WHAT DOES CHANGING THE TEMPERATURE DO TO THE MELATONIN RHYTHM IN CULTURED CHICK PINEAL CELLS

Chick pineal cells in static culture display a persistent, photosensit ive circadian rhythm of melatonin production and release. We previousl y described the effects of light, the major physiological regulator of circadian rhythms, on the amplitude, period, and phase of the melaton in rhythm. Here we describe the effects of temperature, another physio logical regulator of circadian rhythms, on the amplitude, period, and phase of this rhythm. Maintaining cells at 40.0-43.3 degrees C (104-11 O degrees F) instead of 36.7 degrees C (98 degrees F) doubled the ampl itude of the melatonin rhythm. In contrast, amplitude was reduced by a bout half at 33.3 degrees C (92 degrees F), and at 46.7 degrees C (116 degrees F) melatonin production was stopped within a few hours. Altho ugh temperatures of 40.0-43.3 degrees C raised melatonin output (unlik e light, which suppresses it), they lengthened the period of the rhyth m (as does constant light). Exposure of cells to 8-h pulses of these t emperatures (40.0-43.3 degrees C) induced both phase delays and phase advances of the rhythm in subsequent cycles, with a phase dependence s imilar to that for the phase shifts induced by light pulses. Pulses of 40.0-43.3 degrees C were, however, weaker in their phase-shifting eff ects than light pulses. Pulses at still higher temperatures (46.7 degr ees C) markedly inhibited melatonin output and delayed or disrupted th e rhythm. The relationships (physiological and mechanistic) between th e effects of temperature and light on the melatonin rhythm remain to b e determined.