In Vivo Brain Penetration of Peptides

In order to determine whether the peptide could enter the brain, in vivo multiple time regression (MTR) analysis was performed. ICR-CD-1 mice were anesthetized intraperitoneally using a 40% urethane solution (3 g/kg). Then, the jugular vein and carotid artery were isolated and 200 µL of the radiolabeled peptide solution, diluted to 30,000 cpm/µL using Lactated Ringer’s solution containing 1% of BSA (LR/BSA), was injected into the jugular vein. At specified time points after injection (i.e. 1, 3, 5, 10, 12.5 and 15 min, with start and end in duplicate), blood was obtained from the carotid artery followed by decapitation of the mouse. The isolated brain was weighed and radioactivity measured in a gamma counter for 5 min (Wallac Wizard automatic gamma counter, Perkin Elmer, Shelton, CT, USA), as well as from 50 µL serum, which was obtained by centrifuging the collected blood at 10,000g for 15 min at 21 °C. The linear and biphasic modeling of the multiple time regression analysis was performed as previously described^{14 (link)}.