TEMPERATURE COMPENSATION AND TEMPERATURE ENTRAINMENT OF THE CHICK PINEAL CELL CIRCADIAN CLOCK

We have used an in vitro model system of the circadian clock, disperse d chick pineal cells, to examine the effects of temperature on the cir cadian clock of a homeotherm. This preparation enabled us to isolate a circadian clock from in vivo homeostatic temperature regulation and e xpose cells to both constant temperatures and abrupt temperature chang es. By manipulating the temperature of the pineal cells, we have demon strated that (1) the circadian clock compensates its period for temper ature changes over the range of 34-40 degrees C; Q(10) = 0.83, a value within the range of Q(10) values measured for poikilothermic circadia n clocks; (2) temperature pulses (42 degrees C, 6 hr duration) shift t he phase (advance and delay) of the circadian rhythm in a phase-depend ent manner; and (3) a temperature cycle (18 hr at 37 degrees C, 6 hr a t 42 degrees C) will entrain the circadian clock in vitro, This is the first demonstration of temperature entrainment of the circadian clock of a homeotherm in vitro. In addition we have found that temperature directly influences the synthesis and release of melatonin, the primar y hormonal product of the pineal gland. The biosynthesis of melatonin is strongly temperature dependent with a Q(10) > 11 when melatonin rel ease is measured at ambient temperatures between 31 degrees C and 40 d egrees C. In contrast, 6 hr 42 degrees C temperature pulses acutely in hibit melatonin release in a manner similar to that seen previously wi th light pulses. These results demonstrate that a circadian clock from a homeothermic vertebrate is temperature compensated, yet temperature cycles can entrain the circadian melatonin rhythm. Thus, the chick pi neal circadian oscillator has retained all the fundamental properties of circadian rhythms.