Sistemas Hipertexto & Hipermédia - Reflexão, Ensino e Arte

Neste artigo começa por caracterizar-se o desenvolvimento dos sistemas hiper-texto/hipermédia associado ao paradigma da representação mental. Procura-se analisar o fundamento da atitude de mimésis entre os referidos sistemas e as representações internas do indivíduo no processamento de informação. Seguidamente, destaca-se o papel das tecnologias hipertexto/hipermédia no sistema educativo e o impacto inerente à sua implementação. Inclui, no final, uma reflexão sobre a cultura hipertexto/hipermédia e as suas repercussões no mundo da arte

Modulation of arterial pressure by P2 purinoceptors in the paraventricular nucleus of the hypothalamus of awake rats

In the present study we evaluated the role of purinergic mechanisms in the PVN on the tonic modulation of the autonomic function to the cardiovascular system as well on the cardiovascular responses to peripheral chemoreflex activation in awake rats Guide-cannulae were bilaterally Implanted in the direction of the PVN of male Wistar rats Femoral artery and vein were catheterized one day before the experiments Chemoreflex was activated with KCN (30 mu g/0 05 ml iv) before and after microinjections of P2 receptors antagonist into the PVN Microinjection of PPADS a non selective P2X antagonist Into the PVN (n = 6) produced a significant increase in the baseline MAP (99 +/- 2 vs 112 +/- 3 mmHg) and HR (332 +/- 8 vs 375 +/- 8 bpm) but had no effect on the pressor and bradycardic responses to chemoreflex activation Intravenous injection of vasopres in receptors antagonist after microinjection of PPADS into the PVN produced no effect on the increased baseline MAP Simultaneous microinjection of PPADS and KYN into the PVN (n=6) had no effect in the baseline MAP HR or in the pressor and bradycardic responses to chemoreflex activation We conclude that P2 purinoceptors in the PVN are involved in the modulation of baseline autonomic function to the cardiovascular system but not in the cardiovascular responses to chemoreflex activation in awake rats (C) 2010 Elsevier B V All rights reservedFundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)[2004/03285-7]Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)[2009/50113-0

Modulation of respiratory responses to chemoreflex activation by L-glutamate and ATP in the rostral ventrolateral medulla of awake rats

Moraes DJA, Bonagamba LGH, Zoccal DB, Machado BH. Modulation of respiratory responses to chemoreflex activation by L-glutamate and ATP in the rostral ventrolateral medulla of awake rats. Am J Physiol Regul Integr Comp Physiol 300: R1476-R1486, 2011. First published March 16, 2011; doi:10.1152/ajpregu.00825.2010.-Presympathetic neurons in the different anteroposterior aspects of rostral ventrolateral medulla (RVLM) are colocalized with expiratory [Botzinger complex (BotC)] and inspiratory [pre-Botzinger complex (pre-BotC)] neurons of ventral respiratory column (VRC), suggesting that this region integrates the cardiovascular and respiratory chemoreflex responses. In the present study, we evaluated in different anteroposterior aspects of RVLM of awake rats the role of ionotropic glutamate and purinergic receptors on cardiorespiratory responses to chemoreflex activation. The bilateral ionotropic glutamate receptors antagonism with kynurenic acid (KYN) (8 nmol/50 nl) in the rostral aspect of RVLM (RVLM/BotC) enhanced the tachypneic (120 +/- 9 vs. 180 +/- 9 cpm; P < 0.01) and attenuated the pressor response (55 +/- 2 vs. 15 +/- 1 mmHg; P < 0.001) to chemoreflex activation (n = 7). On the other hand, bilateral microinjection of KYN into the caudal aspect of RVLM (RVLM/pre-BotC) caused a respiratory arrest in four awake rats used in the present study. Bilateral P2X receptors antagonism with PPADS (0.25 nmol/50 nl) in the RVLM/BotC reduced chemoreflex tachypneic response (127 +/- 6 vs. 70 +/- 5 cpm; P < 0.001; n = 6), but did not change the chemoreflex pressor response. In addition, PPADS into the RVLM/BtC attenuated the enhancement of the tachypneic response to chemoreflex activation elicited by previous microinjections of KYN into the same subregion (188 +/- 2 vs. 157 +/- 3 cpm; P < 0.05; n = 5). Our findings indicate that: 1) L-glutamate, but not ATP, in the RVLM/BtC is required for pressor response to peripheral chemoreflex and 2) both transmitters in the RVLM/BtC are required for the processing of the ventilatory response to peripheral chemoreflex activation in awake rats.FAPESP Fundacao de Amparo a Pesquisa do Estado de Sao Paulo[2009/50113-0]CNPq Conselho Nacional de Desenvolvimento Cientifico e Technologico[471184/2007-1]CAPES Coordenação de Aperfeiçoamento de Pessoal de Nível Superio

Fos expression in the NTS in response to peripheral chemoreflex activation in awake rats

Chemoreflex afferent fibers terminate in the nucleus tractus solitarii (NTS), but the specific location of the NTS neurons excited by peripheral chemoreflex activation remains to be characterized. Here, the topographic distribution of chemoreflex sensitive cells at the commissural NTS was evaluated. To reach this goal, Fos-immunoreactive neurons (Fos-ir) were accounted in rostro-caudal levels of the intermediate and caudal commissural NTS, after intermittent chemoreflex activation with intravenous injection of potassium cyanide [KCN (80 mu g/kg) or saline (0.9%, vehicle), one injection every 3 min during 30 min]. In response to intermittent intravenous injections of KCN, a significant increase in the number of Fos-ir neurons was observed specifically in the lateral intermediate commissural NTS [(LI)NTS (82 +/- 9 vs. 174 +/- 16, cell number mean per section)] and lateral caudal commissural NTS [(LI)NTS (71 +/- 9 vs. 199 +/- 18, cell number mean per section)]. To evaluate the influence of baroreceptor-mediated inputs following the increase in blood pressure during intermittent chemoreflex activation, we performed an intermittent activation of the arterial baroreflex by intravenous injection of phenylephrine [1.5 mu g/kg iv (one injection every 3 min during 30 min)]. This procedure induced no change in Fos-ir in (LI)NTS (64 +/- 6 vs. 62 +/- 12, cell number mean per section) or (LC)NTS (56 +/- 15 vs. 77 +/- 12, cell number mean per section). These data support the involvement of the commissural NTS in the processing of peripheral chemoreflex, and provide a detailed characterization of the topographical distribution of activated neurons within this brain region. (C) 2009 Elsevier B.V. All rights reserved.FAPESP[2004/03285-7]CNPQ[522150/95-0]CAPESNIH[HL68725

Are l-glutamate and ATP cotransmitters of the peripheral chemoreflex in the rat nucleus tractus solitarius ?

Peripheral chemoreflex activation in awake rats or in the working heart-brainstem preparation (WHBP) produces sympathoexcitation, bradycardia and an increase in the frequency of phrenic nerve activity. Our focus is the neurotransmission of the sympathoexcitatory component of the chemoreflex within the nucleus of the tractus solitarius (NTS), and recently we verified that the simultaneous antagonism of ionotropic glutamate and purinergic P(2) receptors in the NTS blocked the pressor response and increased thoracic sympathetic activity in awake rats and WHBP, respectively, in response to peripheral chemoreflex activation. These previous data suggested the involvement of ATP and L-glutamate in the NTS in the processing of the sympathoexcitatory component of the chemoreflex by unknown mechanisms. For a better understanding of these mechanisms, here we used a patch-clamp approach in brainstem slices to evaluate the characteristics of the synaptic transmission of NTS neurons sending projections to the ventral medulla, which include the premotor neurons involved in the generation of the sympathetic outflow. The NTS neurons sending projections to the ventral medulla were identified by previous microinjection of the membrane tracer dye, 1,1`-dioctadecyl-3,3,3`,3`-tetramethylindocarbocyanine perchlorate (DiI), in the ventral medulla and the spontaneous (sEPSCs) and tractus solitarius (TS)-evoked excitatory postsynaptic current (TS-eEPSCs) were recorded using patch clamp. With this approach, we made the following observations on NTS neurons projecting to the ventral medulla: (i) the sEPSCs and TS-eEPSCs of DiI-labelled NTS neurons were completely abolished by 6,7-dinitroquinoxaline-2,3(1H,4H)-dione (DNQX), an antagonist of ionotropic non-NMDA glutamatergic receptors, showing that they are mediated by L-glutamate; (ii) application of ATP increased the frequency of appearance of spontaneous glutamatergic currents, reflecting an increased exocytosis of glutamatergic vesicles; and (iii) ATP decreased the peak of TS-evoked glutamatergic currents. We conclude that L-glutamate is the main neurotransmitter of spontaneous and TS-evoked synaptic activities in the NTS neurons projecting to the ventral medulla and that ATP has a dual modulatory role on this excitatory transmission, facilitating the spontaneous glutamatergic transmission and inhibiting the TS-evoked glutamatergic transmission. These data also suggest that ATP is not acting as a cotransmitter with L-glutamate, at least at the level of this subpopulation of NTS neurons studied.Fundaccao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)[2004/03285-7]Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPQ)[471184/2007-1

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