A: A phase-contrast photomicrograph of a cultured SCN slice on the MED probe after 14d in culture. (MED-P210A, 100μm inter-polar distance) Scale bar, 150μm

B: Representative circadian firing rhythms of SCN neurons from Clock mutant and wild-type mice in slice cultures.

The firing rhythm was expressed in a histogram of the mean firing rate every 15min. and double- plotted. The numbers in the right margin of the first lane in each panel were the scales of firing rate. The circadian periods of these firing rhythms were 28.1h (left) and 28.0h (right) for Clock/Clock, 25.3h and 24.5h for Clock/+, and 23.3h and 23.8h for +/+ neurons, respectively.