RESUMO
In healthy mature motoneurons (MNs), KCC2 cotransporters maintain the intracellular chloride concentration at low levels, a prerequisite for postsynaptic inhibition mediated by GABA and glycine. KCC2 expression in lumbar MNs is reduced after spinal cord injury (SCI) resulting in a depolarizing shift of the chloride equilibrium potential. Despite modeling studies indicating that such a downregulation of KCC2 function would reduce the strength of postsynaptic inhibition, physiological evidence is still lacking. The present study aimed at investigating the functional impact of a modification of KCC2 function. We focused on a well characterized disynaptic inhibitory pathway responsible for reciprocal inhibition between antagonistic muscles. We performed in vitro extracellular recordings on spinal cords isolated from rodents at the end of the first postnatal week. Genetic reduction of KCC2 expression, pharmacological blockade of KCC2, as well as SCI-induced downregulation of KCC2 all resulted in a reduction of the strength of reciprocal inhibition. We then tried to restore endogenous inhibition after SCI by means of zinc ions that have been shown to boost KCC2 function in other models. Zinc chloride indeed hyperpolarized the chloride equilibrium potential in MNs and increased reciprocal inhibition after neonatal SCI. This study demonstrates that the level of KCC2 function sets the strength of postsynaptic inhibition and suggests that the downregulation of KCC2 after SCI likely contributes to the high occurrence of flexor-extensor cocontractions in SCI patients.
Assuntos
Inibição Neural/fisiologia , Medula Espinal/fisiologia , Simportadores/fisiologia , Animais , Cloretos/farmacologia , Regulação para Baixo , Potenciais da Membrana/fisiologia , Camundongos , Camundongos Transgênicos , Neurônios Motores/efeitos dos fármacos , Neurônios Motores/metabolismo , Neurônios Motores/fisiologia , Inibição Neural/genética , Ratos , Traumatismos da Medula Espinal/metabolismo , Traumatismos da Medula Espinal/fisiopatologia , Simportadores/biossíntese , Simportadores/genética , Compostos de Zinco/farmacologia , Cotransportadores de K e Cl-RESUMO
Vestibulospinal pathways activate contralateral motoneurons (MNs) in the thoracolumbar spinal cord of the neonatal mouse exclusively via axons descending ipsilaterally from the vestibular nuclei via the lateral vestibulospinal tract (LVST; Kasumacic et al., 2010). Here we investigate how transmission from the LVST to contralateral MNs is mediated by descending commissural interneurons (dCINs) in different spinal segments. We test the polysynaptic nature of this crossed projection by assessing LVST-mediated ventral root (VR) response latencies, manipulating synaptic responses pharmacologically, and tracing the pathway transynaptically from hindlimb extensor muscles using rabies virus (RV). Longer response latencies in contralateral than ipsilateral VRs, near-complete abolition of LVST-mediated calcium responses in contralateral MNs by mephenesin, and the absence of transsynaptic RV labeling of contralateral LVST neurons within a monosynaptic time window all indicate an overwhelmingly polysynaptic pathway from the LVST to contralateral MNs. Optical recording of synaptically mediated calcium responses identifies LVST-responsive ipsilateral dCINs that exhibit segmental differences in proportion and dorsoventral distribution. In contrast to thoracic and lower lumbar segments, in which most dCINs are LVST responsive, upper lumbar segments stand out because they contain a much smaller and more ventrally restricted subpopulation of LVST-responsive dCINs. A large proportion of these upper lumbar LVST-responsive dCINs project to contralateral L5, which contains many of the hindlimb extensor MNs activated by the LVST. A selective channeling of LVST inputs through segmentally and dorsoventrally restricted subsets of dCINs provides a mechanism for targeting vestibulospinal signals differentially to contralateral trunk and hindlimb MNs in the mammalian spinal cord.
Assuntos
Interneurônios/fisiologia , Neurônios Motores/fisiologia , Medula Espinal/fisiologia , Núcleos Vestibulares/fisiologia , Animais , Animais Recém-Nascidos , Feminino , Vértebras Lombares , Masculino , Camundongos , Vias Neurais/fisiologia , Vértebras TorácicasRESUMO
In healthy adults, activation of γ-aminobutyric acid (GABA)(A) and glycine receptors inhibits neurons as a result of low intracellular chloride concentration ([Cl(-)](i)), which is maintained by the potassium-chloride cotransporter KCC2. A reduction of KCC2 expression or function is implicated in the pathogenesis of several neurological disorders, including spasticity and chronic pain following spinal cord injury (SCI). Given the critical role of KCC2 in regulating the strength and robustness of inhibition, identifying tools that may increase KCC2 function and, hence, restore endogenous inhibition in pathological conditions is of particular importance. We show that activation of 5-hydroxytryptamine (5-HT) type 2A receptors to serotonin hyperpolarizes the reversal potential of inhibitory postsynaptic potentials (IPSPs), E(IPSP), in spinal motoneurons, increases the cell membrane expression of KCC2 and both restores endogenous inhibition and reduces spasticity after SCI in rats. Up-regulation of KCC2 function by targeting 5-HT(2A) receptors, therefore, has therapeutic potential in the treatment of neurological disorders involving altered chloride homeostasis. However, these receptors have been implicated in several psychiatric disorders, and their effects on pain processing are controversial, highlighting the need to further investigate the potential systemic effects of specific 5-HT(2A)R agonists, such as (4-bromo-3,6-dimethoxybenzocyclobuten-1-yl)methylamine hydrobromide (TCB-2).
Assuntos
Regulação da Expressão Gênica/efeitos dos fármacos , Potenciais Pós-Sinápticos Inibidores/fisiologia , Neurônios Motores/metabolismo , Espasticidade Muscular/tratamento farmacológico , Receptor 5-HT2A de Serotonina/metabolismo , Serotonina/farmacologia , Traumatismos da Medula Espinal/complicações , Simportadores/metabolismo , Animais , Western Blotting , Compostos Bicíclicos com Pontes/farmacologia , Cloretos/metabolismo , Reflexo H , Imuno-Histoquímica , Metilaminas/farmacologia , Espasticidade Muscular/etiologia , Ratos , Serotonina/metabolismo , Agonistas do Receptor 5-HT2 de Serotonina/farmacologia , Cotransportadores de K e Cl-RESUMO
The development and the ionic nature of bistable behavior in lumbar motoneurons were investigated in rats. One week after birth, almost all (â¼80%) ankle extensor motoneurons recorded in whole-cell configuration displayed self-sustained spiking in response to a brief depolarization that emerged when the temperature was raised >30°C. The effect of L-type Ca(2+) channel blockers on self-sustained spiking was variable, whereas blockade of the persistent sodium current (I(NaP)) abolished them. When hyperpolarized, bistable motoneurons displayed a characteristic slow afterdepolarization (sADP). The sADPs generated by repeated depolarizing pulses summed to promote a plateau potential. The sADP was tightly associated with the emergence of Ca(2+) spikes. Substitution of extracellular Na(+) or chelation of intracellular Ca(2+) abolished both sADP and the plateau potential without affecting Ca(2+) spikes. These data suggest a key role of a Ca(2+)-activated nonselective cation conductance ((CaN)) in generating the plateau potential. In line with this, the blockade of (CaN) by flufenamate abolished both sADP and plateau potentials. Furthermore, 2-aminoethoxydiphenyl borate (2-APB), a common activator of thermo-sensitive vanilloid transient receptor potential (TRPV) cation channels, promoted the sADP. Among TRPV channels, only the selective activation of TRPV2 channels by probenecid promoted the sADP to generate a plateau potential. To conclude, bistable behaviors are, to a large extent, determined by the interplay between three currents: L-type I(Ca), I(NaP), and a Na(+)-mediated I(CaN) flowing through putative TRPV2 channels.
Assuntos
Potenciais de Ação , Neurônios Motores/fisiologia , Sódio/metabolismo , Medula Espinal/fisiologia , Animais , Compostos de Boro/farmacologia , Cálcio/metabolismo , Bloqueadores dos Canais de Cálcio/farmacologia , Canais de Cálcio Tipo L/metabolismo , Ácido Flufenâmico/farmacologia , Temperatura Alta , Neurônios Motores/metabolismo , Probenecid/farmacologia , Ratos , Ratos Wistar , Medula Espinal/citologia , Canais de Cátion TRPV/antagonistas & inibidores , Canais de Cátion TRPV/metabolismoRESUMO
BACKGROUND: Perinatal cerebral hypoxia-ischemia (HI) can lead to severe neurodevelopmental disorders. Studies in humans and animal models mainly focused on cerebral outcomes, and little is known about the mechanisms that may affect the brainstem and the spinal cord. Dysfunctions of neuromodulatory systems, such as the serotonergic (5-HT) projections, critical for the development of neural networks, have been postulated to underlie behavioral and motor deficits, as well as metabolic changes. METHODS: The aim of this study was to investigate brainstem and spinal cord functions by means of plethysmography and sensorimotor tests in a neonatal Rice-Vanucci model of HI in mice. We also evaluated bioaminergic contents in central regions dedicated to the motor control of autonomic functions. RESULTS: Mice with cerebral infarct expressed motor disturbances and had a lower body weight and a decreased respiratory frequency than SHAM, suggesting defects of brainstem neural network involved in the motor control of feeding, suckling, swallowing, and respiration. Moreover, our study revealed changes of monoamine and amino acid contents in the brainstem and the spinal cord of HI mice. CONCLUSION: Our results suggest that monoaminergic neuromodulation plays an important role in the physiopathology of HI brain injury that may represent a good therapeutic target.
Assuntos
Animais Recém-Nascidos , Tronco Encefálico/fisiopatologia , Hipóxia-Isquemia Encefálica/fisiopatologia , Medula Espinal/fisiopatologia , Aminoácidos/metabolismo , Animais , Monoaminas Biogênicas/metabolismo , Peso Corporal , Camundongos , Pletismografia , Equilíbrio Postural/fisiologia , Receptores de Neurotransmissores/metabolismo , Estatísticas não ParamétricasRESUMO
Avulsion injury results in motoneuron death due to the increased excitotoxicity developing in the affected spinal segments. This study focused on possible short and long term molecular and receptor expression alterations which are thought to be linked to the excitotoxic events in the ventral horn with or without the anti-excitotoxic riluzole treatment. In our experimental model the left lumbar 4 and 5 (L4, 5) ventral roots of the spinal cord were avulsed. Treated animals received riluzole for 2 weeks. Riluzole is a compound that acts to block voltage-activated Na+ and Ca2+ channels. In control animals the L4, 5 ventral roots were avulsed without riluzole treatment. Expression of astrocytic EAAT-2 and that of KCC2 in motoneurons on the affected side of the L4 spinal segment were detected after the injury by confocal and dSTORM imaging, intracellular Ca2+ levels in motoneurons were quantified by electron microscopy. The KCC2 labeling in the lateral and ventrolateral parts of the L4 ventral horn was weaker compared with the medial part of L4 ventral horn in both groups. Riluzole treatment dramatically enhanced motoneuron survival but was not able to prevent the down-regulation of KCC2 expression in injured motoneurons. In contrast, riluzole successfully obviated the increase of intracellular calcium level and the decrease of EAAT-2 expression in astrocytes compared with untreated injured animals. We conclude that KCC2 may not be an essential component for survival of injured motoneurons and riluzole is able to modulate the intracellular level of calcium and expression of EAAT-2.
Assuntos
Riluzol , Simportadores , Animais , Riluzol/farmacologia , Riluzol/metabolismo , Cálcio/metabolismo , Raízes Nervosas Espinhais/lesões , Raízes Nervosas Espinhais/metabolismo , Medula Espinal/metabolismo , Simportadores/genética , Simportadores/metabolismoRESUMO
Patterned, spontaneous activity plays a critical role in the development of neuronal networks. A robust spontaneous activity is observed in vitro in spinal cord preparations isolated from immature rats. The rhythmic ventral root discharges rely mainly on the depolarizing/excitatory action of GABA and glycine early during development, whereas at later stages glutamate drive is primarily responsible for the rhythmic activity and GABA/glycine are thought to play an inhibitory role. However, rhythmic discharges mediated by the activation of GABA(A) receptors are recorded from dorsal roots (DRs). In the present study, we used the in vitro spinal cord preparation of neonatal rats to identify the relationship between discharges that are conducted antidromically along DRs and the spontaneous activity recorded from lumbar motoneurons. We show that discharges in DRs precede those in ventral roots and that primary afferent depolarizations (PADs) start earlier than EPSPs in motoneurons. EPSP-triggered averaging revealed that the action potentials propagate not only antidromically in the DR but also centrally and trigger EPSPs in motoneurons. Potentiating GABAergic antidromic discharges by diazepam increased the EPSPs recorded from motoneurons; conversely, blocking DR bursts markedly reduced these EPSPs. High intracellular concentrations of chloride are maintained in primary afferent terminals by the sodium-potassium-chloride cotransporter NKCC1. Blocking these cotransporters by bumetanide decreased both dorsal and ventral root discharges. We conclude that primary afferent fibers act as excitatory interneurons and that GABA, through PADs reaching firing threshold, is still playing a key role in promoting spontaneous activity in neonates.
Assuntos
Potenciais de Ação/fisiologia , Potenciais Pós-Sinápticos Excitadores/fisiologia , Interneurônios/fisiologia , Neurônios Motores/fisiologia , Medula Espinal/fisiologia , Animais , Animais Recém-Nascidos , Feminino , Masculino , Neurônios Aferentes/fisiologia , Ratos , Ratos Wistar , Receptores de GABA-A/fisiologia , Raízes Nervosas Espinhais/fisiologia , Sinapses/fisiologia , Ácido gama-Aminobutírico/fisiologiaRESUMO
In vitro studies have repeatedly demonstrated that the neurotransmitters γ-aminobutyric acid (GABA) and glycine depolarize immature neurons in many areas of the CNS, including the spinal cord. This widely accepted phenomenon was recently challenged by experiments showing that the depolarizing action of GABA on neonatal hippocampus and neocortex in vitro was prevented by adding energy substrates (ES), such as the ketone body metabolite dl-ß-hydroxybutyric acid (DL-BHB), lactate, or pyruvate to the artificial cerebrospinal fluid (ACSF). It was suggested that GABA-induced depolarizations in vitro might be an artifact due to inadequate energy supply when glucose is the sole energy source, consistent with the energy metabolism of neonatal rat brain being largely dependent on ESs other than glucose. Here we examined the effects of these ESs (DL-BHB, lactate, pyruvate) on inhibitory postsynaptic potentials (IPSPs) recorded from neonatal rat lumbar spinal cord motoneurons (MNs), in vitro. We report that supplementing the ACSF with physiologic concentrations of DL-BHB, lactate, or pyruvate does not alter the reversal potential of IPSPs (E(IPSP)). Only high concentrations of pyruvate hyperpolarized E(IPSP). In addition, the depolarizing action of GABA on primary afferent terminals was not affected by supplementing the ACSF with ES at physiologic concentrations. We conclude that depolarizing IPSPs in immature MNs and the primary afferent depolarizations are not caused by inadequate energy supply. Glucose at its standard concentration appears to be an adequate ES for the neonatal spinal cord in vitro.
Assuntos
Metabolismo Energético/fisiologia , Glucose/metabolismo , Glicina/metabolismo , Fármacos Neuromusculares Despolarizantes/metabolismo , Medula Espinal/metabolismo , Ácido gama-Aminobutírico/metabolismo , Animais , Animais Recém-Nascidos , Metabolismo Energético/efeitos dos fármacos , Feminino , Glucose/fisiologia , Glicina/fisiologia , Potenciais Pós-Sinápticos Inibidores/efeitos dos fármacos , Potenciais Pós-Sinápticos Inibidores/fisiologia , Masculino , Fármacos Neuromusculares Despolarizantes/farmacologia , Ratos , Ratos Wistar , Medula Espinal/efeitos dos fármacos , Especificidade por Substrato/fisiologia , Ácido gama-Aminobutírico/fisiologiaRESUMO
Maturation of inhibitory postsynaptic transmission onto motoneurons in the rat occurs during the perinatal period, a time window during which pathways arising from the brainstem reach the lumbar enlargement of the spinal cord. There is a developmental switch in miniature IPSCs (mIPSCs) from predominantly long-duration GABAergic to short-duration glycinergic events. We investigated the effects of a complete neonatal [postnatal day 0 (P0)] spinal cord transection (SCT) on the expression of Glycine and GABA(A) receptor subunits (GlyR and GABA(A)R subunits) in lumbar motoneurons. In control rats, the density of GlyR increased from P1 to P7 to reach a plateau, whereas that of GABA(A)R subunits dropped during the same period. In P7 animals with neonatal SCT (SCT-P7), the GlyR densities were unchanged compared with controls of the same age, while the developmental downregulation of GABA(A)R was prevented. Whole-cell patch-clamp recordings of mIPSCs performed in lumbar motoneurons at P7 revealed that the decay time constant of miniature IPSCs and the proportion of GABAergic events significantly increased after SCT. After daily injections of the 5-HT(2)R agonist DOI, GABA(A)R immunolabeling on SCT-P7 motoneurons dropped down to values reported in control-P7, while GlyR labeling remained stable. A SCT made at P5 significantly upregulated the expression of GABA(A)R 1 week later with little, if any, influence on GlyR. We conclude that the plasticity of GlyR is independent of supraspinal influences whereas that of GABA(A)R is markedly influenced by descending pathways, in particular serotoninergic projections.
Assuntos
Vias Eferentes/crescimento & desenvolvimento , Neurônios Motores/metabolismo , Inibição Neural/fisiologia , Plasticidade Neuronal/fisiologia , Traumatismos da Medula Espinal/metabolismo , Medula Espinal/crescimento & desenvolvimento , Animais , Animais Recém-Nascidos , Tronco Encefálico/crescimento & desenvolvimento , Modelos Animais de Doenças , Regulação para Baixo/fisiologia , Vias Eferentes/citologia , Vias Eferentes/lesões , Glicina/metabolismo , Imuno-Histoquímica , Potenciais Pós-Sinápticos Inibidores/fisiologia , Masculino , Técnicas de Patch-Clamp , Subunidades Proteicas/metabolismo , Ratos , Ratos Wistar , Receptores de GABA-A/metabolismo , Receptores de Glicina/metabolismo , Medula Espinal/citologia , Traumatismos da Medula Espinal/fisiopatologia , Transmissão Sináptica/fisiologia , Regulação para Cima/fisiologia , Ácido gama-Aminobutírico/metabolismoRESUMO
Spontaneous activity is observed in most developing neuronal circuits, such as the retina, hippocampus, brainstem and spinal cord. In the spinal cord, spontaneous activity is important for generating embryonic movements critical for the proper development of motor axons, muscles and synaptic connections. A spontaneous bursting activity can be recorded in vitro from ventral roots during perinatal development. The depolarizing action of the inhibitory amino acids γ-aminobutyric acid and glycine is widely proposed to contribute to spontaneous activity in several immature systems. During development, the intracellular chloride concentration decreases, leading to a shift of equilibrium potential for Cl(-) ions towards more negative values, and thereby to a change in glycine- and γ-aminobutyric acid-evoked potentials from depolarization/excitation to hyperpolarization/inhibition. The up-regulation of the outward-directed Cl(-) pump, the neuron-specific potassium-chloride co-transporter type 2 KCC2, has been shown to underlie this shift. Here, we investigated whether spontaneous and locomotor-like activities are altered in genetically modified mice that express only 8-20% of KCC2, compared with wild-type animals. We show that a reduced amount of KCC2 leads to a depolarized equilibrium potential for Cl(-) ions in lumbar motoneurons, an increased spontaneous activity and a faster locomotor-like activity. However, the left-right and flexor-extensor alternating pattern observed during fictive locomotion was not affected. We conclude that neuronal networks within the spinal cord are more excitable in KCC2 mutant mice, which suggests that KCC2 strongly modulates the excitability of spinal cord networks.
Assuntos
Neurônios Motores/fisiologia , Rede Nervosa/fisiologia , Medula Espinal/anatomia & histologia , Medula Espinal/fisiologia , Simportadores/metabolismo , Animais , Bumetanida/farmacologia , Furosemida/farmacologia , Vértebras Lombares , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Atividade Motora/efeitos dos fármacos , Atividade Motora/fisiologia , Neurônios Motores/citologia , Neurônios Motores/efeitos dos fármacos , Inibidores de Simportadores de Cloreto de Sódio e Potássio/farmacologia , Simportadores/genética , Cotransportadores de K e Cl-RESUMO
Spasticity is a disabling motor disorder affecting 70% of people with brain and spinal cord injury. The rate-dependent depression (RDD) of the H reflex is the only electrophysiological measurement correlated with the degree of spasticity assessed clinically in spastic patients. Several lines of evidence suggest that the mechanism underlying the H reflex RDD depends on the strength of synaptic inhibition through GABAA (GABAAR) and glycine receptors (GlyR). In adult rats with spinal cord transection (SCT), we studied the time course of the expression of GABAAR and GlyR at the membrane of retrogradely identified Gastrocnemius and Tibialis anterior motoneurons (MNs) 3, 8 and 16 weeks after injury, and measured the RDD of the H reflex at similar post lesion times. Three weeks after SCT, a significant decrease in the expression of GABAA and GlyR was observed compared to intact rats, and the H-reï¬ex RDD was much less pronounced than in controls. Eight weeks after SCT, GlyR values returned to normal. Simultaneously, we observed a tendency to recover normal RDD of the H reflex at higher frequencies. We tested whether an anti-inflammatory treatment using methylprednisolone performed immediately after SCT could prevent alterations in GABAA/glycine receptors and/or the development of spasticity observed 3 weeks after injury. This treatment restored control levels of GlyR but not the expression of GABAAR, and it completely prevented the attenuation of RDD. These data strongly suggest that alteration of glycinergic inhibition of lumbar MNs is involved in the mechanisms underlying spasticity after SCI.
Assuntos
Neurônios Motores/metabolismo , Espasticidade Muscular/metabolismo , Receptores de Glicina/metabolismo , Traumatismos da Medula Espinal/metabolismo , Animais , Feminino , Glicina/metabolismo , Região Lombossacral , Espasticidade Muscular/etiologia , Ratos , Ratos Wistar , Receptores de GABA-A/metabolismo , Medula Espinal/metabolismo , Traumatismos da Medula Espinal/complicaçõesRESUMO
Rhythm generation in neuronal networks relies on synaptic interactions and pacemaker properties. Little is known about the contribution of the latter mechanisms to the integrated network activity underlying locomotion in mammals. We tested the hypothesis that the persistent sodium current (I(NaP)) is critical in generating locomotion in neonatal rodents using both slice and isolated spinal cord preparations. After removing extracellular calcium, 75% of interneurons in the area of the central pattern generator (CPG) for locomotion exhibited bursting properties and I(NaP) was concomitantly upregulated. Putative CPG interneurons such as commissural and Hb9 interneurons also expressed I(NaP)-dependent (riluzole-sensitive) bursting properties. Most bursting cells exhibited a pacemaker-like behavior (i.e., burst frequency increased with depolarizing currents). Veratridine upregulated I(NaP), induced riluzole-sensitive bursting properties, and slowed down the locomotor rhythm. This study provides evidence that I(NaP) generates pacemaker activities in CPG interneurons and contributes to the regulation of the locomotor activity.
Assuntos
Relógios Biológicos/fisiologia , Locomoção/fisiologia , Periodicidade , Canais de Sódio/fisiologia , Medula Espinal/fisiologia , Animais , Animais Recém-Nascidos , Relógios Biológicos/efeitos dos fármacos , Cálcio/metabolismo , Eletrofisiologia , Espaço Extracelular/metabolismo , Corantes Fluorescentes , Proteínas de Fluorescência Verde/genética , Proteínas de Homeodomínio/genética , Técnicas In Vitro , Interneurônios/fisiologia , Camundongos , Camundongos Transgênicos , Ratos , Ratos Wistar , Canais de Sódio/efeitos dos fármacos , Medula Espinal/citologia , Veratridina/farmacologiaRESUMO
Locomotor burst activity in the mature intact spinal cord alternates between the left and right sides of a segment through reciprocal inhibition. By contrast, all motor bursts are in phase in the fetus. The alternating pattern disappears after neonatal spinal cord transection which suppresses supraspinal influences upon the locomotor networks. These data reveal the plasticity of spinal cord locomotor networks. This review describes recent evidence suggesting that regulation of cation-chloride cotransporter expression and activity may underlie this plasticity. GABA and glycine are classically called "inhibitory" amino acids, despite the fact that their action can rapidly switch from inhibition to excitation and vice versa. This post-synaptic action depends on the intracellular concentration of chloride ions ([Cl(-)](i)) which is regulated by a protein in the plasma membrane: the K(+)-Cl(-) cotransporter (KCC2) extruding both K(+) and Cl(-) ions. No or a reduced KCC2 expression leads to a depolarizing (excitatory) action of GABA and glycine. This latter situation is observed early during development and in several pathological conditions, such as epilepsy, neuronal injury and chronic pain.
Assuntos
Locomoção/fisiologia , Rede Nervosa/fisiologia , Plasticidade Neuronal/fisiologia , Simportadores de Cloreto de Sódio-Potássio/fisiologia , Medula Espinal/fisiologia , Animais , Animais Recém-Nascidos , Cloretos/metabolismo , Lateralidade Funcional/fisiologia , Glicina/fisiologia , Homeostase/fisiologia , Humanos , Ácido gama-Aminobutírico/fisiologiaRESUMO
Rats with complete spinal cord transection (SCT) can recover hindlimb locomotor function under strategies combining exercise training and 5-HT agonist treatment. This recovery is expected to result from structural and functional re-organization within the spinal cord below the lesion. To begin to understand the nature of this reorganization, we examined synaptic changes to identified gastrocnemius (GS) or tibialis anterior (TA) motoneurons (MNs) in SCT rats after a schedule of early exercise training and delayed 5-HT agonist treatment. In addition, we analyzed changes in distribution and number of lumbar interneurons (INs) presynaptic to GS MNs using retrograde transneuronal transport of rabies virus. In SCT-untrained rats, we found few changes in the density and size of inhibitory and excitatory inputs impinging on cell bodies of TA and GS MNs compared to intact rats, whereas there was a marked trend for a reduction in the number of premotor INs connected to GS MNs. In contrast, after training of SCT rats, a significant increase of the density of GABAergic and glycinergic axon terminals was observed on both GS and TA motoneuronal cell bodies, as well as of presynaptic P-boutons on VGLUT1 afferents. Despite these changes in innervation the number of premotor INs connected to GS MNs was similar to control values although some new connections to MNs were observed. These results suggest that adaptation of gait patterns in SCT-trained rats was accompanied by changes in the innervation of lumbar MNs while the distribution of the spinal premotor circuitry was relatively preserved.
Assuntos
Região Lombossacral/inervação , Neurônios Motores/patologia , Rede Nervosa/patologia , Condicionamento Físico Animal , Traumatismos da Medula Espinal/fisiopatologia , Animais , Feminino , Glicina/metabolismo , Membro Posterior/fisiologia , Interneurônios/patologia , Locomoção/fisiologia , Músculo Esquelético/inervação , Músculo Esquelético/patologia , Terminações Pré-Sinápticas/patologia , Vírus da Raiva , Ratos , Ratos Wistar , Recuperação de Função Fisiológica , Agonistas do Receptor de Serotonina/uso terapêutico , Proteína Vesicular 1 de Transporte de Glutamato/metabolismo , Ácido gama-Aminobutírico/metabolismoRESUMO
Lead poisoning is one of the most significant health problem of environmental origin. It is known to cause different damages in the central and peripheral nervous system which could be represented by several neurophysiological and behavioral symptoms. In this study we firstly investigated the effect of lead prenatal exposure in rats to (3g/L), from neonatal to young age, on the motor/sensory performances, excitability of the spinal cord and gaits during development. Then we evaluated neuroprotective effects of curcumin I (Cur I) against lead neurotoxicity, by means of grasping and cliff avoidance tests to reveal the impairment of the sensorimotor functions in neonatal rats exposed prenatally to lead. In addition, extracellular recordings of motor output in spinal cord revealed an hyper-excitability of spinal networks in lead treated rats. The frequency of induced fictive locomotion was also increased in treated rats. At the young age, rats exhibited an impaired locomotor gait. All those abnormalities were attenuated by Cur I treatment at a dose of 16g/kg. Based on our finding, Cur I has shown features of a potent chemical compound able to restore the neuronal and the relative locomotor behaviors disturbances induced by lead intoxication. Therefore, this chemical can be recommended as a new therapeutic trial against lead induced neurotoxicity.
Assuntos
Curcumina/farmacologia , Fenômenos Eletrofisiológicos/efeitos dos fármacos , Intoxicação por Chumbo , Fármacos Neuroprotetores/farmacologia , Desempenho Psicomotor/efeitos dos fármacos , Animais , Peso Corporal/efeitos dos fármacos , Feminino , Marcha/efeitos dos fármacos , Locomoção/efeitos dos fármacos , Exposição Materna , Gravidez , Ratos , Medula Espinal/efeitos dos fármacos , Fatores de TempoRESUMO
In mature neurons, low intracellular chloride level required for inhibition is maintained by the potassium-chloride cotransporter, KCC2. Impairment of Cl- extrusion after KCC2 dysfunction has been involved in many central nervous system disorders, such as seizures, neuropathic pain, or spasticity, after a spinal cord injury (SCI). This makes KCC2 an appealing drug target for restoring Cl- homeostasis and inhibition in pathological conditions. In the present study, we screen the Prestwick Chemical Library® and identify conventional antipsychotics phenothiazine derivatives as enhancers of KCC2 activity. Among them, prochlorperazine hyperpolarizes the Cl- equilibrium potential in motoneurons of neonatal rats and restores the reciprocal inhibition post-SCI. The compound alleviates spasticity in chronic adult SCI rats with an efficacy equivalent to the antispastic agent, baclofen, and rescues the SCI-induced downregulation of KCC2 in motoneurons below the lesion. These pre-clinical data support prochlorperazine for a new therapeutic indication in the treatment of spasticity post-SCI and neurological disorders involving a KCC2 dysfunction.
Assuntos
Antagonistas de Dopamina/farmacologia , Espasticidade Muscular/etiologia , Proclorperazina/farmacologia , Traumatismos da Medula Espinal/complicações , Simportadores/efeitos dos fármacos , Animais , Espasticidade Muscular/metabolismo , Ratos , Ratos Wistar , Traumatismos da Medula Espinal/metabolismo , Simportadores/metabolismo , Cotransportadores de K e Cl-Assuntos
Neurônios/fisiologia , Traumatismos da Medula Espinal/fisiopatologia , Animais , Fator Neurotrófico Derivado do Encéfalo/fisiologia , Cloretos/fisiologia , Glicina/fisiologia , Reflexo H , Humanos , Transporte de Íons , Camundongos , Camundongos Transgênicos , Espasticidade Muscular/fisiopatologia , Simportadores/fisiologia , Ácido gama-Aminobutírico/fisiologia , Cotransportadores de K e Cl-RESUMO
Fast synaptic inhibition relies on tight regulation of intracellular Cl(-). Chloride dysregulation is implicated in several neurological and psychiatric disorders. Beyond mere disinhibition, the consequences of Cl(-) dysregulation are multifaceted and best understood in terms of a dynamical system involving complex interactions between multiple processes operating on many spatiotemporal scales. This dynamical perspective helps explain many unintuitive manifestations of Cl(-) dysregulation. Here we discuss how taking into account dynamical regulation of intracellular Cl(-) is important for understanding how synaptic inhibition fails, how to best detect that failure, why Cl(-) regulation is energetically so expensive, and the overall consequences for therapeutics.
Assuntos
Cloretos/metabolismo , Inibição Neural/fisiologia , Dinâmica não Linear , Sinapses/fisiologia , Animais , Homeostase/fisiologia , Humanos , Modelos BiológicosRESUMO
Upregulation of the persistent sodium current (I(NaP)) in motoneurons contributes to the development of spasticity after spinal cord injury (SCI). We investigated the mechanisms that regulate I(NaP) and observed elevated expression of voltage-gated sodium (Nav) 1.6 channels in spinal lumbar motoneurons of adult rats with SCI. Furthermore, immunoblots revealed a proteolysis of Nav channels, and biochemical assays identified calpain as the main proteolytic factor. Calpain-dependent cleavage of Nav channels after neonatal SCI was associated with an upregulation of I(NaP) in motoneurons. Similarly, the calpain-dependent cleavage of Nav1.6 channels expressed in human embryonic kidney (HEK) 293 cells caused the upregulation of I(NaP). The pharmacological inhibition of calpain activity by MDL28170 reduced the cleavage of Nav channels, I(NaP) in motoneurons and spasticity in rats with SCI. Similarly, the blockade of I(NaP) by riluzole alleviated spasticity. This study demonstrates that Nav channel expression in lumbar motoneurons is altered after SCI, and it shows a tight relationship between the calpain-dependent proteolysis of Nav1.6 channels, the upregulation of I(NaP) and spasticity.
Assuntos
Calpaína/metabolismo , Neurônios Motores/patologia , Canal de Sódio Disparado por Voltagem NAV1.6/biossíntese , Traumatismos da Medula Espinal/genética , Animais , Calpaína/genética , Dipeptídeos/administração & dosagem , Regulação da Expressão Gênica/efeitos dos fármacos , Células HEK293 , Humanos , Neurônios Motores/metabolismo , Canal de Sódio Disparado por Voltagem NAV1.1/biossíntese , Canal de Sódio Disparado por Voltagem NAV1.1/metabolismo , Canal de Sódio Disparado por Voltagem NAV1.6/metabolismo , Técnicas de Patch-Clamp , Ratos , Riluzol/administração & dosagem , Medula Espinal/metabolismo , Medula Espinal/patologia , Traumatismos da Medula Espinal/metabolismo , Traumatismos da Medula Espinal/patologiaRESUMO
To assess the organization and functional development of vestibulospinal inputs to cervical motoneurons (MNs), we have used electrophysiology (ventral root and electromyographic [EMG] recording), calcium imaging, trans-synaptic rabies virus (RV) and conventional retrograde tracing and immunohistochemistry in the neonatal mouse. By stimulating the VIIIth nerve electrically while recording synaptically mediated calcium responses in MNs, we characterized the inputs from the three vestibulospinal tracts, the separate ipsilateral and contralateral medial vestibulospinal tracts (iMVST/cMVST) and the lateral vestibulospinal tract (LVST), to MNs in the medial and lateral motor columns (MMC and LMC) of cervical segments. We found that ipsilateral inputs from the iMVST and LVST were differentially distributed to the MMC and LMC in the different segments, and that all contralateral inputs to MMC and LMC MNs in each segment derive from the cMVST. Using trans-synaptic RV retrograde tracing as well as pharmacological manipulation of VIIIth nerve-elicited synaptic responses, we found that a substantial proportion of inputs to both neck and forelimb extensor MNs was mediated monosynaptically, but that polysynaptic inputs were also significant. By recording EMG responses evoked by natural stimulation of the vestibular apparatus, we found that vestibular-mediated motor output to the neck and forelimb musculature became more robust during the first 10 postnatal days, concurrently with a decrease in the latency of MN discharge evoked by VIIIth nerve electrical stimulation. Together, these results provide insight into the complexity of vestibulospinal connectivity in the cervical spinal cord and a cogent demonstration of the functional maturation that vestibulospinal connections undergo postnatally. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 76: 1061-1077, 2016.