The original work using this transgenic rat was published in Science (Yamazaki et al. 2000). This transgenic rat was generated in the Wistar outbred strain (Charles River, Japan). We maintained the L1 line. The transgenic rat was generated using a DNA construct in which the mouse Period1 promoter drives firefly luciferase
The circadian rhythm in Per1 transcription is easily monitored from tissue explants (Yamazaki and Takahashi 2005). This particular strain expresses photoperiodic responses in both testicular size and body weight (Pendergast and Yamazaki unpublished data), therefore it is useful for studying the involvement of circadian rhythms in photoperiodic time measurement.
Breeding is possible in 12 h light: 12 h dark condition, but it may take more than two months for females to deliver pups after breeding pairs are set up. In addition, the litter sizes are relatively small (typically 3 to 8 pups). Breeding in a long day photoperiod (14:10 or 16:8) is recommended.