Description
Wistar rats, purchased from BRL (Fullinsdorf/BL, Switzerland), and WBN/Kob rats, purchased from SLC Inc. (Shizuoka, Japan), were specific pathogen-free. Rats were housed in groups of maximally 4 instandard cages (1,820 cm2 bottom area) and kept in our animal facility for various time periods between 1 week and 36 weeks (free access to standard rat chow and water; specific pathogen-free conditions; 20 degree C; day/night cycle simulated by artificial lighting of 50 lx from 7 a.m. to 7 p.m., dimmed in the remaining hours to almost complete darkness; air humidity 50 to 60%). Prior to surgery or sacrifice, the rats were fasted overnight (16 to18 h) with free access to water. All manipulations conformed with the Swiss Federal Guidelines on Animal Experiments and were approved by the local ethics committee.