Purinergic central pathways involved in the muscle blood flow regulation during alerting defense behaviours.

As reações de alerta e defesa compreendem ajustes cardiovasculares proporcionando um fluxo sangüíneo muscular adequado nas situações de \"luta ou fuga\". As vias centrais e os possíveis neurotransmissores envolvidos nestes ajustes permanecem ainda, em grande parte, desconhecidas. Neste estudo buscamos analisar a participação da neurotransmissão purinérgica e glutamatérgica no núcleo do trato solitário (NTS) na gênese da vasodilatação muscular durante reações de defesa e o papel das vias glutamatérgicas do NTS para o núcleo rostroventrolateral (RVL) nestas respostas. Ratos Wistar machos (250-350 g) foram anestesiados (uretana 600 mg/kg + alpha-chloralose 50 mg/kg, i.v.), paralisados (d-Tubocurarina, 0,5 mg/kg, i.v.) e ventilados artificialmente. Registramos a pressão arterial média (PAM), a freqüência cardíaca (FC) e o fluxo sangüíneo dos membros posteriores (FSMP). A condutância vascular dos membros posteriores (CVMP) foi determinada como a razão FSMP/PAM e expressa como percentagem do valor basal. A estimulação elétrica (EE; 150 MuA; 0,6 ms; 100 Hz; 6 s) do hipotálamo lateral provocou hipertensão, taquicardia e vasodilatação nos membros posteriores. A microinjeção bilateral de suramin (100 pmol/50 nl), um antagonista não específico de receptores P2x no NTS, reduziu a vasodilatação nos membros posteriores durante a EE do hipotálamo (173±19,0 vs 28±14,1% do basal) sem alterar as respostas pressora e taquicárdica. A microinjeção do agonista P2x alpha, beta-methylene ATP (100 pmol/50 nl) no NTS produziu hipotensão, bradicardia e vasodilatação dos membros posteriores. A microinjeção de suramin (100 pmol/50 nl) bloqueou a vasodilatação muscular (76±15,2 vs 9±2,1% do basal) e a hipotensão (-47±4,5 vs -6±2,0 mmHg). A microinjeção de ácido quinurênico (4 nmol/50 nl), um antagonista glutamatérgico ionotrópico não seletivo no NTS bloqueou, de forma semelhante ao suramin, a vasodilatação durante a EE do hipotálamo (134±21,5 vs 27±12,7% do basal) sem alterar as respostas pressora ou taquicárdica. O bloqueio bilateral no RVL com microinjeções de ácido quinurênico reduziu intensamente a resposta hipotensora (-60±6,1 vs -9±3,7 mmHg) e vasodilatadora (126±16,9 vs 17±4,6% do basal) provocada pelas microinjeções de alpha, beta-methylene ATP (100 pmol/50 nl) no NTS. O agonista purinérgico A2a, CGS21680 (20 pmol/50 nl) no NTS, evocou hipotensão, bradicardia e vasodilatação muscular de longa duração. O bloqueio do RVL com ácido quinurênico (4 nmol/50 nl) reduziu a hipotensão (- 41±4,7 vs -7±1,9 mmHg), a bradicardia (-33±9 vs -10±3,1 bpm) e a vasodilatação nos membros posteriores (81±5,6 vs 8±1,5% do basal). Estes resultados sugerem que a vasodilatação muscular nas repostas de defesa depende da ativação de receptores P2x e receptores glutamatérgicos no NTS. Ajustes cardiovasculares por ativação dos receptores purinérgicos P2x e A2a no NTS provocam vasodilatação muscular que depende da liberação de glutamato no RVL, provavelmente ativando interneurônios inibitórios ali presentes.The electrical stimulation (ES) of the hypothalamus in the rat produces a well- defined pattern of cardiovascular adjustments including hypertension, tachycardia and skeletal muscle vasodilation. These hemodynamic responses can also be observed in natural conditions during fight and/or flight behaviors. However the neural pathways and possible neurotransmitters involved remain largely unknown. In this study we sought to determine the role of purinergic and glutamatergic receptors into the nucleus tractus solitarius (NTS) in the cardiovascular responses induced by hypothalamic ES, also we aimed to analyze the role of glutamatergic neural pathways from the NTS to the rostral ventrolateral medulla (RVLM) in these responses. Male Wistar rats (250-350 g) were anesthetized (urethane 600 mg/kg + alpha-chloralose 50 mg/kg, iv), paralyzed (d-tubocurarine 0.5 mg/kg, iv) and artificially ventilated. Mean arterial blood pressure (MAP), heart rate (HR) and hindquarter blood flow (HQBF) were recorded. Hindquarter vascular conductance (HQVC) was calculated as the ratio HQBF/MAP and expressed as percentage of baseline. Hypothalamic ES (6s trains, 0.6 ms square pulses, 100 Hz, 150 MuA) evoked a transitory hypertension, tachycardia and hindlimb muscle vasodilation. After bilateral microinjections of suramin (100 pmol /50 nl), a non-specific P2x receptor antagonist, into the NTS the hindlimb vasodilation was reduced (173±19.0 vs 28±14.1% of baseline), even so the transitory hypertension and tachycardia remained unchanged. A similar vasodilation reduction (134±21.5 vs 27±12.7% of baseline) was observed after microinjections of kynurenic acid bilaterally at the same NTS sites. Microinjections of the P2x receptor agonist alpha, beta-methylene ATP (100 pmol/50 nl) into the NTS produced hypotension, bradycardia and hindlimb muscle vasodilation. Bilateral microinjections of suramin at the same NTS site reduced the hypotension (-47±4.5 vs -6±2.0 mmHg) and the vasodilation (76±15.2 vs 9±2.1% of baseline). After bilateral microinjection of kynurenic acid into the RVLM, both hypotension (-60±6.1 vs -9±3.7 mmHg) and the vasodilation response (126±16.9 vs 17±4.6% of baseline) induced by alpha, beta- methylene ATP into the NTS were reduced. The A2a agonist CGS21680 (20 pmol/50 nl) into the NTS produced a long-lasting hypotension, bradycardia and hindlimb vasodilation. Bilateral RVLM glutamatergic blockade reduced the hypotension (-41±4.7 vs -7±1.9 mmHg), the tachycardia (-33±9.0 vs -10±3.1 bpm) and the muscle vasodilation (81±5.6 vs 8±1.5% of baseline) when CGS21680 was injected into the NTS. Therefore the results suggest that in alerting defense reaction, hindquarter vasodilation is mediated by NTS P2x and also by glutamatergic receptors into the intermediate NTS. Cardiovascular responses evoked by either P2x or A2a receptors stimulation in the NTS are mediated by glutamatergic synapses into the RVLM probably through activation of inhibitory interneurones in this area

Purinergic central pathways involved in the muscle blood flow regulation during alerting defense behaviours.

As reações de alerta e defesa compreendem ajustes cardiovasculares proporcionando um fluxo sangüíneo muscular adequado nas situações de \"luta ou fuga\". As vias centrais e os possíveis neurotransmissores envolvidos nestes ajustes permanecem ainda, em grande parte, desconhecidas. Neste estudo buscamos analisar a participação da neurotransmissão purinérgica e glutamatérgica no núcleo do trato solitário (NTS) na gênese da vasodilatação muscular durante reações de defesa e o papel das vias glutamatérgicas do NTS para o núcleo rostroventrolateral (RVL) nestas respostas. Ratos Wistar machos (250-350 g) foram anestesiados (uretana 600 mg/kg + alpha-chloralose 50 mg/kg, i.v.), paralisados (d-Tubocurarina, 0,5 mg/kg, i.v.) e ventilados artificialmente. Registramos a pressão arterial média (PAM), a freqüência cardíaca (FC) e o fluxo sangüíneo dos membros posteriores (FSMP). A condutância vascular dos membros posteriores (CVMP) foi determinada como a razão FSMP/PAM e expressa como percentagem do valor basal. A estimulação elétrica (EE; 150 MuA; 0,6 ms; 100 Hz; 6 s) do hipotálamo lateral provocou hipertensão, taquicardia e vasodilatação nos membros posteriores. A microinjeção bilateral de suramin (100 pmol/50 nl), um antagonista não específico de receptores P2x no NTS, reduziu a vasodilatação nos membros posteriores durante a EE do hipotálamo (173±19,0 vs 28±14,1% do basal) sem alterar as respostas pressora e taquicárdica. A microinjeção do agonista P2x alpha, beta-methylene ATP (100 pmol/50 nl) no NTS produziu hipotensão, bradicardia e vasodilatação dos membros posteriores. A microinjeção de suramin (100 pmol/50 nl) bloqueou a vasodilatação muscular (76±15,2 vs 9±2,1% do basal) e a hipotensão (-47±4,5 vs -6±2,0 mmHg). A microinjeção de ácido quinurênico (4 nmol/50 nl), um antagonista glutamatérgico ionotrópico não seletivo no NTS bloqueou, de forma semelhante ao suramin, a vasodilatação durante a EE do hipotálamo (134±21,5 vs 27±12,7% do basal) sem alterar as respostas pressora ou taquicárdica. O bloqueio bilateral no RVL com microinjeções de ácido quinurênico reduziu intensamente a resposta hipotensora (-60±6,1 vs -9±3,7 mmHg) e vasodilatadora (126±16,9 vs 17±4,6% do basal) provocada pelas microinjeções de alpha, beta-methylene ATP (100 pmol/50 nl) no NTS. O agonista purinérgico A2a, CGS21680 (20 pmol/50 nl) no NTS, evocou hipotensão, bradicardia e vasodilatação muscular de longa duração. O bloqueio do RVL com ácido quinurênico (4 nmol/50 nl) reduziu a hipotensão (- 41±4,7 vs -7±1,9 mmHg), a bradicardia (-33±9 vs -10±3,1 bpm) e a vasodilatação nos membros posteriores (81±5,6 vs 8±1,5% do basal). Estes resultados sugerem que a vasodilatação muscular nas repostas de defesa depende da ativação de receptores P2x e receptores glutamatérgicos no NTS. Ajustes cardiovasculares por ativação dos receptores purinérgicos P2x e A2a no NTS provocam vasodilatação muscular que depende da liberação de glutamato no RVL, provavelmente ativando interneurônios inibitórios ali presentes.The electrical stimulation (ES) of the hypothalamus in the rat produces a well- defined pattern of cardiovascular adjustments including hypertension, tachycardia and skeletal muscle vasodilation. These hemodynamic responses can also be observed in natural conditions during fight and/or flight behaviors. However the neural pathways and possible neurotransmitters involved remain largely unknown. In this study we sought to determine the role of purinergic and glutamatergic receptors into the nucleus tractus solitarius (NTS) in the cardiovascular responses induced by hypothalamic ES, also we aimed to analyze the role of glutamatergic neural pathways from the NTS to the rostral ventrolateral medulla (RVLM) in these responses. Male Wistar rats (250-350 g) were anesthetized (urethane 600 mg/kg + alpha-chloralose 50 mg/kg, iv), paralyzed (d-tubocurarine 0.5 mg/kg, iv) and artificially ventilated. Mean arterial blood pressure (MAP), heart rate (HR) and hindquarter blood flow (HQBF) were recorded. Hindquarter vascular conductance (HQVC) was calculated as the ratio HQBF/MAP and expressed as percentage of baseline. Hypothalamic ES (6s trains, 0.6 ms square pulses, 100 Hz, 150 MuA) evoked a transitory hypertension, tachycardia and hindlimb muscle vasodilation. After bilateral microinjections of suramin (100 pmol /50 nl), a non-specific P2x receptor antagonist, into the NTS the hindlimb vasodilation was reduced (173±19.0 vs 28±14.1% of baseline), even so the transitory hypertension and tachycardia remained unchanged. A similar vasodilation reduction (134±21.5 vs 27±12.7% of baseline) was observed after microinjections of kynurenic acid bilaterally at the same NTS sites. Microinjections of the P2x receptor agonist alpha, beta-methylene ATP (100 pmol/50 nl) into the NTS produced hypotension, bradycardia and hindlimb muscle vasodilation. Bilateral microinjections of suramin at the same NTS site reduced the hypotension (-47±4.5 vs -6±2.0 mmHg) and the vasodilation (76±15.2 vs 9±2.1% of baseline). After bilateral microinjection of kynurenic acid into the RVLM, both hypotension (-60±6.1 vs -9±3.7 mmHg) and the vasodilation response (126±16.9 vs 17±4.6% of baseline) induced by alpha, beta- methylene ATP into the NTS were reduced. The A2a agonist CGS21680 (20 pmol/50 nl) into the NTS produced a long-lasting hypotension, bradycardia and hindlimb vasodilation. Bilateral RVLM glutamatergic blockade reduced the hypotension (-41±4.7 vs -7±1.9 mmHg), the tachycardia (-33±9.0 vs -10±3.1 bpm) and the muscle vasodilation (81±5.6 vs 8±1.5% of baseline) when CGS21680 was injected into the NTS. Therefore the results suggest that in alerting defense reaction, hindquarter vasodilation is mediated by NTS P2x and also by glutamatergic receptors into the intermediate NTS. Cardiovascular responses evoked by either P2x or A2a receptors stimulation in the NTS are mediated by glutamatergic synapses into the RVLM probably through activation of inhibitory interneurones in this area

Asymmetrical changes in lumbar sympathetic nerve activity following stimulation of the sciatic nerve in rat

Noxious stimulation of the leg increases hind limb blood flow (HBF) to the ipsilateral side and decreases to the contralateral in rat. Whether or not this asymmetrical response is due to direct control by sympathetic terminals or mediated by other factors such as local metabolism and hormones remains unclear. the aim of this study was to compare responses in lumbar sympathetic nerve activity, evoked by stimulation of the ipsilateral and contralateral sciatic nerve (SN). We also sought to determine the supraspinal mechanisms involved in the observed responses. in anesthetized and paralyzed rats, intermittent electrical stimulation (1 mA, 0.5 Hz) of the contralateral SN evoked a biphasic sympathoexcitation. Following ipsilateral SN stimulation, the response is preceded by an inhibitory potential with a latency of 50 ms (N=26). Both excitatory and inhibitory potentials are abolished following cervical Cl spinal transection (N=6) or bilateral microinjections of muscimol (N=6) in the rostral ventrolateral medulla (RVLM). This evidence is suggestive that both sympathetic potentials are supraspinally mediated in this nucleus. Blockade of RVLM glutamate receptors by microinjection of kynurenic acid (N=4) selectively abolished the excitatory potential elicited by ipsilateral SN stimulation. This study supports the physiological model that activation of hind limb nociceptors evokes a generalized sympathoexcitation, with the exception of the ipsilateral side where there is a withdrawal of sympathetic tone resulting in an increase in HBF. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.Macquarie Research Excellence scholarshipCoordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)National Health and Medical Research Council of AustraliaAustralian Research CouncilGarnett Passe and Rodney Williams Memorial FoundationMacquarie UniversityMacquarie Univ, Australian Sch Adv Med, Sydney, NSW 2109, AustraliaUniv São Paulo, Programa Neurociencias & Comportamento, São Paulo, BrazilUniversidade Federal de São Paulo, Dept Fisiol, São Paulo, BrazilUniversidade Federal de São Paulo, Dept Fisiol, São Paulo, BrazilNational Health and Medical Research Council of Australia: 457069National Health and Medical Research Council of Australia: 457080National Health and Medical Research Council of Australia: 604002Australian Research Council: DP110102110Web of Scienc

Interaction of medullary P2 and glutamate receptors mediates the vasodilation in the hindlimb of rat

In the nucleus tractus solitarii (NTS) of rats, blockade of extracellular ATP breakdown to adenosine reduces arterial blood pressure (AP) increases that follow stimulation of the hypothalamic defense area (HDA). the effects of ATP on NTS P2 receptors, during stimulation of the HDA, are still unclear. the aim of this study was to determine whether activation of P2 receptors in the NTS mediates cardiovascular responses to HDA stimulation. Further investigation was taken to establish if changes in hindlimb vascular conductance (HVC) elicited by electrical stimulation of the HDA, or activation of P2 receptors in the NTS, are relayed in the rostral ventrolateral medulla (RVLM); and if those responses depend on glutamate release by ATP acting on presynaptic terminals. in anesthetized and paralyzed rats, electrical stimulation of the HDA increased AP and HVC. Blockade of P2 or glutamate receptors in the NTS, with bilateral microinjections of suramin (10 mM) or kynurenate (50 mM) reduced only the evoked increase in HVC by 75 % or more. Similar results were obtained with the blockade combining both antagonists. Blockade of P2 and glutamate receptors in the RVLM also reduced the increases in HVC to stimulation of the HDA by up to 75 %. Bilateral microinjections of kynurenate in the RVLM abolished changes in AP and HVC to injections of the P2 receptor agonist alpha,beta-methylene ATP (20 mM) into the NTS. the findings suggest that HDA-NTS-RVLM pathways in control of HVC are mediated by activation of P2 and glutamate receptors in the brainstem in alerting-defense reactions.Macquarie Research Excellence ScholarshipCoordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)National Health and Medical Research Council of AustraliaAustralian Research CouncilGarnett Passe and Rodney Williams Memorial FoundationMacquarie UniversityConselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Universidade Federal de São Paulo, Dept Fisiol, BR-04023062 São Paulo, BrazilMacquarie Univ, Australian Sch Adv Med, Sydney, NSW 2109, AustraliaUniv Fed Uberlandia, Fac Educ Fis, BR-38400 Uberlandia, MG, BrazilUniv Fed Goias, Dept Ciencias Fisiol, Goiania, Go, BrazilUniversidade Federal de São Paulo, Dept Fisiol, BR-04023062 São Paulo, BrazilNational Health and Medical Research Council of Australia: 457069National Health and Medical Research Council of Australia: 457080National Health and Medical Research Council of Australia: 604002Australian Research Council: DP110102110CNPq: 477832/2010-5Web of Scienc