Period and Phase Control in a Multioscillatory Circadian System (Iguana Iguana)

Feb 18, 2004Journal of biological rhythms

Timing and cycle control in the multiple body clocks of the green iguana

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Abstract

Pinealectomy lengthened the locomotor activity period in all tested juvenile iguanas and abolished the body temperature rhythm in two-thirds of the animals.

The circadian system of Iguana iguana involves several independent pacemakers, including the pineal gland and retinae.
Pinealectomy lengthened the period of locomotor activity and affected the body temperature rhythm, with most animals losing their rhythm entirely.
In cases where the body temperature rhythm persisted after pinealectomy, its period adjusted to match that of locomotor activity.
Pinealectomy also altered the timing of activity onset in relation to body temperature in constant darkness.
Enucleation did not significantly impact the periods of locomotor activity or body temperature rhythms but caused a phase shift between them.

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The circadian system of the lizard Iguana iguana is composed of several independent pacemakers that work in concert: the pineal gland, retinae of the lateral eyes, and a fourth oscillator presumed to be located in the hypothalamus. These pacemakers govern the circadian expression of multiple behaviors and physiological processes, including rhythms in locomotor activity, endogenous body temperature, electroretinogram, and melatonin synthesis. The numerous, easily measurable rhythmic outputs make the iguana an ideal organism for examining the contributions of individual oscillators and their interactions in governing the expression of overt circadian rhythms. The authors have examined the effects of pinealectomy and enucleation on the endogenous body temperature rhythm (BTR) and locomotor activity rhythm (LAR) of juvenile iguanas at constant temperature both in LD cycles and in constant darkness (DD). They measured the periods (tau) of the circadian rhythms of LAR and BTR, the phase relationships between them in DD (psiAT), and the phase relationship between each rhythm and the light cycle (psiRL). Pinealectomy lengthened tau of locomotor activity in all animals tested and abolished the BTR in two-thirds of the animals. In those animals in which the BTR did persist following pinealectomy, tau lengthened to the same extent as that of locomotor activity. Pinealectomy also delayed the onset of activity with respect to its normal phase relationship with body temperature in DD. Enucleation alone had no significant effect on tau of LAR or BTR; however, after enucleation, BTR became 180 degrees out of phase from LAR in DD. After both pinealectomy and enucleation, 4 of 16 animals became arrhythmic in both activity and body temperature. Their data suggest that rhythmicity, period, and phase of overt circadian behaviors are regulated through the combined output of multiple endogenous circadian oscillators.

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Period and Phase Control in a Multioscillatory Circadian System (Iguana Iguana)

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