Fig. 6

Tracer delivered into the spinal cord parenchyma accumulated around ependymal and extramedullary structures. Fluorescent (a) and confocal (b) micrographs demonstrating tracer accumulation in the central canal. Note the presence of tracer within the lumen in b (12 o’clock position). c Confocal microscopy of central canal in another experiment. The ependymal cells were heterogeneously delineated by fluorescence, with the noted absence of nuclear tracer signal. In both b and c, the apical ends displayed greater tracer intensity compared to the basal surface. d, e Tracer deposition around the arterial vasocorona (arrow heads, note RECA-1 and SMA positivity) of the dorsal spinal cord surface. f Confocal microscopy view of the same arterial vasocorona demonstrating the characteristic “peri-arterial” and “para-arterial” distribution of the tracer (arrow heads) with respect to the tunica media (asterisk) and endothelium (arrow). The absence of subpial tracer signal excludes the possibility of contiguous tracer spread from injection site to artery. The arterial vasocorona could be the dominant pathway for fluid outflow from the white matter. g Fluid outflow appeared to involve all vascular structures. Confocal microscopy of grey matter showing arteriolar (arrow head), venular (asterisk) and capillary (arrow) labelling by tracer. Note the “paravascular” location of tracer in venules and capillaries. h, i Fluorescent microscopy of grey matter injection demonstrating conduction of tracer along the central branch of the anterior spinal artery towards the ventral median fissure. This suggests drainage of interstitial fluid towards the pial surface via vascular structures. All fluorescent and confocal photomicrographs were taken at ×20 and ×63 magnification respectively