MULTIOSCILLATORY CIRCADIAN ORGANIZATION IN A VERTEBRATE, IGUANA-IGUANA

The lizard Iguana iguana when kept in constant ambient temperature dis plays endogenously generated circadian rhythms of body temperature and locomotor activity. Although surgical removal of the parietal eye has only slight effects on overt circadian rhythmicity, subsequent pineal ectomy completely abolishes the rhythm of body temperature. However, t he rhythm of locomotor activity is only slightly affected by parieta l ectomy plus pinealectomy. Our results demonstrate that the pineal comp lex is centrally involved in the generation and control of the circadi an rhythm of body temperature but is only marginally involved in locom otor rhythmicity. Plasma melatonin levels are not significantly reduce d by parietalectomy, whereas pinealectomy dramatically lowers the leve l and completely eliminates the circadian rhythm of melatonin in the c irculation. Isolated parietal eye, pineal, and retina all synthesize m elatonin with robust circadian rhythmicity when maintained for greater than or equal to 4 d in culture, although in the intact animal all or almost all of the circulating melatonin comes from the pineal. The ci rcadian system of I. iguana is composed of multiple circadian oscillat ors that reside in different tissues and have specific and different r oles.