Phox2b-Expressing Retrotrapezoid Neurons Are Intrinsically Responsive to H<sup>+</sup>and CO<sub>2</sub>

Wang, Sheng; Shi, Yingtang; Shu, Shaofang; Guyenet, Patrice G.; Bayliss, Douglas A.

doi:10.1523/jneurosci.5550-12.2013

Cited by 90 publications

(101 citation statements)

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“…In contrast, the phrenic response to increasing end-expiratory CO 2 from 5 to 10% was only reduced by 30% after bilateral injection of pyridoxalphosphate-6-azophenyl-2=,4=-disulfonic acid into the RTN of anesthetized vago-sino-aortic-denervated rats (56). In addition, dispersed Phox2b-expressing RTN neurons have been shown to be intrinsically chemosensitive (53). Thus the relative contributions of neurons vs. astrocytes to the overall respiratory response to CO 2 in vivo are not presently known.…”

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confidence: 96%

Conditional depletion of methyl-CpG-binding protein 2 in astrocytes depresses the hypercapnic ventilatory response in mice

Garg

Lioy

Knopp³

et al. 2015

Journal of Applied Physiology

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Garg SK, Lioy DT, Knopp SJ, Bissonnette JM. Conditional depletion of methyl-CpG-binding protein 2 in astrocytes depresses the hypercapnic ventilatory response in mice. J Appl Physiol 119: 670 -676, 2015. First published July 23, 2015 doi:10.1152/japplphysiol.00411.2015Mice that are deficient in the transcription factor methyl-CpG-binding protein 2 (MeCP2) have a depressed hypercapnic ventilatory response (HCVR). The expression of MeCP2 can be selectively removed from astrocytes or neurons, thus offering a tool to dissect the role of this transcription factor in astrocytes from that in neurons. Studies were carried out in the progeny of mice that were a cross between those harboring a tamoxifen (TAM)-inducible Cre recombinase transgene driven by the human astrocytic glial fibrillary acidic protein (hGFAP) promoter, or Cre recombinase under control of the synapsin promoter, with mice containing a Cre-excisable exon III in the Mecp2 gene. The TAM-conditional excision of the Mecp2 exon allowed the respiratory CO2 response to be studied in the same animals before and after selective depletion of MeCP2 in astrocytes. Immunohistochemistry showed that following TAM treatment only ϳ20% of GFAP-labeled cells in the retrotrapazoid nucleus and in the raphé magnus were positive for MeCP2. The slope of the relative increase in minute ventilation as a function of 1, 3, and 5% inspired CO2 was depressed in mice with depleted astrocyte MeCP2 compared with wild-type littermates. In contrast, selective depletion of MeCP2 in neurons did not significantly affect slope. While neurons which constitute the respiratory network ultimately determine the ventilatory response to CO2, this study demonstrates that loss of MeCP2 in astrocytes alone is sufficient to result in a dramatic attenuation of the HCVR. We propose that the glial contribution to HCVR is under the control of the MeCP2 gene.astrocyte; hypercapnic ventilatory response; Rett syndrome HYDROGEN ION HOMEOSTASIS IS largely dependent on CO 2 /pH regulation of minute ventilation. Thus the cellular and molecular mechanisms that transduce changes in blood and brain parenchymal CO 2 /pH to increase the rate and depth of breathing are important areas of current study (12,17,18,21,26,27,40). While the generally accepted view holds that response to CO 2 is a property of neurons, recent work has pointed to an important contribution from astrocytes (14,15,18,21,27). Respiratory CO 2 ventilatory response is significantly depressed in mice that lack or are deficient in the X-linked transcription factor methyl-CpG-binding protein 2 (MeCP2) (6,50,58). Mutations in this nuclear protein cause the neurological disorder Rett syndrome (RTT) (3).A previous study suggested that activation of chemosensitive neurons of the retrotrapezoid nucleus (RTN) could affect CO 2 levels by both their intrinsic pH sensitivity of as well as by non-cell-autonomous activity of neighboring astrocytes (19). The extent of astrocyte contribution by release of ATP to signal RTN neurons is unsettled. Photoactivation of a...

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confidence: 96%

Conditional depletion of methyl-CpG-binding protein 2 in astrocytes depresses the hypercapnic ventilatory response in mice

Garg

Lioy

Knopp³

et al. 2015

Journal of Applied Physiology

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“…O conhecimento desse padrão formado por 3 fases levou a uma série de estudos que se iniciaram em 1970 por Richter e colaboradores em gatos anestesiados utilizando registros intracelulares (RICHTER, 1982). Esses estudos demonstraram que, durante o processo respiratório, atividades fásicas são geradas na região ventral do bulbo sem a necessidade de uma retroalimentação periférica, envolvendo uma rede neuronal coordenada por interações sinápticas que foi chamada posteriormente de coluna respiratória ventral (SMITH et al, 1991 (GUYENET et al, 2005;MULKEY et al, 2004;TAKAKURA et al, 2006;WANG et al, 2013 2) Complexo Bötzinger, um grupamento que contém interneurônios inibitórios predominantemente expiratórios (EZURE, 1990;SCHREIHOFER;GUYENET, 1997).…”

Section: Mecanismos Encefálicos De Controle Da Respiraçãounclassified

Envolvimento do núcleo Kölliker-Fuse e do núcleo parabraquial lateral no controle cardiorrespiratório promovido pela ativação dos quimiorreceptores centrais e periféricos.

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Moreira²

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The pontine nuclei, particularly the Kölliker-Fuse (KF) and the lateral parabrachial nucleus (LPBN) have been implicated in the maintenance of cardiorespiratory control. However, most of the experiments showing the role of pontine KF region were done in anesthetized animals. Here we investigated the involvement of KF region and LPBN in the cardiorespiratory responses elicited by chemoreceptor activation in conscious rats. Male Wistar rats (280-300g, n=5-9) with bilateral stainless steel guide-cannulas implanted into the KF region or LPBN were used. In conscious rats, injections of muscimol (100 and 200 pmol/100 nl) into the KF decreased resting ventilation (1140 ± 68 and 978 ± 100, vs. saline: 1436 ± 155 ml/kg/min) without change mean arterial pressure (MAP) and heart rate (HR). Bilateral injection of the GABA-A antagonist bicuculline (1 nmol/100 nl) into the KF blocked the inhibitory effect on ventilation (1418 ± 138, vs. muscimol: 978 ± 100 ml/kg/min) elicited by muscimol within the KF. Muscimol injection into the KF reduced the increase in ventilation produced by hypoxia (8% O 2 -10 min) (1827 ± 61, vs. saline: 3179 ± 325 ml/kg/min) or hypercapnia (7% CO 2 -10 min) (1488 ± 277, vs. saline: 3539 ± 374 ml/kg/min) in unanesthetized rats. Bilateral injection of bicuculline into the KF was able to block the decrease in ventilation produced by muscimol into the KF during peripheral or central chemoreflex activation. Bilateral injection of muscimol into the LPBN did not change resting ventilation, or the increase in ventilation elicited by hypoxia or hypercapnia. The injection of muscimol into the LPBN increased resting MAP (119 ± 2, vs. saline: 104 ± 2 mmHg), without change resting HR. Muscimol into the LPBN did not change the increase in ventilation elicited by hypoxia or hypercapnia in unanesthetized rats. Selective bilateral lesion with antidopamine-β-hydroxylase-saporin (anti-DβH-SAP) into the A7 region promoted a reduction of hyperventilation (1667 ± 180, vs. saline: 2209 ± 358 ml/kg/min), without changing the tachycardia (471 ± 18, vs. saline: 509 ± 12 bpm) elicited by hypoxia (8% O 2 -10 min) in unanesthetized rats. Bilateral injection of anti-DβH-SAP into the A7 region was able to attenuate the hypotension elicited by hypoxia (112 ± 3, vs. saline: 99 ± 5 mmHg). Anti-DβH-SAP into the A7 region was also able to reduce hyperventilation (1513 ± 167 vs saline: ± 144 2333 ml/kg/min) elicited by hypercapnia (7% CO2 -10 min) in unanesthetized rats. The results of the present study suggest that KF region, but not LPBN, have mechanisms to control the ventilation in resting, hypoxic or hypercapnic conditions in conscious rats.

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“…In coronal slices of the neonate rat brainstem acidification causes excitation even in the presence of glutamatergic, glycinergic and GABAergic ionotropic blockers plus PPADS (blocks ATP receptors) (Mulkey et al, 2004;Lazarenko et al, 2009). When neonate RTN neurons are isolated in a dish their pH sensitivity remains (Wang et al, 2013c). When RTN neurons are inhibited under normoxic conditions in conscious rats both breathing frequency and tidal volume decrease showing that these neurons are necessary to the drive to breathe (Basting et al, 2015).…”

Section: Definitions Of Central Chemoreception and The Retrotrapezoidmentioning

confidence: 99%

“…RTN neurons in slices or isolated from slices have similar characteristics (Lazarenko et al, 2009;Wang et al, 2013c).…”

Section: Hypoxia Silences the Rtnmentioning

confidence: 99%

“…Excitation could be caused by direct effects of acid, produced by CO 2 being rapidly converted to carbonic acid and then a balance between bicarbonate and H+, on the neurons or paracrine effects of CO 2 on the vasculature and astrocytes Gourine & Kasparov, 2011). However, when isolated, the RTN neurons remain extremely sensitive to pH and respond with high levels of activation supporting the idea that this population is intrinsically chemosensitive (Wang et al, 2013c). Finally, the RTN's projections further strengthen its hypothesized role in respiratory chemoreception.…”

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Neural Control of Respiration by the Retrotrapezoid Nucleus.

Basting¹

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Rationale and objectives: Central respiratory chemoreceptors (CRCs) detect brain PaCO 2 and adjust lung ventilation to maintain PaCO 2 and pH constant regardless of the absolute level of lung ventilation. They perform this function in cooperation with the carotid bodies, sensory organs that respond to hypoxia in a pH-dependent manner. The existence of CRCs has been known for over a century but their cellular nature and location have remained highly controversial until recently. The retrotrapezoid nucleus (RTN), a collection of ~2000 glutamatergic neurons in rats that are activated by hypercapnia in vivo and by acidification in slices, had been identified as a CRC candidate just prior to my PhD work. My first objective was to seek additional and critical evidence that RTN neurons are CRCs by determining whether these neurons stimulate breathing in proportion to arterial PCO 2 in intact unanesthetized rats.Having verified that this was the case I tested a logical corollary of this theory namely that RTN is silenced under hypoxic conditions due to respiratory alkalosis. Then I proceeded to test whether RTN neurons sustain breathing automaticity during sleep. Finally, I tested whether RTN compensates for the lack peripheral chemoreceptor input.Methods: RTN neurons were bilaterally transduced to express the proton pump archaerhodopsin using a lentiviral vector. Using anesthetized rats, I confirmed that RTN neurons were silenced by activating archaerhodopsin with green light. I examined the effect of short periods of RTN inhibition (10s) on breathing (plethysmography), EEG and neck EMG in conscious rats in which arterial pH was changed by exposing the animals to various FiO 2 levels alone or with the addition of 3% FiCO 2 or acetazolamide (ACTZ). Rats were studied in different states of vigilance (quiet awake/non-REM/REM). Arterial blood gases (PaO 2 , PaCO 2 ), pHa and HCO 3 were measured under each condition.ii Results: RTN inhibition (bilateral) reduced breathing frequency and amplitude in direct proportion to arterial plasma pH (pHa) below a threshold of 7.53. Above this level, RTN inhibition had no effect suggesting that the nucleus was silent. In normoxia, RTN inhibition reduced breathing equally during non-REM sleep and quiet wake. By contrast RTN inhibition had very little effect on breathing during REM sleep.Conclusions: RTN drives breathing in direct proportion to arterial PCO 2 in intact unaesthetized rats, consistent with the theory that these neurons are CRCs. RTN neurons are silent above pHa 7.5 and increasingly active below this value. RTN regulates breathing automaticity about equally during non-REM sleep and quiet waking, conditions under which the respiratory pattern generator is autorhythmic. By contrast, RTN has a much reduced influence on breathing during Viar for surgery skills, science advice, life advice, wanted/unwanted music advice and so much more. Together, they made a dynamic group of personalities that provided a stimulating and encouraging atmosphere that will never be forgotten....

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Phox2b-Expressing Retrotrapezoid Neurons Are Intrinsically Responsive to H⁺and CO₂

Cited by 90 publications

References 24 publications

Conditional depletion of methyl-CpG-binding protein 2 in astrocytes depresses the hypercapnic ventilatory response in mice

Conditional depletion of methyl-CpG-binding protein 2 in astrocytes depresses the hypercapnic ventilatory response in mice

Envolvimento do núcleo Kölliker-Fuse e do núcleo parabraquial lateral no controle cardiorrespiratório promovido pela ativação dos quimiorreceptores centrais e periféricos.

Neural Control of Respiration by the Retrotrapezoid Nucleus.

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Phox2b-Expressing Retrotrapezoid Neurons Are Intrinsically Responsive to H+and CO2

Cited by 90 publications

References 24 publications

Conditional depletion of methyl-CpG-binding protein 2 in astrocytes depresses the hypercapnic ventilatory response in mice

Conditional depletion of methyl-CpG-binding protein 2 in astrocytes depresses the hypercapnic ventilatory response in mice

Envolvimento do núcleo Kölliker-Fuse e do núcleo parabraquial lateral no controle cardiorrespiratório promovido pela ativação dos quimiorreceptores centrais e periféricos.

Neural Control of Respiration by the Retrotrapezoid Nucleus.

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Phox2b-Expressing Retrotrapezoid Neurons Are Intrinsically Responsive to H⁺and CO₂