65Reali et al. 2011 ) and the fact that CSFcNs receive functional GABAergic contacts
(Russo et al. 2004 ) suggest that there is an active GABAergic signaling in this stem
cell niche. Indeed, functional studies in turtles (Reali et al. 2011 ) have shown that in
clusters of gap junction coupled BLBP+ progenitors lining the CC (Fig. 5.3a),
GABA generates currents with components mediated by GABA transporters (GAT,
Fig. 5.3b1–3) and GABAA receptors (Fig. 5.3c1–3). Uncoupling BLBP+ progeni-
tors with carbenoxolone suggests that individual progenitors react differently to
GABA with various combinations of GABA transporter- and ionic- induced cur-
rents. GABA also depolarizes ependymal cells of the spinal cord of juvenile rats
(Corns et al. 2013 ), suggesting that GABAergic signaling on CC-contacting pro-
genitors is a phylogenetically preserved trait.
CSFcNs in close contact with ependymal cells also have functional GABAA
receptors (Russo et al. 2004 ; Marichal et al. 2009 ; Reali et al. 2011 ). Gramicidin
perforated patch recordings showed that GABAA receptor activation generate
Fig. 5.2 GABA around the central canal (CC). (a) Immunohistochemistry for GAD-65/67 (red)
and brain lipid binding protein (BLBP, green) reveals a plexus of GAD+ terminals surrounding the
CC. A few CC-contacting cells on the dorso-lateral aspect of the CC are reactive for GAD (arrow-
heads). Many GAD+ terminals are in close apposition with either proximal (upper inset, arrows)
or distal (lower inset, arrow) processes of BLBP+ cells. (b) In contrast to GAD expression, the CC
is surrounded by a large number of cells containing GABA ( 1 ) which co-express HuC/D ( 2 and 3 ).
Main panel in A and B are confocal optical sections. Upper and lower insets are stacks of ten opti-
cal sections. Scale bars: (a), main panel 20 μm, upper and lower insets, 10 μm; (b), 10 μm. Modified
with permission from The Journal of Physiology (Reali et al. 2011 )
5 Spinal Cord Stem Cells In Their Microenvironment: The Ependyma as a Stem Cell...