69CC-contacting RG may generate changes in this cellular compartment with major
functional consequences (Fig. 5.6).Whether the increase in Ca2+ induced by P2X7
receptor activation is beneficial by awakening the “dormant” progenitors in the
ependyma or detrimental by activation of caspases inducing apoptosis (Gandelman
et al. 2013 ) is a key question to solve in future studies.
5.8 A Perspective: The Ependyma as a Source of Plasticity
for Spinal Cord Repair
Anamniotes like cyclostomes (Rovainen 1976 ; Wood and Cohen 1979 ; Armstrong
et al. 2003 ; Shifman et al. 2007 ), certain fish (Hooker 1932 ; Coggeshall and
Youngblood 1983 ; Dervan and Roberts 2003 ; Takeda et al. 2007 ; Reimer et al.
2008 ), anuran larvae (Michel and Reier 1979 ; Beattie et al. 1997 ; Gibbs and Szaro
2006 ) and tailed amphibians (Piatt and Piatt 1958 ; Sims 1962 ; Butler and Ward
1965 ; Davis et al. 1990 ; Chevallier et al. 2004 ; McHedlishvili et al. 2007 ) have
remarkable endogenous mechanisms of regeneration that lead to functional recov-
ery after spinal cord injury (Diaz Queiroz and Echeverri 2013 ; Lee-Liu et al. 2013 ).
We have shown that this ability is partly shared by the fresh-water turtle Trachemys
dorbignyi, an amniote vertebrate. Turtles spontaneously reconnect their transected
spinal cord with the formation of a cellular bridge that serves as a permissive scaf-
fold for regenerating axons (Rehermann et al. 2009 ). This is in sharp contrast to
Fig. 5.5 ATP signaling in the CC. (a) RG in the dorsal pole of the CC filled with Fluo-4 before
( 1 ), during ( 2 ) and after ( 3 , 4 ) application of BzATP (1 s, 1 mM) on the apical process that contacts
the CC. The cell morphology is shown in the inset in 6. The arrowheads indicate the sequence of
Ca2+ increase along the cell. (b) ΔF/F0 analysis of ROIs in A1 (open circles) shows the time course
of (Ca2+)i increase after BzATP application. (c) Time lapse imaging of an ependymocyte filled with
Fluo-4 in the lateral domain of the CC (inset in 1 ) before ( 1 ), during ( 2 ) and after ( 3 , 4 ) application
of BzATP (1 mM). (d) ΔF/F0 in the ROI (circle in A1) and the simultaneous inward current (black
trace) generated by BzATP. (a) and (b), pseudocolor images in a living slice. Modified with per-
mission from Purinergic Signalling (Marichal et al. 2009 )
5 Spinal Cord Stem Cells In Their Microenvironment: The Ependyma as a Stem Cell...