Morphometric analysis of effects of spinal cord transection

After spinal cord transection in the rat, endothelial reactivity to horseradish peroxidase (HRP) was quantified at the ultrastructural level. The ratio of the area of labeled endothelial vesicles to area of endothelium (pinocytotic index) was established using morphometric techniques. From 3 h through 7 days the pinocytotic index was significantly elevated as far as 10 mm distal to the transection site. Correlating these findings with a previously established blood vessel classification model, the tracer uptake was identified as both a pinocytotic and vesicular transport mechanism. The latter was associated with an acute response lasting as long as 1 day after transection. Thereafter, the barrier appeared to reestablish its selectivity and only pinocytotic uptake of HRP was apparent.