Wallac wizard automatic gamma counter

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)}.

The present study includes data obtained from a total of 50 animals. Four animals (body weight 227 ± 10 g) for each time point were injected intravenously into a tail vein or subcutaneously with approximately 0.3 MBq (0.8 µCi) [⁶⁴Cu]Cu-NOTA-HsTX1[R14A] conjugate in 0.5 mL electrolyte solution E-153 (Serumwerk Bernburg, Germany). Animals were euthanised at 5, 60, 240, 1440 and 2880 min post-injection. Blood and the major organs were collected, weighed, and counted in a cross-calibrated γ-counter (Isomed 1000, Isomed GmbH, Dresden) and Wallac WIZARD Automatic Gamma Counter (PerkinElmer, Germany). The radioactivity of the tissue samples was decay-corrected and calibrated by comparing the counts in tissue with the counts in aliquots of the injected radiotracer that had been measured in the γ-counter at the same time. The activity in the selected organs was expressed as percent-injected dose per organ (% ID) and the activity concentration in tissues and organs as standardised uptake value (SUV). Values are quoted as mean ± standard error of mean (SEM) for each group of four animals.