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 maximum during the later hours of darkness. The CW rotation exerts a greater effect than CCW during the darkened portion of the subjective day and a lesser effect during the illuminated portion. The two directions of rotation yield, simultaneously, similar 24-h patterns of effect related to hour of solar day (CST). These are independent of phase of light-synchronized cycles or of free-running cycles. Differences between effects of CCW and CW rotations strongly suggest a bimodal 24-h pattern with CCW exceeding CW effects twice a day over sunrise and sunset. A mean lunar day (24.8-h) cycle was disclosed. The pattern, grossly unimodal, has a range about 14% of the daily mean with maximum lying between moonrise and upper transit and minimum between moonset and lower transit. The CW rotation reduces the amplitude of the cycle and CCW rotation completely inverts it. A synodic monthly cycle was described. Rotation tended to produce cycle inversion, CCW rotation weakly and CW strongly. An annual variation in effect of rotation is described. Statistically significant cycles in the response to rotation were described for each of the geophysical periods. These cycles are postulated to comprise phase-response variations to a pervasive atmospheric parameter such as the atmospheric electromagnetic field. Possibilities for these specialized responsivenesses to very weak, pervasive, atmospheric fields serving as the primary timers for the biological clock complex are suggested and discussed.