The main clinical symptoms of spasticity, hyperreflexia and spasms, develop after spinal cord injury (SCI) due in part to the hyperexcitability of motoneurons (Hultborn, 2003; Gorassini, 2004; Nielsen et al., 2007; D'Amico et al., 2014; Thomas et al., 2014). Understanding the cellular pathophysiological processes underlying this hyperexcitability might offer new therapeutic perspectives for spasticity.

SCI enhances the intrinsic excitability of motoneurons by upregulating their persistent sodium (I_NaP) and calcium (I_CaP) currents, leading to muscle spasms and hyperreflexia in both humans and adult rats (Li and Bennett, 2003; Li et al., 2004; Harvey et al., 2005; Harvey et al., 2006b; Harvey et al., 2006a; ElBasiouny et al., 2010; Theiss et al., 2011; Brocard et al., 2016). In addition, a concomitant synaptic disinhibition of motoneurons due to a decrease of the main chloride extruder KCC2 also takes place after SCI in both humans and adult rodents (Boulenguez et al., 2010; Mòdol et al., 2014; Klomjai et al., 2019). In vitro experiments from neonatal rats show that this form of disinhibition stems primarily from an impaired Cl⁻ extrusion, typically identified by a depolarizing shift of the reversal potential of inhibitory postsynaptic potentials (E_IPSP) (Boulenguez et al., 2010), which may facilitate the recruitment of persistent inward currents after SCI (Venugopal et al., 2011). Thus, up-regulation of persistent inward currents concomitant with down-regulation of KCC2 may have a synergistic effect causing spasticity.

Remarkable advances have been made in the molecular mechanisms involved in alterations of persistent inward currents after SCI. SCI-induced constitutive 5-HT_2B/C receptor activity leads to an increase in I_CaP (Murray et al., 2010), while calpain-mediated proteolysis of Nav1.6 channels up-regulates I_NaP (Brocard et al., 2016). Although the mechanisms involved in alterations of KCC2 after SCI remain elusive, it is worth mentioning that calpain-mediated cleavage of KCC2 depolarizes the E_IPSP in some pathophysiological conditions (Puskarjov et al., 2012; Zhou et al., 2012; Wan et al., 2018). Our study investigates whether SCI-induced activation of calpains is upstream of the up- and down-regulation of I_NaP and KCC2 in motoneurons after SCI. If so, we aim at demonstrating whether a cooperation between calpain-mediated alterations of I_NaP and E_IPSP is a necessary element driving spasticity. For this purpose, we characterized signs of spasticity from the neonatal rat SCI model to obtain easier in vitro correlates of the hyperexcitability of lumbar motoneurons controlling hindlimb muscles.

Numerous studies on adult animal models delineate the hyperexcitable state of motoneurons as one of the causes of spasticity, presumably because of an increase of I_NaP and a decrease of KCC2 expression. The present study performed in neonatal rats identifies the activation of calpains as the upstream mechanism of the hyperexcitability of motoneurons after SCI. Calpain-mediated cleavage of Nav channels and KCC2 up- and down-regulates I_NaP and inhibition, respectively, in lumbar motoneurons. The reduction of calpain activity normalizes I_NaP and the strength of inhibitory transmission, and thereby alleviates spasticity. Altogether, these findings uncover a new cellular mechanism contributing to spasticity and provide novel therapeutic targets. Rather than targeting Nav channels or KCC2 independently, inhibition of calpains appears as a promising therapy by targeting two pathways that are crucial for the development of spasticity, ‘killing two birds with one stone’.

The main spasticity symptoms develop within one week following SCI in neonatal rats, and correlate with an early appearance of hyperexcitability in the spinal cord. The emergence of spasticity is surprisingly faster than that of adult animals, which appears several weeks after the injury. A more active calpain-mediated proteolysis during early development may explain this age-dependent discrepancy. Indeed, calpain proteolysis is necessary for the pruning of axons during development (Yang et al., 2013) and the natural calpain inhibitory peptide, calpastatin, increases slowly in the CNS during the first weeks of life (Li et al., 2009). The lower presence of this inhibitor in newborn rats may explain why hyperexcitability after a neonatal SCI developed faster. Also at birth, rat motoneurons overexpress NMDA receptors (Vinay et al., 2000) which have been demonstrated to be efficient in activating calpains in pathological conditions (Zhou et al., 2012). In sum, the low expression of calpastatin combined with a high expression of NMDA receptors may contribute to a fast increase of motoneuronal excitability after a SCI in newborn rats.

This hyperexcitability emerges in vitro in the form of high-frequency spontaneous bursting activity and enhanced, prolonged sensory-evoked LLR. We provided evidence that both are dependent on I_NaP and KCC2 dysfunction. I_NaP plays an important role in the operation of the spinal locomotor network (Tazerart et al., 2007; Tazerart et al., 2008; Brocard et al., 2010; Bouhadfane et al., 2013; Brocard et al., 2013) and its increase after SCI promotes prolonged plateau potential firing in motoneurons and hyperreflexia, both in animal models and humans (Li and Bennett, 2003; Li et al., 2004; Kitzman, 2009; Theiss et al., 2011). Supersensitivity of motoneurons to residual serotonin after SCI leads to the facilitation of I_NaP (Harvey et al., 2006a; Harvey et al., 2006b). Here, we demonstrate that calpain-dependent cleavage of Nav channels also upregulates I_NaP in lumbar motoneurons. If serotonin recruits calpains after SCI, similarly to what observed in Aplysia motoneurons (Bougie et al., 2012), remains to be tested.

The exact mechanisms involved in the facilitation of I_NaP by calpain are not fully understood. As previously observed after a traumatic brain injury (von Reyn et al., 2009), proteolyzed Nav channels remain in the plasma membrane and thus might interfere with biophysical properties of full-length voltage-gated channels (Michailidis et al., 2014). On the other hand, some determinants governing the inactivation of Nav channels are sensitive to proteases, which can increase I_NaP (Armstrong et al., 1973; Gonoi and Hille, 1987; Clarkson, 1990). Whatever the mechanisms, a clear relationship is given by our previous study in which calpain-mediated cleavage of Nav1.6 channels in HEK-293 cells up-regulates I_NaP (Brocard et al., 2016). Because Nav1.6 channels are highly expressed in spinal motoneurons (Alessandri-Haber et al., 2002; Duflocq et al., 2008; Brocard et al., 2016), their cleavage likely contributes to increase I_NaP after SCI. This is consistent with our result that pharmacological inhibition of Nav1.6 channels significantly reduced hyperexcitability after SCI. Further support comes from mutation of Nav1.6 channels that leads to severe myoclonic spasms with a fivefold increase of I_NaP (Veeramah et al., 2012). It is noteworthy that the rescue of I_NaP by MDL28170 is only partial. Although an incomplete block of calpains by MDL28170 cannot be excluded, calpain-independent mechanism(s) may contribute to increase I_NaP. Since the activation of 5HT₂ receptors facilitates I_NaP (Harvey et al., 2006b), the constitutive activation of 5HT₂ receptors after SCI (Murray et al., 2010) might be one of them. Also, the amount of full-length Nav channels (~250 kDa) at the plasma membrane never changed after either the post-SCI activation of calpains (Brocard et al., 2016) or their inhibition by a MDL28170 treatment (see Figure 3F). As a compensation mechanism depending on the number of proteolytic fragments, it is possible that the translocation of fragments into the nucleus maintains constant the expression level of the full-length channel at the membrane by regulating the Nav channel transcription (Onwuli et al., 2017).

Synaptic disinhibition of motoneurons after SCI also contributes to spasticity and results from a decreased expression of KCC2 (Boulenguez et al., 2010). Although a down-regulation of KCC2 has been described after SCI (Boulenguez et al., 2010; Côté et al., 2014; Mòdol et al., 2014; Chang et al., 2018; Chen et al., 2018), the causal molecular mechanisms remain unknown. Here, we provide evidence that activation of calpains is one of the molecular basis for disinhibition of motoneurons after SCI. A direct relationship between calpain and KCC2 is given by our studies on spinal cord homogenates, in which exogenous application of active calpains reduces KCC2 in its oligo and monomeric forms. The sensitivity of KCC2 to calpain is consistent with the presence of two predicted sites (PEST motifs) for cleavage by calpain within the C-terminal domain (Mercado et al., 2006; Acton et al., 2012). Since the ability of KCC2 to extrude Cl^- requires the C-terminal domain (Mercado et al., 2006; Acton et al., 2012) and that the KCC2 antibody targets the C-tail, its cleavage by calpains after SCI likely accounts for both the immunostaining decrease of KCC2 at the plasma membrane and the loss of chloride extrusion resulting in the depolarizing shift of E_IPSP in motoneurons (Boulenguez et al., 2010). The tight relationship between the calpain-mediated proteolysis of KCC2 and the altered Cl^- homeostasis is supported by our observation that an acute inhibition of calpains by MDL28170 rapidly restores both E_IPSP and KCC2. The rapid rescue of KCC2 by the acute application of MDL28170 is in agreement with the fast pharmacodynamic of MDL28170 to cross the brain blood barrier (Markgraf et al., 1998) and the extremely high rate (minutes) in KCC2 turnover at the plasma membrane (Lee et al., 2007). Regarding the rescue of KCC2 by MDL28170, oligomers appear more sensitive to calpains than monomers after SCI. As phosphorylation regulates the vulnerability of substrates to calpains (Sprague et al., 2008), the post-SCI dephosphorylation of KCC2 at the serine 960 (Mòdol et al., 2014), in the vicinity of PEST motifs, might contribute to sensitize more oligomers to calpains.

Our results suggest that KCC2 and I_NaP appear to cooperate in promoting spinal hyperexcitability after SCI. In line with this, a modeling investigation demonstrated that the depolarizing shift of E_IPSP after SCI facilitates the recruitment of persistent inward currents in motoneurons (Venugopal et al., 2011). The depolarizing shift of E_IPSP after a decrease in KCC2 may enable the unusual long-lasting depolarization reported in motoneurons after SCI (Li et al., 2004), which is required to recruit I_NaP. In turn, I_NaP will promote plateau potentials resulting in self-sustaining spiking in motoneurons (Li and Bennett, 2003; Bouhadfane et al., 2013) that drives spasticity (Bennett et al., 2001; Gorassini, 2004; Li et al., 2004). Furthermore, termination of plateau potentials by hyperpolarizing the motoneuron (Hounsgaard et al., 1984) will be much more difficult in a context of disinhibition; this may explain the fasciculation-like contractions commonly recorded in spastic subjects (Gorassini, 2004; Winslow et al., 2009; Zijdewind and Thomas, 2012). Therefore, I_NaP-blockers such as riluzole, or KCC2 enhancers likely alleviate spasticity (Brocard et al., 2016; Liabeuf et al., 2017) by decoupling the tandem response driven by enhanced I_NaP and decreased KCC2. The riluzole is currently approved for humans affected by Amyotrophic Lateral Sclerosis (ALS). Our data provide strong preclinical evidence for translation to chronic SCI subjects, a process that will likely be facilitated by clinical trials that are currently in progress to test the neuroprotective effects of riluzole in the acute phase of SCI (Grossman et al., 2014).

We identify calpain as the upstream mechanism responsible for the hyperexcitability of motoneurons after SCI. Calpains exist in the CNS mainly as two major isoforms, µ-calpain (calpain-I) and m-calpain (calpain-II) that differ on the range of [Ca²⁺] required for their activation (µM and mM, respectively). As previously observed in adult rodents (Springer et al., 1997; Du et al., 1999; Schumacher et al., 1999; Yu et al., 2013), we found that the expression of calpain-I increases after SCI in neonatal rats. However, the protease protein expression does not necessarily correspond to enzyme’s catalytic activity. Furthermore, calpain-I and -II may have opposite functions. After a traumatic brain injury (TBI), calpain-I and -II appear neuroprotective and neurodegenerative, respectively (Baudry and Bi, 2016). Therefore, the respective contribution of calpain-I and -II in the hyperexcitability of motoneurons after SCI remains to be clarified.

Calpain-mediated changes in motoneurons alone are unlikely to account for all the post-injury spinal hyperexcitability. Premotor excitatory interneurons, including locomotor network-related interneurons, may play a critical role in initiating muscle spasm activity (Husch et al., 2012; Bellardita et al., 2017; Lin et al., 2019). In line with this, we found that most sensory-evoked LLRs are composed of a fictive locomotor episode, suggesting enhanced sensory recruitment of the locomotor central pattern generator (CPG). This leads us to believe that part of muscle spasm, and especially clonus (involuntary rhythmic contractions), might be a manifestation of a hyperexcitable locomotor CPG. Enhanced sensory-evoked LLR has been previously described in the sacrocaudal spinal cord from adult SCI rodents but differs in some aspects from our results with neonatal lumbar motoneurons. Indeed, I_CaP contributes to sacrocaudal hyperreflexia by promoting plateaus in motoneurons (Li and Bennett, 2003; Li et al., 2004) while disinhibition appears negligible (Bellardita et al., 2017). The I_CaP appears to have a negligible role in lumbar hyperreflexia from neonatal SCI rats, in line with previous work showing a full maturation of L-type Ca²⁺ channels at second/third post-natal weeks (Jiang et al., 1999). However, we also demonstrate that some of these channels are already expressed in the first post-natal week, as their pharmacological activation by Bay-K triggered LLRs. Thus, it is likely that the contribution of L-type Ca²⁺ channels to the LLR increases with age. Alternatively, temperature and ionic composition of the extracellular medium may account for the relative contribution of I_NaP and I_CaP in generating LLRs. In vitro studies in adults were performed at room temperature with high extracellular [Ca²⁺] (≥2.5 mM) (Li and Bennett, 2003; Li et al., 2004; Bellardita et al., 2017), far from physiological conditions [body temperature 37°C; 1.2 mM of Ca²⁺ in the CSF (Nicholson et al., 1977; Jones and Keep, 1988; Brocard et al., 2013). As a consequence, Ca²⁺ currents are potentiated (Carlin et al., 2000; Carlin et al., 2009), I_NaP is reduced (Tazerart et al., 2008) and thermosensitive I_NaP-dependent plateaus in motoneurons are dampened down (Bouhadfane et al., 2013). Also, the disinhibition seen in the SCI lumbar enlargement, linked to the decrease of KCC2 (Boulenguez et al., 2010), seems unimportant in the sacrocaudal spinal cord (Bellardita et al., 2017). Diversity of KCC2 expression between motoneurons innervating distinct muscles (Ueno et al., 2002) or variation in the sacral inhibitory circuitry (Jankowska et al., 1978) may account for this discrepancy. Spinal cord level-specific differences in neuronal responses to SCI are probable with respect to the special anatomy and function of the sacrocaudal spinal cord (Ritz et al., 1992; Ritz et al., 2001).

To conclude, our study sheds light on the etiology of spasticity and opens novel perspectives to develop therapies by targeting calpains. The discovery of calpain as a new upstream mechanism leading to spasticity, is of special importance given the lack of translational results obtained from previously tested therapeutic approaches. Since spinal maladaptive mechanisms triggered by calpain start taking place within the first hours after injury in our SCI model, it is conceivable that early therapies against calpain might show a higher effectiveness. Because altered chloride homeostasis and proteolysis of Nav channels have been implicated in other neurological disorders such as traumatic brain injury for which calpains are recruited (Kahle et al., 2008; von Reyn et al., 2009; Wang et al., 2018), the involvement of calpains might be broadened to other pathologies leading to an excitatory/inhibitory imbalance.

All data generated or analysed during this study are included in the manuscript and supporting files. Source data files have been provided for all figures and figure supplements.

1. 1. Acton BA
   2. Mahadevan V
   3. Mercado A
   4. Uvarov P
   5. Ding Y
   6. Pressey J
   7. Airaksinen MS
   8. Mount DB
   9. Woodin MA

   (2012) Hyperpolarizing GABAergic transmission requires the KCC2 C-terminal ISO domain

   Journal of Neuroscience 32:8746–8751.

   https://doi.org/10.1523/JNEUROSCI.6089-11.2012

   • PubMed
   • Google Scholar
2. 1. Alessandri-Haber N
   2. Alcaraz G
   3. Deleuze C
   4. Jullien F
   5. Manrique C
   6. Couraud F
   7. Crest M
   8. Giraud P

   (2002) Molecular determinants of emerging excitability in rat embryonic motoneurons

   The Journal of Physiology 541:25–39.

   https://doi.org/10.1113/jphysiol.2001.013371

   • PubMed
   • Google Scholar
3. 1. Alkadhi KA
   2. Tian LM

   (1996) Veratridine-enhanced persistent sodium current induces bursting in CA1 pyramidal neurons

   Neuroscience 71:625–632.

   https://doi.org/10.1016/0306-4522(95)00488-2

   • PubMed
   • Google Scholar
4. 1. Armstrong CM
   2. Bezanilla F
   3. Rojas E

   (1973) Destruction of sodium conductance inactivation in squid axons perfused with pronase

   The Journal of General Physiology 62:375–391.

   https://doi.org/10.1085/jgp.62.4.375

   • PubMed
   • Google Scholar
5. 1. Baudry M
   2. Bi X

   (2016) Calpain-1 and Calpain-2: the yin and yang of synaptic plasticity and neurodegeneration

   Trends in Neurosciences 39:235–245.

   https://doi.org/10.1016/j.tins.2016.01.007

   • PubMed
   • Google Scholar
6. 1. Bellardita C
   2. Caggiano V
   3. Leiras R
   4. Caldeira V
   5. Fuchs A
   6. Bouvier J
   7. Löw P
   8. Kiehn O

   (2017) Spatiotemporal correlation of spinal network dynamics underlying spasms in chronic spinalized mice

   eLife 6:e23011.

   https://doi.org/10.7554/eLife.23011

   • PubMed
   • Google Scholar
7. 1. Bennett DJ
   2. Li Y
   3. Siu M

   (2001) Plateau potentials in sacrocaudal motoneurons of chronic spinal rats, recorded in vitro

   Journal of Neurophysiology 86:1955–1971.

   https://doi.org/10.1152/jn.2001.86.4.1955

   • PubMed
   • Google Scholar
8. 1. Bos R
   2. Sadlaoud K
   3. Boulenguez P
   4. Buttigieg D
   5. Liabeuf S
   6. Brocard C
   7. Haase G
   8. Bras H
   9. Vinay L

   (2013) Activation of 5-HT2A receptors upregulates the function of the neuronal K-Cl cotransporter KCC2

   PNAS 110:348–353.

   https://doi.org/10.1073/pnas.1213680110

   • PubMed
   • Google Scholar
9. 1. Bougie JK
   2. Cai D
   3. Hastings M
   4. Farah CA
   5. Chen S
   6. Fan X
   7. McCamphill PK
   8. Glanzman DL
   9. Sossin WS

   (2012) Serotonin-induced cleavage of the atypical protein kinase C apl III in Aplysia

   Journal of Neuroscience 32:14630–14640.

   https://doi.org/10.1523/JNEUROSCI.3026-11.2012

   • PubMed
   • Google Scholar
10. 1. Bouhadfane M
    2. Tazerart S
    3. Moqrich A
    4. Vinay L
    5. Brocard F

    (2013) Sodium-mediated plateau potentials in lumbar motoneurons of neonatal rats

    The Journal of Neuroscience 33:15626–15641.

    https://doi.org/10.1523/JNEUROSCI.1483-13.2013

    • PubMed
    • Google Scholar
11. 1. Boulenguez P
    2. Liabeuf S
    3. Bos R
    4. Bras H
    5. Jean-Xavier C
    6. Brocard C
    7. Stil A
    8. Darbon P
    9. Cattaert D
    10. Delpire E
    11. Marsala M
    12. Vinay L

    (2010) Down-regulation of the potassium-chloride cotransporter KCC2 contributes to spasticity after spinal cord injury

    Nature Medicine 16:302–307.

    https://doi.org/10.1038/nm.2107

    • PubMed
    • Google Scholar
12. 1. Brocard F
    2. Clarac F
    3. Vinay L

    (2003) Gravity influences the development of inputs from the brain to lumbar motoneurons in the rat

    NeuroReport 14:1697–1700.

    https://doi.org/10.1097/00001756-200309150-00008

    • PubMed
    • Google Scholar
13. 1. Brocard F
    2. Tazerart S
    3. Vinay L

    (2010) Do pacemakers drive the central pattern generator for locomotion in mammals?

    The Neuroscientist 16:139–155.

    https://doi.org/10.1177/1073858409346339

    • PubMed
    • Google Scholar
14. 1. Brocard F
    2. Shevtsova NA
    3. Bouhadfane M
    4. Tazerart S
    5. Heinemann U
    6. Rybak IA
    7. Vinay L

    (2013) Activity-Dependent changes in extracellular Ca2+ and K+ reveal pacemakers in the spinal Locomotor-Related network

    Neuron 77:1047–1054.

    https://doi.org/10.1016/j.neuron.2013.01.026

    • Google Scholar
15. 1. Brocard C
    2. Plantier V
    3. Boulenguez P
    4. Liabeuf S
    5. Bouhadfane M
    6. Viallat-Lieutaud A
    7. Vinay L
    8. Brocard F

    (2016) Cleavage of na(+) channels by calpain increases persistent na(+) current and promotes spasticity after spinal cord injury

    Nature Medicine 22:404–411.

    https://doi.org/10.1038/nm.4061

    • PubMed
    • Google Scholar
16. 1. Carlin KP
    2. Jones KE
    3. Jiang Z
    4. Jordan LM
    5. Brownstone RM

    (2000) Dendritic L-type calcium currents in mouse spinal motoneurons: implications for bistability

    European Journal of Neuroscience 12:1635–1646.

    https://doi.org/10.1046/j.1460-9568.2000.00055.x

    • PubMed
    • Google Scholar
17. 1. Carlin KP
    2. Bui TV
    3. Dai Y
    4. Brownstone RM

    (2009) Staircase currents in motoneurons: insight into the spatial arrangement of calcium channels in the dendritic tree

    Journal of Neuroscience 29:5343–5353.

    https://doi.org/10.1523/JNEUROSCI.5458-08.2009

    • PubMed
    • Google Scholar
18. 1. Chang KV
    2. WT W
    3. Ozcakar L

    (2018) Intramuscular hemangioma but not adductor muscle strain: ultrasound imaging for an adolescent with posterior proximal thigh pain

    American Journal of Physical Medicine & Rehabilitation 98:e84–e85.

    https://doi.org/10.1097/PHM.0000000000001079

    • Google Scholar
19. 1. Chen B
    2. Li Y
    3. Yu B
    4. Zhang Z
    5. Brommer B
    6. Williams PR
    7. Liu Y
    8. Hegarty SV
    9. Zhou S
    10. Zhu J
    11. Guo H
    12. Lu Y
    13. Zhang Y
    14. Gu X
    15. He Z

    (2018) Reactivation of dormant relay pathways in injured spinal cord by KCC2 manipulations

    Cell 174:1599.

    https://doi.org/10.1016/j.cell.2018.08.050

    • PubMed
    • Google Scholar
20. 1. Clarkson CW

    (1990) Modification of na channel inactivation by alpha-chymotrypsin in single cardiac myocytes

    Pflugers Archiv European Journal of Physiology 417:48–57.

    https://doi.org/10.1007/BF00370768

    • PubMed
    • Google Scholar
21. 1. Corleto JA
    2. Bravo-Hernández M
    3. Kamizato K
    4. Kakinohana O
    5. Santucci C
    6. Navarro MR
    7. Platoshyn O
    8. Cizkova D
    9. Lukacova N
    10. Taylor J
    11. Marsala M

    (2015) Thoracic 9 spinal Transection-Induced model of muscle spasticity in the rat: a systematic electrophysiological and histopathological characterization

    PLOS ONE 10:e0144642.

    https://doi.org/10.1371/journal.pone.0144642

    • PubMed
    • Google Scholar
22. 1. Côté MP
    2. Gandhi S
    3. Zambrotta M
    4. Houlé JD

    (2014) Exercise modulates chloride homeostasis after spinal cord injury

    Journal of Neuroscience 34:8976–8987.

    https://doi.org/10.1523/JNEUROSCI.0678-14.2014

    • PubMed
    • Google Scholar
23. 1. D'Amico JM
    2. Condliffe EG
    3. Martins KJ
    4. Bennett DJ
    5. Gorassini MA

    (2014) Recovery of neuronal and network excitability after spinal cord injury and implications for spasticity

    Frontiers in Integrative Neuroscience 8:36.

    https://doi.org/10.3389/fnint.2014.00036

    • PubMed
    • Google Scholar
24. 1. Du S
    2. Rubin A
    3. Klepper S
    4. Barrett C
    5. Kim YC
    6. Rhim HW
    7. Lee EB
    8. Park CW
    9. Markelonis GJ
    10. Oh TH

    (1999) Calcium influx and activation of calpain I mediate acute reactive gliosis in injured spinal cord

    Experimental Neurology 157:96–105.

    https://doi.org/10.1006/exnr.1999.7041

    • PubMed
    • Google Scholar
25. 1. Duflocq A
    2. Le Bras B
    3. Bullier E
    4. Couraud F
    5. Davenne M

    (2008) Nav1.1 is predominantly expressed in nodes of Ranvier and axon initial segments

    Molecular and Cellular Neuroscience 39:180–192.

    https://doi.org/10.1016/j.mcn.2008.06.008

    • PubMed
    • Google Scholar
26. 1. ElBasiouny SM
    2. Schuster JE
    3. Heckman CJ

    (2010) Persistent inward currents in spinal motoneurons: important for normal function but potentially harmful after spinal cord injury and in amyotrophic lateral sclerosis

    Clinical Neurophysiology 121:1669–1679.

    https://doi.org/10.1016/j.clinph.2009.12.041

    • PubMed
    • Google Scholar
27. 1. Gonoi T
    2. Hille B

    (1987) Gating of na channels. Inactivation modifiers discriminate among models

    The Journal of General Physiology 89:253–274.

    https://doi.org/10.1085/jgp.89.2.253

    • PubMed
    • Google Scholar
28. 1. Gorassini MA

    (2004) Role of motoneurons in the generation of muscle spasms after spinal cord injury

    Brain 127:2247–2258.

    https://doi.org/10.1093/brain/awh243

    • Google Scholar
29. 1. Gramsbergen A
    2. Schwartze P
    3. Prechtl HF

    (1970) The postnatal development of behavioral states in the rat

    Developmental Psychobiology 3:267–280.

    https://doi.org/10.1002/dev.420030407

    • PubMed
    • Google Scholar
30. 1. Grossman RG
    2. Fehlings MG
    3. Frankowski RF
    4. Burau KD
    5. Chow DS
    6. Tator C
    7. Teng A
    8. Toups EG
    9. Harrop JS
    10. Aarabi B
    11. Shaffrey CI
    12. Johnson MM
    13. Harkema SJ
    14. Boakye M
    15. Guest JD
    16. Wilson JR

    (2014) A prospective, multicenter, phase I matched-comparison group trial of safety, pharmacokinetics, and preliminary efficacy of riluzole in patients with traumatic spinal cord injury

    Journal of Neurotrauma 31:239–255.

    https://doi.org/10.1089/neu.2013.2969

    • PubMed
    • Google Scholar
31. 1. Harvey PJ
    2. Li Y
    3. Li X
    4. Bennett DJ

    (2005) Persistent sodium currents and repetitive firing in motoneurons of the sacrocaudal spinal cord of adult rats

    Journal of Neurophysiology 96:141–157.

    https://doi.org/10.1152/jn.00335.2005

    • Google Scholar
32. 1. Harvey PJ
    2. Li X
    3. Li Y
    4. Bennett DJ

    (2006a) Endogenous monoamine receptor activation is essential for enabling persistent sodium currents and repetitive firing in rat spinal motoneurons

    Journal of Neurophysiology 96:1171–1186.

    https://doi.org/10.1152/jn.00341.2006

    • PubMed
    • Google Scholar
33. 1. Harvey PJ
    2. Li X
    3. Li Y
    4. Bennett DJ

    (2006b) 5-HT₂ receptor activation facilitates a persistent sodium current and repetitive firing in spinal motoneurons of rats with and without chronic spinal cord injury

    Journal of Neurophysiology 96:1158–1170.

    https://doi.org/10.1152/jn.01088.2005

    • PubMed
    • Google Scholar
34. 1. Hounsgaard J
    2. Hultborn H
    3. Jespersen B
    4. Kiehn O

    (1984) Intrinsic membrane properties causing a bistable behaviour of alpha-motoneurones

    Experimental Brain Research 55:391–394.

    https://doi.org/10.1007/BF00237290

    • PubMed
    • Google Scholar
35. 1. Hultborn H

    (2003) Changes in neuronal properties and spinal reflexes during development of spasticity following spinal cord lesions and stroke: studies in animal models and patients

    Journal of Rehabilitation Medicine 35:46–55.

    https://doi.org/10.1080/16501960310010142

    • Google Scholar
36. 1. Husch A
    2. Van Patten GN
    3. Hong DN
    4. Scaperotti MM
    5. Cramer N
    6. Harris-Warrick RM

    (2012) Spinal cord injury induces serotonin supersensitivity without increasing intrinsic excitability of mouse V2a interneurons

    Journal of Neuroscience 32:13145–13154.

    https://doi.org/10.1523/JNEUROSCI.2995-12.2012

    • PubMed
    • Google Scholar
37. 1. Jankowska E
    2. Padel Y
    3. Zarzecki P

    (1978) Crossed disynaptic inhibition of sacral motoneurones

    The Journal of Physiology 285:425–444.

    https://doi.org/10.1113/jphysiol.1978.sp012580

    • PubMed
    • Google Scholar
38. 1. Jean-Xavier C
    2. Pflieger JF
    3. Liabeuf S
    4. Vinay L

    (2006) Inhibitory postsynaptic potentials in lumbar motoneurons remain depolarizing after neonatal spinal cord transection in the rat

    Journal of Neurophysiology 96:2274–2281.

    https://doi.org/10.1152/jn.00328.2006

    • PubMed
    • Google Scholar
39. 1. Jiang Z
    2. Rempel J
    3. Li J
    4. Sawchuk MA
    5. Carlin KP
    6. Brownstone RM

    (1999) Development of L-type calcium channels and a nifedipine-sensitive motor activity in the postnatal mouse spinal cord

    European Journal of Neuroscience 11:3481–3487.

    https://doi.org/10.1046/j.1460-9568.1999.00765.x

    • PubMed
    • Google Scholar
40. 1. Jones HC
    2. Keep RF

    (1988) Brain fluid calcium concentration and response to acute hypercalcaemia during development in the rat

    The Journal of Physiology 402:579–593.

    https://doi.org/10.1113/jphysiol.1988.sp017223

    • PubMed
    • Google Scholar
41. 1. Kahle KT
    2. Staley KJ
    3. Nahed BV
    4. Gamba G
    5. Hebert SC
    6. Lifton RP
    7. Mount DB

    (2008) Roles of the cation-chloride cotransporters in neurological disease

    Nature Clinical Practice Neurology 4:490–503.

    https://doi.org/10.1038/ncpneuro0883

    • PubMed
    • Google Scholar
42. 1. Kawamura M
    2. Nakajima W
    3. Ishida A
    4. Ohmura A
    5. Miura S
    6. Takada G

    (2005) Calpain inhibitor MDL 28170 protects hypoxic–ischemic brain injury in neonatal rats by inhibition of both apoptosis and necrosis

    Brain Research 1037:59–69.

    https://doi.org/10.1016/j.brainres.2004.12.050

    • Google Scholar
43. 1. Kitzman PH

    (2009) Effectiveness of riluzole in suppressing spasticity in the spinal cord injured rat

    Neuroscience Letters 455:150–153.

    https://doi.org/10.1016/j.neulet.2009.03.016

    • PubMed
    • Google Scholar
44. 1. Klomjai W
    2. Roche N
    3. Lamy JC
    4. Bede P
    5. Giron A
    6. Bussel B
    7. Bensmail D
    8. Katz R
    9. Lackmy-Vallée A

    (2019) Furosemide unmasks inhibitory dysfunction after spinal cord injury in humans: implications for spasticity

    Journal of Neurotrauma 36:1469–1477.

    https://doi.org/10.1089/neu.2017.5560

    • PubMed
    • Google Scholar
45. 1. Lee HH
    2. Walker JA
    3. Williams JR
    4. Goodier RJ
    5. Payne JA
    6. Moss SJ

    (2007) Direct protein kinase C-dependent phosphorylation regulates the cell surface stability and activity of the potassium chloride cotransporter KCC2

    The Journal of Biological Chemistry 282:29777–29784.

    https://doi.org/10.1074/jbc.M705053200

    • PubMed
    • Google Scholar
46. 1. Li Y
    2. Gorassini MA
    3. Bennett DJ

    (2004) Role of persistent sodium and calcium currents in motoneuron firing and spasticity in chronic spinal rats

    Journal of Neurophysiology 91:767–783.

    https://doi.org/10.1152/jn.00788.2003

    • PubMed
    • Google Scholar
47. 1. Li Y
    2. Bondada V
    3. Joshi A
    4. Geddes JW

    (2009) Calpain 1 and calpastatin expression is developmentally regulated in rat brain

    Experimental Neurology 220:316–319.

    https://doi.org/10.1016/j.expneurol.2009.09.004

    • PubMed
    • Google Scholar
48. 1. Li Y
    2. Bennett DJ

    (2003) Persistent sodium and calcium currents cause plateau potentials in motoneurons of chronic spinal rats

    Journal of Neurophysiology 90:857–869.

    https://doi.org/10.1152/jn.00236.2003

    • PubMed
    • Google Scholar
49. 1. Liabeuf S
    2. Stuhl-Gourmand L
    3. Gackière F
    4. Mancuso R
    5. Sanchez Brualla I
    6. Marino P
    7. Brocard F
    8. Vinay L

    (2017) Prochlorperazine increases KCC2 function and reduces spasticity after spinal cord injury

    Journal of Neurotrauma 34:3397–3406.

    https://doi.org/10.1089/neu.2017.5152

    • PubMed
    • Google Scholar
50. 1. Lin S
    2. Li Y
    3. Lucas-Osma AM
    4. Hari K
    5. Stephens MJ
    6. Singla R
    7. Heckman CJ
    8. Zhang Y
    9. Fouad K
    10. Fenrich KK
    11. Bennett DJ

    (2019) Locomotor-related V3 interneurons initiate and coordinate muscles spasms after spinal cord injury

    Journal of Neurophysiology 121:1352–1367.

    https://doi.org/10.1152/jn.00776.2018

    • PubMed
    • Google Scholar
51. 1. Markgraf CG
    2. Velayo NL
    3. Johnson MP
    4. McCarty DR
    5. Medhi S
    6. Koehl JR
    7. Chmielewski PA
    8. Linnik MD

    (1998) Six-hour window of opportunity for calpain inhibition in focal cerebral ischemia in rats

    Stroke 29:152–158.

    https://doi.org/10.1161/01.STR.29.1.152

    • PubMed
    • Google Scholar
52. 1. Mercado A
    2. Broumand V
    3. Zandi-Nejad K
    4. Enck AH
    5. Mount DB

    (2006) A C-terminal domain in KCC2 confers constitutive K+-Cl- cotransport

    The Journal of Biological Chemistry 281:1016–1026.

    https://doi.org/10.1074/jbc.M509972200

    • PubMed
    • Google Scholar
53. 1. Michailidis IE
    2. Abele-Henckels K
    3. Zhang WK
    4. Lin B
    5. Yu Y
    6. Geyman LS
    7. Ehlers MD
    8. Pnevmatikakis EA
    9. Yang J

    (2014) Age-related homeostatic midchannel proteolysis of neuronal L-type voltage-gated Ca²⁺ channels

    Neuron 82:1045–1057.

    https://doi.org/10.1016/j.neuron.2014.04.017

    • PubMed
    • Google Scholar
54. 1. Mòdol L
    2. Mancuso R
    3. Alé A
    4. Francos-Quijorna I
    5. Navarro X

    (2014) Differential effects on KCC2 expression and spasticity of ALS and traumatic injuries to motoneurons

    Frontiers in Cellular Neuroscience 8:7.

    https://doi.org/10.3389/fncel.2014.00007

    • PubMed
    • Google Scholar
55. 1. Murray KC
    2. Nakae A
    3. Stephens MJ
    4. Rank M
    5. D'Amico J
    6. Harvey PJ
    7. Li X
    8. Harris RL
    9. Ballou EW
    10. Anelli R
    11. Heckman CJ
    12. Mashimo T
    13. Vavrek R
    14. Sanelli L
    15. Gorassini MA
    16. Bennett DJ
    17. Fouad K

    (2010) Recovery of motoneuron and locomotor function after spinal cord injury depends on constitutive activity in 5-HT2C receptors

    Nature Medicine 16:694–700.

    https://doi.org/10.1038/nm.2160

    • PubMed
    • Google Scholar
56. 1. Nicholson C
    2. Bruggencate GT
    3. Steinberg R
    4. Stöckle H

    (1977) Calcium modulation in brain extracellular microenvironment demonstrated with ion-selective micropipette

    PNAS 74:1287–1290.

    https://doi.org/10.1073/pnas.74.3.1287

    • PubMed
    • Google Scholar
57. 1. Nielsen JB
    2. Crone C
    3. Hultborn H

    (2007) The spinal pathophysiology of spasticity--from a basic science point of view

    Acta Physiologica 189:171–180.

    https://doi.org/10.1111/j.1748-1716.2006.01652.x

    • PubMed
    • Google Scholar
58. 1. Onwuli DO
    2. Yañez-Bisbe L
    3. Pinsach-Abuin ML
    4. Tarradas A
    5. Brugada R
    6. Greenman J
    7. Pagans S
    8. Beltran-Alvarez P

    (2017) Do sodium channel proteolytic fragments regulate sodium channel expression?

    Channels 11:476–481.

    https://doi.org/10.1080/19336950.2017.1355663

    • PubMed
    • Google Scholar
59. 1. Puskarjov M
    2. Ahmad F
    3. Kaila K
    4. Blaesse P

    (2012) Activity-dependent cleavage of the K-Cl cotransporter KCC2 mediated by calcium-activated protease calpain

    Journal of Neuroscience 32:11356–11364.

    https://doi.org/10.1523/JNEUROSCI.6265-11.2012

    • PubMed
    • Google Scholar
60. 1. Ritz LA
    2. Bailey SM
    3. Murray CR
    4. Sparkes ML

    (1992) Organizational and morphological features of cat sacrocaudal motoneurons

    The Journal of Comparative Neurology 318:209–221.

    https://doi.org/10.1002/cne.903180206

    • PubMed
    • Google Scholar
61. 1. Ritz LA
    2. Murray CR
    3. Foli K

    (2001) Crossed and uncrossed projections to the cat sacrocaudal spinal cord: iii. axons expressing calcitonin gene-related peptide immunoreactivity

    The Journal of Comparative Neurology 438:388–398.

    https://doi.org/10.1002/cne.1322

    • PubMed
    • Google Scholar
62. 1. Rosker C
    2. Lohberger B
    3. Hofer D
    4. Steinecker B
    5. Quasthoff S
    6. Schreibmayer W

    (2007) The TTX metabolite 4,9-anhydro-TTX is a highly specific blocker of the Na_v1.6 voltage-dependent sodium channel

    American Journal of Physiology-Cell Physiology 293:C783–C789.

    https://doi.org/10.1152/ajpcell.00070.2007

    • PubMed
    • Google Scholar
63. 1. Schumacher PA
    2. Eubanks JH
    3. Fehlings MG

    (1999) Increased calpain I-mediated proteolysis, and preferential loss of dephosphorylated NF200, following traumatic spinal cord injury

    Neuroscience 91:733–744.

    https://doi.org/10.1016/S0306-4522(98)00552-1

    • PubMed
    • Google Scholar
64. 1. Sprague CR
    2. Fraley TS
    3. Jang HS
    4. Lal S
    5. Greenwood JA

    (2008) Phosphoinositide binding to the substrate regulates susceptibility to proteolysis by calpain

    Journal of Biological Chemistry 283:9217–9223.

    https://doi.org/10.1074/jbc.M707436200

    • PubMed
    • Google Scholar
65. 1. Springer JE
    2. Azbill RD
    3. Kennedy SE
    4. George J
    5. Geddes JW

    (1997) Rapid calpain I activation and cytoskeletal protein degradation following traumatic spinal cord injury: attenuation with riluzole pretreatment

    Journal of Neurochemistry 69:1592–1600.

    https://doi.org/10.1046/j.1471-4159.1997.69041592.x

    • PubMed
    • Google Scholar
66. 1. Stil A
    2. Liabeuf S
    3. Jean-Xavier C
    4. Brocard C
    5. Viemari JC
    6. Vinay L

    (2009) Developmental up-regulation of the potassium-chloride cotransporter type 2 in the rat lumbar spinal cord

    Neuroscience 164:809–821.

    https://doi.org/10.1016/j.neuroscience.2009.08.035

    • PubMed
    • Google Scholar
67. 1. Tazerart S
    2. Viemari JC
    3. Darbon P
    4. Vinay L
    5. Brocard F

    (2007) Contribution of persistent sodium current to locomotor pattern generation in neonatal rats

    Journal of Neurophysiology 98:613–628.

    https://doi.org/10.1152/jn.00316.2007

    • PubMed
    • Google Scholar
68. 1. Tazerart S
    2. Vinay L
    3. Brocard F

    (2008) The persistent sodium current generates pacemaker activities in the central pattern generator for locomotion and regulates the locomotor rhythm

    Journal of Neuroscience 28:8577–8589.

    https://doi.org/10.1523/JNEUROSCI.1437-08.2008

    • PubMed
    • Google Scholar
69. 1. Theiss RD
    2. Hornby TG
    3. Rymer WZ
    4. Schmit BD

    (2011) Riluzole decreases flexion withdrawal reflex but not voluntary ankle torque in human chronic spinal cord injury

    Journal of Neurophysiology 105:2781–2790.

    https://doi.org/10.1152/jn.00570.2010

    • PubMed
    • Google Scholar
70. 1. Thomas CK
    2. Bakels R
    3. Klein CS
    4. Zijdewind I

    (2014) Human spinal cord injury: motor unit properties and behaviour

    Acta Physiologica 210:5–19.

    https://doi.org/10.1111/apha.12153

    • PubMed
    • Google Scholar
71. 1. Thompson SN
    2. Carrico KM
    3. Mustafa AG
    4. Bains M
    5. Hall ED

    (2010) A pharmacological analysis of the neuroprotective efficacy of the brain- and cell-permeable calpain inhibitor MDL-28170 in the mouse controlled cortical impact traumatic brain injury model

    Journal of Neurotrauma 27:2233–2243.

    https://doi.org/10.1089/neu.2010.1474

    • PubMed
    • Google Scholar
72. 1. Ueno T
    2. Okabe A
    3. Akaike N
    4. Fukuda A
    5. Nabekura J

    (2002) Diversity of neuron-specific K⁺-Cl- cotransporter expression and inhibitory postsynaptic potential depression in rat motoneurons

    The Journal of Biological Chemistry 277:4945–4950.

    https://doi.org/10.1074/jbc.M109439200

    • PubMed
    • Google Scholar
73. 1. Veeramah KR
    2. O'Brien JE
    3. Meisler MH
    4. Cheng X
    5. Dib-Hajj SD
    6. Waxman SG
    7. Talwar D
    8. Girirajan S
    9. Eichler EE
    10. Restifo LL
    11. Erickson RP
    12. Hammer MF

    (2012) De novo pathogenic SCN8A mutation identified by whole-genome sequencing of a family quartet affected by infantile epileptic encephalopathy and SUDEP

    The American Journal of Human Genetics 90:502–510.

    https://doi.org/10.1016/j.ajhg.2012.01.006

    • PubMed
    • Google Scholar
74. 1. Venugopal S
    2. Hamm TM
    3. Crook SM
    4. Jung R

    (2011) Modulation of inhibitory strength and kinetics facilitates regulation of persistent inward currents and motoneuron excitability following spinal cord injury

    Journal of Neurophysiology 106:2167–2179.

    https://doi.org/10.1152/jn.00359.2011

    • PubMed
    • Google Scholar
75. 1. Vinay L
    2. Brocard F
    3. Pflieger JF
    4. Simeoni-Alias J
    5. Clarac F

    (2000) Perinatal development of lumbar motoneurons and their inputs in the rat

    Brain Research Bulletin 53:635–647.

    https://doi.org/10.1016/S0361-9230(00)00397-X

    • PubMed
    • Google Scholar
76. 1. von Reyn CR
    2. Spaethling JM
    3. Mesfin MN
    4. Ma M
    5. Neumar RW
    6. Smith DH
    7. Siman R
    8. Meaney DF

    (2009) Calpain mediates proteolysis of the voltage-gated sodium channel alpha-subunit

    Journal of Neuroscience 29:10350–10356.

    https://doi.org/10.1523/JNEUROSCI.2339-09.2009

    • PubMed
    • Google Scholar
77. 1. Wan L
    2. Ren L
    3. Chen L
    4. Wang G
    5. Liu X
    6. Wang BH
    7. Wang Y

    (2018) M-Calpain activation facilitates seizure induced KCC2 down regulation

    Frontiers in Molecular Neuroscience 11:287.

    https://doi.org/10.3389/fnmol.2018.00287

    • PubMed
    • Google Scholar
78. 1. Wang Y
    2. Liu Y
    3. Lopez D
    4. Lee M
    5. Dayal S
    6. Hurtado A
    7. Bi X
    8. Baudry M

    (2018) Protection against TBI-Induced neuronal death with Post-Treatment with a selective Calpain-2 inhibitor in mice

    Journal of Neurotrauma 35:105–117.

    https://doi.org/10.1089/neu.2017.5024

    • PubMed
    • Google Scholar
79. 1. Winslow J
    2. Dididze M
    3. Thomas CK

    (2009) Automatic classification of motor unit potentials in surface EMG recorded from thenar muscles paralyzed by spinal cord injury

    Journal of Neuroscience Methods 185:165–177.

    https://doi.org/10.1016/j.jneumeth.2009.09.012

    • PubMed
    • Google Scholar
80. 1. Yang J
    2. Weimer RM
    3. Kallop D
    4. Olsen O
    5. Wu Z
    6. Renier N
    7. Uryu K
    8. Tessier-Lavigne M

    (2013) Regulation of axon degeneration after injury and in development by the endogenous calpain inhibitor calpastatin

    Neuron 80:1175–1189.

    https://doi.org/10.1016/j.neuron.2013.08.034

    • PubMed
    • Google Scholar
81. 1. Yu CG
    2. Li Y
    3. Raza K
    4. Yu XX
    5. Ghoshal S
    6. Geddes JW

    (2013) Calpain 1 knockdown improves tissue sparing and functional outcomes after spinal cord injury in rats

    Journal of Neurotrauma 30:427–433.

    https://doi.org/10.1089/neu.2012.2561

    • PubMed
    • Google Scholar
82. 1. Zhou HY
    2. Chen SR
    3. Byun HS
    4. Chen H
    5. Li L
    6. Han HD
    7. Lopez-Berestein G
    8. Sood AK
    9. Pan HL

    (2012) N-methyl-D-aspartate receptor- and calpain-mediated proteolytic cleavage of K⁺-Cl- cotransporter-2 impairs spinal chloride homeostasis in neuropathic pain

    The Journal of Biological Chemistry 287:33853–33864.

    https://doi.org/10.1074/jbc.M112.395830

    • PubMed
    • Google Scholar
83. 1. Zijdewind I
    2. Thomas CK

    (2012) Firing patterns of spontaneously active motor units in spinal cord-injured subjects

    The Journal of Physiology 590:1683–1697.

    https://doi.org/10.1113/jphysiol.2011.220103

    • PubMed
    • Google Scholar

Author details

1. Vanessa Plantier

   Institut de Neurosciences de la Timone (UMR7289), Aix-Marseille Université and CNRS, Marseille, France

   Contribution

   Data curation, Formal analysis, Validation, Investigation, Performed and analyzed most of in vitro and in vivo experiments

   Contributed equally with

   Irene Sanchez-Brualla

   Competing interests

   No competing interests declared

2. Irene Sanchez-Brualla

   Institut de Neurosciences de la Timone (UMR7289), Aix-Marseille Université and CNRS, Marseille, France

   Contribution

   Data curation, Formal analysis, Validation, Investigation, Methodology, Performed and analyzed most of in vitro and in vivo experiments

   Contributed equally with

   Vanessa Plantier

   Competing interests

   No competing interests declared

3. Nejada Dingu

   Institut de Neurosciences de la Timone (UMR7289), Aix-Marseille Université and CNRS, Marseille, France

   Contribution

   Data curation, Formal analysis, Investigation, Methodology, Performed and analyzed some in vitro experiments

   Competing interests

   No competing interests declared

4. Cécile Brocard

   Institut de Neurosciences de la Timone (UMR7289), Aix-Marseille Université and CNRS, Marseille, France

   Contribution

   Data curation, Formal analysis, Investigation, Methodology, Performed and analyzed most of biochemistry and immunohistochemistry experiments

   Competing interests

   No competing interests declared

5. Sylvie Liabeuf

   Institut de Neurosciences de la Timone (UMR7289), Aix-Marseille Université and CNRS, Marseille, France

   Contribution

   Formal analysis, Methodology, Performed some biochemistry experiments

   Competing interests

   No competing interests declared

6. Florian Gackière

   Institut de Neurosciences de la Timone (UMR7289), Aix-Marseille Université and CNRS, Marseille, France

   Contribution

   Data curation, Formal analysis, Methodology, Performed and analyzed most of intracellular recordings

   Competing interests

   No competing interests declared

7. Frédéric Brocard

   Institut de Neurosciences de la Timone (UMR7289), Aix-Marseille Université and CNRS, Marseille, France

   Contribution

   Conceptualization, Formal analysis, Supervision, Funding acquisition, Validation, Investigation, Visualization, Methodology, Project administration, Designed, supervised the whole project, performed and analyzed some in vitro experiments and wrote the manuscript

   For correspondence

   frederic.brocard@univ-amu.fr

   Competing interests

   No competing interests declared

   "This ORCID iD identifies the author of this article:" 0000-0001-9444-9586

• 1,428

  views

• 225

  downloads

• 20

  citations

Views, downloads and citations are aggregated across all versions of this paper published by eLife.