RESUMO
Breathing is fundamental to life and any adverse change in respiratory function can endanger the health of an organism or even be fatal. Perinatal inflammation is known to adversely affect breathing in preterm babies, but lung infection/inflammation impacts all stages of life from birth to death. Little is known about the role of inflammation in respiratory control, neuronal morphology, or neural function during development. Animal models of inflammation can provide understanding and insight into respiratory development and how inflammatory processes alter developmental phenotype in addition to providing insight into new treatment modalities. In this review, we focus on recent work concerning the development of neurons, models of perinatal inflammation with an emphasis on two common LPS-based models, inflammation and its impact on development, and current and potential treatments for inflammation within the respiratory control circuitry of the mammalian brainstem. We have also discussed models of inflammation in adults and have specifically focused on hypoglossal motoneurons (XII) and neurons of the nucleus tractus solitarii (nTS) as these nuclei have been studied more extensively than other brainstem nuclei participating in breathing and airway control. Understanding the impact of inflammation on the developmental aspects of respiratory control and breathing pattern is critical to addressing problems of cardiorespiratory dysregulation in disease and this overview points out many gaps in our current knowledge.
Assuntos
Tronco Encefálico/fisiologia , Nervo Hipoglosso/fisiologia , Inflamação/fisiopatologia , Rede Nervosa/fisiologia , Complicações Infecciosas na Gravidez/fisiopatologia , Respiração , Adulto , Animais , Tronco Encefálico/crescimento & desenvolvimento , Tronco Encefálico/metabolismo , Feminino , Humanos , Nervo Hipoglosso/crescimento & desenvolvimento , Recém-Nascido , Rede Nervosa/crescimento & desenvolvimento , GravidezRESUMO
We hypothesize that developmental changes in motoneuron volume or surface area in the hypoglossal motor nucleus (XII) can alter the biophysical properties that contribute to motor output. We used the Golgi-Cox technique to stain developing hypoglossal motoneurons (XII MNs) at three postnatal ages (P3, 10, & 17). We removed Sprague-Dawley rat pup brains, processed, sectioned, stained, imaged, and performed 3D reconstructions to quantify the morphometrics of XII MNs. We then used the simulation environment, NEURON, to model the biophysical properties from digitally reconstructed neurons and compared our results to previously published experiments. The total volume of neurons increased from 4766 µ m3 for P3 to 16,904 µ m3 for P17 while the total surface area increased from 4258 µ m2 to 13,510 µ m2 respectively. The P3 simulations required a 10-fold reduction in the hyperpolarization-activated current and doubling of the membrane capacitance to match experimental results. XII MN morphology showed a direct relationship with passive electrophysiological properties and recapitulates the changes seen experimentally.
Assuntos
Fenômenos Eletrofisiológicos , Nervo Hipoglosso/crescimento & desenvolvimento , Modelos Biológicos , Neurônios Motores/fisiologia , Animais , Animais Recém-Nascidos , Feminino , Gravidez , Ratos , Ratos Sprague-DawleyRESUMO
Developmental nicotine exposure (DNE) is associated with increased risk of cardiorespiratory, intellectual, and behavioral abnormalities in neonates, and is a risk factor for apnea of prematurity, altered arousal responses and Sudden Infant Death Syndrome. Alterations in nicotinic acetylcholine receptor signaling (nAChRs) after DNE lead to changes in excitatory neurotransmission in neural networks that control breathing, including a heightened excitatory response to AMPA microinjection into the hypoglossal motor nucleus. Here, we report on experiments designed to probe possible postsynaptic and presynaptic mechanisms that may underlie this plasticity. Pregnant dams were exposed to nicotine or saline via an osmotic mini-pump implanted on the 5th day of gestation. We used whole-cell patch clamp electrophysiology to record from hypoglossal motoneurons (XIIMNs) in thick medullary slices from neonatal rat pups (N=26 control and 24 DNE cells). To enable the translation of our findings to breathing-related consequences of DNE, we only studied XIIMNs that were receiving rhythmic excitatory drive from the respiratory central pattern generator. Tetrodotoxin was used to isolate XIIMNs from presynaptic input, and their postsynaptic responses to bath application of l-glutamic acid (glutamate) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) were studied under voltage clamp. DNE had no influence on inward current magnitude evoked by either glutamate or AMPA. However, in cells from DNE animals, bath application of AMPA was associated with a right shift in the amplitude distribution (P=0.0004), but no change in the inter-event interval distribution of miniature excitatory postsynaptic currents (mEPSCs). DNE had no influence on mEPSC amplitude or frequency evoked by glutamate application, or under (unstimulated) baseline conditions. Thus, in the presence of AMPA, DNE is associated with a small but significant increase in quantal size, but no change in the probability of glutamate release.
Assuntos
Ácido Glutâmico/metabolismo , Nervo Hipoglosso/citologia , Neurônios Motores/efeitos dos fármacos , Nicotina/farmacologia , Agonistas Nicotínicos/farmacologia , Transmissão Sináptica/efeitos dos fármacos , Fatores Etários , Animais , Animais Recém-Nascidos , Interações Medicamentosas , Potenciais Pós-Sinápticos Excitadores/efeitos dos fármacos , Feminino , Nervo Hipoglosso/crescimento & desenvolvimento , Técnicas In Vitro , Masculino , Bulbo/citologia , Potenciais da Membrana/efeitos dos fármacos , Técnicas de Patch-Clamp , Ratos , Ratos Sprague-Dawley , Bloqueadores dos Canais de Sódio/farmacologia , Transmissão Sináptica/fisiologia , Tetrodotoxina/farmacologiaRESUMO
Maternal smoking or use of other products containing nicotine during pregnancy can have significant adverse consequences for respiratory function in neonates. We have shown, in previous studies, that developmental nicotine exposure (DNE) in a model system compromises the normal function of respiratory circuits within the brainstem. The effects of DNE include alterations in the excitability and synaptic interactions of the hypoglossal motoneurons, which innervate muscles of the tongue. This study was undertaken to test the hypothesis that these functional consequences of DNE are accompanied by changes in the dendritic morphology of hypoglossal motoneurons. Hypoglossal motoneurons in brain stem slices were filled with neurobiotin during whole-cell patch clamp recordings and subjected to histological processing to reveal dendrites. Morphometric analysis, including the Sholl method, revealed significant effects of DNE on dendritic branching patterns. In particular, whereas within the first five postnatal days there was significant growth of the higher-order dendritic branches of motoneurons from control animals, the growth was compromised in motoneurons from neonates that were subjected to DNE. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 76: 1125-1137, 2016.
Assuntos
Tronco Encefálico/crescimento & desenvolvimento , Nervo Hipoglosso/crescimento & desenvolvimento , Neurônios Motores/patologia , Nicotina/toxicidade , Agonistas Nicotínicos/toxicidade , Efeitos Tardios da Exposição Pré-Natal , Animais , Animais Recém-Nascidos , Tronco Encefálico/efeitos dos fármacos , Tronco Encefálico/patologia , Tronco Encefálico/fisiopatologia , Dendritos/efeitos dos fármacos , Dendritos/patologia , Dendritos/fisiologia , Modelos Animais de Doenças , Feminino , Nervo Hipoglosso/efeitos dos fármacos , Nervo Hipoglosso/patologia , Nervo Hipoglosso/fisiopatologia , Neurônios Motores/efeitos dos fármacos , Neurônios Motores/fisiologia , Técnicas de Rastreamento Neuroanatômico , Técnicas de Patch-Clamp , Gravidez , Ratos Sprague-Dawley , Transmissão Sináptica , Técnicas de Cultura de TecidosRESUMO
Previously, our electrophysiological studies revealed a transient imbalance between suppressed excitation and enhanced inhibition in hypoglossal motoneurons of rats on postnatal days (P) 12-13, a critical period when abrupt neurochemical, metabolic, ventilatory and physiological changes occur in the respiratory system. The mechanism underlying the imbalance is poorly understood. We hypothesised that the imbalance was contributed by a reduced expression of brain-derived neurotrophic factor (BDNF), which normally enhances excitation and suppresses inhibition. We also hypothesised that exogenous BDNF would partially reverse this synaptic imbalance. Immunohistochemistry/single-neuron optical densitometry, real-time quantitative PCR (RT-qPCR) and whole-cell patch-clamp recordings were done on hypoglossal motoneurons in brainstem slices of rats during the first three postnatal weeks. Our results indicated that: (1) the levels of BDNF and its high-affinity tyrosine receptor kinase B (TrkB) receptor mRNAs and proteins were relatively high during the first 1-1.5 postnatal weeks, but dropped precipitously at P12-13 before rising again afterwards; (2) exogenous BDNF significantly increased the normally lowered frequency of spontaneous excitatory postsynaptic currents but decreased the normally heightened amplitude and frequency of spontaneous inhibitory postsynaptic currents (sIPSCs) during the critical period; (3) exogenous BDNF also decreased the normally heightened frequency of miniature IPSCs at P12-13; and (4) the effect of exogenous BDNF was partially blocked by K252a, a TrkB receptor antagonist. Thus, our results are consistent with our hypothesis that BDNF and TrkB play an important role in the synaptic imbalance during the critical period. This may have significant implications for the mechanism underlying sudden infant death syndrome.
Assuntos
Tronco Encefálico/crescimento & desenvolvimento , Fator Neurotrófico Derivado do Encéfalo/metabolismo , Nervo Hipoglosso/crescimento & desenvolvimento , Neurônios Motores/fisiologia , Respiração , Sinapses/fisiologia , Animais , Animais Recém-Nascidos , Tronco Encefálico/efeitos dos fármacos , Tronco Encefálico/fisiologia , Carbazóis/farmacologia , Fármacos do Sistema Nervoso Central/farmacologia , Potenciais Pós-Sinápticos Excitadores/efeitos dos fármacos , Potenciais Pós-Sinápticos Excitadores/fisiologia , Feminino , Regulação da Expressão Gênica no Desenvolvimento , Nervo Hipoglosso/efeitos dos fármacos , Nervo Hipoglosso/fisiologia , Alcaloides Indólicos/farmacologia , Potenciais Pós-Sinápticos Inibidores/efeitos dos fármacos , Potenciais Pós-Sinápticos Inibidores/fisiologia , Masculino , Potenciais Pós-Sinápticos em Miniatura/efeitos dos fármacos , Potenciais Pós-Sinápticos em Miniatura/fisiologia , Neurônios Motores/efeitos dos fármacos , RNA Mensageiro/metabolismo , Ratos Sprague-Dawley , Receptor trkB/antagonistas & inibidores , Receptor trkB/metabolismo , Respiração/efeitos dos fármacos , Sinapses/efeitos dos fármacos , Técnicas de Cultura de TecidosRESUMO
Developmental nicotine exposure (DNE) impacts central respiratory control in neonates born to smoking mothers. We previously showed that DNE enhances the respiratory motor response to bath application of AMPA to the brainstem, although it was unclear which brainstem respiratory neurons mediated these effects (Pilarski and Fregosi, 2009). Here we examine how DNE influences AMPA-type glutamatergic neurotransmission in the pre-Bötzinger complex (pre-BötC) and the hypoglossal motor nucleus (XIIMN), which are neuronal populations located in the medulla that are necessary for normal breathing. Using rhythmic brainstem slices from neonatal rats, we microinjected AMPA into the pre-BötC or the XIIMN while recording from XII nerve rootlets (XIIn) as an index of respiratory motor output. DNE increased the duration of tonic activity and reduced rhythmic burst amplitude after AMPA microinjection into the XIIMN. Also, DNE led to an increase in respiratory burst frequency after AMPA injection into the pre-BötC. Whole-cell patch-clamp recordings of XII motoneurons showed that DNE increased motoneuron excitability but did not change inward currents. Immunohistochemical studies indicate that DNE reduced the expression of glutamate receptor subunits 2 and 3 (GluR2/3) in the XIIMN and the pre-BötC. Our data show that DNE alters AMPAergic synaptic transmission in both the XIIMN and pre-BötC, although the mechanism by which this occurs is unclear. We suggest that the DNE-induced reduction in GluR2/3 may represent an attempt to compensate for increased cell excitability, consistent with mechanisms underlying homeostatic plasticity.
Assuntos
Tronco Encefálico/crescimento & desenvolvimento , Nervo Hipoglosso/crescimento & desenvolvimento , Nicotina/administração & dosagem , Transmissão Sináptica/fisiologia , Ácido alfa-Amino-3-hidroxi-5-metil-4-isoxazol Propiônico/administração & dosagem , Animais , Animais Recém-Nascidos , Tronco Encefálico/efeitos dos fármacos , Feminino , Nervo Hipoglosso/efeitos dos fármacos , Masculino , Microinjeções/métodos , Nicotina/toxicidade , Gravidez , Efeitos Tardios da Exposição Pré-Natal/induzido quimicamente , Efeitos Tardios da Exposição Pré-Natal/metabolismo , Distribuição Aleatória , Ratos , Ratos Sprague-Dawley , Transmissão Sináptica/efeitos dos fármacos , Ácido alfa-Amino-3-hidroxi-5-metil-4-isoxazol Propiônico/metabolismoRESUMO
Rho-associated kinase (ROCK) regulates neural cell migration, proliferation and survival, dendritic spine morphology, and axon guidance and regeneration. There is, however, little information about whether ROCK modulates the electrical activity and information processing of neuronal circuits. At neonatal stage, ROCKα is expressed in hypoglossal motoneurons (HMNs) and in their afferent inputs, whereas ROCKß is found in synaptic terminals on HMNs, but not in their somata. Inhibition of endogenous ROCK activity in neonatal rat brainstem slices failed to modulate intrinsic excitability of HMNs, but strongly attenuated the strength of their glutamatergic and GABAergic synaptic inputs. The mechanism acts presynaptically to reduce evoked neurotransmitter release. ROCK inhibition increased myosin light chain (MLC) phosphorylation, which is known to trigger actomyosin contraction, and reduced the number of synaptic vesicles docked to active zones in excitatory boutons. Functional and ultrastructural changes induced by ROCK inhibition were fully prevented/reverted by MLC kinase (MLCK) inhibition. Furthermore, ROCK inhibition drastically reduced the phosphorylated form of p21-associated kinase (PAK), which directly inhibits MLCK. We conclude that endogenous ROCK activity is necessary for the normal performance of motor output commands, because it maintains afferent synaptic strength, by stabilizing the size of the readily releasable pool of synaptic vesicles. The mechanism of action involves a tonic inhibition of MLCK, presumably through PAK phosphorylation. This mechanism might be present in adults since unilateral microinjection of ROCK or MLCK inhibitors into the hypoglossal nucleus reduced or increased, respectively, whole XIIth nerve activity.
Assuntos
Nervo Hipoglosso/enzimologia , Neurônios Motores/enzimologia , Terminações Pré-Sinápticas/enzimologia , Transmissão Sináptica/fisiologia , Vesículas Sinápticas/enzimologia , Quinases Associadas a rho/fisiologia , Animais , Animais Recém-Nascidos , Feminino , Nervo Hipoglosso/crescimento & desenvolvimento , Nervo Hipoglosso/ultraestrutura , Sistema de Sinalização das MAP Quinases/fisiologia , Masculino , Neurônios Motores/efeitos dos fármacos , Neurônios Motores/ultraestrutura , Técnicas de Cultura de Órgãos , Terminações Pré-Sinápticas/metabolismo , Terminações Pré-Sinápticas/ultraestrutura , Ratos , Ratos Wistar , Transmissão Sináptica/efeitos dos fármacos , Vesículas Sinápticas/metabolismo , Vesículas Sinápticas/ultraestrutura , Quinases Associadas a rho/antagonistas & inibidoresRESUMO
Hypoglossal motoneurons (HMs) innervate tongue muscles and are critical in maintaining patency of the upper airway during respiration. Abnormalities in HMs have been implicated in sudden infant death syndrome (SIDS) and obstructive sleep apnoea. Previously, we found a critical period in respiratory network development in rats around postnatal day (P) 12-13, when abrupt neurochemical, metabolic and physiological changes occurred. To test our hypothesis that an imbalance between inhibitory and excitatory synaptic transmission exists during the critical period, whole-cell patch-clamp recordings of HMs were done in brainstem slices of rats daily from P0 to P16. The results indicated that: (1) the amplitude and charge transfer of miniature excitatory postsynaptic currents (mEPSCs) were significantly reduced at P12-13; (2) the amplitude, mean frequency and charge transfer of miniature inhibitory postsynaptic currents (mIPSCs) were significantly increased at P12-13; (3) the kinetics (rise time and decay time) of both mEPSCs and mIPSCs accelerated with age; (4) the amplitude and frequency of spontaneous EPSCs were significantly reduced at P12-13, whereas those of spontaneous IPSCs were significantly increased at P12-13; and (5) both glycine and GABA contributed to mIPSCs. However, GABAergic currents fluctuated within a narrow range during the first three postnatal weeks, whereas glycinergic ones exhibited age-dependent changes comparable to those of total mIPSCs, indicating a reversal in dominance from GABA to glycine with development. Thus, our results provide strong electrophysiological evidence for an excitatory-inhibitory imbalance in HMs during the critical period of postnatal development in rats that may have significant implications for SIDS.
Assuntos
Tronco Encefálico/crescimento & desenvolvimento , Nervo Hipoglosso/crescimento & desenvolvimento , Neurônios Motores/fisiologia , Inibição Neural , Transmissão Sináptica , Língua/inervação , Fatores Etários , Envelhecimento , Análise de Variância , Animais , Animais Recém-Nascidos , Tronco Encefálico/citologia , Tronco Encefálico/efeitos dos fármacos , Tronco Encefálico/metabolismo , Estimulação Elétrica , Potenciais Pós-Sinápticos Excitadores , Glicina/metabolismo , Humanos , Nervo Hipoglosso/citologia , Nervo Hipoglosso/efeitos dos fármacos , Nervo Hipoglosso/metabolismo , Técnicas In Vitro , Lactente , Potenciais Pós-Sinápticos Inibidores , Cinética , Neurônios Motores/efeitos dos fármacos , Neurônios Motores/metabolismo , Neurotransmissores/farmacologia , Técnicas de Patch-Clamp , Ratos , Ratos Sprague-Dawley , Morte Súbita do Lactente/etiologia , Transmissão Sináptica/efeitos dos fármacos , Ácido gama-Aminobutírico/metabolismoRESUMO
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.
Assuntos
Fenômenos Fisiológicos Cardiovasculares , Bulbo/anatomia & histologia , Bulbo/metabolismo , Receptor 5-HT2A de Serotonina/metabolismo , Fenômenos Fisiológicos Respiratórios , Serotonina/metabolismo , Vias Autônomas/anatomia & histologia , Vias Autônomas/crescimento & desenvolvimento , Vias Autônomas/metabolismo , Mapeamento Encefálico , Humanos , Nervo Hipoglosso/anatomia & histologia , Nervo Hipoglosso/crescimento & desenvolvimento , Nervo Hipoglosso/metabolismo , Imuno-Histoquímica , Lactente , Recém-Nascido , Bulbo/crescimento & desenvolvimento , Núcleo Olivar/anatomia & histologia , Núcleo Olivar/crescimento & desenvolvimento , Núcleo Olivar/metabolismo , Centro Respiratório/anatomia & histologia , Centro Respiratório/crescimento & desenvolvimento , Centro Respiratório/metabolismo , Formação Reticular/anatomia & histologia , Formação Reticular/crescimento & desenvolvimento , Formação Reticular/metabolismo , Núcleo Solitário/anatomia & histologia , Núcleo Solitário/crescimento & desenvolvimento , Núcleo Solitário/metabolismo , Transmissão Sináptica/fisiologia , Nervo Vago/anatomia & histologia , Nervo Vago/crescimento & desenvolvimento , Nervo Vago/metabolismoRESUMO
In the hypoglossal nucleus of wild-type mice, early mixed glycinergic-GABAergic inhibitory transmission becomes mainly glycinergic during postnatal maturation. In spastic mice (SPA), a model of human hyperekplexic syndrome, an insertion into the gene of the glycine receptor (GlyR) beta subunit results in a decreased accumulation of GlyRs at postsynaptic sites and an impaired glycinergic neurotransmission. In SPA mice displaying a mild phenotype (B6C3Fe strain), a compensatory process involving an increased aggregation of GABA(A) receptors (GABA(A)Rs) at postsynaptic sites was proposed to explain survival of mutant animals until adulthood. However, C57BL/6J strain SPA mice which express a lower amount of GlyR beta subunit die 2-3 weeks after birth, suggesting that GABAergic compensation does not necessarily take place. We performed a morphofunctional study of inhibitory synapses in the developing hypoglossal nucleus of C57BL/6J SPA mice. In this mutant, the inhibitory synaptic activity was mainly GABAergic. Accordingly, we observed a developmental loss of glycinergic presynaptic terminals and an increase in the density of GABAergic presynaptic terminals during the first two postnatal weeks. In addition, while C57BL/6J SPA mice displayed a strong impairment in GlyR aggregation at postsynaptic loci, the proportion of inhibitory presynaptic terminals facing diffuse GABA(A)Rs significantly increased during development. Our results suggest crosstalk between postsynaptic and presynaptic elements, leading to the developmental regulation of the presynaptic terminal neurotransmitter content according to the level of postsynaptic GlyR aggregation. They also indicate that GABAergic neurotransmission does not compensate for defects in GlyR postsynaptic aggregation leading to spastic syndrome in C57BL/6J SPA mice.
Assuntos
Nervo Hipoglosso/metabolismo , Neurônios Motores/metabolismo , Inibição Neural/genética , Receptores de Glicina/metabolismo , Sinapses/metabolismo , Ácido gama-Aminobutírico/metabolismo , Envelhecimento/fisiologia , Animais , Diferenciação Celular/genética , Nervo Hipoglosso/citologia , Nervo Hipoglosso/crescimento & desenvolvimento , Bulbo/citologia , Bulbo/crescimento & desenvolvimento , Bulbo/metabolismo , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Mutantes Neurológicos , Neurônios Motores/efeitos dos fármacos , Espasticidade Muscular/genética , Espasticidade Muscular/metabolismo , Espasticidade Muscular/fisiopatologia , Inibição Neural/efeitos dos fármacos , Terminações Pré-Sinápticas/efeitos dos fármacos , Terminações Pré-Sinápticas/metabolismo , Agregação de Receptores/efeitos dos fármacos , Agregação de Receptores/genética , Receptor Cross-Talk/fisiologia , Receptores de GABA-A/efeitos dos fármacos , Receptores de GABA-A/metabolismo , Receptores de Glicina/efeitos dos fármacos , Receptores de Glicina/genética , Sinapses/efeitos dos fármacos , Membranas Sinápticas/efeitos dos fármacos , Membranas Sinápticas/metabolismo , Transmissão Sináptica/efeitos dos fármacos , Transmissão Sináptica/genéticaRESUMO
The neuroprotective agent riluzole is used for the symptomatic treatment of motoneuron disease, which strongly affects the brainstem nucleus hypoglossus. The mechanism of action of riluzole was investigated using, as a model, patch-clamp recording from hypoglossal motoneurons of the neonatal rat brainstem slice preparation. In the presence of riluzole (10 microm), theta-rhythm oscillations evoked by nicotine continued even though the persistent inward current (comprising sodium and calcium components) was halved, but they disappeared when the high frequency of spontaneous glutamatergic currents waned. Riluzole fully inhibited the persistent sodium current and partly depressed a tetrodotoxin (TTX)-insensitive slow current antagonized by Mn(2+) or Cd(2+). Repetitive firing was inhibited by riluzole without changing single action potentials. In the presence of TTX, riluzole depressed miniature glutamatergic currents occurring at high rate. Synaptic transmission with low release probability became sensitive to riluzole if release was stimulated by high potassium solution. Miniature current frequency was depressed by the N-methyl-D-aspartic acid (NMDA) receptor antagonist D-amino-phosphonovaleriate (50 microm), which fully occluded the action of riluzole. As riluzole is a protein kinase C (PKC) inhibitor, the PKC antagonist chelerythrine (2.5 microm) mimicked the effect of riluzole and prevented it. In summary, riluzole blocked the persistent sodium current fully, and the calcium one partly, plus it decreased glutamatergic transmission probably via inhibition of PKC that regulated presynaptic NMDA receptors having a facilitatory effect on glutamate release. Controlling NMDA receptor function and, thus, excitatory transmitter release via modulation of PKC suggests a novel potential target to contrast glutamate excitotoxicity in this motor nucleus.
Assuntos
Ácido Glutâmico/metabolismo , Nervo Hipoglosso/metabolismo , Canais Iônicos/metabolismo , Neurônios Motores/metabolismo , Receptores de N-Metil-D-Aspartato/metabolismo , Riluzol/farmacologia , Potenciais de Ação/efeitos dos fármacos , Potenciais de Ação/fisiologia , Animais , Animais Recém-Nascidos , Canais de Cálcio/efeitos dos fármacos , Canais de Cálcio/metabolismo , Inibidores Enzimáticos/farmacologia , Antagonistas de Aminoácidos Excitatórios/farmacologia , Nervo Hipoglosso/efeitos dos fármacos , Nervo Hipoglosso/crescimento & desenvolvimento , Canais Iônicos/efeitos dos fármacos , Neurônios Motores/efeitos dos fármacos , Fármacos Neuroprotetores/farmacologia , Nicotina/antagonistas & inibidores , Técnicas de Cultura de Órgãos , Técnicas de Patch-Clamp , Proteína Quinase C/antagonistas & inibidores , Proteína Quinase C/metabolismo , Ratos , Ratos Wistar , Receptores de N-Metil-D-Aspartato/efeitos dos fármacos , Bloqueadores dos Canais de Sódio/antagonistas & inibidores , Canais de Sódio/efeitos dos fármacos , Canais de Sódio/metabolismo , Transmissão Sináptica/efeitos dos fármacos , Transmissão Sináptica/fisiologia , Ritmo Teta/efeitos dos fármacosRESUMO
Tadpoles, Lithobates (formerly Rana) catesbeiana, were held for 8-12 weeks in pond water that was either teratogen free or contained 0.15% ethanol or 30 microg/L nicotine. The ventilatory and neuroventilatory consequences of these developmental exposures were assessed. Developmental exposure to ethanol or nicotine blocked the hypercapnia-induced increase in surfacing frequency typically exhibited by tadpoles, as well as the hypercapnia-induced increase in putative lung ventilation exhibited by isolated tadpole brainstems. It was specifically the hypercapnic ventilatory response, previously characterized as an increase in lung activity, that was affected by developmental exposure to these teratogens. Developmental exposure to ethanol or nicotine did not affect the frequency of surfacing or putative lung breaths exhibited by the intact tadpoles or their isolated brainstems when not subjected to a hypercapnic challenge.
Assuntos
Depressores do Sistema Nervoso Central/toxicidade , Etanol/toxicidade , Hipercapnia/fisiopatologia , Larva/crescimento & desenvolvimento , Larva/fisiologia , Nicotina/toxicidade , Agonistas Nicotínicos/toxicidade , Mecânica Respiratória/efeitos dos fármacos , Animais , Comportamento Animal/efeitos dos fármacos , Comportamento Animal/fisiologia , Eletrofisiologia , Feminino , Nervo Hipoglosso/efeitos dos fármacos , Nervo Hipoglosso/crescimento & desenvolvimento , Nervo Hipoglosso/fisiologia , Masculino , Rana catesbeiana , Nervo Trigêmeo/efeitos dos fármacos , Nervo Trigêmeo/crescimento & desenvolvimento , Nervo Trigêmeo/fisiologia , Água/análiseRESUMO
Hypoglossal motoneuron output to the genioglossus muscle contributes to upper airway patency. Serotonin (5HT) plays an important role in regulating hypoglossal motoneuron excitability via serotonin 2A receptors (5HT(2A)). The purpose of this study was to investigate whether there are age-associated changes in 5HT(2A) receptor expression in the hypoglossal nucleus of male and female rats. The brains of young, middle-aged and old F344 rats were sectioned, reacted immunocytochemically for the presence of 5HT(2A) receptor, and the staining density quantified. The estrus stage of female rats was determined and circulating sex hormone levels measured and correlated with 5HT(2A) levels. The results show that there was significantly greater 5HT(2A) receptor immunoreactivity in the hypoglossal nucleus of female than of male rats. With increasing age, there was an increase in 5HT(2A) receptor immunoreactivity in the hypoglossal nucleus of female rats, whereas no age-associated changes were observed in male rats. Previous studies have shown a reduction in 5HT-dependent respiratory plasticity and an age-associated decrease in 5HT in the hypoglossal nucleus in male but not female rats. Data from the present study suggest that aging male rats fail to compensate adequately for reduced 5HT in the hypoglossal nucleus by upregulating the expression of the 5HT(2A) receptor.
Assuntos
Envelhecimento/fisiologia , Nervo Hipoglosso/fisiologia , Receptor 5-HT2A de Serotonina/metabolismo , Animais , Estradiol/sangue , Feminino , Nervo Hipoglosso/crescimento & desenvolvimento , Imuno-Histoquímica , Masculino , Bulbo/crescimento & desenvolvimento , Progesterona/sangue , Ratos , Ratos Endogâmicos F344 , Caracteres SexuaisRESUMO
The effects of the anesthetic ketamine on properties of inspiratory bursts (I-bursts) in mouse hypoglossal nerve activity were studied in vivo and in vitro. In urethane anesthetized mice we observed rhythmic I-phase activity in only one of eight pups at P9 days. In contrast in older mice rhythmic I-phase hypoglossal activity was almost always observed. Ketamine caused a reduction in I-burst frequency and an increase in peak integrated hypoglossal nerve activity in all three age groups studied (P10-P13, P15-P20 and adult mice). In these mice I-phase oscillations, due to hypoglossal motoneurons firing clusters of action potentials at a particular frequency, were observed in control and after ketamine. Ketamine did not change the frequency of the dominant spectral peak determined from power spectra examined from 0 to 200 Hz. The effects of ketamine were also studied in vitro in the mouse rhythmic medullary slice preparation. Ketamine reduced hypoglossal I-burst frequency and I-burst peak integrated amplitude. Oscillations were observed in I-phase activity, and as in the in vivo studies ketamine did not shift the dominant spectral peak frequency. These results demonstrate that in vivo and in vitro ketamine results in significant changes in I-burst frequency and peak integrated hypoglossal nerve activity, but changes in the oscillation frequency are minimal.
Assuntos
Anestésicos Dissociativos/farmacologia , Nervo Hipoglosso/efeitos dos fármacos , Nervo Hipoglosso/crescimento & desenvolvimento , Inalação/efeitos dos fármacos , Ketamina/farmacologia , Fatores Etários , Animais , Animais Recém-Nascidos , Relação Dose-Resposta a Droga , Nervo Hipoglosso/citologia , Técnicas In Vitro , Camundongos , Neurônios Motores/efeitos dos fármacos , Neurônios Motores/fisiologiaRESUMO
At postsynaptic densities of mouse hypoglossal motoneurons, the proportion of glycine receptors co-clustered with GABAA receptors increases from neonatal to adult animals, suggesting that mixed synapses might play a greater role in adult synaptic inhibition. We visualized the presynaptic correlates of these developmental changes using immunocytochemistry. At P5, presynaptic terminals contained glycine and GlyT2 and/or GABA and GAD65, but at P15, the majority of inhibitory terminals contained glycine and GlyT2 only. The GABAergic component of evoked inhibitory postsynaptic currents in HMs decreased strongly between P5 and P15. Similarly, miniature inhibitory postsynaptic currents evolved from mainly glycinergic and mixed glycinergic/GABAergic events at P3-5 to predominantly glycinergic currents at P15. These results indicate that the decrease in the proportion of functional mixed inhibitory synapses with maturation results from a loss of the ability of presynaptic terminals to release both neurotransmitters during development while co-aggregation of GlyRs + GABAARs at postsynaptic loci remained.
Assuntos
Nervo Hipoglosso/crescimento & desenvolvimento , Nervo Hipoglosso/metabolismo , Inibição Neural/fisiologia , Agregação de Receptores/fisiologia , Receptores Pré-Sinápticos/metabolismo , Membranas Sinápticas/química , Membranas Sinápticas/metabolismo , Animais , Animais Recém-Nascidos , Nervo Hipoglosso/química , Camundongos , Receptores de GABA-A/metabolismo , Receptores de GABA-A/fisiologia , Receptores de Glicina/metabolismo , Receptores de Glicina/fisiologia , Receptores Pré-Sinápticos/fisiologia , Membranas Sinápticas/fisiologiaRESUMO
Postnatal development of hyoglossus and styloglossus motoneurons was studied in this investigation of the hypoglossal nucleus. Our findings show separate and distinct locations for hyoglossus and styloglossus motoneurons within the retrusor (dorsal) subdivision of the hypoglossal nucleus for all age groups. Hyoglossus and styloglossus motoneuron cross-sectional area reached their adult size at different times (by weeks 2 and 3, respectively). Cell roundness, as measured by form factor (measure of cell perimeter relative to its area), decreased with advancing postnatal age for both populations of motoneurons. Differences in the direction of the dendritic projection between hyoglossus and styloglossus motoneurons were found. Hyoglossus and styloglossus motoneuron development was compared to genioglossus motoneuron postnatal development.
Assuntos
Nervo Hipoglosso/citologia , Nervo Hipoglosso/crescimento & desenvolvimento , Neurônios Motores/citologia , Músculo Esquelético/inervação , Língua/inervação , Animais , Animais Recém-Nascidos , Toxina da Cólera/química , Toxina da Cólera/metabolismo , Peroxidase do Rábano Silvestre/química , Peroxidase do Rábano Silvestre/metabolismo , Nervo Hipoglosso/metabolismo , Indicadores e Reagentes/química , Indicadores e Reagentes/metabolismo , Neurônios Motores/metabolismo , Ratos , Ratos Sprague-DawleyRESUMO
The hypoglossal nucleus of young rats contains vasopressin binding sites and vasopressin can directly excite hypoglossal motoneurons. In addition, indirect evidence suggests that vasopressin can enhance the synaptic input to motoneurons. We have characterized this latter effect by using brainstem slices and whole-cell recordings. We found that, in the presence of blockers of fast glutamatergic transmission, vasopressin strongly facilitated inhibitory synaptic activity. On average, vasopressin caused a six-fold increase in the frequency and a 1.5-fold increase in the amplitude of GABAergic postsynaptic currents. The effect of vasopressin on glycinergic postsynaptic currents was similar in magnitude. Vasopressin did not affect the frequency of GABAergic or glycinergic miniature postsynaptic currents, indicating that the peptide-induced facilitation of inhibitory transmission was mediated by receptors located on the somatodendritic region rather than on axon terminals of presynaptic neurons. The pharmacological profile of these receptors was determined by using d[Cha4]AVP and dVDAVP, selective agonists of V1b and V2 vasopressin receptors, respectively, and Phaa-D-Tyr-(Et)-Phe-Gln-Pro-Arg-Arg-NH2, a selective antagonist of V1a vasopressin receptors. The two agonists had no effect on the frequency of inhibitory postsynaptic currents. By contrast, the antagonist suppressed the vasopressin-induced facilitation of these currents, indicating that the receptors involved were exclusively of the V1a type. Thus, vasopressin exerts a dual action on hypoglossal motoneurons: a direct excitatory action and an indirect action mediated by GABAergic and glycinergic synapses. By virtue of this dual effect, vasopressin could alter the input-output properties of these motoneurons. Alternatively, it could play a role in generating or modulating specific motor patterns.
Assuntos
Glicina/fisiologia , Nervo Hipoglosso/crescimento & desenvolvimento , Neurônios Motores/fisiologia , Transmissão Sináptica/fisiologia , Vasopressinas/farmacologia , Ácido gama-Aminobutírico/fisiologia , Animais , Antagonistas dos Receptores de Hormônios Antidiuréticos , Relação Dose-Resposta a Droga , Nervo Hipoglosso/efeitos dos fármacos , Neurônios Motores/efeitos dos fármacos , Inibição Neural/efeitos dos fármacos , Inibição Neural/fisiologia , Ratos , Ratos Sprague-Dawley , Receptores de Vasopressinas/agonistas , Receptores de Vasopressinas/fisiologia , Transmissão Sináptica/efeitos dos fármacos , Vasopressinas/fisiologiaRESUMO
To further our understanding of the role that voltage-activated Ca2+ channels play in the development, physiology and pathophysiology of motoneurones (MNs), we used whole-cell patch-clamp recording to compare voltage-activated Ca2+ currents in oculomotor (III) and hypoglossal (XII) MNs of neonatal [postnatal day (P)1-5] and juvenile (P14-19) rats. In contrast to III MNs that innervate extraocular muscles, XII MNs that innervate tongue muscles mature more rapidly, fire bursts of low frequency action potentials and are vulnerable to degeneration in amyotrophic lateral sclerosis. In neonates, low voltage-activated (LVA) Ca2+ current densities are similar in XII and III MNs but high voltage-activated (HVA) Ca2+ current densities are twofold higher in XII MNs. The HVA Ca2+ channel antagonists (nimodipine and nifedipine for L-type, omega-agatoxin-TK for P/Q-type and omega-conotoxin-GVIA for N-type) revealed that, while N- and P/Q-type HVA Ca2+ channels are present in both MN pools, a 3.5-fold greater P/Q-type Ca2+ current in XII MNs accounts for their greater HVA Ca2+ currents. Developmentally, LVA and HVA Ca2+ current densities decrease in III MNs but remain unchanged in XII MNs. Thus, the differences between these MN pools increase developmentally so that, in juveniles, the LVA Ca2+ current density is twofold greater and the HVA Ca2+ current density is threefold greater in XII compared with III MNs. We propose that this differential expression of LVA and HVA Ca2+ channels in XII and III MNs during development contributes to their distinct physiology and may also be a factor contributing to the greater susceptibility of XII MNs to degeneration as seen in amyotrophic lateral sclerosis.
Assuntos
Canais de Cálcio/biossíntese , Regulação da Expressão Gênica no Desenvolvimento/fisiologia , Nervo Hipoglosso/metabolismo , Neurônios Motores/metabolismo , Nervo Oculomotor/metabolismo , Animais , Animais Recém-Nascidos , Cloreto de Cádmio/farmacologia , Regulação da Expressão Gênica no Desenvolvimento/efeitos dos fármacos , Nervo Hipoglosso/efeitos dos fármacos , Nervo Hipoglosso/crescimento & desenvolvimento , Neurônios Motores/química , Neurônios Motores/efeitos dos fármacos , Nervo Oculomotor/efeitos dos fármacos , Nervo Oculomotor/crescimento & desenvolvimento , Ratos , Ratos WistarRESUMO
We studied the effects of GABA(B) receptor activation on either glycine or GABA(A) receptor-mediated synaptic transmission to hypoglossal motoneurons (HMs, P8-13) using a rat brainstem slice preparation. Activation of GABA(B) receptors with baclofen, a GABA(B) receptor agonist, inhibited the amplitude of evoked glycine and GABA(A) receptor-mediated inhibitory postsynaptic currents. Additionally, with blockade of postsynaptic GABA(B) receptors baclofen decreased the frequency of both glycine and GABA(A) receptor-mediated spontaneous miniature inhibitory postsynaptic currents (mIPSCs), indicating a presynaptic site of action. Conversely, the GABA(B) receptor antagonist CGP 35348 increased the frequency of glycine receptor-mediated mIPSCs. Application of the GABA transport blocker SKF 89976A decreased the frequency of glycinergic mIPSCs. Lastly, we compared the effects of baclofen on the frequency of glycine and GABA(A) receptor-mediated mIPSC during HM development. At increased postnatal ages (P8-13 versus P1-3) mIPSC frequency was more strongly reduced by baclofen. These results show that presynaptic GABA(B) receptors inhibits glycinergic and GABAergic synaptic transmission to HMs, and the presynaptic sensitivity to baclofen is increased in P8-13 versus P1-3 HMs. Further, endogenous GABA is capable of modulating inhibitory synaptic transmission to HMs.
Assuntos
Nervo Hipoglosso/metabolismo , Inibição Neural/fisiologia , Receptores de GABA-A/metabolismo , Receptores de GABA-B/fisiologia , Receptores de Glicina/metabolismo , Transmissão Sináptica/fisiologia , Animais , Baclofeno/farmacologia , Tronco Encefálico/citologia , Tronco Encefálico/fisiologia , GABAérgicos/farmacologia , Agonistas dos Receptores de GABA-B , Nervo Hipoglosso/citologia , Nervo Hipoglosso/crescimento & desenvolvimento , Neurônios Motores/metabolismo , Ácidos Nipecóticos/farmacologia , Técnicas de Cultura de Órgãos , Ratos , Ratos Sprague-Dawley , Mecânica Respiratória/fisiologiaRESUMO
The effects of serotonin (5-HT) on motoneurons are mediated via multiple receptor subtypes. In hypoglossal (XII) motoneurons, the prototypic brainstem motoneurons whose functions change during the postnatal period, 5-HT effects evolve from inhibitory to excitatory, probably in association with changes in receptor expression. We studied 5-HT1B, 5-HT2A and 5-HT2C receptor mRNA in 414 dissociated XII motoneurons and 5-HT2A protein in the XII, facial and spinal cervical (C2-3) motor nuclei. The percentage of motoneurons expressing distinct mRNAs varied with the postnatal age (P3-33 days) and receptor subtype. Initially, 5-HT1B mRNA was present in 50-85% of cells, but on P14 its expression transiently decreased below 35%. 5-HT2A mRNA was present in nearly all cells after P6, but in less than 65% on P3-5. Normal and/or short splice variants of the 5-HT2C mRNA were expressed in less than 20% of motoneurons on P3-9, and in approximately 35% thereafter. 5-HT1B and 5-HT2A mRNAs often were expressed in different cells during early and intermediate postnatal periods, whereas 5-HT2C mRNA never occurred alone. The 5-HT2A receptor protein level gradually increased through P15 in the XII and facial nuclei, with dendritic labelling appearing in XII motoneurons only after P12. In spinal motoneurons, both somatic and dendritic labelling was strongest on P5 and then decreased. The development of 5-HT receptors in XII motoneurons may be related to changes in feeding behaviour, whereas different cues regulate 5-HT receptor expression in upper spinal motoneurons.