Serotonergic modulation of sacral dorsal root stimulation-induced locomotor output in newborn rat
Introduction
The control of locomotor behaviors relies on dynamic interactions between the supraspinal locomotor centers (from the cortex to brainstem), the spinal central pattern generators (CPGs) for locomotion and segmental sensory afferent information. In rat, the spinal locomotor network begins to develop during the embryonnic stage, is functional at birth but continues to mature up to 3 weeks of age (Brocard et al., 1999a, 1999b; Cazalets et al., 1990; Clarac et al., 2004; Vinay et al., 2002). During this postnatal period, neuromodulatory pathways originating from the brain progressively descend along the spinal cord and mature to reach their adult pattern of innervation between the second and fourth post-natal weeks (Vinay et al., 2000). Consequently, the operation of the locomotor network evolves over time, as does the repertoire of behaviors it produces, including the expression of adult locomotion from two post-natal weeks (Altman and Sudarshan, 1975; Clarac et al., 2004).
The isolated neonatal rat spinal cord preparation provides the opportunity to study the central genesis of locomotor outputs during the first few post-natal days, since this preparation continues to generate in vitro an array of rhythmical motor outputs, including locomotor-like activities, that the CNS produces in vivo. Activation methods include exogenous application of neurotransmitters and neuromodulators (Barrière et al., 2005, 2004; Beliez et al., 2014; Cazalets et al., 1992; Cowley and Schmidt, 1994; Juvin et al., 2005; Kiehn and Kjaerulff, 1996; Kiehn et al., 1999; Smith and Feldman, 1987; Smith et al., 1988; Sqalli-Houssaini and Cazalets, 2000) and electrical stimulation of specific brainstem areas (Atsuta et al., 1990; Juvin et al., 2007; Oueghlani et al., 2018; Zaporozhets et al., 2004), descending pathways (Iwahara et al., 1991; Magnuson et al., 1995; Magnuson and Trinder, 1997) or segmental sensory afferent pathways (Juvin et al., 2012; Lev-Tov et al., 2000; Marchetti et al., 2001; Smith and Feldman, 1987). At the lumbar level, where the hindlimb CPG for locomotion is located (Cazalets et al., 1995), rhythmical alternations of left-right segmental motor bursts as well as of ipsilateral flexor-like and extensor-like motor bursts recorded from the second (L2) and fifth (L5) lumbar ventral roots respectively, are a major hallmark of so-called “fictive locomotion” (Cazalets et al., 1992; Kiehn and Kjaerulff, 1996).
Tonic electrical stimulations of one of the sacral/coccygeal dorsal roots that notably convey sensory afferent inputs from the tail in rodent, is one relevant method for activating the lumbar locomotor networks in the isolated neonatal rat spinal cord (Lev-Tov et al., 2000). Activation of these networks is mediated by a sacral relay pathway that projects rostrally through the ventral funiculi (Cherniak et al., 2017; Etlin et al., 2010, 2014; 2013; Strauss and Lev-Tov, 2003). This pathway is also probably involved in the pro-locomotor action of perineal stimulations below a spinal cord lesion in cat and rat (Alluin et al., 2015; Barbeau and Rossignol, 1987; Fouad et al., 2000). Until now, however, no developmental investigation of this sacral ascending control of the lumbar network has been carried out. Thus, whether this sensory derived activation modality of the lumbar networks remains capable of triggering episodes of fictive locomotion during the first few days after birth, while the spinal neuromodulatory environment is evolving rapidly, remains to be established.
In the present work, we investigated the temporal organization of the rhythmic lumbar motor outputs triggered by a tonic electrical stimulation of a single sacral dorsal root of isolated spinal cord preparations from neonatal (postnatal day (P) 0–5) rats (Cazalets et al., 1992; Smith and Feldman, 1987). Specifically, we focused on the motor outputs recorded simultaneously from the L2 and L5 segments that convey motor commands to mostly flexor and extensor muscles, respectively. We found that the nature of motor output pattern induced by the sacral stimulation varies as a function of the developmental stage. Moreover, our data provide evidence that over time, serotonin (5-HT)-mediated modulatory signaling in the spinal cord becomes necessary to convert non-locomotor output into a fully organized locomotory pattern.
Section snippets
Material and methods
Experiments were performed on Sprague Dawley newborn rats (n = 101) of either sex aged from 0 to 5 days (P0–P5). The repartition of all animals was as followed: 5-HT only experiments (n = 14), partitionned spinal cord experiments (n = 9), quipazine experiments (n = 10), ketanserin experiments (n = 18), LP-44 experiments (n = 9), SB269970 experiments (n = 13), 8-OH-DPAT experiments n = 16, immunohistochemistry (n = 12 including 3 for antibody testing). All procedures were conducted in accordance
Characterization of sacral dorsal root stimulation-induced rhythmic activity
Unilateral tonic electrical stimulation (2Hz for 30s, 1 to 5x threshold) of a single sacral dorsal root which subsequently will be referred to as sacral DR stimulation (Lev-Tov et al., 2000), was very effective in triggering rhythmic motor outputs in ventral roots at the lumbar level. Bilateral alternation of motor bursts recorded from the L2 segment (lL2/rL2) was systematically expressed, although ipsilateral flexor- (L2)/extensor-like (L5) motor burst alternation was mainly obtained in
Discussion
The present work investigated the generation of fictive locomotor episodes elicited by unilateral tonic electrical stimulation of a single sacral (S2) dorsal root. We show that during the first 2 post-natal days (P0–P2), sacral DR stimulation triggers a complete locomotor output in most of the preparations tested. After P2, however, the same stimulation protocol mostly induces partial burst patterns and/or with inappropriate, non-locomotor phase relationships. However, at these later stages,
Declaration of competing interest
The authors declare no conflict of interest.
Acknowledgements
The authors are very grateful to Dr John Simmers for his constructive comments on this manuscript and its editing. The authors also thank Anne Fayoux for taking care of the animals and her management of breeding. The authors are also grateful to Aslak Grinsted for the matlab wavelet coherence package (http://noc.ac.uk/using-science/crosswavelet-wavelet-coherence) and Philipp Berens for the circular statistics toolbox.
References (117)
- et al.
Postnatal development of locomotion in the laboratory rat
Anim. Behav.
(1975) - et al.
Long-lasting recovery of locomotor function in chronic spinal rat following chronic combined pharmacological stimulation of serotonergic receptors with 8-OHDPAT and quipazine
Neurosci. Lett.
(2005) - et al.
Initiation and modulation of the locomotor pattern in the adult chronic spinal cat by noradrenergic, serotonergic and dopaminergic drugs
Brain Res.
(1991) - et al.
Recovery of locomotion after chronic spinalization in the adult cat
Brain Res.
(1987) - et al.
Peptidergic neuromodulation of the lumbar locomotor network in the neonatal rat spinal cord
Peptides
(2005) - et al.
Postnatal development of cell columns and their associated dendritic bundles in the lumbosacral spinal cord of the rat. I. The ventrolateral cell column
Brain Res.
(1987) - et al.
Postnatal development of cell columns and their associated dendritic bundles in the lumbosacral spinal cord of the rat. II. The ventromedial cell column
Brain Res.
(1987) Development of serotonin immunoreactivity in the rat spinal cord and its plasticity after neonatal spinal cord lesions
Brain Res.
(1987)- et al.
Development of hindlimb postural control during the first postnatal week in the rat
Brain Res Dev Brain Res
(1999) - et al.
Gradual development of the ventral funiculus input to lumbar motoneurons in the neonatal rat
Neuroscience
(1999)
Variability as a characteristic of immature motor systems: an electromyographic study of swimming in the newborn rat
Behav. Brain Res.
The maturation of locomotor networks
Prog. Brain Res.
Role of gravity in the development of posture and locomotion in the neonatal rat
Brain Res Brain Res Rev
Development of catecholaminergic nerves in the spinal cord of the rat
Brain Res.
The development of catecholaminergic nerves in the spinal cord of rat. II. Regional development
Brain Res.
A comparison of motor patterns induced by N-methyl-D-aspartate, acetylcholine and serotonin in the in vitro neonatal rat spinal cord
Neurosci. Lett.
Prenatal and postnatal development of lamina IX neurons in the rat thoracic spinal cord
Exp. Neurol.
Treadmill training in incomplete spinal cord injured rats
Behav. Brain Res.
Spinal locomotor circuits develop using hierarchical rules based on motorneuron position and identity
Neuron
Development of the spatial pattern of 5-HT-induced locomotor rhythm in the lumbar spinal cord of rat fetuses in vitro
Neurosci. Res.
Receptor subtypes mediating facilitation by serotonin of excitability of spinal motoneurons
Neuropharmacology
Descending command systems for the initiation of locomotion in mammals
Brain Res Brain Res Rev
Propriospinal neurons involved in the control of locomotion: potential targets for repair strategies?
Prog. Brain Res.
Effect of transient neonatal muscle paralysis on the growth of soleus motoneurones in the rat
Brain Res Dev Brain Res
Differential effects of 5-HT1 and 5-HT2 receptor agonists on hindlimb movements in paraplegic mice
Prog. Neuro Psychopharmacol. Biol. Psychiatry
Pattern generation in non-limb moving segments of the mammalian spinal cord
Brain Res. Bull.
The cellular localization of 5-HT2A receptors in the spinal cord and spinal ganglia of the adult rat
Brain Res.
Long-duration, frequency-dependent motor responses evoked by ventrolateral funiculus stimulation in the neonatal rat spinal cord
Neurosci. Lett.
Autoradiographic mapping of 5-HT1, 5-HT1A, 5-HT1B and 5-HT2 receptors in the rat spinal cord
Brain Res.
Postnatal development of locomotor movements in normal and para-chlorophenylalanine-treated newborn rats
Neurosci. Res.
Prenatal administration of para-chlorophenylalanine results in suppression of serotonergic system and disturbance of swimming movements in newborn rats
Neurosci. Res.
5-Hydroxytryptamine-induced locomotor rhythm in the neonatal mouse spinal cord in vitro
Neurosci. Lett.
Development of locomotor activity induced by NMDA receptor activation in the lumbar spinal cord of the rat fetus studied in vitro
Brain Res Dev Brain Res
Plasticity and ontogeny of the central 5-HT transporter: effect of neonatal 5,7-dihydroxytryptamine lesions in the rat
Brain Res Dev Brain Res
Pre- and postnatal development of noradrenergic projections to the rat spinal cord: an immunocytochemical study
Brain Res Dev Brain Res
Inducing hindlimb locomotor recovery in adult rat after complete thoracic spinal cord section using repeated treadmill training with perineal stimulation only
J. Neurophysiol.
Neurons labeled from locomotor-related ventrolateral funiculus stimulus sites in the neonatal rat spinal cord
J. Comp. Neurol.
5-HT1A receptors are involved in short- and long-term processes responsible for 5-HT-induced locomotor function recovery in chronic spinal rat
Eur. J. Neurosci.
Locomotor recovery in the chronic spinal rat: effects of long-term treatment with a 5-HT2 agonist
Eur. J. Neurosci.
Characteristics of electrically induced locomotion in rat in vitro brain stem-spinal cord preparation
J. Neurophysiol.
Why does infant stepping disappear and can it be stimulated by optic flow?
Child Dev.
Neuromodulation of the locomotor network by dopamine in the isolated spinal cord of newborn rat
Eur. J. Neurosci.
Serotonin-induced inhibition of locomotor rhythm of the rat isolated spinal cord is mediated by the 5-HT1 receptor class
Proc. Biol. Sci.
Multiple monoaminergic modulation of posturo-locomotor network activity in the newborn rat spinal cord
Front. Neural Circuits
CircStat: a matlab toolbox for circular statistics
J. Stat. Softw.
Differential effects of opioids on sacrocaudal afferent pathways and central pattern generators in the neonatal rat spinal cord
J. Neurophysiol.
Activation of 5-HT2A receptors upregulates the function of the neuronal K-Cl cotransporter KCC2
Proc. Natl. Acad. Sci. U.S.A.
The serotonergic agonists quipazine, CGS-12066A, and alpha-methylserotonin alter motor activity and induce hindlimb stepping in the intact and spinal rat fetus
Behav. Neurosci.
Prenatal development of the serotonin transporter in mouse brain
Cell Tissue Res.
Serotonin controls initiation of locomotion and afferent modulation of coordination via 5-HT7 receptors in adult rats
J. Physiol. (Lond.)
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These authors contributed equally to this work.