Spike Coding During Locomotor Network Activity in Ventrally Located Neurons in the Isolated Spinal Cord From Neonatal Rat

2000 ◽  
Vol 83 (5) ◽  
pp. 2825-2834 ◽  
Author(s):  
Morten Raastad ◽  
Ole Kiehn
Keyword(s):  
Spinal Cord ◽  
Locomotor Activity ◽  
Spike Trains ◽  
Neonatal Rat ◽  
Network Activity ◽  
Lumbar Spinal Cord ◽  
Patch Clamp Technique ◽  
Important Distinction ◽  
Spike Coding ◽  
The Individual

To characterize spike coding in spinal neurons during rhythmic locomotor activity, we recorded from individual cells in the lumbar spinal cord of neonatal rats by using the on-cell patch-clamp technique. Locomotor activity was induced by N-methyl-d aspartate (NMDA) and 5-hydroxytryptamine (5-HT) and monitored by ventral root recording. We made an estimator based on the assumption that the number of spikes arriving during two halves of the locomotor cycle could be a code used by the neuronal network to distinguish between the halves. This estimator, termed the spike contrast, was calculated as the difference between the number of spikes in the most and least active half of an average cycle. The root activity defined the individual cycles and the positions of the spikes were calculated relative to these cycles. By comparing the average spike contrast to the spike contrast in noncyclic, randomized spike trains we found that approximately one half the cells (19 of 42) contained a significant spike contrast, averaging 1.25 ± 0.23 (SE) spikes/cycle. The distribution of spike contrasts in the total population of cells was exponential, showing that weak modulation was more typical than strong modulation. To investigate if this low spike contrast was misleading because a higher spike contrast averaged out by occurring at different positions in the individual cycles we compared the spike contrast obtained from the average cycle to its maximal value in the individual cycles. The value was larger (3.13 ± 0.25 spikes) than the spike contrast in the average cycle but not larger than the spike contrast in the individual cycles of a random, noncyclic spike trains (3.21 ± 0.21 spikes). This result suggested that the important distinction between cyclic and noncyclic cells was only the repeated cycle position of the spike contrast and not its magnitude. Low spike frequencies (5.2 ± 0.82 spikes/cycle, that were on average 3.5 s long) and a minimal spike interval of 100–200 ms limited the spike contrast. The standard deviation (SD) of the spike contrast in the individual neurons was similar to the average spike contrasts and was probably stochastic because the SDs of the simulated, noncyclic spike trains were also similar. In conclusion we find a highly distributed and variable locomotor related cyclic signal that is represented in the individual neurons by very few spikes and that becomes significant only because the spike contrast is repeated at a preferred phase of the locomotor cycle.

Whole Cell Recordings From Visualized Neurons in the Inner Laminae of the Functionally Intact Spinal Cord

2009 ◽  
Vol 102 (1) ◽  
pp. 590-597 ◽  
Author(s):  
Jason Dyck ◽  
Simon Gosgnach
Keyword(s):  
Neural Network ◽  
Spinal Cord ◽  
Locomotor Activity ◽  
Patch Clamp ◽  
Lumbar Spinal Cord ◽  
Whole Cell ◽  
Neuronal Populations ◽  
Cell Patch Clamp ◽  
Whole Cell Patch Clamp

The in vitro whole spinal cord preparation has been an invaluable tool for the study of the neural network that underlies walking because it provides a means of recording fictive locomotor activity following surgical and/or pharmacological manipulation. The recent use of molecular genetic techniques to identify discrete neuronal populations in the spinal cord and subsequent studies showing some of these populations to be involved in locomotor activity have been exciting developments that may lead to a better understanding of the structure and mechanism of function of this neural network. It would be of great benefit if the in vitro whole spinal cord preparation could be updated to allow for the direct targeting of genetically defined neuronal populations, allowing each to be characterized physiologically and anatomically. This report describes a new technique that enables the visualization of, and targeted whole cell patch-clamp recordings from, genetically defined populations of neurons while leaving connectivity largely intact. The key feature of this technique is a small notch cut in the lumbar spinal cord that reveals cells located in the intermediate laminae while leaving the ventral portion of the spinal cord—the region containing the locomotor neural network—untouched. Whole cell patch-clamp recordings demonstrate that these neurons are healthy and display large rhythmic depolarizations that are related to electroneurogram bursts recorded from ventral roots during fictive locomotion. Intracellular labeling demonstrates that this technique can also be used to map axonal projection patterns of neurons. We expect that this procedure will greatly facilitate electrophysiological and anatomical study of important neuronal populations that constitute neural networks throughout the CNS.

Monoaminergic Establishment of Rostrocaudal Gradients of Rhythmicity in the Neonatal Mouse Spinal Cord

2005 ◽  
Vol 94 (2) ◽  
pp. 1554-1564 ◽  
Author(s):  
Kimberly J. Christie ◽  
Patrick J. Whelan
Keyword(s):  
Spinal Cord ◽  
Locomotor Activity ◽  
Spinal Cord Injuries ◽  
Neonatal Mouse ◽  
Network Activity ◽  
Neonatal Rats ◽  
Mouse Spinal Cord ◽  
Bath Application ◽  
Rats And Mice ◽  
Calcium Green

Bath application of monoamines is a potent method for evoking locomotor activity in neonatal rats and mice. Monoamines also promote functional recovery in adult animals with spinal cord injuries by activating spinal cord networks. However, the mechanisms of their actions on spinal networks are largely unknown. In this study, we tested the hypothesis that monoamines establish rostrocaudal gradients of rhythmicity in the thoracolumbar spinal cord. Isolated neonatal mouse spinal cord preparations (P0–P2) were used. To assay excitability of networks by monoamines, we evoked a disinhibited rhythm by bath application of picrotoxin and strychnine and recorded neurograms from several thoracolumbar ventral roots. We first established that rostral and caudal segments of the thoracolumbar spinal cord had equal excitability by completely transecting preparations at the L3 segmental level and recording the frequency of the disinhibited rhythm from both segments. Next we established that a majority of ventral interneurons retrogradely labeled by calcium green dextran were active during network activity. We then bath applied combinations of monoaminergic agonists [5-HT and dopamine (DA)] known to elicit locomotor activity. Our results show that monoamines establish rostrocaudal gradients of rhythmicity in the thoracolumbar spinal cord. This may be one mechanism by which combinations of monoaminergic compounds normally stably activate locomotor networks.

Lasting paraplegia caused by loss of lumbar spinal cord interneurons in rats: no direct correlation with motor neuron loss

2000 ◽  
Vol 93 (2) ◽  
pp. 266-275 ◽  
Author(s):  
Bassam Hadi ◽  
Y. Ping Zhang ◽  
Darlene A. Burke ◽  
Christopher B. Shields ◽  
David S. K. Magnuson
Keyword(s):  
Spinal Cord ◽  
Locomotor Activity ◽  
Motor Neuron ◽  
Motor Neurons ◽  
Lumbar Spinal Cord ◽  
Neuron Loss ◽  
Content Type ◽  
Motor Neuron Loss ◽  
Lumbar Spinal ◽  
Fine Print

Object. The aims of this study were to investigate further the role played by lumbar spinal cord interneurons in the generation of locomotor activity and to develop a model of spinal cord injury suitable for testing neuron replacement strategies. Methods. Adult rats received intraspinal injections of kainic acid (KA). Locomotion was assessed weekly for 4 weeks by using the Basso, Beattie, and Bresnahan (BBB) 21-point locomotor scale, and transcranial magnetic motor evoked potentials (MMEPs) were recorded in gastrocnemius and quadriceps muscles at 1 and 4 weeks. No changes in transcranial MMEP latency were noted following KA injection, indicating that the descending motor pathways responsible for these responses, including the alpha motor neurons, were not compromised. Rats in which KA injections included much of the L-2 segment (10 animals) showed severe locomotor deficits, with a mean BBB score of 4.5 ± 3.6 (± standard deviation). Rats that received lesions rostral to the L-2 segment (four animals) were able to locomote and had a mean BBB score of 14.6 ± 2.6. Three rats that received only one injection bilaterally centered at L-2 (three animals) had a mean BBB score of 3.2 ± 2. Histological examination revealed variable loss of motor neurons limited to the injection site. There was no correlation between motor neuron loss and BBB score. Conclusions. Interneuron loss centered on the L-2 segment induces lasting paraplegia independent of motor neuron loss and white matter damage, supporting earlier suggestions that circuitry critical to the generator of locomotor activity (the central pattern generator) resides in this area. This injury model may prove ideal for studies of neuron replacement strategies.

scholarly journals Glucose is an adequate energy substrate for the depolarizing action of GABA and glycine in the neonatal rat spinal cord in vitro

2012 ◽  
Vol 107 (11) ◽  
pp. 3107-3115 ◽  
Author(s):  
Rémi Bos ◽  
Laurent Vinay
Keyword(s):  
Spinal Cord ◽  
Energy Supply ◽  
Reversal Potential ◽  
Neonatal Rat ◽  
Lumbar Spinal Cord ◽  
Primary Afferent ◽  
Artificial Cerebrospinal Fluid ◽  
High Concentrations ◽  
Lumbar Spinal

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-β-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 ( EIPSP). Only high concentrations of pyruvate hyperpolarized EIPSP. 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.

Initiation and modulation of locomotor circuitry output with multisite transcutaneous electrical stimulation of the spinal cord in noninjured humans

2015 ◽  
Vol 113 (3) ◽  
pp. 834-842 ◽  
Author(s):  
Yury Gerasimenko ◽  
Ruslan Gorodnichev ◽  
Aleksandr Puhov ◽  
Tatiana Moshonkina ◽  
Aleksandr Savochin ◽  
...  
Keyword(s):  
Spinal Cord ◽  
Electrical Stimulation ◽  
Locomotor Activity ◽  
Interactive Effects ◽  
Lumbar Spinal Cord ◽  
Neutral Position ◽  
Transcutaneous Electrical Stimulation ◽  
Spinal Circuitry ◽  
Cord Injury ◽  
Stimulation Of

The mammalian lumbar spinal cord has the capability to generate locomotor activity in the absence of input from the brain. Previously, we reported that transcutaneous electrical stimulation of the spinal cord at vertebral level T11 can activate the locomotor circuitry in noninjured subjects when their legs are placed in a gravity-neutral position (Gorodnichev RM, Pivovarova EA, Pukhov A, Moiseev SA, Savokhin AA, Moshonkina TR, Shcherbakova NA, Kilimnik VA, Selionov VA, Kozlovskaia IB, Edgerton VR, Gerasimenko IU. Fiziol Cheloveka 38: 46–56, 2012). In the present study we hypothesized that stimulating multiple spinal sites and therefore unique combinations of networks converging on postural and locomotor lumbosacral networks would be more effective in inducing more robust locomotor behavior and more selective control than stimulation of more restricted networks. We demonstrate that simultaneous stimulation at the cervical, thoracic, and lumbar levels induced coordinated stepping movements with a greater range of motion at multiple joints in five of six noninjured subjects. We show that the addition of stimulation at L1 and/or at C5 to stimulation at T11 immediately resulted in enhancing the kinematics and interlimb coordination as well as the EMG patterns in proximal and distal leg muscles. Sequential cessation of stimulation at C5 and then at L1 resulted in a progressive degradation of the stepping pattern. The synergistic and interactive effects of transcutaneous stimulation suggest a multisegmental convergence of descending and ascending, and most likely propriospinal, influences on the spinal neuronal circuitries associated with locomotor activity. The potential impact of using multisite spinal cord stimulation as a strategy to neuromodulate the spinal circuitry has significant implications in furthering our understanding of the mechanisms controlling posture and locomotion and for regaining significant sensorimotor function even after a severe spinal cord injury.

Effects of Noradrenaline on Locomotor Rhythm–Generating Networks in the Isolated Neonatal Rat Spinal Cord

1999 ◽  
Vol 82 (2) ◽  
pp. 741-746 ◽  
Author(s):  
Ole Kiehn ◽  
Keith T. Sillar ◽  
Ole Kjaerulff ◽  
Jonathan R. McDearmid
Keyword(s):  
Spinal Cord ◽  
Locomotor Activity ◽  
Motor Activity ◽  
Ventral Root ◽  
Time Dependent ◽  
Neonatal Rat ◽  
Root Activity ◽  
Rat Spinal Cord ◽  
Locomotor Rhythm ◽  
Variable Nature

We have studied the effects of the biogenic amine noradrenaline (NA) on motor activity in the isolated neonatal rat spinal cord. The motor output was recorded with suction electrodes from the lumbar ventral roots. When applied on its own, NA (0.5–50 μM) elicited either no measurable root activity, or activity of a highly variable nature. When present, the NA-induced activity consisted of either low levels of unpatterned tonic discharges, or an often irregular, slow rhythm that displayed a high degree of synchrony between antagonistic motor pools. Finally, in a few cases, NA induced a slow locomotor-like rhythm, in which activity alternated between the left and right sides, and between rostral and caudal roots on the same side. As shown previously, stable locomotor activity could be induced by bath application of N-methyl-d-aspartate (NMDA; 4–8.5 μM) and/or serotonin (5-HT; 4–20 μM). NA modulated this activity by decreasing the cycle frequency and increasing the ventral root burst duration. These effects were dose dependent in the concentration range 1–5 μM. In contrast, at no concentration tested did NA have consistent effects on burst amplitudes or on the background activity of the ongoing rhythm. Moreover, NA did not obviously affect the left/right and rostrocaudal alternation of the NMDA/5-HT rhythm. The NMDA/5-HT locomotor rhythm sometimes displayed a time-dependent breakdown in coordination, ultimately resulting in tonic ventral root activity. However, the addition of NA to the NMDA/5-HT saline could reinstate a well-coordinated locomotor rhythm. We conclude that exogenously applied NA can elicit tonic activity or can trigger a slow, irregular and often synchronous motor pattern. When NA is applied during ongoing locomotor activity, the amine has a distinct slowing effect on the rhythm while preserving the normal coordination between flexors and extensors. The ability of NA to “rescue” rhythmic locomotor activity after its time-dependent deterioration suggests that the amine may be important in the maintenance of rhythmic motor activity.

5-HT Modulation of Multiple Inward Rectifiers in Motoneurons in Intact Preparations of the Neonatal Rat Spinal Cord

2001 ◽  
Vol 85 (2) ◽  
pp. 580-593 ◽  
Author(s):  
Ole Kjaerulff ◽  
Ole Kiehn
Keyword(s):  
Spinal Cord ◽  
Neonatal Rat ◽  
Inward Rectification ◽  
Lumbar Spinal Cord ◽  
Slow Time ◽  
Biophysical Parameters ◽  
Time Constants ◽  
Low Concentrations ◽  
Order Of Magnitude ◽  
Lumbar Spinal

This study introduces novel aspects of inward rectification in neonatal rat spinal motoneurons (MNs) and its modulation by serotonin (5-HT). Whole cell tight-seal recordings were made from MNs in an isolated lumbar spinal cord preparation from rats 1–2 days of age. In voltage clamp, hyperpolarizing step commands were generated from holding potentials of −50 to −40 mV. Discordant with previous reports involving slice preparations, fast inward rectification was commonly expressed and in 44% of the MNs co-existed with a slow inward rectification related to activation of I h. The fast inward rectification is likely caused by an I Kir. Thus it appeared around E K and was sensitive to low concentrations (100–300 μM) of Ba2+ but not to ZD 7288, which blocked I h. Both I Kir and I h were inhibited by Cs2+ (0.3–1.5 mM). Extracellular addition of 5-HT (10 μM) reduced the instantaneous conductance, most strongly at membrane potentials above E K. Low [Ba2+] prevented the 5-HT–induced instantaneous conductance reduction below, but not that above, E K. This suggests that 5-HT inhibits I Kir, but also other instantaneous conductances. The biophysical parameters of I h were evaluated before and under 5-HT. The maximal I h conductance, G max, was 12 nS, much higher than observed in slice preparations. G maxwas unaffected by 5-HT. In contrast, 5-HT caused a 7-mV depolarizing shift in the activation curve of I h. Double-exponential fits were generally needed to describe I h activation. The fast and slow time constants obtained by these fits differed by an order of magnitude. Both time constants were accelerated by 5-HT, the slow time constant to the largest extent. We conclude that spinal neonatal MNs possess multiple forms of inward rectification. I h may be carried by two spatially segregated channel populations, which differ in kinetics and sensitivity to 5-HT. 5-HT increases MN excitability in several ways, including inhibition of a barium-insensitive leak conductance, inhibition of I Kir, and enhancement of I h. The quantitative characterization of these effects should be useful for further studies seeking to understand how neuromodulation prepares vertebrate MNs for concerted behaviors such as locomotor activity.

Spatiotemporal Patterns of Dorsal Root–Evoked Network Activity in the Neonatal Rat Spinal Cord: Optical and Intracellular Recordings

2005 ◽  
Vol 94 (3) ◽  
pp. 1952-1961 ◽  
Author(s):  
Lea Ziskind-Conhaim ◽  
Stephen Redman
Keyword(s):  
Spinal Cord ◽  
Action Potentials ◽  
Dorsal Root ◽  
Spatiotemporal Patterns ◽  
Neonatal Rat ◽  
Network Activity ◽  
Rat Spinal Cord ◽  
Optical Signals ◽  
Postsynaptic Potentials ◽  
Neuronal Ensembles

Spatiotemporal patterns of dorsal root–evoked potentials were studied in transverse slices of the rat spinal cord by monitoring optical signals from a voltage-sensitive dye with multiple-photodiode optic camera. Typically, dorsal root stimulation generated two basic waveforms of voltage images: dual-component images consisting of fast, spike-like signal followed by a slow signal in the dorsal horn, and small, slow signals in the ventral horn. To qualitatively relate the optical signals to membrane potentials, whole cell recordings were combined with measurements of light absorption in the area around the soma. The slow optical signals correlated closely with subthreshold postsynaptic potentials in all regions of the cord. The spike-like component was not associated with postsynaptic action potentials, suggesting that the fast signal was generated by presynaptic action potentials. Firing in a single neuron could not be detected optically, implying that local voltage images originated from synchronously activated neuronal ensembles. Blocking glutamatergic synaptic transmission inhibited excitatory postsynaptic potentials (EPSPs) and significantly reduced the slow optical signals, indicating that they were mediated by glutamatergic synapses. Suppressing glycine-mediated inhibition increased the amplitude of both optical signals and EPSPs, while blocking GABAA receptor–mediated synapses, increased the amplitude and time course of EPSPs and prolonged the duration of voltage images in larger areas of the slice. The close correlation between evoked EPSPs and their respective local voltage images shows the advantage of the high temporal resolution optical system in measuring both the spatiotemporal dynamics of segmental network excitation and integrated potentials of neuronal ensembles at identified sites.

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