Coding of Locomotor Phase in Populations of Neurons in Rostral and Caudal Segments of the Neonatal Rat Lumbar Spinal Cord

1999 ◽  
Vol 82 (6) ◽  
pp. 3563-3574 ◽  
Author(s):  
Matthew C. Tresch ◽  
Ole Kiehn
Keyword(s):  
Spinal Cord ◽  
Spike Activity ◽  
Neuronal Population ◽  
Ventral Root ◽  
Neonatal Rat ◽  
Lumbar Spinal Cord ◽  
Spinal Segment ◽  
Rhythmic Motor ◽  
Lumbar Spinal ◽  
Rostrocaudal Gradient

Several experiments have demonstrated that rostral segments of the vertebrate lumbar spinal cord produce a rhythmic motor output more readily and of better quality than caudal segments. Here we examine how this rostrocaudal gradient of rhythmogenic capability is reflected in the spike activity of neurons in the rostral (L2) and caudal (L5) lumbar spinal cord of the neonatal rat. The spike activity of interneurons in the ventromedial cord, a region necessary for the production of locomotion, was recorded intracellularly with patch electrodes and extracellularly with tetrodes during pharmacologically induced locomotion. Both L2 and L5 neurons tended to be active in phase with their homologous ventral root. L5 neurons, however, had a wider distribution of their preferred phases of activity throughout the locomotor cycle than L2 neurons. The strength of modulation of the activity of individual L2 neurons was also larger than that of L5 neurons. These differences resulted in a stronger rhythmic signal from the L2 neuronal population than from the L5 population. These results demonstrate that the rhythmogenic capability of each spinal segment was reflected in the activity of interneurons located in the same segment. In addition to paralleling the rostrocaudal gradient of rhythmogenic capability, these results further suggest a colocalization of motoneurons and their associated interneurons involved in the production of locomotion.

scholarly journals Locomotor-Activated Neurons of the Cat. I. Serotonergic Innervation and Co-Localization of 5-HT7, 5-HT2A, and 5-HT1A Receptors in the Thoraco-Lumbar Spinal Cord

2009 ◽  
Vol 102 (3) ◽  
pp. 1560-1576 ◽  
Author(s):  
Brian R. Noga ◽  
Dawn M. G. Johnson ◽  
Mirta I. Riesgo ◽  
Alberto Pinzon
Keyword(s):  
Spinal Cord ◽  
Lumbar Spinal Cord ◽  
Lumbar Spinal ◽  
Rostrocaudal Gradient ◽  
Activity Dependent ◽  
Decerebrate Cats ◽  
Intermediolateral Nucleus ◽  
Serotonergic Modulation ◽  
Stimulation Of ◽  
Serotonergic Innervation

Monoamines are strong modulators and/or activators of spinal locomotor networks. Thus monoaminergic fibers likely contact neurons involved in generating locomotion. The aim of the present study was to investigate the serotonergic innervation of locomotor-activated neurons within the thoraco-lumbar spinal cord following induction of hindlimb locomotion. This was determined by immunohistochemical co-localization of serotonin (5-HT) fibers or 5-HT7/5-HT2A/5-HT1A receptors with cells expressing the activity-dependent marker c-fos. Experiments were performed on paralyzed, decerebrate cats in which locomotion was induced by electrical stimulation of the mesencephalic locomotor region. Abundant c-fos immunoreactive cells were observed in laminae VII and VIII throughout the thoraco-lumbar segments of locomotor animals. Control sections from the same segments showed significantly fewer labeled neurons, mostly within the dorsal horn. Multiple serotonergic boutons were found in close apposition to the majority (80–100%) of locomotor cells, which were most abundant in lumbar segments L3–7. 5-HT7 receptor immunoreactivity was observed on cells across the thoraco-lumbar segments (T7–L7), in a dorsoventral gradient. Most locomotor-activated cells co-localized with 5-HT7, 5-HT2A, and 5-HT1A receptors, with largest numbers in laminae VII and VIII. Co-localization of c-fos and 5-HT7 receptor was highest in the L5–L7 segments (>90%) and decreased rostrally (to ∼50%) due to the absence of receptors on cells within the intermediolateral nucleus. In contrast, 60–80 and 35–80% of c-fos immunoreactive cells stained positive for 5-HT2A and 5-HT1A receptors, respectively, with no rostrocaudal gradient. These results indicate that serotonergic modulation of locomotion likely involves 5-HT7/5-HT2A/5-HT1A receptors located on the soma and proximal dendrites of serotonergic-innervated locomotor-activated neurons within laminae VII and VIII of thoraco-lumbar segments.

Formation of primary and secondary myotubes in rat lumbrical muscles

Development ◽  
1987 ◽  
Vol 100 (3) ◽  
pp. 383-394 ◽  
Author(s):  
J.J. Ross ◽  
M.J. Duxson ◽  
A.J. Harris
Keyword(s):  
Spinal Cord ◽  
Ventral Root ◽  
Lumbar Spinal Cord ◽  
Muscle Fibres ◽  
Final Size ◽  
Root Death ◽  
Undifferentiated Cells ◽  
Major Period ◽  
Lumbrical Muscles ◽  
Lumbar Spinal

Numbers of myoblasts, primary myotubes and secondary myotubes in developing rat embryo hindlimb IVth lumbrical muscles were counted at daily intervals up until the time of birth, using electron microscopy. Motoneurone death at the spinal cord level supplying the lumbricals was assessed by counting axons in the 4th lumbar ventral root. Death of the motoneurones that supply the intrinsic muscles of the hindfoot was monitored by comparing the timecourse of development of total muscle choline acetyltransferase activity in control embryos with that in embryos where motoneurone death was inhibited by chronic paralysis with TTX, and by counting axons in the mixed nerve trunks at the level of the ankle at daily intervals. Condensations of undifferentiated cells marking the site of formation of the muscle were seen on embryonic day 15 (E15). Primary myotubes began to appear on E16 and reached a stable number (102 +/− 4) by E17. Secondary myotubes first appeared two days later, on E19, and numbered 280 at the time of birth (E22). The adult total of about 1000 muscle fibres, derived from both primary and secondary myotubes, was reached at postnatal day 7 (PN7) so considerable generation of secondary myotubes occurred after birth. There was a linear correlation between the number of undifferentiated mononucleate cells in a muscle and the rate of formation of secondary myotubes. The major period of motoneurone death in lumbar spinal cord was during E16-E17, when axon numbers in the L4 ventral root fell from 12,000 to 4000, but a discontinuity in the curve of muscle ChAT activity versus time indicated that death in the lumbrical motor pool occurred during E17-E19, after all primary myotubes had formed and before generation of secondary myotubes began. We suggest that motoneurone death, by regulating the final size of the motoneurone pool, regulates the ratio of secondary to primary myotube numbers in a muscle.

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.

Functional involvement of the lumbar spinal cord after contusion to T8 spinal segment of the rat

2010 ◽  
Vol 28 (6) ◽  
pp. 781-792
Author(s):  
Guillermo García-Alías ◽  
Abel Torres-Espín ◽  
Carolina Vallejo ◽  
Xavier Navarro
Keyword(s):  
Spinal Cord ◽  
Lumbar Spinal Cord ◽  
Spinal Segment ◽  
Functional Involvement ◽  
Lumbar Spinal

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.

Rhythmic Motor Activity in Thin Transverse Slice Preparations of the Fetal Rat Spinal Cord

2004 ◽  
Vol 92 (1) ◽  
pp. 648-652 ◽  
Author(s):  
Kiyomi Nakayama ◽  
Hiroshi Nishimaru ◽  
Norio Kudo
Keyword(s):  
Spinal Cord ◽  
Motor Activity ◽  
Temporal Correlation ◽  
Rhythmic Activity ◽  
Lumbar Spinal Cord ◽  
Rat Spinal Cord ◽  
Commissural Neurons ◽  
Rhythmic Motor ◽  
Lumbar Spinal ◽  
Transverse Slice

Networks generating locomotor-like rhythmic motor activity are formed during the last week of the fetal period in the rat spinal cord. We investigated the coordinated rhythmic motor activity induced in transverse slice preparations of the lumbar spinal cord taken from fetal rats as early as embryonic day (E) 16.5. In slices as thin as 100 μm, bath-application of 5-hydroxytryptamine (5-HT) induced rhythmic [Ca2+]i elevations in motoneurons labeled with Calcium Green-1 dextran. The rhythmic [Ca2+]i elevations were similar in frequency to that in the intact lumbar spinal cord, although there was no temporal correlation between the activity in the left and right sides of 100-μm slices. Such rhythmic [Ca2+]i elevations were observed in the slices taken from all lumbar segments. Moreover, the rhythmic activity was abolished by simultaneous blockade of glutamate, glycine, and GABAA receptors, indicating that synaptic transmission mediated by these receptors is important for the generation of the rhythm in these slices. Synchronous rhythmic activity between the left-right sides was found in slices thicker than 200 μm taken from any segmental level of the lumbar spinal cord. In these preparations, commissural neurons were activated synchronously with ipsilateral motoneurons. These results indicate that the neuronal networks sufficient to generate coordinated rhythmic activity are contained in one-half of a single lumbar segment at E16.5. Such spinal cord slices are a promising experimental model to investigate the neuronal mechanisms and the development of rhythm generation in the spinal cord.

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