Uniform Daily Rotation and Biological Rhythms and Clocks in Hamsters

Abstract

The mean forms of 24-h circadian patterns of 12 male hamsters differed as a function of the clock hour of dark onsets in 24 h (12:12) light-dark cycles, independently of time of year. The forms of activity cycles for dark onset at 18:00 CST for three 3-mo periods, at three different times of year and including the first and third years, were strikingly similar to one another and moderately similar to cycles with dark onset at noon but were significantly different from cycles with dark onset at hours 24:00 and 6:00. The latter two were also different from one another. A very high correlation is seen for all series, between concurrent-cycle forms obtained on a stationary table and on tables rotating uniformly clockwise (CW) and counterclockwise (CCW) at 1 rpd. Uniform daily CW and CCW rotations (from above) effect a small phase delay in circadian cycles phase synchronized to imposed 12:12 light/dark (LD) cycles set to various times of day. A major minimum occurs during the first hours of darkness, a major m...