NTS. Microinjection of substance P (50 pmol/50 nl, N = 12, and 5 nmol/50 nl, N = 8) into the commissural NTS of unanesthetized rats produced a significant increase in mean arterial pressure (101 +/- 1 vs 108 +/- 2 and 107 +/- 3 vs 115 +/- 4 mmHg, respectively) and no significant changes in heart rate (328 +/- 11 vs 347 +/- 15 and 332 +/- 7 vs 349 +/- 13 bpm, respectively) 2 min after microinjection. Previous treatment with WIN, an NK-1 receptor antagonist (2.5 nmol/50 nl), microinjected into the NTS of a specific group of rats, blocked the pressor (11 +/- 5 vs 1 +/- 2 mmHg) and tachycardic (31 +/- 6 vs 4 +/- 3 bpm) responses to substance P (50 pmol/50 nl, N = 5) observed 10 min after microinjection. Bilateral microinjection of WIN into the lateral commissural NTS (N = 8) had no significant effect on the pressor (50 +/- 4 vs 42 +/- 6 mmHg) or bradycardic (-230 +/- 16 vs -220 +/- 36 bpm) responses to chemoreflex activation with potassium cyanide (iv). These data indicate that the activation of NK-1 receptors by substance P in the NTS produces an increase in baseline mean arterial pressure and heart rate. However, the data obtained with WIN suggest that substance P and NK-1 receptors do not play a major role in the neurotransmission of the chemoreflex in the lateral commissural NTS
Assuntos
Animais , Ratos , Masculino , Pressão Sanguínea/efeitos dos fármacos , Frequência Cardíaca/efeitos dos fármacos , Receptores da Neurocinina-1/antagonistas & inibidores , Núcleo Solitário , Microinjeções , Ratos WistarRESUMO
The neurotransmission of the chemoreflex in the nucleus tractus solitarii (NTS), particularly of the sympatho-excitatory component, is not completely understood. There is evidence that substance P may play a role in the neurotransmission of the chemoreflex in the NTS. Microinjection of substance P (50 pmol/50 nl, N = 12, and 5 nmol/50 nl, N = 8) into the commissural NTS of unanesthetized rats produced a significant increase in mean arterial pressure (101 +/- 1 vs 108 +/- 2 and 107 +/- 3 vs 115 +/- 4 mmHg, respectively) and no significant changes in heart rate (328 +/- 11 vs 347 +/- 15 and 332 +/- 7 vs 349 +/- 13 bpm, respectively) 2 min after microinjection. Previous treatment with WIN, an NK-1 receptor antagonist (2.5 nmol/50 nl), microinjected into the NTS of a specific group of rats, blocked the pressor (11 +/- 5 vs 1 +/- 2 mmHg) and tachycardic (31 +/- 6 vs 4 +/- 3 bpm) responses to substance P (50 pmol/50 nl, N = 5) observed 10 min after microinjection. Bilateral microinjection of WIN into the lateral commissural NTS (N = 8) had no significant effect on the pressor (50 +/- 4 vs 42 +/- 6 mmHg) or bradycardic (-230 +/- 16 vs -220 +/- 36 bpm) responses to chemoreflex activation with potassium cyanide (iv). These data indicate that the activation of NK-1 receptors by substance P in the NTS produces an increase in baseline mean arterial pressure and heart rate. However, the data obtained with WIN suggest that substance P and NK-1 receptors do not play a major role in the neurotransmission of the chemoreflex in the lateral commissural NTS.
Assuntos
Pressão Sanguínea/efeitos dos fármacos , Células Quimiorreceptoras/efeitos dos fármacos , Frequência Cardíaca/efeitos dos fármacos , Antagonistas dos Receptores de Neurocinina-1 , Núcleo Solitário/efeitos dos fármacos , Análise de Variância , Animais , Masculino , Microinjeções , Ratos , Ratos Wistar , Substância P/farmacologiaRESUMO
Previous reports have described that glutamate ionotropic receptors in the nucleus tractus solitarius (NTS) are involved in the reflex control of heart rate, and that such a control can be inhibited by NTS-5-HT(3) receptor stimulation. In the present study, we examined in urethane anaesthetized rats the effects of intra-NTS microinjection of 1-(m-chlorophenyl)-biguanide (CPBG), a potent and selective 5-HT(3) receptor agonist, on the cardiovascular responses to local administration of glutamate ionotropic receptor agonists. Intra-NTS microinjection of CPBG reduced the atropine-sensitive bradycardia elicited by local microinjection of NMDA without affecting the cardiovascular responses to intra-NTS microinjections of AMPA or kainic acid. The reduction by CPBG of the NMDA-evoked cardiac response was blocked by prior intra-NTS microinjection of granisetron, a 5-HT(3) receptor antagonist, as well as bicuculline, a GABA(A) receptor antagonist. These results suggest that the stimulation of NTS 5-HT(3) receptors specifically reduces, via a GABA-dependent mechanism, the cardiac response to local NMDA administration.
Assuntos
Agonistas de Aminoácidos Excitatórios/farmacologia , Frequência Cardíaca/efeitos dos fármacos , N-Metilaspartato/farmacologia , Receptores de Serotonina/efeitos dos fármacos , Núcleo Solitário/fisiologia , Animais , Barorreflexo/efeitos dos fármacos , Bicuculina/farmacologia , Biguanidas/farmacologia , Agonistas de Aminoácidos Excitatórios/administração & dosagem , Antagonistas GABAérgicos/farmacologia , Granisetron/farmacologia , Hemodinâmica/efeitos dos fármacos , Masculino , Microinjeções , N-Metilaspartato/administração & dosagem , Ratos , Ratos Sprague-Dawley , Receptores de Ácido Caínico/antagonistas & inibidores , Receptores 5-HT3 de Serotonina , Antagonistas da Serotonina/farmacologia , Agonistas do Receptor de Serotonina/farmacologia , Sistema Nervoso Simpático/efeitos dos fármacos , Ácido alfa-Amino-3-hidroxi-5-metil-4-isoxazol Propiônico/farmacologiaRESUMO
The effect of sequential blockade of N-methyl-D-aspartic acid (NMDA) receptors with DL-2-amino-5-phosphonopentanoic acid (AP-5) and non-NMDA receptors with 6,7-dinitroquinoxaline-2,3 dione (DNQX) in the nucleus tractus solitarii (NTS) on the cardiovascular responses to electrical stimulation (ES) of the aortic depressor nerve (ADN) was evaluated in awake rats. Two protocols were used. In protocol 1, bilateral microinjection of AP-5 into the NTS (n = 7) reduced the hypotensive response to ES of the ADN; subsequent microinjection of DNQX produced additional reduction in this response. AP-5 reduced the bradycardic response, and DNQX almost abolished this response. In protocol 2, bilateral microinjection of DNQX into the NTS (n = 6) reduced the hypotensive response, and subsequent microinjection of AP-5 significantly reduced this response. DNQX produced a significant reduction in bradycardic response, and AP-5 abolished this response. The data indicate that processing of the parasympathetic component of the NTS aortic baroreceptor afferents is mediated by both NMDA and non-NMDA receptors, whereas processing of the sympathoinhibitory component seems to be only partially mediated by ionotropic receptors.
Assuntos
Aorta/inervação , Sistema Nervoso Autônomo/fisiologia , Pressorreceptores/fisiologia , Núcleo Solitário/fisiologia , Transmissão Sináptica/fisiologia , Vias Aferentes/fisiologia , Animais , Pressão Sanguínea/efeitos dos fármacos , Pressão Sanguínea/fisiologia , Tronco Encefálico/citologia , Tronco Encefálico/fisiologia , Estimulação Elétrica , Antagonistas de Aminoácidos Excitatórios/administração & dosagem , Antagonistas de Aminoácidos Excitatórios/farmacologia , Frequência Cardíaca/efeitos dos fármacos , Frequência Cardíaca/fisiologia , Masculino , Microinjeções , Músculo Liso Vascular/efeitos dos fármacos , Músculo Liso Vascular/fisiologia , Quinoxalinas/administração & dosagem , Quinoxalinas/farmacologia , Ratos , Ratos Wistar , VigíliaRESUMO
The baroreflex activation with phenylephrine infusion produces a bradycardic response. In the present study, the role of NMDA receptors in the nucleus tractus solitarii (NTS) in the processing of the parasympathetic component of the baroreflex was evaluated using acid phosphonivaleric (AP-5), a selective NMDA receptor antagonist. Baroreflex activation was performed before and after bilateral microinjection of AP-5 into the intermediate commissural NTS (0.5 mm lateral to the midline). Microinjection of the vehicle (saline, 0.9%) or a dose of 2 nmol/50 nl of AP-5 into the NTS produced no effect on the gain of the baroreflex while a dose of 10 nmol/50 nl of AP-5 produced a significant reduction in the gain of the baroreflex 2 min after microinjection [-1.43+/-0.22 vs. -0. 43+/-0.03 bpm/mmHg, (n=6)], with a return to control levels 10 min after the microinjections. The dose of 10 nmol/50 nl was selective for NMDA receptors considering that the cardiovascular responses to microinjection of AMPA (0.05 pmol/50 nl), a non-NMDA receptor agonist, were not affected by this dose of AP-5 and the responses to microinjection of NMDA (2 nmol/50 nl) were blocked. The data show that the bradycardic response to baroreflex activation was blocked by AP-5 microinjected into the NTS, indicating that the neurotransmission of the parasympathetic component of the baroreflex is mediated by NMDA receptors in the NTS.