Glial cells modulate the synaptic transmission of NTS neurons sending projections to ventral medulla of Wistar rats

There is evidence that sympathoexcitatory and respiratory responses to chemoreflex activation involve ventrolateral medulla-projecting nucleus tractus solitarius (NTS) neurons (NTS-VLM neurons) and also that ATP modulates this neurotransmission. Here, we evaluated whether or not astrocytes is the source of endogenous ATP modulating the synaptic transmission in NTSVLM neurons. Synaptic activities of putative astrocytes or NTS-VLM neurons were recorded using whole cell patch clamp. Tractus solitarius (TS) stimulation induced TS-evoked excitatory postsynaptic currents (TS-eEPSCs) in NTSVLM neurons as well in NTS putative astrocytes, which were also identified by previous labeling. Fluoracetate (FAC), an inhibitor of glial metabolism, reduced TS-eEPSCs amplitude ( 85.6 16 vs. 39 7.1 pA, n = 12) and sEPSCs frequency (2.8 0.5 vs. 1.8 0.46 Hz, n = 10) in recorded NTSVLM neurons, indicating a gliomodulation of glutamatergic currents. To verify the involvement of endogenous ATP a purinergic antagonist was used, which reduced the TS-eEPSCs amplitude ( 207 50 vs. 149 50 pA, n = 6), the sEPSCs frequency (1.19 0.2 vs. 0.62 0.11 Hz, n = 6), and increased the paired-pulse ratio (PPR) values (~20%) in NTS-VLM neurons. Simultaneous perfusion of Pyridoxalphosphate-6-azophenyl-2′,5′-disulfonic acid (iso-PPADS) and FAC produced reduction in TS-eEPSCs similar to that observed with iso-PPADS or FAC alone, indicating that glial cells are the source of ATP released after TS stimulation. Extracellular ATP measurement showed that FAC reduced evoked and spontaneous ATP release. All together these data show that putative astrocytes are the source of endogenous ATP, which via activation of presynaptic P2X receptors, facilitates the evoked glutamate release and increases the synaptic transmission efficacy in the NTS-VLM neurons probably involved with the peripheral chemoreflex pathways.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Cietnífico e Tecnológico (CNPq

DIFERENTES ABORDAGENS EXPERIMENTAIS NO ESTUDO DA MODULAÇÃO DA ATIVIDADE SIMPÁTICA NO SISTEMA NERVOSO CENTRAL DE RATOS

The main purpose of the present review is to present the experience of our laboratory on the last few years on studies related to the neurotransmission of the sympatho- xcitatory component of the chemoreflex in the nucleus tractus solitary (NTS) of rats. The experimental approach of the chemoreflex activation has been used as a model for the understanding of the neurochemical mechanisms involved in the generation and modulation of the sympathetic activity, which have influence on the cardiovascular system on physiological and pathophysiological circumstances such as arterial hypertension. The specific focus of this review is the neurotransmission of the sympatho-excitatory component of the chemoreflex in the NTS but also we present several methods and experimental approaches used currently in our laboratory in order to understand this complex neurotransmission system. Using this combination of methods from the NTS neurons to the awake rat, we wish to discuss the use of several contemporary techniques, which are allowing us to expand the frontiers of this important scientific area.Essa revisão tem como objetivo apresentar a experiência do nosso laboratório, acumulada ao longo dos últimos anos no estudo da neurotransmissão do componente simpatoexcitatório do quimiorreflexo no núcleo do trato solitário (NTS) de ratos. Essa abordagem experimental tem sido utilizada como um modelo para o melhor entendimento dos mecanismos neuroquímicos envolvidos na geração e modulação da atividade simpática, a qual tem importantes repercussões para o sistema cardiovascular tanto em condições fisiológicas quanto em condições fisiopatológicas como a hipertensão arterial. O foco específico dessa revisão está centrado na neurotransmissão do componente simpato-excitatório do quimiorreflexo no núcleo do trato solitário (NTS) e apresentamos vários métodos e abordagens experimentais que estão sendo utilizados com vistas ao melhor entendimento desse complexo sistema de neurotransmissão. Com essa combinação de métodos, que vão desde um neurônio do NTS até o rato acordado e com livre movimentação, queremos ilustrar as múltiplas possibilidades de abordagens experimentais contemporâneas, as quais estão nos proporcionando as condições materiais para estender os horizontes dessa importante área do conhecimento

DIFERENTES ABORDAGENS EXPERIMENTAIS NO ESTUDO DA MODULAÇÃO DA ATIVIDADE SIMPÁTICA NO SISTEMA NERVOSO CENTRAL DE RATOS

Essa revisão tem como objetivo apresentar a experiência do nosso laboratório, acumulada ao longo dos últimos anos no estudo da neurotransmissão do componente simpatoexcitatório do quimiorreflexo no núcleo do trato solitário (NTS) de ratos. Essa abordagem experimental tem sido utilizada como um modelo para o melhor entendimento dos mecanismos neuroquímicos envolvidos na geração e modulação da atividade simpática, a qual tem importantes repercussões para o sistema cardiovascular tanto em condições fisiológicas quanto em condições fisiopatológicas como a hipertensão arterial. O foco específico dessa revisão está centrado na neurotransmissão do componente simpato-excitatório do quimiorreflexo no núcleo do trato solitário (NTS) e apresentamos vários métodos e abordagens experimentais que estão sendo utilizados com vistas ao melhor entendimento desse complexo sistema de neurotransmissão. Com essa combinação de métodos, que vão desde um neurônio do NTS até o rato acordado e com livre movimentação, queremos ilustrar as múltiplas possibilidades de abordagens experimentais contemporâneas, as quais estão nos proporcionando as condições materiais para estender os horizontes dessa importante área do conhecimento.The main purpose of the present review is to present the experience of our laboratory on the last few years on studies related to the neurotransmission of the sympatho- xcitatory component of the chemoreflex in the nucleus tractus solitary (NTS) of rats. The experimental approach of the chemoreflex activation has been used as a model for the understanding of the neurochemical mechanisms involved in the generation and modulation of the sympathetic activity, which have influence on the cardiovascular system on physiological and pathophysiological circumstances such as arterial hypertension. The specific focus of this review is the neurotransmission of the sympatho-excitatory component of the chemoreflex in the NTS but also we present several methods and experimental approaches used currently in our laboratory in order to understand this complex neurotransmission system. Using this combination of methods from the NTS neurons to the awake rat, we wish to discuss the use of several contemporary techniques, which are allowing us to expand the frontiers of this important scientific area

PACEMAKING PROPERTY OF RVLM PRESYMPATHETIC NEURONS

Despite several studies describing the electrophysiological properties of RVLM presympathetic neurons, there is no consensus in the literature about their pacemaking property, mainly due to different experimental approaches used for recordings of neuronal intrinsic properties. In this review we are presenting a historical retrospective about the pioneering studies and their controversies on the intrinsic electrophysiological property of auto-depolarization of these cells in conjunction with recent studies from our laboratory documenting that RVLM presympathetic neurons present pacemaking capacity. We also discuss whether increased sympathetic activity observed in animal models of neurogenic hypertension (CIH and SHR) are dependent on changes in the intrinsic electrophysiological properties of these cells or due to changes in modulatory inputs from neurons of the respiratory network. We also highlight the key role of INaP as the major current contributing to the pacemaking property of RVLM presympathetic neurons