Fig. 6

Tracer inflow into the spinal cord occurs via perivascular and transpial routes. A After injection into the cisterna magna in a spontaneous breathing rat, fluorescent ovalbumin (AFO-647) appeared to cross the pia circumferentially, diffusing into the spinal interstitium (left pointing arrow). Perivascular labelling was also prominent (right pointing arrowhead) with notable intramedullary penetration, towards the central canal (*). Note the deposition of AFO-647 tracer around the anterior spinal artery and the central branches distal to the ventral median sulcus (left arrowhead and right arrow respectively). B–D Tracer colocalised with both arterioles (up arrow) and venules (right arrowhead), confirmed with immunofluorescent stains for smooth muscle actin (B), and an endothelial cell marker (RECA-1) (C). The merged fluorescent channel is shown in D. In a mechanically ventilated control rat at C2 (E), there was reduced tracer signal across the whole axial section. Transpial fluorescence was conspicuously reduced, although perivascular deposition was still present