MULTIPLE CIRCADIAN OSCILLATORS IN THE PHOTOSENSITIVE PIKE PINEAL-GLAND - A STUDY USING ORGAN AND CELL-CULTURE

The fish pineal organ contains typical and, in some species, modified photoreceptor cells involved in the photoperiodic control of melatonin production. In the majority of species studied, the rhythm in melaton in production is driven by an intra-pineal circadian oscillator synchr onized by the light:dark cycle. In the present study, it is shown that the endogenous rhythm in melatonin release of superfused pike pineals maintained under constant darkness is expressed at temperatures of 19 degrees C, 20 degrees C, 25 degrees C, and 30 degrees C (period > 24 hr), but not at temperatures of 10 degrees C and 15 degrees C. Under c onstant darkness, pineal fractions containing either typical photorece ptors, modified photoreceptors, or both behaved like total organs. Dis sociated pike pineal cells, cultured statically at 20 degrees C, expre ssed a high amplitude rhythm in melatonin secretion under a light:dark cycle. Under constant darkness, circadian oscillations, which appeare d better sustained than in organ culture, were also observed. This stu dy provides the first evidence that the rhythmic production of melaton in, by a fish pineal, is driven by a population of circadian oscillato rs or clocks. It is hypothesized that each typical and modified photor eceptor might be the locus of a circadian clock. Damping of the overal l rhythm under constant darkness might reflect the desynchronization ( uncoupling) between these clocks and/or damping of individual oscillat ors.