RESUMO
Breathing is an integrated motor behavior that is driven and controlled by a network of brainstem neurons. Zfhx4 is a zinc finger transcription factor and our results showed that it was specifically expressed in several regions of the mouse brainstem. Mice lacking Zfhx4 died shortly after birth from an apparent inability to initiate respiration. We also found that the electrical rhythm of brainstemâspinal cord preparations was significantly depressed in Zfhx4-null mice compared to wild-type mice. Immunofluorescence staining revealed that Zfhx4 was coexpressed with Phox2b and Math1 in the brainstem and that Zfhx4 ablation greatly decreased the expression of these proteins, especially in the retrotrapezoid nucleus. Combined ChIPâseq and mRNA expression microarray analysis identified Phox2b as the direct downstream target gene of Zfhx4, and this finding was validated by ChIPâqPCR. Previous studies have reported that both Phox2b and Math1 play key roles in the development of the respiratory center, and Phox2b and Math1 knockout mice are neonatal lethal due to severe central apnea. On top of this, our study revealed that Zfhx4 is a critical regulator of Phox2b expression and essential for perinatal breathing.
Assuntos
Apneia , Proteínas de Homeodomínio/genética , Centro Respiratório , Animais , Apneia/metabolismo , Apneia/mortalidade , Fatores de Transcrição Hélice-Alça-Hélice Básicos/metabolismo , Encéfalo/metabolismo , Tronco Encefálico/metabolismo , Regulação da Expressão Gênica , Proteínas de Homeodomínio/metabolismo , Camundongos , Camundongos Knockout/genética , Neurônios/metabolismo , Respiração , Centro Respiratório/embriologia , Centro Respiratório/metabolismo , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismoRESUMO
The respiratory circuit is comprised of over a dozen functionally and anatomically segregated brainstem nuclei that work together to control respiratory rhythms. These respiratory rhythms emerge prenatally but only acquire vital importance at birth, which is the first time the respiratory circuit faces the sole responsibility for O2 /CO2 homeostasis. Hence, the respiratory circuit has little room for trial-and-error-dependent fine tuning and relies on a detailed genetic blueprint for development. This blueprint is provided by transcription factors that have specific spatiotemporal expression patterns along the rostral-caudal or dorsal-ventral axis of the developing brainstem, in proliferating precursor cells and postmitotic neurons. Studying these transcription factors in mice has provided key insights into the functional segregation of respiratory control and the vital importance of specific respiratory nuclei. Many studies converge on just two respiratory nuclei that each have rhythmogenic properties during the prenatal period: the preBötzinger complex (preBötC) and retrotrapezoid nucleus/parafacial nucleus (RTN/pF). Here, we discuss the transcriptional regulation that guides the development of these nuclei. We also summarize evidence showing that normal preBötC development is necessary for neonatal survival, and that neither the preBötC nor the RTN/pF alone is sufficient to sustain normal postnatal respiratory rhythms. Last, we highlight several studies that use intersectional genetics to assess the necessity of transcription factors only in subregions of their expression domain. These studies independently demonstrate that lack of RTN/pF neurons weakens the respiratory circuit, yet these neurons are not necessary for neonatal survival because developmentally related populations can compensate for abnormal RTN/pF function at birth. This article is categorized under: Nervous System Development > Vertebrates: Regional Development.
Assuntos
Neurogênese , Centro Respiratório/metabolismo , Animais , Regulação da Expressão Gênica no Desenvolvimento , Humanos , Centro Respiratório/embriologia , Centro Respiratório/fisiologiaRESUMO
The central command for breathing arises mainly from two interconnected rhythmogenic hindbrain networks, the parafacial respiratory group (pFRG or epF at embryonic stages) and the preBötzinger complex (preBötC), which are comprised of a limited number of neurons located in confined regions of the ventral medulla. In rodents, both networks become active toward the end of gestation but little is known about the signaling pathways involved in their anatomical and functional establishment during embryogenesis. During embryonic development, epF and preBötC neurons migrate from their territories of origin to their final positions in ventral brainstem areas. Planar Cell Polarity (PCP) signaling, including the molecule Scrib, is known to control the developmental migration of several hindbrain neuronal groups. Accordingly, a homozygous mutation of Scrib leads to severe disruption of hindbrain anatomy and function. Here, we aimed to determine whether Scrib is also involved in the prenatal development of the hindbrain nuclei controlling breathing. We combined immunostaining, calcium imaging and electrophysiological recordings of neuronal activity in isolated in vitro preparations. In the Scrib mutant, despite severe neural tube defects, epF and preBötC neurons settled at their expected hindbrain positions. Furthermore, both networks remained capable of generating rhythmically organized, respiratory-related activities and exhibited normal sensitivity to pharmacological agents known to modify respiratory circuit function. Thus Scrib is not required for the proper migration of epF and preBötC neurons during mouse embryogenesis. Our findings thus further illustrate the robustness and specificity of the developmental processes involved in the establishment of hindbrain respiratory circuits.
Assuntos
Peptídeos e Proteínas de Sinalização Intracelular/metabolismo , Respiração , Centro Respiratório/embriologia , Centro Respiratório/metabolismo , Rombencéfalo/embriologia , Rombencéfalo/metabolismo , Animais , Cálcio/metabolismo , Cátions Bivalentes/metabolismo , Movimento Celular/fisiologia , Peptídeos e Proteínas de Sinalização Intracelular/genética , Camundongos Transgênicos , Mutação , Vias Neurais/efeitos dos fármacos , Vias Neurais/embriologia , Vias Neurais/metabolismo , Vias Neurais/patologia , Neurônios/efeitos dos fármacos , Neurônios/metabolismo , Neurônios/patologia , Respiração/efeitos dos fármacos , Centro Respiratório/efeitos dos fármacos , Centro Respiratório/patologia , Medicamentos para o Sistema Respiratório/farmacologia , Rombencéfalo/efeitos dos fármacos , Rombencéfalo/patologia , Técnicas de Cultura de TecidosRESUMO
Breathing is a vital rhythmic behavior generated by hindbrain neuronal circuitry, including the preBötzinger complex network (preBötC) that controls inspiration. The emergence of preBötC network activity during prenatal development has been described, but little is known regarding inspiratory neurons expressing pacemaker properties at embryonic stages. Here, we combined calcium imaging and electrophysiological recordings in mouse embryo brainstem slices together with computational modeling to reveal the existence of heterogeneous pacemaker oscillatory properties relying on distinct combinations of burst-generating INaP and ICAN conductances. The respective proportion of the different inspiratory pacemaker subtypes changes during prenatal development. Concomitantly, network rhythmogenesis switches from a purely INaP/ICAN-dependent mechanism at E16.5 to a combined pacemaker/network-driven process at E18.5. Our results provide the first description of pacemaker bursting properties in embryonic preBötC neurons and indicate that network rhythmogenesis undergoes important changes during prenatal development through alterations in both circuit properties and the biophysical characteristics of pacemaker neurons.
Assuntos
Relógios Biológicos , Tronco Encefálico/embriologia , Tronco Encefálico/fisiologia , Neurônios/fisiologia , Centro Respiratório/embriologia , Centro Respiratório/fisiologia , Animais , Neuroimagem Funcional , Camundongos , Técnicas de Patch-ClampRESUMO
From birth onwards, rhythmic breathing is required for blood oxygenation and survival in mammals. During their lifespan, human or mouse or elephant will spontaneously produce several hundreds of millions of respiratory movements. The central nervous command responsible for these spontaneous rhythmic movements is elaborated by a complex neural network extending within the brainstem. In the medulla, a special part of this network contains respiratory pacemaker neurons that play a crucial role in respiratory rhythmogenesis: the pre-Bötzinger complex. This review summarizes and discusses the main electrophysiological, molecular and genetic mechanisms contributing to the function and the perinatal maturation of the pre-Bötzinger complex.
Assuntos
Fenômenos Eletrofisiológicos , Respiração/genética , Centro Respiratório , Adulto , Animais , Humanos , Recém-Nascido , Mamíferos , Camundongos , Neurônios Motores/citologia , Neurônios Motores/fisiologia , Periodicidade , Centro Respiratório/embriologia , Centro Respiratório/crescimento & desenvolvimento , Centro Respiratório/fisiologiaRESUMO
Foetal breathing in mice results from prenatal activity of the two coupled hindbrain oscillators considered to be responsible for respiratory rhythm generation after birth: the pre-Bötzinger complex (preBötC) is active shortly before the onset of foetal breathing; the parafacial respiratory group (e-pF in embryo) starts activity one day earlier. Transcription factors have been identified that are essential to specify neural progenitors and lineages forming each of these oscillators during early development of the neural tube: Hoxa1, Egr2 (Krox20), Phox2b, Lbx1 and Atoh1 for the e-pF; Dbx1 and Evx1 for the preBötC which eventually grow contralateral axons requiring expression of Robo3. Inactivation of the genes encoding these factors leads to mis-specification of these neurons and distinct breathing abnormalities: apneic patterns and loss of central chemosensitivity for the e-pF (central congenital hypoventilation syndrome, CCHS, in humans), complete loss of breathing for the preBötC, right-left desynchronized breathing in Robo3 mutants. Mutations affecting development in more rostral (pontine) respiratory territories change the shape of the inspiratory drive without affecting the rhythm. Other (primordial) embryonic oscillators start in the mouse three days before the e-pF, to generate low frequency (LF) rhythms that are probably required for activity-dependent development of neurones at embryonic stages; in the foetus, however, they are actively silenced to avoid detrimental interaction with the on-going respiratory rhythm. Altogether, these observations provide a strong support to the previously proposed hypothesis that the functional organization of the respiratory generator is specified at early stages of development and is dual in nature, comprising two serially non-homologous oscillators.
Assuntos
Embrião de Mamíferos/fisiologia , Centro Respiratório/embriologia , Animais , CamundongosRESUMO
Although extracellular calcium ionic concentration ([Ca](o) ) is known to increase during late gestation and to drop after parturition, little is known about the influence of [Ca](o) on fetal brain function. We have investigated the influence of [Ca](o) , calcium-sensing receptors/nonselective cation currents (CaSR/NSCC), and GABAergic inhibitions on maturation of brainstem-spinal motor activities: the primary low-frequency embryonic rhythm [LF; silent since embryonic day (E)16] and the fetal respiratory rhythm (RR; emerging at E14-E15). Using in vitro isolated brainstem-spinal cord preparations of mice at different fetal and postnatal (P) stages (E16-P1), we demonstrate that reducing fetal [Ca](o) from 1.2 mM to 0.7 mM at E16-E18 or blocking GABA(A) receptors at E16-P0 reactivates LF and reveals LF-related disturbance of RR at E16-E18. This LF is stopped by adding gadolinium or spermidine (CaSR/NSCC agonists) at E18-P0 or GABA(A) receptor agonists at E16-E18. In contrast, [Ca](o) -induced slowing of RR at E16-E18 is not reproduced by gadolinium and spermidine. We conclude that perinatal CaSR/NSCC and GABA(A) inhibition allow quiescence of the LF, thereby improving functional maturation of the RR.
Assuntos
Relógios Biológicos/fisiologia , Sinalização do Cálcio/fisiologia , Neurônios Motores/metabolismo , Receptores de Detecção de Cálcio/metabolismo , Receptores de GABA-A/metabolismo , Centro Respiratório/embriologia , Animais , Tronco Encefálico/citologia , Tronco Encefálico/embriologia , Tronco Encefálico/metabolismo , Ondas Encefálicas/fisiologia , Cálcio/metabolismo , Cátions , Embrião de Mamíferos , Desenvolvimento Fetal/fisiologia , Técnicas In Vitro , Canais Iônicos/metabolismo , Camundongos , Centro Respiratório/citologia , Centro Respiratório/metabolismo , Mecânica Respiratória/fisiologia , Medula Espinal/citologia , Medula Espinal/embriologia , Medula Espinal/metabolismoRESUMO
The retrotrapezoid nucleus (RTN) is a group of neurons in the rostral medulla, defined here as Phox2b-, Vglut2-, neurokinin1 receptor-, and Atoh1-expressing cells in the parafacial region, which have been proposed to function both as generators of respiratory rhythm and as central respiratory chemoreceptors. The present study was undertaken to assess these two putative functions using genetic tools. We generated two conditional Phox2b mutations, which target different subsets of Phox2b-expressing cells, but have in common a massive depletion of RTN neurons. In both conditional mutants as well as in the previously described Phox2b(27Ala) mutants, in which the RTN is also compromised, the respiratory-like rhythmic activity normally seen in the parafacial region of fetal brainstem preparations was completely abrogated. Rhythmic motor bursts were recorded from the phrenic nerve roots in the mutants, but their frequency was markedly reduced. Both the rhythmic activity in the RTN region and the phrenic nerve discharges responded to a low pH challenge in control, but not in the mutant embryos. Together, our results provide genetic evidence for the essential role of the Phox2b-expressing RTN neurons both in establishing a normal respiratory rhythm before birth and in providing chemosensory drive.
Assuntos
Células Quimiorreceptoras/metabolismo , Proteínas de Homeodomínio/genética , Respiração , Centro Respiratório/metabolismo , Rombencéfalo/metabolismo , Fatores de Transcrição/genética , Potenciais de Ação/fisiologia , Animais , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Mutação/genética , Rede Nervosa/embriologia , Rede Nervosa/metabolismo , Rede Nervosa/fisiopatologia , Técnicas de Cultura de Órgãos , Nervo Frênico/fisiologia , Centro Respiratório/embriologia , Centro Respiratório/fisiopatologia , Rombencéfalo/embriologia , Rombencéfalo/fisiopatologiaRESUMO
The hindbrain transcription factors Phox2b and Egr2 (also known as Krox20) are linked to the development of the autonomic nervous system and rhombomere-related regulation of breathing, respectively. Mutations in these proteins can lead to abnormal breathing behavior as a result of an alteration in an unidentified neuronal system. We characterized a bilateral embryonic parafacial (e-pF) population of rhythmically bursting neurons at embryonic day (E) 14.5 in mice. These cells expressed Phox2b, were derived from Egr2-expressing precursors and their development was dependent on the integrity of the Egr2 gene. Silencing or eliminating the e-pF oscillator, but not the putative inspiratory oscillator (preBötzinger complex, preBötC), led to an abnormally slow rhythm, demonstrating that the e-pF controls the respiratory rhythm. The e-pF oscillator, the only one active at E14.5, entrained and then coupled with the preBötC, which emerged independently at E15.5. These data establish the dual organization of the respiratory rhythm generator at the time of its inception, when it begins to drive fetal breathing.
Assuntos
Relógios Biológicos/genética , Tronco Encefálico/embriologia , Tronco Encefálico/metabolismo , Regulação da Expressão Gênica no Desenvolvimento/genética , Centro Respiratório/embriologia , Centro Respiratório/metabolismo , Animais , Tronco Encefálico/citologia , Diferenciação Celular/genética , Proteína 2 de Resposta de Crescimento Precoce/genética , Proteína 2 de Resposta de Crescimento Precoce/metabolismo , Proteínas de Homeodomínio/genética , Proteínas de Homeodomínio/metabolismo , Inalação/genética , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Endogâmicos DBA , Camundongos Transgênicos , Rede Nervosa/citologia , Rede Nervosa/embriologia , Rede Nervosa/metabolismo , Neurogênese/genética , Neurônios/citologia , Neurônios/metabolismo , Periodicidade , Centro Respiratório/citologia , Fenômenos Fisiológicos Respiratórios/genética , Formação Reticular/citologia , Formação Reticular/embriologia , Formação Reticular/metabolismo , Células-Tronco/citologia , Células-Tronco/metabolismo , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismoAssuntos
Relógios Biológicos/fisiologia , Tronco Encefálico/embriologia , Rede Nervosa/embriologia , Centro Respiratório/embriologia , Fenômenos Fisiológicos Respiratórios , Animais , Evolução Biológica , Tronco Encefálico/metabolismo , Proteína 2 de Resposta de Crescimento Precoce/metabolismo , Proteínas de Homeodomínio/metabolismo , Humanos , Camundongos , Rede Nervosa/metabolismo , Neurogênese/fisiologia , Neurônios/citologia , Neurônios/metabolismo , Receptores da Neurocinina-1/metabolismo , Centro Respiratório/metabolismo , Células-Tronco/citologia , Células-Tronco/metabolismo , Fatores de Transcrição/metabolismoRESUMO
Breathing is vital for life ex utero and therefore requires that the respiratory rhythm generator (RRG), the central neural network generating the continuous rhythmic motor command, be functional at birth. The RRG, located in the brainstem, appears to comprise two interacting respiratory oscillators: the parafacial respiratory group (pFRG), and the preBötzinger complex (preBötC). Data on the establishment of these respiratory oscillators during embryonic and foetal periods are beginning to be produced. The present paper provides a short review of the current knowledge regarding: (i) the emergence of activity in the two respiratory oscillators and (ii) their functional coupling during prenatal development in rodents.
Assuntos
Tronco Encefálico/embriologia , Periodicidade , Respiração , Centro Respiratório/embriologia , Animais , Tronco Encefálico/citologia , Tronco Encefálico/crescimento & desenvolvimento , Vias Neurais/citologia , Vias Neurais/embriologia , Vias Neurais/crescimento & desenvolvimento , Neurônios/fisiologia , Centro Respiratório/fisiologia , Roedores/fisiologiaRESUMO
Serotonin receptors (5-HTRs) are known to be involved in the regulation of breathing behavior and to mediate neurotrophic actions that exert a significant function in network formation during development. We studied neuronal 5-HT(4(a))R-immunoreactivity (-IR) at developmental ages from E14 to P10. Within the pre-Bötzinger complex (pre-BötC), a part of the respiratory network important for rhythmogenesis, 5-HT(4(a))R-IR was most extensive in rats at an age of E18. The 5-HT(4(a))-IR was found predominantly in the neuropil, whereas somatic staining was sporadic at late embryonic (E18-E20) stages. At birth, we observed a dramatic change to a predominantly somatic staining, and neuropil staining was greatly reduced and disappeared at an age of P4. In all developmental stages, 5-HT(4(a)) and mu-opioid receptors were strongly coexpressed in neurons of the pre-BötC, whereas 5-HT(4(a))R expression was absent in neurons within the dorsal horn. Nestin, a marker for CNS progenitor cells, was used to obtain information about the degree of pre-BötC differentiation. Nestin-positive cells did not appear within the pre-BötC before age E20. At E16, nestin-expressing cells were absent in the nucleus ambiguus (NA) and its ventral periphery. The number of nestin-positive cells increased after birth within and outside the pre-BötC, the majority of cells being glial. Coexpression of nestin and 5-HT(4(a))R was localized predominantly within the NA and appeared only sporadically within the pre-BötC. We conclude that 5-HT(4(a))Rs are important not only for neuromodulation of cellular excitability but also for respiratory network formation.
Assuntos
Regulação da Expressão Gênica no Desenvolvimento , Neurônios/metabolismo , Receptores 5-HT4 de Serotonina/metabolismo , Centro Respiratório/metabolismo , Animais , Ritmo Circadiano/fisiologia , Imuno-Histoquímica , Técnicas In Vitro , Proteínas de Filamentos Intermediários/metabolismo , Bulbo/embriologia , Bulbo/crescimento & desenvolvimento , Bulbo/metabolismo , Proteínas do Tecido Nervoso/metabolismo , Nestina , Ratos , Ratos Sprague-Dawley , Receptores Opioides mu/metabolismo , Centro Respiratório/embriologia , Centro Respiratório/crescimento & desenvolvimento , Células-Tronco , Distribuição TecidualRESUMO
Using voltage-sensitive dye recording, we surveyed neural responses related to the vagus nerve in the embryonic chick brainstem. In our previous studies, we identified four vagus nerve-related response areas in the brainstem. On the stimulated side, they included (1) the nucleus of the tractus solitarius (NTS: the primary sensory nucleus) and (2) the dorsal motor nucleus of the vagus nerve (DMNV), whereas on the contralateral side, they corresponded to (3) the parabrachial nucleus (PBN: the second/higher-ordered nucleus) and (4) the medullary non-NTS region. In the present study, in addition to these areas, we identified another response area circumflex to the obex. The intensity of the optical signal in the response area was much smaller than that in the NTS/DMNV, and the spatio-temporal pattern could be discerned after signal averaging. The conduction rate to the response area was slower than that to the other four areas. Ontogenetically, the response area was distributed on the stimulated side at the 6-day embryonic stage, and it spread into the contralateral side in 7- and 8-day embryonic stages. These distribution patterns were consistent with projection patterns of vagal afferent fibers stained with a fluorescent tracer, suggesting that the response area included a primary sensory nucleus. In comparison with the functional development of the other four response areas, we traced the functional organization of vagus nerve-related nuclei in the embryonic brainstem.
Assuntos
Vias Aferentes/embriologia , Tronco Encefálico/embriologia , Neurônios Aferentes/citologia , Nervo Vago/embriologia , Potenciais de Ação/fisiologia , Vias Aferentes/fisiologia , Animais , Área Postrema/embriologia , Área Postrema/fisiologia , Axônios/fisiologia , Axônios/ultraestrutura , Mapeamento Encefálico/métodos , Tronco Encefálico/fisiologia , Carbocianinas , Embrião de Galinha , Estimulação Elétrica , Eletrofisiologia/métodos , Potenciais Pós-Sinápticos Excitadores/fisiologia , Corantes Fluorescentes , Quarto Ventrículo/anatomia & histologia , Lateralidade Funcional/fisiologia , Neurônios Aferentes/fisiologia , Óptica e Fotônica , Técnicas de Cultura de Órgãos , Centro Respiratório/embriologia , Centro Respiratório/fisiologia , Núcleo Solitário/embriologia , Núcleo Solitário/fisiologia , Coloração e Rotulagem/métodos , Nervo Vago/fisiologiaRESUMO
How regional patterning of the neural tube in vertebrate embryos may influence the emergence and the function of neural networks remains elusive. We have begun to address this issue in the embryonic mouse hindbrain by studying rhythmogenic properties of different neural tube segments. We have isolated pre- and post-otic hindbrain segments and spinal segments of the mouse neural tube, when they form at embryonic day (E) 9, and grafted them into the same positions in stage-matched chick hosts. Three days after grafting, in vitro recordings of the activity in the cranial nerves exiting the grafts indicate that a high frequency (HF) rhythm (order: 10 bursts/min) is generated in post-otic segments while more anterior pre-otic and more posterior spinal territories generate a low frequency (LF) rhythm (order: 1 burst/min). Comparison with homo-specific grafting of corresponding chick segments points to conservation in mouse and chick of the link between the patterning of activities and the axial origin of the hindbrain segment. This HF rhythm is reminiscent of the respiratory rhythm known to appear at E15 in mice. We also report on pre-/post-otic interactions. The pre-otic rhombomere 5 prevents the emergence of the HF rhythm at E12. Although the nature of the interaction with r5 remains obscure, we propose that ontogeny of fetal-like respiratory circuits relies on: (i) a selective developmental program enforcing HF rhythm generation, already set at E9 in post-otic segments, and (ii) trans-segmental interactions with pre-otic territories that may control the time when this rhythm appears.
Assuntos
Região Branquial/embriologia , Vias Eferentes/embriologia , Respiração , Centro Respiratório/embriologia , Rombencéfalo/embriologia , Medula Espinal/embriologia , Potenciais de Ação/fisiologia , Animais , Padronização Corporal/fisiologia , Transplante de Tecido Encefálico/métodos , Região Branquial/fisiologia , Embrião de Galinha , Nervos Cranianos/embriologia , Nervos Cranianos/fisiologia , Vias Eferentes/fisiologia , Desenvolvimento Embrionário/fisiologia , Camundongos , Centro Respiratório/fisiologia , Rombencéfalo/fisiologia , Especificidade da Espécie , Medula Espinal/fisiologia , Quimeras de Transplante/embriologia , Quimeras de Transplante/fisiologiaRESUMO
Adrenaline is a potent respiratory regulator. However, adrenergic contribution to the developing respiratory center has not been studied extensively. Adrenaline application on embryonic day 17 medulla-spinal cord block preparations abolished non-respiratory activity and enhanced respiratory frequency. Phentolamine application on neonatal blocks that produced stable neonatal respiration resulted in respiratory destabilization. These results suggest that central adrenergic modulation is involved in fetal respiratory development and maintenance of stable respiration.
Assuntos
Vias Eferentes/embriologia , Epinefrina/metabolismo , Bulbo/embriologia , Neurônios/metabolismo , Centro Respiratório/embriologia , Medula Espinal/embriologia , Potenciais de Ação/efeitos dos fármacos , Potenciais de Ação/fisiologia , Antagonistas Adrenérgicos alfa/farmacologia , Envelhecimento/efeitos dos fármacos , Envelhecimento/fisiologia , Animais , Animais Recém-Nascidos , Diferenciação Celular/efeitos dos fármacos , Diferenciação Celular/fisiologia , Vias Eferentes/crescimento & desenvolvimento , Vias Eferentes/metabolismo , Epinefrina/farmacologia , Bulbo/crescimento & desenvolvimento , Bulbo/metabolismo , Rede Nervosa/embriologia , Rede Nervosa/crescimento & desenvolvimento , Rede Nervosa/metabolismo , Neurônios/efeitos dos fármacos , Técnicas de Cultura de Órgãos , Fentolamina/farmacologia , Ratos , Ratos Wistar , Centro Respiratório/crescimento & desenvolvimento , Centro Respiratório/metabolismo , Fenômenos Fisiológicos Respiratórios/efeitos dos fármacos , Medula Espinal/crescimento & desenvolvimento , Medula Espinal/metabolismo , Transmissão Sináptica/efeitos dos fármacos , Transmissão Sináptica/fisiologiaRESUMO
By birth, the regulatory neural network responsible for respiratory control is capable of generating robust rhythm-driving ventilation that can adjust to homeostatic needs. The advent of in vitro models isolated from prenatal rodents has significantly advanced our understanding of these processes. In this topical review, we examine the development of medullary respiratory rhythm-generating centres and phrenic motoneurone-diaphragm properties during the prenatal period.
Assuntos
Nervo Frênico/embriologia , Nervo Frênico/fisiologia , Centro Respiratório/embriologia , Centro Respiratório/fisiologia , Mecânica Respiratória/fisiologia , Animais , Feto/fisiologia , Neurônios Motores/fisiologia , Nervo Frênico/citologia , Centro Respiratório/citologiaRESUMO
The survival of neonatal mammals requires a correct function of the respiratory rhythm generator (RRG), and therefore, the processes that control its prenatal maturation are of vital importance. In humans, lambs and rodents, foetal breathing movements (FBMs) occur early during gestation, are episodic, sensitive to bioamines, central hypoxia and inputs from CNS upper structures, and evolve with developmental age. In vitro, the foetal rodent RRG studied in preparations where the upper CNS structures are lacking continuously produces a rhythmic command, which is sensitive to hypoxia and bioaminergic inputs. The rhythm is slow with variable periods 4 days before birth. It becomes faster 2 days before birth, similar to the postnatal rhythm. Compelling evidence suggests that a region of the RRG called the preBötzinger complex (PBC) contains respiratory pacemaker neurones which play a primary role in perinatal rhythmogenesis. Although the RRG functions during early gestation, no pacemakers are found in the putative PBC area and its electrical stimulation and lesion do not affect the early foetal rhythm. To know whether the early foetal and perinatal rhythms originate from either pacemaker neurones or network connection properties, and to know which maturational processes might explain the appearance of PBC pacemakers and the rhythm increase during perinatal development, we computationally modelled maturing RRG. Our model shows that both network noise and persistent sodium conductance are crucial for rhythmogenesis and that a slight increase in the persistent sodium conductance can solve the pacemaker versus network dilemma in a noisy network.
Assuntos
Simulação por Computador , Periodicidade , Centro Respiratório/embriologia , Centro Respiratório/crescimento & desenvolvimento , Fenômenos Fisiológicos Respiratórios , Animais , Animais Recém-Nascidos , Humanos , Recém-NascidoRESUMO
Compared with birds and mammals, very little is known about the development and regulation of respiratory rhythm generation in ectothermic vertebrates. The development and regulation of respiratory rhythm generation in ectothermic vertebrates (fish, amphibians and reptiles) should provide insight into the evolution of these mechanisms. One useful model for examining the development of respiratory rhythm generation in ectothermic vertebrates has emerged from studies with the North American bullfrog (Rana catesbeiana). A major advantage of bullfrogs as a comparative model for respiratory rhythm generation is that respiratory output may be measured at all stages of development, both in vivo and in vitro. An emerging view of recent studies in developing bullfrogs is that many of the mechanisms of respiratory rhythm generation are very similar to those seen in birds and mammals. The overall conclusion from these studies is that respiratory rhythm generation during development may be highly conserved during evolution. The development of respiratory rhythm generation in mammals may, therefore, reflect the antecedent mechanisms seen in ectothermic vertebrates. The main focus of this brief review is to discuss recent data on the development of respiratory rhythm generation in ectothermic vertebrates, with particular emphasis on the North American bullfrog (R. catesbeiana) as a model.
Assuntos
Anfíbios/fisiologia , Rana catesbeiana/fisiologia , Fenômenos Fisiológicos Respiratórios , Animais , Periodicidade , Centro Respiratório/embriologia , Centro Respiratório/crescimento & desenvolvimento , Sistema Respiratório/embriologia , Sistema Respiratório/crescimento & desenvolvimentoRESUMO
To obtain insights into the emergence of rhythmogenic circuits supporting respiration, we monitored spontaneous activities in isolated brainstem and medullary transverse slice preparations of mouse embryos, combining electrophysiological and calcium imaging techniques. At embryonic day 15 (E15), in a restricted region ventral to the nucleus ambiguus, we observed the onset of a sustained high-frequency (HF) respiratory-like activity in addition to a preexisting low-frequency activity having a distinct initiation site, spatial extension, and susceptibility to gap junction blockers. At the time of its onset, the HF generator starts to express the neurokinin 1 receptor, is connected bilaterally, requires active AMPA/kainate glutamatergic synapses, and is modulated by substance P and the mu-opioid agonist D-Ala2-N-Me-Phe4-Glycol5-enkephalin. We conclude that a rhythm generator sharing the properties of the neonatal pre-Bötzinger complex becomes active during E15 in mice.
Assuntos
Tronco Encefálico/citologia , Neurônios Motores/fisiologia , Periodicidade , Respiração , Centro Respiratório/fisiologia , 6-Ciano-7-nitroquinoxalina-2,3-diona/farmacologia , Fatores Etários , Analgésicos Opioides/farmacologia , Animais , Cálcio/metabolismo , Toxina da Cólera/farmacologia , Diagnóstico por Imagem/métodos , Relação Dose-Resposta à Radiação , Estimulação Elétrica/métodos , Embrião de Mamíferos , Ala(2)-MePhe(4)-Gly(5)-Encefalina/farmacologia , Antagonistas de Aminoácidos Excitatórios/farmacologia , Feminino , Imunofluorescência/métodos , Técnicas In Vitro , Masculino , Camundongos , Técnicas de Patch-Clamp/métodos , Gravidez , Receptores da Neurocinina-1/metabolismo , Centro Respiratório/efeitos dos fármacos , Centro Respiratório/embriologia , Substância P/farmacologia , Ácido gama-Aminobutírico/farmacologiaRESUMO
Na+, K+-ATPase 2 subunit gene (Atp1a2) knock-out homozygous mice (Atp1a2-/-) died immediately after birth resulting from lack of breathing. The respiratory-related neuron activity in Atp1a2-/- was investigated using a brainstem-spinal cord en bloc preparation. The respiratory motoneuron activity recorded from the fourth cervical ventral root (C4) was defective in Atp1a2-/- fetuses of embryonic day 18.5. The C4 response to electrical stimulation of the ventrolateral medulla (VLM) recovered more slowly in Atp1a2-/- than in wild type during superfusion with Krebs' solution, consistent with the high extracellular GABA in brain of Atp1a2-/-. Lack of inhibitory neural activities in VLM of Atp1a2-/- was observed by optical recordings. High intracellular Cl- concentrations in neurons of the VLM of Atp1a2-/- were detected in gramicidin-perforated patch-clamp recordings. The alpha2 subunit and a neuron-specific K-Cl cotransporter KCC2 were coimmunoprecipitated in a purified synaptic membrane fraction of wild-type fetuses. Based on these results, we propose a model for functional coupling between the Na+, K+-ATPase alpha2 subunit and KCC2, which excludes Cl- from the cytosol in respiratory center neurons.