Single Spinal Motoneurons Research Articles

Dipolar cortico-muscular electrical stimulation: a novel method that enhances motor function in both - normal and spinal cord injured mice

BackgroundElectrical stimulation of the central and peripheral nervous systems is a common tool that is used to improve functional recovery after neuronal injury.MethodsHere we described a new configuration of electrical stimulation as it was tested in anesthetized control and spinal cord injury (SCI) mice. Constant voltage output was delivered through two electrodes. While the negative voltage output (ranging from -1.8 to -2.6 V) was delivered to the muscle via transverse wire electrodes (diameter, 500 μm) located at opposite ends of the muscle, the positive output (ranging from + 2.4 to +3.2 V) was delivered to the primary motor cortex (M1) (electrode tip, 100 μm). The configuration was named dipolar cortico-muscular stimulation (dCMS) and consisted of 100 pulses (1 ms pulse duration, 1 Hz frequency).ResultsIn SCI animals, after dCMS, cortically-elicited muscle contraction improved markedly at the contralateral (456%) and ipsilateral (457%) gastrocnemius muscles. The improvement persisted for the duration of the experiment (60 min). The enhancement of cortically-elicited muscle contraction was accompanied by the reduction of M1 maximal threshold and the potentiation of spinal motoneuronal evoked responses at the contralateral (313%) and ipsilateral (292%) sides of the spinal cord. Moreover, spontaneous activity recorded from single spinal motoneurons was substantially increased contralaterally (121%) and ipsilaterally (54%). Interestingly, spinal motoneuronal responses and muscle twitches evoked by the test stimulation of non-treated M1 (received no dCMS) were significantly enhanced as well. Similar results obtained from normal animals albeit the changes were relatively smaller.ConclusionThese findings demonstrated that dCMS could improve functionality of corticomotoneuronal pathway and thus it may have therapeutic potential.

Reduced corticomotoneuronal excitatory postsynaptic potentials (EPSPs) with normal Ia afferent EPSPs in amyotrophic lateral sclerosis.

We studied excitatory postsynaptic potentials (EPSPs) arising in single spinal motoneurons (composite EPSPs) induced by Ia afferent and magnetic cortical stimulation in 28 normal subjects ranging in age from 24 to 84 years and 28 patients with amyotrophic lateral sclerosis (ALS) aged 34 to 82 years. The subjects voluntarily recruited single motor units of the first dorsal interosseous muscle. Using peristimulus time histograms, we determined changes in the firing probability of the first dorsal interosseous motor units and measured the magnitude of the EPSP. An early period of increased firing probability (primary peak) occurred at approximately 30 msec after la afferent and 25 msec after cortical stimulation, reflecting underlying EPSPs arising in spinal motoneurons induced by either projection. The latency of the primary peaks for both Ia afferent and cortical stimulation was mildly prolonged in ALS, suggesting a loss of the fastest-conducting spinal motoneurons. Patients with ALS had la afferent-driven EPSPs whose amplitude and rise time were equivalent to those of normal subjects. However, the ratio of cortical to la afferent-driven composite EPSPs in ALS was significantly lower than that for normal subjects. Fourteen of 28 ALS motor units had cortically driven EPSPs that were small or large only because of a prolonged rise time. The findings suggest that in ALS, corticomotoneuronal attrition or dispersion of the descending volley occurs in the presence of normally functioning spinal motoneurons to which they project.

Suppression and long latency excitation of single spinal motoneurons by transcranial magnetic stimulation in health, multiple sclerosis, and stroke

Whether or not suppression at the level of the spinal motoneuron plays a role in motor deficits such as central paresis is unknown. In this study suppression in the firing of tonically active low threshold single motoneurons following low intensity transcranial magnetic stimulation is described in health and disease. Changes in firing probability in the absence of an early excitatory response were studied in a total of 14 motor units from 4 healthy subjects, 5 patients with multiple sclerosis, and 1 patient with stroke. Firing probability began to fall 18-59 ms after the stimulus and remained low for a period of 27-133 ms. There were no obvious differences between the three subject groups. The change in firing probability was not associated with specific physical signs. Late rises in firing probability were seen in 7 of the 14 motor units at latencies that were similar to the secondary peak which is known to occur with higher stimulus intensities. It is argued that the mechanism of partial suppression is not dependent on the full integrity of the pyramidal tract and is likely to involve a transient withdrawal of descending excitatory drive rather than an inhibitory postsynaptic potential at the spinal motoneuron.

Responses of single spinal motoneurons to transcranial magnetic stimulation in patients with ALS

Responses of single spinal motoneurons to transcranial magnetic stimulation in patients with ALS

Corticospinal projections to lower limb motoneurons in man.

The projections of cortical neurons activated by transcranial magnetic stimulation to single lower limb spinal motoneurons were examined in 34 normal subjects. Peristimulus time histograms of the discharge times of single, voluntarily activated motor units were used to derive information about postsynaptic potentials in single spinal motoneurons produced by magnetic stimuli applied over the contralateral scalp. All tibialis anterior motor units and the majority of motoneurons innervating the small muscles of the foot showed strong short latency facilitation. About half of the motoneurons of proximal lower limb muscles showed this facilitation. Short latency facilitation of the motoneurons of soleus and medial gastrocnemius was only rarely observed and when present was weak. The short latency facilitation is attributed to the projections of the fast corticospinal pathway with monosynaptic projections to motoneurons. The relative strength of the facilitation in different motoneuron pools is considered to reflect the density of corticospinal projections to that motoneuron pool. The observed pattern of projections in man shows some differences from the pattern of projections in subhuman primates that might reflect the different use of the limb.

Effects of stimulation of group I afferents from flexor muscles on heterosynaptic facilitation of monosynaptic reflexes produced by Ia and descending inputs: a test for presynaptic inhibition

1. In the chloralose anesthetized cat, conditioning stimulation of group I flexor afferents depresses the monosynaptic potentials generated by Ia afferents in single spinal motoneurons or in populations of motoneurons without affecting the monosynaptic potentials produced by stimulation of descending fibers in the ipsilateral ventromedial fasciculus (VMF). 2. Heterosynaptic facilitation of monosynaptic reflexes was used to test changes in the presynaptic effectiveness of excitatory inputs with direct connections with motoneurons. We found that the heterosynaptic facilitation of Ia origin was reduced by conditioning stimulation of group I afferents from flexors, without affecting the heterosynaptic facilitation produced by stimulation of the VMF. 3. These results confirm and expand previous observations showing that the synaptic effectiveness of descending fibers synapsing with motoneurons is not subjected to a presynaptic control mechanism of the type acting on Ia fiber terminals, and provide further basis for the use of changes in heterosynaptic facilitation of monosynaptic reflexes of Ia origin as an estimate of changes in presynaptic inhibition of Ia fibers (Hultborn et al. 1987a).

Immunohistochemical evidence for convergence of GABA-containing and glycine-containing axon terminals on single spinal motoneurons of the rat.

GABA- and glycine-containing neuronal elements were visualized in the rat spinal cord by immunohistochemistry employing antisera raised against conjugated GABA and glycine. GABA- and glycine-like immunoreactivities were localized in axon terminals and neuronal perikarya. GABA- and glycine-like immunoreactive terminals were in synaptic contact with perikarya and dendrites of most spinal neurons. Single spinal motoneurons appeared to be in contact with GABA- or glycine-like immunoreactive terminals. These findings suggest that these neurons are regulated postsynaptically by both GABA and glycine.

Inhibition of neighboring motoneurons in conscious control of single spinal motoneurons.

Multiple fine-wire electrodes were implanted in the biceps brachii of five subjects, and artificial electronic feedback was provided to subjects from only one electrode. By this technique, it was shown that neighboring units progressively stop firing as subjects concentrate on activating an isolated unit. The inhibition of neighboring spinal motoneurons in the same pool further indicates that selective inhibition is an automatic part of single motor-unit training.

Effects of stimulation of pontine and bulbar reticular formation upon spinal motoneurons of the cat.

1. Pontine and bulbar reticular formation (RF) and Deiters' nucleus were stimulated stereotaxically with brief electric stimuli (2-3msec.) and their effects. on the intracellular potential of lumbar alpha motoneurons as wall as on the size of monosynaptic reflex were studied in the cat. Secondary effects through. the gamma efferents-muscle spindle loop were eliminated.2. Stimulation of pontine RF, especially its rostral part, produced a marked inhibition of extensor monosynaptic reflex at a latency of 15-20msec. and a slight facilitation of flexor monosynaptic reflex at a latency of about 10msec.3. Stimulation of Deiters' nucleus was facilitatory to extensor monosynaptic reflex. The facilitation appeared in two separate phases, the one set up at a latency of less than 10msec. with relatively short and simple time course and the other at a latency of 15-20msec. with a longer duration.4. The effect of stimulation of the bulbar RF varied extensively with a, slight change in the electrode position. The most prevalent effect was facilitatory to extensor monosynaptic reflex, which in some cases resembled that of Deiters' nucleus in its time course.5. Generally speaking, changes by stimulation of intracellular potential of spinal motoneurons reflected the influences elicitable from the same site upon the size of monosynaptic reflex. Facilitatory or inhibitory influence upon the reflex size could mostly be accounted for by the potential change of the motoneuron membrane which was most likely due to EPSP's and IPSP's.6. Single spinal motoneurons fired from different levels of depolarization, when the rate of rise of depolarizing PSP's was different according to the stimulated site in the brain stem.7. The effect of repetitive stimulation of the RF on the membrane potential. of single spinal motoneurons could be illustrated in general as a summated. effect of single stimulation of the same site.8. Tonic suprasegmental influences and their modification by reticular stimulation were visualized as maintained discharges of descending tract fibers and. spinal interneurons.9. A hypothetical accout for the decerebrate rigidity was put forward based on the present findings.

An analysis of intra- versus extracellular potential changes associated with activity of single spinal motoneurons.

Annals of the New York Academy of SciencesVolume 94, Issue 2 p. 547-558 AN ANALYSIS OF INTRA- VERSUS EXTRACELLULAR POTENTIAL CHANGES ASSOCIATED WITH ACTIVITY OF SINGLE SPINAL MOTONEURONS* Carlo A. Terzuolo, Carlo A. Terzuolo Department of Anatomy, University of California at Los Angeles, Calif. The research reported in this paper was completed after this author moved to his present address: Department of Physiology, University of Minnesota, Minneapolis, Minn.Search for more papers by this authorT. Araki, T. Araki Department of Anatomy, University of California at Los Angeles, Calif. Department of Physiology, University of Kyoto, Kyoto, Japan.Search for more papers by this author Carlo A. Terzuolo, Carlo A. Terzuolo Department of Anatomy, University of California at Los Angeles, Calif. The research reported in this paper was completed after this author moved to his present address: Department of Physiology, University of Minnesota, Minneapolis, Minn.Search for more papers by this authorT. Araki, T. Araki Department of Anatomy, University of California at Los Angeles, Calif. Department of Physiology, University of Kyoto, Kyoto, Japan.Search for more papers by this author First published: September 1961 https://doi.org/10.1111/j.1749-6632.1961.tb35558.xCitations: 88 * The work described in this paper was supported in part by Research Grants B-1143 and B-5260 from the National Institute of Neurological Diseases and Blindness, Public Health Service, Bethesda, Md. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume94, Issue2Current Problems in ElectrobiologySeptember 1961Pages 547-558 RelatedInformation

Accommodation in spinal motoneurons of the cat.

1. Single spinal motoneurons of the cat were directly stimulated with linearly increasing currents flowing through an intracellular micropipette. Intensities of currents of varying slopes at the moment of spike generation were measured on the oscilloscopic records and compared with the rheobase.2. According to different courses of the threshold-latency curves, the motoneurons can be classified into two groups. In the first group motoneurons, the threshold current intensity is progressively increased, to attain a certain final value, with decreasing rate of current rise. Electrical differentiation of the spike potentials reveals that they are initiated at the initial segment when the rise of current is rapid, and from the soma when the rise of current is slow enough. These motoneurons are characterized by relatively short after-hyperpolarization and considered to be phasic or fast mtoneurons.3. The second group motoneurons have a threshold current intensity almost constant within a wide range of slopes of current rise. The spikes are initiated always at the initial segment. They are considered functionally to be tonic or slow motoneurons with the after-hyperpolarization of rather long duration.4. Deeper Nembutal anesthesia and reduced synaptic inflow to the motoneuron seem to favor the chance to encounter the first group motoneurons. Accommodation of the initial segment is in general faster than that of the soma, but the former may change its rate with ease depending on the environmental conditions.5. Two alternative interpretations of the threshold-latency curve of the first group motoneuron were proposed and their implications were discussed. The hypothesis admitting a transition zone between the initial segment and the soma seems to be preferable, being consistent with an assumption of constant threshold depolarization at fixed areas of the motoneuron.