In Vivo PET, Dose–Response, and Receptor Occupancy Studies

All animal studies were conducted in accordance with the ARRIVE guidelines and the local animal protection law, with the further approval of the cantonal veterinary office in Zurich, Switzerland.

Wistar rats were purchased from Charles River and kept in a room with controlled temperature (21°C) under a 12-h light/12-h dark cycle, with ad libitum access to food and water. The animals were allowed to acclimatize for 1 wk before the start of the experiments. The animals were anesthetized with isoflurane and scanned in a PET/CT scanner (Super Argus; Sedecal) for 60 min on tail-vein injection of either (R)- or (S)-¹¹C-Me-NB1 (28–37 MBq, 0.5–2.3 nmol/kg). PET scans were followed by CT for anatomic orientation.

For dose–response and receptor occupancy studies, eliprodil (0.002, 0.006, 0.02, and 2 mg/kg) and CP101,606 (0.3, 1, 3, and 10 mg/kg) in an aqueous vehicle (pH 7.0) consisting of glucose (5%), NaCl (0.45%), and citric acid (1 mM) for eliprodil and saline for CP101,606, respectively, were injected shortly before tracer administration. For the CP101,606 scans, the blocker was further infused during the 60-min PET scan with the protocol (0.4, 1.3, 4, and 13.3 mg/kg/h) illustrated in Supplemental Figure 8 (supplemental materials are available at http://jnm.snmjournals.org). For baseline scans, the vehicle was injected shortly before tracer administration and further infused in the control animals of the CP101,606 study.

Data were reconstructed in user-defined time frames with a voxel size of 0.3875 × 0.3875 × 0.775 mm as previously described by our group (14). Time–activity curves were calculated by PMOD, version 3.7 (PMOD Technologies), with predefined regions of interest as previously reported (14). Results are presented as SUVs, indicating the decay-corrected radioactivity per cm³ divided by the injected dose per gram of body weight. Receptor occupancy was calculated as indicated in Supplemental Figure 8B.