RESUMEN
In mammals, the neural control of breathing is attributed to circuits distributed along the ventral respiratory column (VRC) in the ventrolateral medulla. The VRC contains the kernel for generation of the inspiratory phase of respiratory rhythm and nuclei involved in central chemoreception. During development, the respiratory rhythm, as well as central chemosensitivity, adjusts to meet the changing physiological requirements associated with increased body weight and size. Gene expression in VRC ontogeny is well characterized. However, little is known about gene expression in the VRC during postnatal development. Here, we sought to characterize the changes in gene expression that occur in the VRC of the adult rat (5-6 months of age) in comparison with the VRC of neonate rat (1-4 days old). We isolated total RNA from VRC tissue punches collected from thick transversal slices. We hybridized cDNA to a 5000-oligonucleotide rat microarray. We found that 218 genes (4.4%) of the 5000 genes in the microarray changed their expression in adult VRC with respect to that from neonate. To further analyze the modified expression of specific genes, we quantified the differential expression of 84 genes of neuronal ion channels using a quantitative RT-PCR array. This analysis confirmed the overexpression of 68 genes and the underexpression of 14 genes in the VRC from adult compared with that from neonate. Our findings may help to explain the functional changes in respiratory rhythm and chemosensitivity occurring throughout life.
Asunto(s)
Regulación del Desarrollo de la Expresión Génica , Canales Iónicos/genética , Centro Respiratorio/metabolismo , Animales , Canales Iónicos/metabolismo , Masculino , Ratas , Ratas Wistar , Centro Respiratorio/crecimiento & desarrolloRESUMEN
Somatostatin is a peptide able to stop breathing, acting in the neural network that generates and control the respiratory rhythm. In this chapter, we present data on the early postnatal development of somatostatinergic systems in the mouse brainstem and summarize evidence for their influence on the generation and control of the respiratory rhythm.
Asunto(s)
Tronco Encefálico/fisiología , Neuronas/metabolismo , Respiración , Centro Respiratorio/fisiología , Somatostatina/metabolismo , Animales , Tronco Encefálico/crecimiento & desarrollo , Tronco Encefálico/metabolismo , Ratones , Centro Respiratorio/crecimiento & desarrollo , Centro Respiratorio/metabolismoRESUMEN
On postnatal days P10-P15 in rat medulla, neurotransmitter receptor subunit composition shifts toward a more mature phenotype. Since medullary GABAARs regulate cardiorespiratory function, abrupt alterations in GABAergic synaptic inhibition could disrupt homeostasis. We hypothesized that GABAARs on medullary neurons become more resistant to positive allosteric modulation during P10-P15. Medullary and cortical slices from P10 to P20 rats were used to record spontaneous action potentials in pre-Botzinger Complex (preBötC-region), hypoglossal (XII) motor nucleus, nucleus tractus solitarius (NTS), and cortex during exposure to pentobarbital (positive allosteric modulator of GABAARs). On P14, pentobarbital resistance abruptly increased in preBötC-region and decreased in NTS, but these changes in pentobarbital resistance were not present on P15. Pentobarbital resistance decreased in XII motor nucleus during P11-P15 with a nadir at P14. Abrupt changes in pentobarbital resistance indicate changes in GABAergic receptor composition and function that may compensate for potential increased GABAergic inhibition and respiratory depression that occurs during this key developmental transitional period.
Asunto(s)
Corteza Cerebral , Hipnóticos y Sedantes/farmacología , Neuronas/efectos de los fármacos , Pentobarbital/farmacología , Centro Respiratorio , Núcleo Solitario , Potenciales de Acción/efectos de los fármacos , Factores de Edad , Animales , Animales Recién Nacidos , Corteza Cerebral/citología , Corteza Cerebral/efectos de los fármacos , Corteza Cerebral/crecimiento & desarrollo , Técnicas In Vitro , Vías Nerviosas/efectos de los fármacos , Vías Nerviosas/fisiología , Neuronas/fisiología , Ratas , Ratas Wistar , Centro Respiratorio/citología , Centro Respiratorio/efectos de los fármacos , Centro Respiratorio/crecimiento & desarrollo , Núcleo Solitario/citología , Núcleo Solitario/efectos de los fármacos , Núcleo Solitario/crecimiento & desarrollo , Factores de TiempoRESUMEN
In vertebrates, respiratory control is ascribed to heterogeneous respiration-modulated neurons along the Ventral Respiratory Column (VRC) in medulla, which includes the preBötzinger Complex (preBötC), the putative respiratory rhythm generator. Here, the functional anatomy of the VRC was characterized via optical recordings in the sagittaly sectioned neonate rat hindbrain, at sampling rates permitting coupling estimation between neuron pairs, so that each neuron was described using unitary, neuron-system, and coupling attributes. Structured coupling relations in local networks, significantly oriented coupling in the peri-inspiratory interval detected in pooled data, and significant correlations between firing rate and expiratory duration in subsets of neurons revealed network regulation at multiple timescales. Spatially averaged neuronal attributes, including coupling vectors, revealed a sharp boundary at the rostral margin of the preBötC, as well as other functional anatomical features congruent with identified structures, including the parafacial respiratory group and the nucleus ambiguus. Cluster analysis of attributes identified two spatially compact, homogenous groups: the first overlapped with the preBötC, and was characterized by strong respiratory modulation and dense bidirectional coupling with itself and other groups, consistent with a central role for the preBötC in respiratory control; the second lay between preBötC and the facial nucleus, and was characterized by weak respiratory modulation and weak coupling with other respiratory neurons, which is congruent with cardiovascular regulatory networks that are found in this region. Other groups identified using cluster analysis suggested that networks along VRC regulated expiratory duration, and the transition to and from inspiration, but these groups were heterogeneous and anatomically dispersed. Thus, by recording local networks in parallel, this study found evidence for respiratory regulation at multiple timescales along the VRC, as well as a role for the preBötC in the integration of functionally disparate respiratory neurons.
Asunto(s)
Bulbo Raquídeo/fisiología , Red Nerviosa/fisiología , Neuronas/fisiología , Respiración , Centro Respiratorio/fisiología , Animales , Animales Recién Nacidos , Bulbo Raquídeo/crecimiento & desarrollo , Ratas , Ratas Sprague-Dawley , Centro Respiratorio/crecimiento & desarrolloRESUMEN
Central CO(2) chemosensitivity is crucial for all air-breathing vertebrates and raises the question of its role in ventilatory rhythmogenesis. In this study, neurograms of ventilatory motor outputs recorded in facial nerve of premetamorphic and postmetamorphic tadpole isolated brainstems, under normo- and hypercapnia, are investigated using Continuous Wavelet Transform spectral analysis for buccal activity and computation of number and amplitude of spikes during buccal and lung activities. Buccal bursts exhibit fast oscillations (20-30Hz) that are prominent in premetamorphic tadpoles: they result from the presence in periodic time windows of high amplitude spikes. Hypercapnia systematically decreases the frequency of buccal rhythm in both pre- and postmetamorphic tadpoles, by a lengthening of the interburst duration. In postmetamorphic tadpoles, hypercapnia reduces buccal burst amplitude and unmasks small fast oscillations. Our results suggest a common effect of the hypercapnia on the buccal part of the Central Pattern Generator in all tadpoles and a possible effect at the level of the motoneuron recruitment in postmetamorphic tadpoles.
Asunto(s)
Potenciales de Acción/fisiología , Branquias/fisiología , Metamorfosis Biológica/fisiología , Neuronas/fisiología , Respiración , Centro Respiratorio/citología , Animales , Nervio Facial/fisiología , Análisis de Fourier , Hipercapnia/fisiopatología , Técnicas In Vitro , Larva/fisiología , Centro Respiratorio/crecimiento & desarrollo , Factores de TiempoRESUMEN
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.
Asunto(s)
Fenómenos Electrofisiológicos , Respiración/genética , Centro Respiratorio , Adulto , Animales , Humanos , Recién Nacido , Mamíferos , Ratones , Neuronas Motoras/citología , Neuronas Motoras/fisiología , Periodicidad , Centro Respiratorio/embriología , Centro Respiratorio/crecimiento & desarrollo , Centro Respiratorio/fisiologíaRESUMEN
Respiratory control entails coordinated activities of peripheral chemoreceptors (mainly the carotid bodies) and central chemosensors within the brain stem respiratory network. Candidates for central chemoreceptors include Phox2b-containing neurons of the retrotrapezoid nucleus, serotonergic neurons of the medullary raphé, and/or multiple sites within the brain stem. Extensive interconnections among respiratory-related nuclei enable central chemosensitive relay. Both peripheral and central respiratory centers are not mature at birth, but undergo considerable development during the first two postnatal weeks in rats. A critical period of respiratory development (â¼P12-P13 in the rat) exists when abrupt neurochemical, metabolic, ventilatory, and electrophysiological changes occur. Environmental perturbations, including hypoxia, intermittent hypoxia, hypercapnia, and hyperoxia alter the development of the respiratory system. Carotid body denervation during the first two postnatal weeks in the rat profoundly affects the development and functions of central respiratory-related nuclei. Such denervation delays and prolongs the critical period, but does not eliminate it, suggesting that the critical period may be intrinsically and genetically determined.
Asunto(s)
Cuerpo Carotídeo/crecimiento & desarrollo , Cuerpo Carotídeo/fisiología , Centro Respiratorio/crecimiento & desarrollo , Centro Respiratorio/fisiología , Animales , Humanos , RatasRESUMEN
Previously, we found a transient imbalance between suppressed excitation and enhanced inhibition in the respiratory network of the rat around postnatal days (P) 12-13, a critical period when the hypoxic ventilatory response is at its weakest. The mechanism underlying the imbalance is poorly understood. Brain-derived neurotrophic factor (BDNF) and its tyrosine protein kinase B (TrkB) receptors are known to potentiate glutamatergic and attenuate gamma-aminobutyric acid (GABA)ergic neurotransmission, and BDNF is essential for respiratory development. We hypothesized that the excitation-inhibition imbalance during the critical period stemmed from a reduced expression of BDNF and TrkB at that time within respiratory-related nuclei of the brain stem. An in-depth, semiquantitative immunohistochemical study was undertaken in seven respiratory-related brain stem nuclei and one nonrespiratory nucleus in P0-21 rats. The results indicate that the expressions of BDNF and TrkB: 1) in the pre-Bötzinger complex, nucleus ambiguus, commissural and ventrolateral subnuclei of solitary tract nucleus, and retrotrapezoid nucleus/parafacial respiratory group were significantly reduced at P12, but returned to P11 levels by P14; 2) in the lateral paragigantocellular nucleus and parapyramidal region were increased from P0 to P7, but were strikingly reduced at P10 and plateaued thereafter; and 3) in the nonrespiratory cuneate nucleus showed a gentle plateau throughout the first 3 postnatal weeks, with only a slight decline of BDNF expression after P11. Thus, the significant downregulation of both BDNF and TrkB in respiratory-related nuclei during the critical period may form the basis of, or at least contribute to, the inhibitory-excitatory imbalance within the respiratory network during this time.
Asunto(s)
Factor Neurotrófico Derivado del Encéfalo/metabolismo , Regulación del Desarrollo de la Expresión Génica/fisiología , Receptor trkB/metabolismo , Centro Respiratorio/crecimiento & desarrollo , Centro Respiratorio/metabolismo , Factores de Edad , Animales , Animales Recién Nacidos , Densitometría , Femenino , Masculino , Ratas , Ratas Sprague-DawleyRESUMEN
Previously, we reported that in rats, GABA(A) and glycine receptor immunoreactivity increased markedly in multiple brain stem respiratory nuclei around postnatal days (P) 12-13, a critical period when abrupt neurochemical, metabolic, ventilatory, and electrophysiological changes occur in the respiratory network and when the system is under greater inhibition than excitation. Since Na(+)-K(+)-2Cl(-) co-transporter 1 (NKCC1) and K(+)-Cl(-) co-transporter 2 (KCC2) play pivotal roles in determining the responses of GABA(A) and glycine receptors, we hypothesized that NKCC1 and KCC2 undergo significant changes during the critical period. An in-depth immunohistochemical and single neuron optical densitometric study of neurons in seven respiratory-related nuclei (the pre-Bötzinger complex [PBC], nucleus ambiguus [Amb], hypoglossal nucleus [XII], ventrolateral subnucleus of solitary tract nucleus [NTS(VL)], retrotrapezoid nucleus/parafacial respiratory group [retrotrapezoid nucleus/parafacial respiratory group (RTN/pFRG)], dorsal motor nucleus of the vagus nerve [dorsal motor nucleus of the vagus nerve (DMNX)], and inferior olivary nucleus [IO]) and a non-respiratory cuneate nucleus (CN, an internal control) was undertaken in P0-P21 rats. Our data revealed that (1) NKCC1 immunoreactivity exhibited a developmental decrease from P0 to P21 in all eight nuclei examined, being relatively high during the first 1½ postnatal weeks and decreased thereafter. The decrease was abrupt and statistically significant at P12 in the PBC, Amb, and XII; (2) KCC2 immunoreactivity in these eight nuclei showed a developmental increase from P0 to P21; and (3) the significant reduction in NKCC1 and the greater dominance of KCC2 around P12 in multiple respiratory nuclei of the brain stem may form the basis of an enhanced inhibition in the respiratory network during the critical period before the system stabilizes to a more mature state.
Asunto(s)
Animales Recién Nacidos/metabolismo , Neuronas/metabolismo , Centro Respiratorio/crecimiento & desarrollo , Centro Respiratorio/metabolismo , Simportadores de Cloruro de Sodio-Potasio/biosíntesis , Simportadores/biosíntesis , Animales , Animales Recién Nacidos/crecimiento & desarrollo , Femenino , Inmunohistoquímica , Masculino , Ratones , Ratones Noqueados , Ratas , Ratas Sprague-Dawley , Miembro 2 de la Familia de Transportadores de Soluto 12 , Cotransportadores de K ClRESUMEN
The present study was conducted in order to observe the potential participation of the nitric oxide synthase-NO pathway in CO-mediated regulation of respiration of neonatal rats. An immunofluorescent histochemical technique was used to examine the existence of the neuronal nitric oxide synthase, a key enzyme of synthesizing NO, in medullary respiratory nuclei. The rhythmic respiratory-like discharges of hypoglossal rootlets of medullary slices were recorded to test the role of the nitric oxide synthase in CO-mediated respiratory effects. We observed neuronal nitric oxide synthase expressed in the medullary respiratory nuclei in conjunction with CO lengthened expiratory duration, decreased respiratory frequency, and increased inspiratory amplitude. These CO-mediated respiratory effects could be partially eliminated by prior treatment of the slices with Nω-nitro-L-arginine methyl ester, an inhibitor of nitric oxide synthase. The results suggest that nitric oxide synthase-NO pathway might be involved in the CO-mediated central regulation of respiration at the level of medulla oblongata in neonatal rats.
Asunto(s)
Monóxido de Carbono/toxicidad , Bulbo Raquídeo/enzimología , Óxido Nítrico Sintasa/biosíntesis , Centro Respiratorio/enzimología , Fenómenos Fisiológicos Respiratorios/efectos de los fármacos , Animales , Animales Recién Nacidos , Monóxido de Carbono/metabolismo , Femenino , Masculino , Bulbo Raquídeo/efectos de los fármacos , Bulbo Raquídeo/crecimiento & desarrollo , Óxido Nítrico/biosíntesis , Óxido Nítrico Sintasa/fisiología , Técnicas de Cultivo de Órganos , Ratas , Ratas Sprague-Dawley , Centro Respiratorio/efectos de los fármacos , Centro Respiratorio/crecimiento & desarrolloRESUMEN
A subset of preBötzinger Complex (preBötC) neurokinin 1 receptor (NK1R) and somatostatin peptide (SST)-expressing neurons are necessary for breathing in adult rats, in vivo. Their developmental origins and relationship to other preBötC glutamatergic neurons are unknown. Here we show, in mice, that the "core" of preBötC SST(+)/NK1R(+)/SST 2a receptor(+) (SST2aR) neurons, are derived from Dbx1-expressing progenitors. We also show that Dbx1-derived neurons heterogeneously coexpress NK1R and SST2aR within and beyond the borders of preBötC. More striking, we find that nearly all non-catecholaminergic glutamatergic neurons of the ventrolateral medulla (VLM) are also Dbx1 derived. PreBötC SST(+) neurons are born between E9.5 and E11.5 in the same proportion as non-SST-expressing neurons. Additionally, preBötC Dbx1 neurons are respiratory modulated and show an early inspiratory phase of firing in rhythmically active slice preparations. Loss of Dbx1 eliminates all glutamatergic neurons from the respiratory VLM including preBötC NK1R(+)/SST(+) neurons. Dbx1 mutant mice do not express any spontaneous respiratory behaviors in vivo. Moreover, they do not generate rhythmic inspiratory activity in isolated en bloc preparations even after acidic or serotonergic stimulation. These data indicate that preBötC core neurons represent a subset of a larger, more heterogeneous population of VLM Dbx1-derived neurons. These data indicate that Dbx1-derived neurons are essential for the expression and, we hypothesize, are responsible for the generation of respiratory behavior both in vitro and in vivo.
Asunto(s)
Diferenciación Celular/genética , Proteínas de Homeodominio/genética , Neurogénesis/genética , Neuronas/citología , Neuronas/fisiología , Centro Respiratorio/crecimiento & desarrollo , Animales , Regulación del Desarrollo de la Expresión Génica/fisiología , Proteínas de Homeodominio/fisiología , Ratones , Ratones Transgénicos , Células-Madre Neurales/citología , Células-Madre Neurales/metabolismo , Neuronas/efectos de los fármacos , Técnicas de Cultivo de Órganos , Receptores de Neuroquinina-1/fisiología , Receptores de Somatostatina/genética , Receptores de Somatostatina/fisiología , Centro Respiratorio/citología , Centro Respiratorio/efectos de los fármacos , Fenómenos Fisiológicos Respiratorios/genética , Somatostatina/metabolismo , Somatostatina/fisiologíaRESUMEN
Previously, we reported that a critical period in respiratory network development exists in rats around postnatal days (P; P12-P13), when abrupt neurochemical, metabolic, and physiological changes occur. Specifically, the expressions of glutamate and N-methyl-d-aspartate (NMDA) receptor (NR) subunit 1 in the pre-Bötzinger complex (PBC), nucleus ambiguus (Amb), hypoglossal nucleus (XII), and ventrolateral subnucleus of solitary tract nucleus (NTS(VL)) were significantly reduced at P12. To test our hypothesis that other NR subunits also undergo postnatal changes, we undertook an in-depth immunohistochemical study of NR2A, 2B, 2C, 2D, and 3B in these four respiratory nuclei in P2-P21 rats, using the non-respiratory cuneate nucleus (CN) as a control. Our results revealed that: (1) NR2A expression increased gradually from P2 to P11, but fell significantly at P12 in all four respiratory nuclei (but not in the CN), followed by a quick rise and a relative plateau until P21; (2) NR2B expression remained relatively constant from P2 to P21 in all five nuclei examined; (3) NR2C expression had an initial rise from P2 to P3, but remained relatively constant thereafter until P21, except for a significant fall at P12 in the PBC; (4) NR2D expression fell significantly from P2 to P3, then plateaued until P12, and declined again until P21; and (5) in contrast to NR2D, NR3B expression rose gradually from P2 to P21. These patterns reflect a dynamic remodeling of NMDA receptor subunit composition during postnatal development, with a distinct reduction of NR2A expression during the critical period (P12), just as NR1 did in various respiratory nuclei. There was also a potential switch between the neonatal NR2D and the more mature NR3B subunit, possibly around the critical period. Thus, during the critical period, NMDA receptors are undergoing greater adjustments that may contribute to attenuated excitatory synaptic transmission in the respiratory network.
Asunto(s)
Tronco Encefálico/crecimiento & desarrollo , Tronco Encefálico/metabolismo , Subunidades de Proteína/metabolismo , Receptores de N-Metil-D-Aspartato/metabolismo , Centro Respiratorio/crecimiento & desarrollo , Centro Respiratorio/metabolismo , Animales , Animales Recién Nacidos , Tronco Encefálico/inmunología , Femenino , Inmunohistoquímica , Masculino , Glicoproteínas de Membrana/metabolismo , Subunidades de Proteína/inmunología , Ratas , Ratas Sprague-Dawley , Receptores de N-Metil-D-Aspartato/agonistas , Receptores de N-Metil-D-Aspartato/inmunología , Centro Respiratorio/citologíaRESUMEN
Menthol is known as an agonist for cold-sensitive transient receptor potential channels (TRPM8) and also as a direct modulator of GABA channels. We examined the effects of menthol on respiratory rhythm generation in the brainstem-spinal cord preparations isolated from newborn rats. Menthol decreased respiratory rhythm dose-dependently (0.1-1 mM). Effects of menthol were reversed by the GABAA antagonist, bicuculline. Menthol caused pronounced reduction in the driving potential of pre-inspiratory but not inspiratory neurons. Expression of the TRPM8 channel protein was not detected in the respiratory related region of the rostral ventrolateral medulla by immunohistochemistry. The results suggest that the potent inhibitory action of menthol on burst generation of pre-inspiratory neurons is because of direct activation of tonic GABA channels by menthol.
Asunto(s)
Relojes Biológicos/efectos de los fármacos , Bulbo Raquídeo/efectos de los fármacos , Mentol/farmacología , Receptores de GABA/efectos de los fármacos , Centro Respiratorio/efectos de los fármacos , Animales , Animales Recién Nacidos , Relojes Biológicos/fisiología , Antagonistas del GABA/farmacología , Bulbo Raquídeo/crecimiento & desarrollo , Bulbo Raquídeo/metabolismo , Inhibición Neural/efectos de los fármacos , Inhibición Neural/fisiología , Periodicidad , Ratas , Ratas Wistar , Receptores de GABA/fisiología , Centro Respiratorio/crecimiento & desarrollo , Centro Respiratorio/metabolismo , Transmisión Sináptica/efectos de los fármacos , Transmisión Sináptica/fisiología , Canales Catiónicos TRPM/efectos de los fármacos , Canales Catiónicos TRPM/fisiología , Ácido gamma-Aminobutírico/fisiologíaRESUMEN
Neuroventilation is highly plastic and exposure to either of two distinct teratogens, nicotine or ethanol, during development results in a similar loss of the neuroventilatory response to hypercapnia in bullfrog tadpoles. Whether this functional deficit is permanent or transient following nicotine or ethanol exposure was unknown. Here, we tested the persistence of hypercapnic neuroventilatory response impairments in tadpoles exposed to either 30 microg/L nicotine or 0.12-0.06 g/dL ethanol for 10 weeks. Brainstem breathing-related neural activity was assessed in tadpoles allowed to develop teratogen-free after either nicotine or ethanol exposure. Nicotine-exposed animals responded normally to hypercapnia after a 3-week teratogen-free period but the hypercapnic response in ethanol-exposed tadpoles remained impaired. Tadpoles allowed to develop for only 1 week nicotine free after chronic exposure were unable to respond to hypercapnia. The hypercapnic response of ethanol-exposed tadpoles returned by 6 weeks following chronic ethanol exposure. These findings suggest that some nicotine- and ethanol-induced impairments can be resolved during early development. Understanding both the disruptive effects of nicotine and ethanol exposure and how impaired responses return when teratogen exposure stops may offer insight on the function and plasticity of respiratory control.
Asunto(s)
Tronco Encefálico/crecimiento & desarrollo , Hipercapnia/fisiopatología , Plasticidad Neuronal/fisiología , Centro Respiratorio/crecimiento & desarrollo , Teratógenos/farmacología , Animales , Tronco Encefálico/efectos de los fármacos , Depresores del Sistema Nervioso Central/toxicidad , Etanol/toxicidad , Larva , Red Nerviosa/efectos de los fármacos , Red Nerviosa/crecimiento & desarrollo , Plasticidad Neuronal/efectos de los fármacos , Nicotina/toxicidad , Agonistas Nicotínicos/toxicidad , Rana catesbeiana , Recuperación de la Función/efectos de los fármacos , Recuperación de la Función/fisiología , Centro Respiratorio/efectos de los fármacos , Fenómenos Fisiológicos Respiratorios/efectos de los fármacos , TiempoRESUMEN
ATP released during hypoxia from the ventrolateral medulla activates purinergic receptors (P2Rs) to attenuate the secondary hypoxic depression of breathing by a mechanism that likely involves a P2Y(1)R-mediated excitation of preBötzinger complex (preBötC) inspiratory rhythm-generating networks. In this study, we used rhythmically active in vitro preparations from embryonic and postnatal rats and ATP microinjection into the rostral ventral respiratory group (rVRG)/preBötC to reveal that these networks are sensitive to ATP when rhythm emerges at embryonic day 17 (E17). The peak frequency elicited by ATP at E19 and postnatally was the same ( approximately 45 bursts/min), but relative sensitivity was threefold greater at E19, reflecting a lower baseline frequency (5.6 +/- 0.9 vs 19.0 +/- 1.3 bursts/min). Combining microinjection techniques with ATP biosensors revealed that ATP concentration in the rVRG/preBötC falls rapidly as a result of active processes and closely correlates with inspiratory frequency. A phosphate assay established that preBötC-containing tissue punches degrade ATP at rates that increase perinatally. Thus, the agonist profile [ATP/ADP/adenosine (ADO)] produced after ATP release in the rVRG/preBötC will change perinatally. Electrophysiology further established that the ATP metabolite ADP is excitatory and that, in fetal but not postnatal animals, ADO at A(1) receptors exerts a tonic depressive action on rhythm, whereas A(1) antagonists extend the excitatory action of ATP on inspiratory rhythm. These data demonstrate that ATP is a potent excitatory modulator of the rVRG/preBötC inspiratory network from the time it becomes active and that ATP actions are determined by a dynamic interaction between the actions of ATP at P2 receptors, ectonucleotidases that degrade ATP, and ATP metabolites on P2Y and P1 receptors.
Asunto(s)
Adenosina Trifosfato/metabolismo , Centro Respiratorio/crecimiento & desarrollo , Centro Respiratorio/metabolismo , Rombencéfalo/crecimiento & desarrollo , Rombencéfalo/metabolismo , 5'-Nucleotidasa/metabolismo , Potenciales de Acción/efectos de los fármacos , Potenciales de Acción/fisiología , Adenosina/metabolismo , Agonistas del Receptor de Adenosina A1 , Antagonistas del Receptor de Adenosina A1 , Adenosina Difosfato/metabolismo , Adenosina Difosfato/farmacología , Adenosina Trifosfato/farmacología , Animales , Animales Recién Nacidos , Potenciales Postsinápticos Excitadores/efectos de los fármacos , Potenciales Postsinápticos Excitadores/fisiología , Inhibición Neural/efectos de los fármacos , Inhibición Neural/fisiología , Técnicas de Cultivo de Órganos , Periodicidad , Ratas , Ratas Sprague-Dawley , Receptor de Adenosina A1/metabolismo , Receptores Purinérgicos P2/efectos de los fármacos , Receptores Purinérgicos P2/metabolismo , Respiración , Centro Respiratorio/efectos de los fármacos , Rombencéfalo/efectos de los fármacosRESUMEN
The serotonergic (5-HT) system in the human medulla oblongata is well-recognized to play an important role in the regulation of respiratory and autonomic function. In this study, using both immunocytochemistry (n=5) and tissue section autoradiography with the radioligand (125)I-1-(2,5-dimethoxy-4-iodo-phenyl)2-aminopropane (n=7), we examine the normative development and distribution of the 5-HT(2A) receptor in the human medulla during the last part of gestation and first postnatal year when dramatic changes are known to occur in respiratory and autonomic control, in part mediated by the 5-HT(2A) receptor. High 5-HT(2A) receptor binding was observed in the dorsal motor nucleus of the vagus (preganglionic parasympathetic output) and hypoglossal nucleus (airway patency); intermediate binding was present in the nucleus of the solitary tract (visceral sensory input), gigantocellularis, intermediate reticular zone, and paragigantocellularis lateralis. Negligible binding was present in the raphé obscurus and arcuate nucleus. The pattern of 5-HT(2A) immunoreactivity paralleled that of binding density. By 15 gestational weeks, the relative distribution of the 5-HT(2A) receptor was similar to that in infancy. In all nuclei sampled, 5-HT(2A) receptor binding increased with age, with significant increases in the hypoglossal nucleus (p=0.027), principal inferior olive (p=0.044), and medial accessory olive (0.038). Thus, 5-HT(2A) receptors are concentrated in regions involved in autonomic and respiratory control in the human infant medulla, and their developmental profile changes over the first year of life in the hypoglossal nucleus critical to airway patency and the inferior olivary complex essential to cerebellar function.
Asunto(s)
Fenómenos Fisiológicos Cardiovasculares , Bulbo Raquídeo/anatomía & histología , Bulbo Raquídeo/metabolismo , Receptor de Serotonina 5-HT2A/metabolismo , Fenómenos Fisiológicos Respiratorios , Serotonina/metabolismo , Vías Autónomas/anatomía & histología , Vías Autónomas/crecimiento & desarrollo , Vías Autónomas/metabolismo , Mapeo Encefálico , Humanos , Nervio Hipogloso/anatomía & histología , Nervio Hipogloso/crecimiento & desarrollo , Nervio Hipogloso/metabolismo , Inmunohistoquímica , Lactante , Recién Nacido , Bulbo Raquídeo/crecimiento & desarrollo , Núcleo Olivar/anatomía & histología , Núcleo Olivar/crecimiento & desarrollo , Núcleo Olivar/metabolismo , Centro Respiratorio/anatomía & histología , Centro Respiratorio/crecimiento & desarrollo , Centro Respiratorio/metabolismo , Formación Reticular/anatomía & histología , Formación Reticular/crecimiento & desarrollo , Formación Reticular/metabolismo , Núcleo Solitario/anatomía & histología , Núcleo Solitario/crecimiento & desarrollo , Núcleo Solitario/metabolismo , Transmisión Sináptica/fisiología , Nervio Vago/anatomía & histología , Nervio Vago/crecimiento & desarrollo , Nervio Vago/metabolismoRESUMEN
We examined developmental changes in alpha-adrenoceptor influences and descending pontine inputs on the medullary respiratory network in the neonatal rat in vitro brainstem-spinal cord preparation. Using a split bath preparation to isolate the pons from the medulla, antagonists for alpha1 and alpha2 adrenoreceptors were applied to only the medulla at postnatal days 0, 2 and 4, before and after transection of the pons. Blocking alpha1 and alpha2 receptors in the medulla in the absence of a pons reduced burst frequency at all ages with a more pronounced effect in younger animals. At all ages the presence of a pons diminished the effect of blocking alpha2 receptors in the medulla and eliminated the effect of blocking alpha1 receptors. These results indicate that there is a tonic release of catecholamines within the medulla that is under influence from the pons. Additionally, transection experiments indicated that during development, the net influence of the pons changed from one of excitation to one of inhibition.
Asunto(s)
Bulbo Raquídeo/crecimiento & desarrollo , Bulbo Raquídeo/fisiología , Puente/crecimiento & desarrollo , Puente/fisiología , Receptores Adrenérgicos alfa 1/fisiología , Receptores Adrenérgicos alfa 2/fisiología , Antagonistas de Receptores Adrenérgicos alfa 1 , Antagonistas de Receptores Adrenérgicos alfa 2 , Antagonistas Adrenérgicos alfa/farmacología , Factores de Edad , Animales , Animales Recién Nacidos , Catecolaminas/metabolismo , Técnicas In Vitro , Bulbo Raquídeo/citología , Puente/citología , Prazosina/farmacología , Ratas , Ratas Sprague-Dawley , Centro Respiratorio/citología , Centro Respiratorio/crecimiento & desarrollo , Centro Respiratorio/fisiología , Mecánica Respiratoria/fisiología , Yohimbina/farmacologíaRESUMEN
Phox2b protein is a specific marker for neurons in the parafacial region of the ventral medulla, which are proposed to play a role in central chemoreception and postnatal survival. Mutations of PHOX2B cause congenital central hypoventilation syndrome. However, there have been no reports concerning electrophysiological characteristics of these Phox2b-expressing neurons in the parafacial region of the neonate immediately after birth. This region overlaps with the parafacial respiratory group (pFRG) composed predominantly of preinspiratory (Pre-I) neurons that are involved in respiratory rhythm generation. We studied (1) whether pFRG neurons are Phox2b immunoreactive or not and (2) whether they show intrinsic CO(2) chemosensitivity. We found that most pFRG/Pre-I neurons were Phox2b immunoreactive and depolarized upon increase in CO(2) concentration under condition of action potential-dependent synaptic transmission blockade by tetrodotoxin. We also confirmed that these pFRG neurons expressed neurokinin-1 receptor. They were tyrosine hydroxylase negative and presumed to be glutamatergic. Our findings suggest that Phox2b-expressing parafacial neurons play a role in respiratory rhythm generation as well as central chemoreception and thus are essential for postnatal survival.
Asunto(s)
Células Quimiorreceptoras/metabolismo , Proteínas de Homeodominio/metabolismo , Bulbo Raquídeo/metabolismo , Neuronas/metabolismo , Respiración , Centro Respiratorio/metabolismo , Factores de Transcripción/metabolismo , Potenciales de Acción/fisiología , Animales , Animales Recién Nacidos , Relojes Biológicos/fisiología , Dióxido de Carbono/metabolismo , Nervio Facial/anatomía & histología , Ácido Glutámico/metabolismo , Inmunohistoquímica , Bulbo Raquídeo/citología , Bulbo Raquídeo/crecimiento & desarrollo , Técnicas de Cultivo de Órganos , Técnicas de Placa-Clamp , Periodicidad , Ratas , Ratas Wistar , Receptores de Neuroquinina-1/metabolismo , Centro Respiratorio/citología , Centro Respiratorio/crecimiento & desarrollo , Bloqueadores de los Canales de Sodio/farmacología , Transmisión Sináptica/fisiologíaRESUMEN
The shape of the three-phase respiratory motor pattern (inspiration, postinspiration, late expiration) is controlled by a central pattern generator (CPG) located in the ponto-medullary brainstem. Synaptic interactions between and within specific sub-compartments of the CPG are subject of intensive research. This review addresses the neural control of postinspiratory activity as the essential determinant of inspiratory/expiratory phase duration. The generation of the postinspiratory phase depends on synaptic interaction between neurones of the nucleus tractus solitarii (NTS), which relay afferent inputs from pulmonary stretch receptors, and the pontine Kölliker-Fuse nucleus (KF) as integral parts of the CPG. Both regions undergo significant changes during the first three postnatal weeks in rodents. Developmental changes in glutamatergic synaptic functions and its modulation by brain-derived neurotrophic factor may have implications in synaptic plasticity within the NTS/KF axis. We propose that dependent on these developmental changes, the CPG becomes permissive for short- and long-term plasticity associated with environmental, metabolic and behavioural adaptation of the breathing pattern.
Asunto(s)
Adaptación Fisiológica/fisiología , Plasticidad Neuronal/fisiología , Neuronas/fisiología , Dinámicas no Lineales , Centro Respiratorio/citología , Centro Respiratorio/crecimiento & desarrollo , Animales , Animales Recién Nacidos , Vías Nerviosas/fisiología , RespiraciónRESUMEN
We discuss the time course of postnatal development of selected neurotransmitter receptors in motoneurons that innervate respiratory pump and accessory respiratory muscles, with emphasis on other than classic respiratory signals as important regulatory factors. Functions of those brainstem motoneurons that innervate the pharynx and larynx change more dramatically during early postnatal development than those of spinal respiratory motoneurons. Possibly in relation to this difference, the time course of postnatal expression of distinct receptors for serotonin differ between the hypoglossal (XII) and phrenic motoneurons. In rats, distinct developmental patterns include a decline or increase that extends over the first 3-4 postnatal weeks, a rapid increase during the first 2 weeks, or a transient decline on postnatal days 11-14. The latter period coincides with major changes in many transmitters in brainstem respiratory regions that may be related to a brain-wide reconfiguration of sensorymotor processing resulting from eye and ear opening and beginning of a switch from suckling to mature forms of food seeking and processing. Such rapid neurochemical changes may impart increased vulnerability on the respiratory system. We also consider rapid eye movement sleep as a state during which some brain functions may revert to conditions typical of perinatal period. In addition to normal developmental processes, changes in the expression or function of neurotransmitter receptors may occur in respiratory motoneurons in response to injury, perinatal stress, or disease conditions that increase the load on respiratory muscles or alter the normal levels and patterns of oxygen delivery.