Elsevier

Brain Research Bulletin

Volume 53, Issue 5, 15 November 2000, Pages 711-718
Brain Research Bulletin

Development of lumbar rhythmic networks: from embryonic to neonate locomotor-like patterns in the mouse

https://doi.org/10.1016/S0361-9230(00)00403-2Get rights and content

Abstract

Different aspects of spinal locomotor organization have been studied in the mouse during embryonic and neonatal development using in vitro preparations of isolated lumbosacral cords. The first consideration was the embryonic development of an alternating bilateral pattern. From embryonic day (E) 12, perfusion of serotonin could induce relatively synchronous lumbar bursts across the cord. Bilateral activity became progressively alternate at E15 due to the appearance of glycinergic inhibitory interactions (revealed by strychnine application). Strictly alternating patterns were expressed at E18 and were maintained after birth. In a second step, we investigated cellular properties involved in lumbar rhythmogenesis in postnatal day 0–2 preparations which displayed spontaneous locomotor-like activity. Perfusion of receptor antagonists showed the co-operative involvement of N-methyl-D-aspartate (NMDA)- and non-NMDA-receptors for excitatory amino acids-mediated operation of locomotor networks. In a final step we investigated the localization of locomotor networks within the lumbar cord. Data obtained from preparations exhibiting spontaneous or Mg2+-free induced bursts revealed that the networks are present throughout the lumbar cord and that rhythmogenesis is distributed throughout all segmental levels.

Introduction

In vitro brainstem-spinal cord preparations from newborn rats were used to investigate both the organization and localization of spinal locomotor generators [(or central pattern generators (CPGs)] in mammals [33]. Rhythmic bursts recorded on lumbar ventral roots were considered as locomotor-like on the basis of their alternating bilateral pattern as well as their cycle frequency. Pharmacological activation, using N-methyl-D-aspartate (NMDA) [33] or NMDA and serotonin (5-HT) [11], is commonly used to induce fictive locomotion which rarely occurs spontaneously. Although much attention has been given to NMDA receptors, non-NMDA excitatory amino acid (EAA) receptors are no less essential, as reflected by the fact that CNQX blocks rhythm production in the in vitro rat spinal cord 8, 11, 27. In fact, because Mg2+ ions block NMDA receptors at resting potential, NMDA receptor activation by glutamate quite predictably depends on non-NMDA EAA receptor to initiate depolarization and thereby remove the Mg2+ blockade of NMDA receptor channels. 5-HT is more likely able to trigger locomotor activity via release from descending pathways [11].

More recently, the in vitro spinal cord preparation has also provided the unique opportunity to access earlier stages of development during embryonic life in the rat [23]. We have developed a spinal cord preparation of embryonic and newborn mice 4, 5, 6, which allows investigation of different ontogenic aspects of central locomotor organization and neurochemical involvement in the activation of locomotion in late postnatal mouse preparation 12, 24, 25.

Section snippets

Development of alternating bilateral coupling in rhythmic lumbar motor activity

In a study of the pharmacological induction of fictive locomotion in neonatal rat, Cowley and Schmidt [14] claimed that 5-HT is the best single agent for the induction of a locomotor-like activity patterned with alternating coupling both in bilateral activity and homolateral flexor-extensor bursting.

In the rat spinal cord, an immunohistochemical study has shown that 5-HT descending pathways develop as early as embryonic day (E) 15 [30]. In an equivalent analysis of embryonic mouse spinal cord

Endogenous neurochemical control of spinal networks involved in locomotor rhythmogenesis in the neonate mouse

Twenty-five percent of our low spinal preparations of neonate mice had the capacity to generate spontaneous locomotor-like rhythmic activity, which is consistent with the findings of Hernandez et al. [20], who described spontaneous electromyographic (EMG) activity in in vitro isolated spinal cords of postnatal day (P) 2 mice with hindlimbs attached. This spontaneous rhythmicity was unexpected in our experiments because in numerous studies on neonate rat, it has never been reported when a

Segmental localization of rhythmic networks in the lumbar spinal cord of the neonate mouse

We have also tried to determine, in the neonate mouse, the localization and the organization of the lumbar locomotor network. To this end, we isolated the smallest piece of cord capable of generating spontaneous spinal motor rhythm without any pharmacological activation. Transections were first performed on isolated cords, at P0–2, which displayed spontaneous locomotor-like bursts under normal bathing medium. Transections carried out on thoracic segments (Th5 to Th13) did not reduce or suppress

Conclusion

Development of locomotor activity induced by NMDA receptor agonists in the lumbar spinal cord of the rat fetus has been studied in vitro [29], where a rhythmic motor activity that matures from bilateral synchrony (at E15.5–E16.5) to alternation (at E20.5) has been described. Iizuka et al. [28] also recently described the developmental transition from a synchronous to alternating bilateral pattern of 5-HT-induced locomotor rhythm in rat embryos. This transition was achieved between E16.5 (strict

Acknowledgements

We are very grateful to Dr. John Simmers for his valuable comments on the manuscript. We also thank Drs. Ole Kjaerulff and Ole Kiehn for helping in the construction of circular phase-diagrams. This study was supported by grants from Université Bordeaux 1 and the C.N.R.S.

References (35)

  • J.C Smith et al.

    In vitro brainstem-spinal cord preparations for the study of motor systems for mammalian respiration and locomotion

    J. Neurosci. Methods

    (1987)
  • M Beato et al.

    Contribution of NMDA and non-NMDA glutamate receptors to locomotor pattern generation in the neonatal rat spinal cord

    Proc. R. Soc. Lond. B Biol. Sci.

    (1997)
  • A Bonnot et al.

    Organization of rhythmic motor patterns in the lumbosacral spinal cord of neonate mouse

    Ann. N.Y. Acad. Sci.

    (1998)
  • E Bracci et al.

    Spontaneous rhythmic bursts induced by pharmacological block of inhibition in lumbar motoneurons of the neonatal rat spinal cord

    J. Neurophysiol.

    (1996)
  • E Bracci et al.

    Extracellular K+ induces locomotor-like patterns in the rat spinal cord in vitroComparison with NMDA or 5-HT induced activity

    J. Neurophysiol.

    (1998)
  • J.-R Cazalets et al.

    Localization and organization of the central pattern generator for hindlimb locomotion in newborn rat

    J. Neurosci.

    (1995)
  • J.-R Cazalets et al.

    Activation of the central pattern generators for locomotion by serotonin and excitatory amino acids in neonatal rats

    J. Physiol. (Lond.)

    (1992)
  • Cited by (84)

    • Prenatal exposure to nicotine disrupts synaptic network formation by inhibiting spontaneous correlated wave activity

      2020, IBRO Reports
      Citation Excerpt :

      The pattern of embryonic motility does not markedly change during E4-E7, except for the number of successions, initiation sites, and contribution of the wings and legs (Hamburger and Balaban, 1963). Although embryonic movements are observed beyond the stage at which the large-scale correlated wave is detected (E4-E8) (Momose-Sato and Sato, 2016a), they are associated with reflexogenic activity that appears from E7-E7.5 (Hamburger and Balaban, 1963), respiratory and locomotor functions that differentiate later than correlated wave activity (Branchereau et al., 2000; Thoby-Brisson et al., 2005, 2009; Momose-Sato et al., 2012a), and sleeping behavior (Corner, 1977). Since the purpose of the in ovo application of nicotine was to affect the wave during E4-E7, we targeted wave-related body movement observed in earlier stages and did not perform detailed analyses on embryonic motility in later stages.

    • Embryonic alteration of motoneuronal morphology induces hyperexcitability in the mouse model of amyotrophic lateral sclerosis

      2013, Neurobiology of Disease
      Citation Excerpt :

      This indicates that toxic form of mutated SOD1 may be present at perinatal stages. In the present study, by analyzing SOD1G93A MNs at the late embryonic stage E17.5 when they undergo major developmental changes and when motor spinal networks become functional (Branchereau et al., 2000), we show that SOD1G93A MNs are hyperexcitable and exhibit a reduced dendritic arborization. Interestingly, using computer simulations, we show that the reduced growth of embryonic SOD1G93A MNs accounts, for the most part, for their hyperexcitability.

    • Investigation of central pattern generators in the spinal cord of chicken embryos

      2024, Journal of Comparative Physiology A: Neuroethology, Sensory, Neural, and Behavioral Physiology
    View all citing articles on Scopus
    1

    Pascal Branchereau and Didier Morin contributed equally to this work.

    View full text