scholarly journals Alterations of action potentials and the localization of Nav1.6 sodium channels in spared axons after hemisection injury of the spinal cord in adult rats

2011 ◽  
Vol 105 (3) ◽  
pp. 1033-1044 ◽  
Author(s):  
Arsen S. Hunanyan ◽  
Valentina Alessi ◽  
Samik Patel ◽  
Damien D. Pearse ◽  
Gary Matthews ◽  
...  
Keyword(s):  
Spinal Cord ◽  
Sodium Channels ◽  
Action Potentials ◽  
Molecular Mechanisms ◽  
Input Resistance ◽  
Ultrastructural Changes ◽  
Resting Membrane Potential ◽  
Adult Rats ◽  
Cord Injury

Previously, we reported a pronounced reduction in transmission through surviving axons contralateral to chronic hemisection (HX) of adult rat spinal cord. To examine the cellular and molecular mechanisms responsible for this diminished transmission, we recorded intracellularly from lumbar lateral white matter axons in deeply anesthetized adult rats in vivo and measured the propagation of action potentials (APs) through rubrospinal/reticulospinal tract (RST/RtST) axons contralateral to chronic HX at T10. We found decreased excitability in these axons, manifested by an increased rheobase to trigger APs and longer latency for AP propagation passing the injury level, without significant differences in axonal resting membrane potential and input resistance. These electrophysiological changes were associated with altered spatial localization of Nav1.6 sodium channels along axons: a subset of axons contralateral to the injury exhibited a diffuse localization (>10 μm spread) of Nav1.6 channels, a pattern characteristic of demyelinated axons (Craner MJ, Newcombe J, Black JA, Hartle C, Cuzner ML, Waxman SG. Proc Natl Acad Sci USA 101: 8168–8173, 2004b). This result was substantiated by ultrastructural changes seen with electron microscopy, in which an increased number of large-caliber, demyelinated RST axons were found contralateral to the chronic HX. Therefore, an increased rheobase, pathological changes in the distribution of Nav1.6 sodium channels, and the demyelination of contralateral RST axons are likely responsible for their decreased conduction chronically after HX and thus may provide novel targets for strategies to improve function following incomplete spinal cord injury.

Contribution of Nav1.8 Sodium Channels to Action Potential Electrogenesis in DRG Neurons

2001 ◽  
Vol 86 (2) ◽  
pp. 629-640 ◽  
Author(s):  
Muthukrishnan Renganathan ◽  
Theodore R. Cummins ◽  
Stephen G. Waxman
Keyword(s):  
Action Potential ◽  
Sodium Channels ◽  
Action Potentials ◽  
Input Resistance ◽  
Resting Membrane Potential ◽  
Drg Neurons ◽  
Significant Difference ◽  
Steady State Inactivation ◽  
Current Threshold

C-type dorsal root ganglion (DRG) neurons can generate tetrodotoxin-resistant (TTX-R) sodium-dependent action potentials. However, multiple sodium channels are expressed in these neurons, and the molecular identity of the TTX-R sodium channels that contribute to action potential production in these neurons has not been established. In this study, we used current-clamp recordings to compare action potential electrogenesis in Nav1.8 (+/+) and (−/−) small DRG neurons maintained for 2–8 h in vitro to examine the role of sodium channel Nav1.8 (α-SNS) in action potential electrogenesis. Although there was no significant difference in resting membrane potential, input resistance, current threshold, or voltage threshold in Nav1.8 (+/+) and (−/−) DRG neurons, there were significant differences in action potential electrogenesis. Most Nav1.8 (+/+) neurons generate all-or-none action potentials, whereas most of Nav1.8 (−/−) neurons produce smaller graded responses. The peak of the response was significantly reduced in Nav1.8 (−/−) neurons [31.5 ± 2.2 (SE) mV] compared with Nav1.8 (+/+) neurons (55.0 ± 4.3 mV). The maximum rise slope was 84.7 ± 11.2 mV/ms in Nav1.8 (+/+) neurons, significantly faster than in Nav1.8 (−/−) neurons where it was 47.2 ± 1.3 mV/ms. Calculations based on the action potential overshoot in Nav1.8 (+/+) and (−/−) neurons, following blockade of Ca2+ currents, indicate that Nav1.8 contributes a substantial fraction (80–90%) of the inward membrane current that flows during the rising phase of the action potential. We found that fast TTX-sensitive Na+ channels can produce all-or-none action potentials in some Nav1.8 (−/−) neurons but, presumably as a result of steady-state inactivation of these channels, electrogenesis in Nav1.8 (−/−) neurons is more sensitive to membrane depolarization than in Nav1.8 (+/+) neurons, and, in the absence of Nav1.8, is attenuated with even modest depolarization. These observations indicate that Nav1.8 contributes substantially to action potential electrogenesis in C-type DRG neurons.

scholarly journals An In Vitro Protocol for Recording From Spinal Motoneurons of Adult Rats

2008 ◽  
Vol 100 (1) ◽  
pp. 474-481 ◽  
Author(s):  
Jonathan S. Carp ◽  
Ann M. Tennissen ◽  
Donna L. Mongeluzi ◽  
Christopher J. Dudek ◽  
Xiang Yang Chen ◽  
...  
Keyword(s):  
Spinal Cord ◽  
Action Potential ◽  
Mechanical Stability ◽  
Pharmacological Study ◽  
Input Resistance ◽  
Spinal Motoneurons ◽  
Adult Rats ◽  
Precise Control

In vitro slice preparations of CNS tissue are invaluable for studying neuronal function. However, up to now, slice protocols for adult mammal spinal motoneurons—the final common pathway for motor behaviors—have been available for only limited portions of the spinal cord. In most cases, these preparations have not been productive due to the poor viability of motoneurons in vitro. This report describes and validates a new slice protocol that for the first time provides reliable intracellular recordings from lumbar motoneurons of adult rats. The key features of this protocol are: preexposure to 100% oxygen; laminectomy prior to perfusion; anesthesia with ketamine/xylazine; embedding the spinal cord in agar prior to slicing; and, most important, brief incubation of spinal cord slices in a 30% solution of polyethylene glycol to promote resealing of the many motoneuron dendrites cut during sectioning. Together, these new features produce successful recordings in 76% of the experiments and an average action potential amplitude of 76 mV. Motoneuron properties measured in this new slice preparation (i.e., voltage and current thresholds for action potential initiation, input resistance, afterhyperpolarization size and duration, and onset and offset firing rates during current ramps) are comparable to those recorded in vivo. Given the mechanical stability and precise control over the extracellular environment afforded by an in vitro preparation, this new protocol can greatly facilitate electrophysiological and pharmacological study of these uniquely important neurons and other delicate neuronal populations in adult mammals.

Phenytoin Protects Spinal Cord Axons and Preserves Axonal Conduction and Neurological Function in a Model of Neuroinflammation In Vivo

2003 ◽  
Vol 90 (5) ◽  
pp. 3566-3571 ◽  
Author(s):  
Albert C. Lo ◽  
Carl Y. Saab ◽  
Joel A. Black ◽  
Stephen G. Waxman
Keyword(s):  
Spinal Cord ◽  
Sodium Channels ◽  
Action Potentials ◽  
Axonal Degeneration ◽  
Corticospinal Tract ◽  
Calcium Influx ◽  
Clinical Status ◽  
Channel Blockers ◽  
Sodium Influx

Axonal degeneration within the spinal cord contributes substantially to neurological disability in multiple sclerosis (MS). Thus neuroprotective therapies that preserve axons, so that they maintain their integrity and continue to function, might be expected to result in improved neurological outcome. Sodium channels are known to provide a route for sodium influx that can drive calcium influx, via reverse operation of the Na+/Ca2+ exchanger, after injury to axons within the CNS, and sodium channel blockers have been shown to protect CNS axons from degeneration after experimental anoxic, traumatic, and nitric oxide (NO)-induced injury. In this study, we asked whether phenytoin, which is known to block sodium channels, can protect spinal cord axons from degeneration in mice with experimental allergic encephalomyelitis (EAE), which display substantial axonal degeneration and clinical paralysis. We demonstrate that the loss of dorsal corticospinal tract (63%) and dorsal column (cuneate fasciculus; 43%) axons in EAE is significantly ameliorated (corticospinal tract: 28%; cuneate fasciculus: 17%) by treatment with phenytoin. Spinal cord compound action potentials (CAP) were significantly attenuated in untreated EAE, whereas spinal cords from phenytoin-treated EAE had robust CAPs, similar to those from phenytoin-treated control mice. Clinical scores in phenytoin-treated EAE at 28 days were significantly improved (1.5, i.e., minor righting reflex abnormalities) compared with untreated EAE (3.8, i.e., near-complete hindlimb paralysis). Our results demonstrate that phenytoin has a protective effect in vivo on spinal cord axons, preventing their degeneration, maintaining their ability to conduct action potentials, and improving clinical status in a model of neuroinflammation.

scholarly journals In - Vivo Conversion of Astrocytes to Neuroblasts in the Injured Spinal Cord

2021 ◽  
Author(s):  
Maryam Lale Ataei ◽  
Mohammad Karimipour ◽  
Parviz Shahabi ◽  
Hamid Soltani-Zangbar ◽  
Maryam Pashaiasl
Keyword(s):  
Spinal Cord ◽  
Stem Cells ◽  
Spinal Cord Injury ◽  
Neural Progenitor Cells ◽  
Human Amniotic Fluid ◽  
Adult Rats ◽  
Neurological Outcomes ◽  
Alternative Approach ◽  
Cord Injury

Abstract Direct astrocyte reprogramming to neural progenitor cells and promotion of neurogenesis is considered as an alternative approach to replace the lost neurons in the spinal cord injury(SCI). Herein, we used the human amniotic fluid mesenchymal stem cells (hAF-MSCs) and their conditioned medium (CM), to investigating their ability to reprogramming astrocytes to neuroblasts following SCI. 54 adult rats were randomly divided into 9 groups (n = 6), included: Control, SCI, (SCI + DMEM), (SCI + CM), (SCI + MSCs), (SCI + Astrocyte), (SCI + Astrocyte + DMEM), (SCI + Astrocyte + CM) and SCI + Astrocyte + MSCs). Following laminectomy and SCI induction, DMEM, CM, MSCs and Astrocytes were injected. Wester-blot was performed to explore the levels of the Sox2 protein in the MSCs-CM. The immunofluorescence staining against DCX and GFAP was done. Finally, Basso-Beattie-Brenham (BBB) locomotor test was conducted to assess the neurological outcomes. Our results showed that the MSCs through juxtacrine and paracrine mechanisms induced the promotion of the endogenous neuroblasts and the decline of astrocytes. Moreover, in the present research, MSCs and CM could convert the transplanted human astrocytes to neuroblasts in the spinal cord injury. Taken together, our data indicate the MSCs via juxtacrine and paracrine pathways could direct the spinal cord endogenous neural stem cells(NSCs) to the neuroblasts lineage rather than astrocytes as well as induce reprogramming. Ultimately, MSCs could reverse the neurobehavioral deficit in the SCI. The striking output in our study was the capability of the MSCs in the reprogramming of the astrocytes to neuroblasts via juxtacrine and paracrine pathways in the In-vivo condition.

scholarly journals PP4-dependent HDAC3 dephosphorylation discriminates between axonal regeneration and regenerative failure

2018 ◽  
Author(s):  
Arnau Hervera ◽  
Luming Zhou ◽  
Ilaria Palmisano ◽  
Eilidh McLachlan ◽  
Guiping Kong ◽  
...  
Keyword(s):  
Spinal Cord ◽  
Spinal Cord Injury ◽  
Axonal Regeneration ◽  
Molecular Mechanisms ◽  
Ex Vivo ◽  
Spinal Injury ◽  
Gene Expression Response ◽  
Cord Injury ◽  
Expression Response

The molecular mechanisms discriminating between regenerative failure and success remain elusive. While a regeneration-competent peripheral nerve injury mounts a regenerative gene expression response in bipolar dorsal root ganglia (DRG) sensory neurons, a regeneration-incompetent central spinal cord injury does not. This dichotomic response offers a unique opportunity to investigate the fundamental biological mechanisms underpinning regenerative ability. Following a pharmacological screen with small molecule inhibitors targeting key epigenetic enzymes in DRG neurons we identified HDAC3 signalling as a novel candidate brake to axonal regenerative growth. In vivo, we determined that only a regenerative peripheral but not a central spinal injury induces an increase in calcium, which activates protein phosphatase 4 that in turn dephosphorylates HDAC3 thus impairing its activity and enhancing histone acetylation. Bioinformatics analysis of ex vivo H3K9ac ChIPseq and RNAseq from DRG followed by promoter acetylation and protein expression studies implicated HDAC3 in the regulation of multiple regenerative pathways. Finally, genetic or pharmacological HDAC3 inhibition overcame regenerative failure of sensory axons following spinal cord injury. Together, these data indicate that PP4-dependent HDAC3 dephosphorylation discriminates between axonal regeneration and regenerative failure.

Molecular mechanisms of estrogen for neuroprotection in spinal cord injury and traumatic brain injury

2016 ◽  
Vol 27 (3) ◽  
pp. 271-281 ◽  
Author(s):  
Mrinmay Chakrabarti ◽  
Arabinda Das ◽  
Supriti Samantaray ◽  
Joshua A. Smith ◽  
Naren L. Banik ◽  
...  
Keyword(s):  
Traumatic Brain Injury ◽  
Spinal Cord ◽  
Spinal Cord Injury ◽  
Brain Injury ◽  
Molecular Mechanisms ◽  
Adaptive Immune System ◽  
Cord Injury ◽  
Clinical Benefits

AbstractEstrogen (EST) is a steroid hormone that exhibits several important physiological roles in the human body. During the last few decades, EST has been well recognized as an important neuroprotective agent in a variety of neurological disorders in the central nervous system (CNS), such as spinal cord injury (SCI), traumatic brain injury (TBI), Alzheimer’s disease, and multiple sclerosis. The exact molecular mechanisms of EST-mediated neuroprotection in the CNS remain unclear due to heterogeneity of cell populations that express EST receptors (ERs) in the CNS as well as in the innate and adaptive immune system. Recent investigations suggest that EST protects the CNS from injury by suppressing pro-inflammatory pathways, oxidative stress, and cell death, while promoting neurogenesis, angiogenesis, and neurotrophic support. In this review, we have described the currently known molecular mechanisms of EST-mediated neuroprotection and neuroregeneration in SCI and TBI. At the same time, we have emphasized on the recent in vitro and in vivo findings from our and other laboratories, implying potential clinical benefits of EST in the treatment of SCI and TBI.

scholarly journals Persistent Sodium Currents and Repetitive Firing in Motoneurons of the Sacrocaudal Spinal Cord of Adult Rats

2006 ◽  
Vol 96 (3) ◽  
pp. 1141-1157 ◽  
Author(s):  
P. J. Harvey ◽  
Y. Li ◽  
X. Li ◽  
D. J. Bennett
Keyword(s):  
Spinal Cord ◽  
Input Resistance ◽  
Calcium Currents ◽  
Repetitive Firing ◽  
Resting Membrane Potential ◽  
Sodium Currents ◽  
Adult Rats ◽  
Acute Spinal Rats ◽  
Chronic Spinal Rats

Months after sacral spinal transection in rats (chronic spinal rats), motoneurons below the injury exhibit large, low-threshold persistent inward currents (PICs), composed of persistent sodium currents (Na PICs) and persistent calcium currents (Ca PICs). Here, we studied whether motoneurons of normal adult rats also exhibited Na and Ca PICs when the spinal cord was acutely transected at the sacral level (acute spinal rats) and examined the role of the Na PIC in firing behavior. Intracellular recordings were obtained from motoneurons of acute and chronic spinal rats while the whole sacrocaudal spinal cord was maintained in vitro. Compared with chronic spinal rats, motoneurons of acute spinal rats were more difficult to activate because the input resistance was 22% lower and resting membrane potential was hyperpolarized 4.1 mV further below firing threshold (−50.9 ± 6.2 mV). In acute spinal rats, during a slow voltage ramp, a PIC was activated subthreshold to the spike (at −57.2 ± 5.0 mV) and reached a peak current of 1.11 ± 1.21 nA. This PIC was less than one-half the size of that in chronic spinal rats (2.79 ± 0.94 nA) and usually was not large enough to produce bistable behavior (plateau potentials and self-sustained firing not present), unlike in chronic spinal rats. The PIC was composed of two components: a TTX-sensitive Na PIC (0.44 ± 0.36 nA) and a nimodipine-sensitive Ca PIC (0.78 ± 0.82 nA). Both were smaller than in chronic spinal rats (but with similar Na/Ca ratio). The presence of the Na PIC was critical for normal repetitive firing, because no detectable Na PIC was found in the few motoneurons that could not fire repetitively during a slow ramp current injection and motoneurons that had large Na PICs more readily produced repetitive firing and had lower minimum firing rates compared with neurons with small Na PICs. Furthermore, when the Na PIC was selectively blocked with riluzole, steady repetitive firing was eliminated, even though transient firing could be evoked on a rapid current step and the spike itself was unaffected. In summary, only small Ca and Na PICs occur in acute spinal motoneurons, but the Na PIC is essential for steady repetitive firing. We discuss how availability of monoamines may explain the variability in Na PICs and firing in the normal and spinal animals.

Further studies on free-radical pathology in the major central nervous system disorders: effect of very high doses of methylprednisolone on the functional outcome, morphology, and chemistry of experimental spinal cord impact injury

1982 ◽  
Vol 60 (11) ◽  
pp. 1415-1424 ◽  
Author(s):  
H. B. Demopoulos ◽  
E. S. Flamm ◽  
M. L. Seligman ◽  
D. D. Pietronigro ◽  
J. Tomasula ◽  
...  
Keyword(s):  
Spinal Cord ◽  
Central Nervous System ◽  
Nervous System ◽  
Free Radical ◽  
Tissue Injury ◽  
Functional Restoration ◽  
Radical Reactions ◽  
Free Radical Reactions ◽  
Cord Injury

The hypothesis that pathologic free-radical reactions are initiated and catalyzed in the major central nervous system (CNS) disorders has been further supported by the current acute spinal cord injury work that has demonstrated the appearance of specific, cholesterol free-radical oxidation products. The significance of these products is suggested by the fact that: (i) they increase with time after injury; (ii) their production is curtailed with a steroidal antioxidant; (iii) high antioxidant doses of the steroidal antioxidant which curtail the development of free-radical product prevent tissue degeneration and permit functional restoration. The role of pathologic free-radical reactions is also inferred from the loss of ascorbic acid, a principal CNS antioxidant, and of extractable cholesterol. These losses are also prevented by the steroidal antioxidant. This model system is among others in the CNS which offer distinctive opportunities to study, in vivo, the onset and progression of membrane damaging free-radical reactions within well-defined parameters of time, extent of tissue injury, correlation with changes in membrane enzymes, and correlation with readily measurable in vivo functions.

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