Table 3.

Calculated approximate diffusion distance of dextran and sucrose in short experiments

	30 s (μm)	5 min (μm)	5 min diffusion distance/E19 cortex thickness (%)	5 min diffusion distance/Adult cortex thickness (%)
Sucrose	205	648	88%	30%
Dextran	20	62	×	3%

Distances calculated as described in text. Thickness of cortex in E19 and adult rats provided in Additional file 1: Table S3. × indicates that the route into the brain is restricted against 70 kDa dextran in E19 due to strap junctions [10]