Figure 2

The percentage of radioactivity remaining in the entire system of frozen brain, blood, CSF, and meninges over time following either intraventricular or intraparenchymal infusion of ¹²⁵I-IGF-1. There were 4–5 experiments per mean and time for the intraventricular infusions but only 2–3 for the intraparenchymal ones, which were accidental and not intended. Data are shown as mean ± SD. The initial phase dominated the first 30 min of clearance and accounted for most of the loss from the system for both sets of infusion data. From 45 min onward, virtually no radioactivity was lost from the system with the intraparenchymal infusion, whereas ¹²⁵I-activity declined very slowly with intraventricular infusion (40% decline from 45 to 180 min).