The activity of interneurons during locomotion in the in vitro necturus spinal cord

1994 ◽  
Vol 71 (6) ◽  
pp. 2025-2032 ◽  
Author(s):  
M. Wheatley ◽  
K. Jovanovic ◽  
R. B. Stein ◽  
V. Lawson
Keyword(s):  
Spinal Cord ◽  
Dorsal Root ◽  
Cervical Spinal Cord ◽  
Legged Locomotion ◽  
Afferent Input ◽  
Inhibitory Input ◽  
Step Cycle ◽  
Locomotor Rhythm ◽  
Dorsal Root Afferents

1. Less than two segments of the cervical spinal cord of the mudpuppy (Necturus maculatus) is sufficient to generate a locomotor rhythm with application of N-methyl-D-aspartic acid (NMDA). We have recorded intracellularly from rhythmically active interneurons in these segments and classified them according to their phase of firing within the step cycle and their afferent input. 2. Four classes of interneurons were found: flexor, flexor-->extensor, extensor, and extensor-->flexor. Interneurons that burst during the transition from flexion to extension or vice versa are referred to as “transitional” interneurons and represent the majority (68%) of rhythmically active interneurons studied in the mudpuppy spinal cord. 3. All flexor interneurons received only inhibitory input from cutaneous and dorsal root afferents, whereas the flexor-->extensor interneurons that responded received only excitatory input from dorsal root and cutaneous afferents. All extensor interneurons and all but one extensor-->flexor interneuron received no afferent input from the cutaneous or dorsal root afferents we stimulated. 4. Other interneurons have been classified as “tonic” cells. They fire continuously when the mudpuppy is walking and are silent when the mudpuppy is not walking. These interneurons receive no afferent input from the sources tested and may be responsible for turning locomotion on and off. 5. In conclusion, the presence of many transitional interneurons with specific patterns of afferent input may be required for the phasing of legged locomotion. We believe the in vitro preparation of the mudpuppy spinal cord and forelimb is an excellent model for studying the firing properties of interneurons during legged locomotion.

Modulation of monosynaptic excitation in the neonatal rat spinal cord

1993 ◽  
Vol 70 (3) ◽  
pp. 1151-1158 ◽  
Author(s):  
M. Pinco ◽  
A. Lev-Tov
Keyword(s):  
Spinal Cord ◽  
Dorsal Root ◽  
Neonatal Rat ◽  
Bathing Solution ◽  
Duration Stimulus ◽  
Low Calcium ◽  
Dorsal Root Afferents ◽  
Stimulation Of ◽  
Monosynaptic Excitation

1. The effects of high-frequency (5-50 Hz) stimulation of dorsal root afferents on monosynaptic excitation of alpha motoneurons was studied in the in vitro spinal cord preparation of the neonatal rat, using sharp-electrode intracellular recordings. 2. Double pulse stimulation of dorsal root afferents induced severe depression of testing excitatory postsynaptic potentials (EPSPs) at each of the tested interstimulus intervals (15 ms-5 s). After perfusion of the preparation with low-calcium, high-magnesium Krebs saline, the amplitude of the conditioning EPSPs was markedly decreased and the testing EPSPs exhibited substantial facilitation that was maximal at the 20-ms interval and that was accompanied by depression at intervals > or = 60-100 ms. 3. Short-duration stimulus trains applied to dorsal root afferents normally induced tetanic depression of the intracellularly recorded monosynaptic EPSPs. Switching the bathing solution to low-calcium, high-magnesium saline decreased the control EPSP and induced facilitation and then tetanic potentiation (TP) of the EPSPs within the applied train. The magnitude of potentiation (% potentiation) of these EPSPs depended on the interpulse interval of the short stimulus train and on the degree of attenuation of the unpotentiated control EPSP after the solution was changed from normal- to low-calcium Krebs solution. 4. Long-duration stimulus trains applied to dorsal root afferents at 5-10 Hz induced marked depression of monosynaptic EPSPs during the train. The depression was alleviated after cessation of the tetanic stimulation and was followed in some cases by slight posttetanic potentiation.(ABSTRACT TRUNCATED AT 250 WORDS)

Small-caliber afferent inputs produce a heterosynaptic facilitation of the synaptic responses evoked by primary afferent A-fibers in the neonatal rat spinal cord in vitro

1993 ◽  
Vol 69 (6) ◽  
pp. 2116-2128 ◽  
Author(s):  
S. W. Thompson ◽  
C. J. Woolf ◽  
L. G. Sivilotti
Keyword(s):  
Spinal Cord ◽  
Dorsal Root ◽  
Fiber Strength ◽  
Conditioning Stimulus ◽  
Neonatal Rat ◽  
Primary Afferent ◽  
Synaptic Potentials ◽  
C Fiber ◽  
Afferent Inputs

1. The effect of brief primary afferent inputs on the amplitude and duration of the synaptic potentials evoked in ventral horn (VH) neurons by the activation of other unconditioned primary afferents was studied by current-clamp intracellular recording in the neonatal rat hemisected spinal cord in vitro. Low-frequency (1 Hz) trains of stimulation were applied to a lumbar dorsal root (Conditioning root) for 20-30 s. Test excitatory synaptic potentials (EPSPs) were evoked by single electrical shocks applied to an adjacent Test dorsal root. 2. Test and Conditioning inputs were generated at stimulation strengths sufficient to activate A beta-, A delta- and C-afferent fibers successively. At A delta- and C-fiber strength the EPSPs lasted for 4-6 s, and, during the repetitive Conditioning inputs, these summated to produce a progressively incrementing cumulative depolarization that slowly decayed back to the control Vm over tens of seconds. 3. Dorsal root conditioning produced heterosynaptic facilitation, defined as an enhancement of Test EPSPs above their DC matched controls, in 7 out of 20 neurons. To facilitate the unconditioned afferent input, the intensity of conditioning stimulation had to exceed the threshold for the activation of thin myelinated (A delta) afferents: conditioning at A beta-fiber strength had no effect, whereas A delta- and C-fiber strength conditioning were equally effective. 4. Heterosynaptic facilitation of only A beta- or A delta-fiber-evoked Test EPSPs was observed, no enhancement of C-fiber strength Test EPSPs could be demonstrated. The facilitation manifested as increases in the EPSP peak amplitude, area or the number of action potentials evoked. 5. Conditioning trials that produced heterosynaptic facilitation generated cumulative depolarizations larger than those produced by ineffective conditioning trials (9.1 +/- 3.1 vs. 3.3 +/- 0.5 mV after 20 s conditioning at resting Vm, mean +/- SE, n = 6 and 13, respectively; P < 0.05). The slope of the Vm trajectory during the summation of the conditioning EPSPs was higher in trials resulting in heterosynaptic facilitation, at 0.31 +/- 0.10 mV/s in neurons with heterosynaptic facilitation and 0.06 +/- 0.02 mV/s in cells without heterosynaptic facilitation (P < 0.05). 5. Four of the 20 VH neurons in our sample responded to A delta/C-fiber conditioning with action-potential windup: all 4 also displayed heterosynaptic facilitation. 6. Heterosynaptic facilitation decayed after the completion of the conditioning stimulus with a time course that was parallel to but not superimposable on that of the slow Vm depolarization evoked by the conditioning.(ABSTRACT TRUNCATED AT 400 WORDS)

GABA-Receptor–Independent Dorsal Root Afferents Depolarization in the Neonatal Rat Spinal Cord

1998 ◽  
Vol 79 (5) ◽  
pp. 2581-2592 ◽  
Author(s):  
E. Kremer ◽  
A. Lev-Tov
Keyword(s):  
Spinal Cord ◽  
Dorsal Root ◽  
Gaba Receptor ◽  
Neonatal Rat ◽  
Extracellular Potassium ◽  
Rat Spinal Cord ◽  
Extracellular Potassium Concentration ◽  
Dorsal Roots ◽  
Intact Brain ◽  
Dorsal Root Afferents

Kremer, E. and A. Lev-Tov. GABA-receptor–independent dorsal root afferents depolarization in the neonatal rat spinal cord. J. Neurophysiol. 79: 2581–2592, 1998. Dorsal root afferent depolarization and antidromic firing were studied in isolated spinal cords of neonatal rats. Spontaneous firing accompanied by occasional bursts could be recorded from most dorsal roots in the majority of the cords. The afferent bursts were enhanced after elevation of the extracellular potassium concentration ([K+]e) by 1–2 mM. More substantial afferent bursts were produced when the cords were isolated with intact brain stems. Rhythmic afferent bursts could be recorded from dorsal roots in some of the cords during motor rhythm induced by bath-applied serotonin and N-methyl-d-aspartate (NMDA). Bilaterally synchronous afferent bursts were produced in pairs of dorsal roots after replacing the NaCl in the perfusate with sodium-2-hydroxyethansulfonate or after application of the γ-aminobutyric acid-A (GABAA) receptor antagonist bicuculline with or without serotonin (5-HT) and NMDA. Antidromic afferent bursts also could be elicited under these conditions by stimulation of adjacent dorsal roots, ventrolateral funiculus axons, or ventral white commissural (VWC) fibers. The antidromic bursts were superimposed on prolonged dorsal root potentials (DRPs) and accompanied by a prolonged increase in intraspinal afferent excitability. Surgical manipulations of the cord revealed that afferent firing in the presence of bicuculline persisted in the hemicords after hemisection and still was observed after removal of their ventral horns. Cutting the VWC throughout its length did not perturb the bilateral synchronicity of the discharge. These findings suggest that the activity of dorsal horn neurons is sufficient to produce the discharge and that the bilateral synchronicity can be maintained by cross connectivity that is relayed from side to side dorsal to the VWC. Antagonists of GABAB, 5-HT2/5-HT1C, or glutamate metabotropic group II and III receptors could not abolish afferent depolarization in the presence of bicuculline. Depolarization comparable in amplitude to DRPs, could be produced in tetrodotoxin-treated cords by elevation of [K+]e to the levels reported to develop in the neonatal rat spinal cord in response to dorsal root stimulation. A mechanism involving potassium transients produced by neuronal activity therefore is suggested to be the major cause of the GABA-independent afferent depolarization reported in our study. Possible implications of potassium transients in the developing and the adult mammalian spinal cord are discussed.

scholarly journals Mechanical Properties of Cervical Spinal Cord in Neonatal Piglet: In Vitro

2020 ◽  
pp. 1-3
Author(s):  
Anita Singh ◽  
Anita Singh ◽  
Rachel Magee ◽  
Sriram Balasubramanian
Keyword(s):  
Spinal Cord ◽  
Maximum Stress ◽  
Cervical Spinal Cord ◽  
Tensile Loading ◽  
Maximum Load ◽  
Spinal Cord Tissue ◽  
Prevention Strategies ◽  
Biomechanical Behavior ◽  
Injury Mechanisms

The response of neonatal spinal cord tissue to tensile loading is not well-studied. In this study, isolated fresh neonatal cervical spinal cord samples, obtained from twelve 2-4 days old piglets, were tested in uniaxial tension at a rate of 500 mm/min until failure. Maximum load, maximum stress, percentage strain at maximum stress and modulus of elasticity were reported to be 14.6±3.4 N, 0.34±0.11 MPa, 29.3±5.4% and 1.52±0.8 MPa, respectively. These data can help understand the biomechanical behavior of the spinal cord in neonates and can be further used in computational modeling to understand injury mechanisms better and help develop injury prevention strategies.

Analysis of high PSA N-CAM expression during mammalian spinal cord and peripheral nervous system development

Development ◽  
1991 ◽  
Vol 112 (1) ◽  
pp. 69-82 ◽  
Author(s):  
S. Boisseau ◽  
J. Nedelec ◽  
V. Poirier ◽  
G. Rougon ◽  
M. Simonneau
Keyword(s):  
Spinal Cord ◽  
Neural Crest ◽  
Dorsal Root Ganglia ◽  
Dorsal Root ◽  
Developmental Stages ◽  
System Development ◽  
Nervous System Development ◽  
Homogeneous Distribution ◽  
Total N

Using a monoclonal antibody that recognizes specifically a high polysialylated form of N-CAM (high PSA N-CAM), the temporal and spatial expression of this molecule was studied in developing spinal cord and neural crest derivatives of mouse truncal region. Temporal expression was analyzed on immunoblots of spinal cord and dorsal root ganglia (DRGs) extracts microdissected at different developmental stages. Analysis of the ratio of high PSA N-CAM to total N-CAM indicated that sialylation and desialylation are independently regulated from the expression of polypeptide chains of N-CAM. Motoneurons, dorsal root ganglia cells and commissural neurons present a homogeneous distribution of high PSA N-CAMs on both their cell bodies and their neurites. Sialylation of N-CAM can occur in neurons after their aggregation in peripheral ganglia as demonstrated for dorsal root ganglia at E12. Furthermore, peripheral ganglia express different levels of high PSA N-CAM. With in vitro models using mouse neural crest cells, we found that expression of high PSA N-CAM was restricted to cells presenting an early neuronal phenotype, suggesting a common regulation for the expression of high PSA N-CAM molecules, neurofilament proteins and sodium channels. Using perturbation experiments with endoneuraminidase, we confirmed that high PSA N-CAM molecules are involved in fasciculation and neuritic growth when neurons derived from neural crest grow on collagen substrata. However, we demonstrated that these two parameters do not appear to depend on high PSA N-CAM molecules when cells were grown on a fibronectin substratum, indicating the existence of a hierarchy among adhesion molecules.

scholarly journals Distribution of purinergic P2X receptors in the equine digit, cervical spinal cord and dorsal root ganglia

2013 ◽  
Vol 9 (3) ◽  
pp. 383-393 ◽  
Author(s):  
D. E. Zamboulis ◽  
J. M. Senior ◽  
P. D. Clegg ◽  
J. A. Gallagher ◽  
S. D. Carter ◽  
...  
Keyword(s):  
Spinal Cord ◽  
Dorsal Root Ganglia ◽  
Dorsal Root ◽  
Cervical Spinal Cord ◽  
P2x Receptors ◽  
Purinergic P2x Receptors

Excitatory convergence of periaqueductal gray and somatic afferents in the solitary tract nucleus: role for neurokinin 1 receptors

2005 ◽  
Vol 288 (1) ◽  
pp. R262-R269 ◽  
Author(s):  
Pedro Boscan ◽  
Julian F. R. Paton
Keyword(s):  
Spinal Cord ◽  
Brachial Plexus ◽  
Cervical Spinal Cord ◽  
Periaqueductal Gray ◽  
Afferent Input ◽  
Baroreceptor Reflex ◽  
Peak Discharge ◽  
Discharge Frequency ◽  
Solitary Tract ◽  
Somatic Afferents

Our previous studies (Boscan P, Kasparov S, and Paton JF. Eur J Neurosci 16: 907–920, 2002) showed that activation of somatic afferents attenuated the baroreceptor reflex via neurokinin type 1 (NK1) and GABAA receptors within the nucleus of the solitary tract (NTS). The periaqueductal gray matter (PAG) can also depress baroreceptor reflex function and project to the NTS. In the present study, we have tested the possibility that the dorsolateral (dl)-PAG projects to the NTS neurons that also respond to somatic afferent input. In an in situ, arterially perfused, unanesthetized decerebrate rat preparation, somatic afferents (brachial plexus), cervical spinal cord, and dl-PAG were stimulated electrically, whereas NTS neurons were recorded extracellularly. From 45 NTS neurons excited by either brachial plexus or dl-PAG stimulation, 41 received convergence excitatory inputs from both afferents. Onset latency and evoked peak discharge frequency from brachial plexus afferents were 39.4 ± 4.7 ms and 10.7 ± 1.1 Hz, whereas this was 43.9 ± 6.4 ms and 7.9 ± 1 Hz, respectively, following dl-PAG stimulation. As revealed by using a paired pulse stimulation protocol, monosynaptic connections were found in 9 of 36 neurons tested from both spinal cord and dl-PAG. We tested NK1-receptor sensitivity in 38 neurons that received convergent inputs from brachial plexus/PAG. Fifteen neurons were sensitive to selective antagonism of NK1 receptors. CP-99994, the NK1 antagonist, failed to alter ongoing firing activity but reduced the evoked peak discharge frequency following stimulation of both brachial plexus (from 12.3 ± 1.8 to 7.2 ± 1.3 Hz; P < 0.01) and PAG (from 7.8 ± 1.5 to 4.5 ± 1 Hz; P < 0.01). We conclude that 1) somatic brachial and PAG afferents can converge onto single NTS neurons; 2) this convergence occurs via either direct or indirect pathways; and 3) NK1 receptors are activated by some of these inputs.

Discharge patterns of reticulospinal and other reticular neurons in chronic, unrestrained cats walking on a treadmill

1986 ◽  
Vol 55 (2) ◽  
pp. 375-401 ◽  
Author(s):  
T. Drew ◽  
R. Dubuc ◽  
S. Rossignol
Keyword(s):  
Spinal Cord ◽  
Reticular Formation ◽  
Muscle Activity ◽  
Discharge Rate ◽  
Muscular Activity ◽  
Step Cycle ◽  
Medullary Reticular Formation ◽  
Locomotor Rhythm ◽  
Reticulospinal Neurons ◽  
Discharge Patterns

Recordings were made from single units in the medullary reticular formation (MRF) between AP-4.2 and AP-12.9 and from the midline to 3.7 mm lateral in chronically prepared, unrestrained cats walking on a treadmill. Recordings were made with rigid microelectrodes held in a microdrive, and reticulospinal neurons were identified by antidromic stimulation of their axons through microwires chronically implanted into the spinal cord at the L2 level. Electromyograms (EMGs) were recorded from flexor and extensor muscles of the fore- and hindlimbs as well as from back and neck muscles. In total, 295 cells were recorded from 40 penetrations in 4 cats; 252 of these cells were recorded from the more medial regions of the reticular formation encompassing the gigantocellular, magnocellular, and lateral tegmental fields; 38.5% of these (97/252) were antidromically identified from the spinal cord. The remaining 43 neurons (43/295) were recorded from a more lateral and ventral position. These medial and ventrolateral groups of neurons differed not only in position but also in aspects of their discharge during locomotion. Rank-ordered raster displays, triggered from the onset of each recorded muscle, were used to correlate neuronal and muscular activity. The discharge rate of 31% of the reticulospinal neurons (30/97) was modulated once or twice in each step cycle and was strictly related to one or more of the recorded EMGs (EMG-related neurons) on the basis of the pattern of discharge. The discharge of 33/97 (34%) of the neurons was modulated at the periodicity of the locomotor rhythm but could not be correlated with any of the recorded EMGs (locomotor-related cells), whereas the remaining 34/97 neurons (35%) were either silent, fired tonically, or were not related to the locomotor pattern (unrelated cells). Of the EMG-related neurons 27% were related to flexor muscles and the remaining 63% to extensor muscle activity. The discharge pattern of all except two of the flexor-related neurons was correlated with hindlimb muscle activity, whereas that of the extensor-related neurons was correlated almost equally with fore- and hindlimb muscles. Correlations were found with muscles lying both ipsilaterally and contralaterally to the site of the recordings. Although the locomotor-related neurons showed no preferential relation with any of the recorded EMGs, a comparison of the depth of modulation of their discharge measured from postevent histograms suggested that more of these cells were related to the forelimb than to the hindlimb.(ABSTRACT TRUNCATED AT 400 WORDS)

Sign in / Sign up

Export Citation Format

Share Document