Fig. 6

Tracer efflux from the grey and white matter follow similar pathways. Qualitative analysis of redistributed fluorescent ovalbumin (AFO-647) after injection into the spinal interstitium. a, b The spinal grey matter was cannulated by a fine needle (at approximately C8). Inert fluorescent microspheres (marked by red arrow) combined with the AFO-647 tracer confirmed the injection point. After grey matter injections, there was radial redistribution of tracer locally into the surrounding white matter and into the contralateral hemicord. There was selective concentration of tracer around radially projecting blood vessels (up arrow) that end ultimately on the pial surface. Extramedullary vessels, such as the anterior spinal artery (left arrowhead) were also labelled by tracer. c, d Three spinal levels rostral to the white matter injection site (approximately C5), tracer was found circumferentially on the pial surface (right arrow) and around penetrating radial blood vessels (left arrow). Note that subpial tracer was absent. e After white matter injections (location marked by red arrow), there was local radial spread of tracer into the grey matter and nearby subpial white matter. Less of the contralateral hemicord was involved. There was accumulation of tracer around radially projecting blood vessels (right arrowhead). f Just caudal to the white matter injection site (approximately T1), intramedullary tracer signal was delimited by the lateral white matter tracts (up arrow). d, f Note AFO-647 tracer deposition around the central canal (*) rostral and caudal to the injection site. This pattern of tracer distribution is highly suggestive of interstitially injected AFO-647 effluxing into the subarachnoid space, redistributing rostrocaudally and re-entering the cord parenchyma via perivascular spaces. Smooth muscle cells were labelled with SMA, endothelial cells by RECA-1