The pineal and circadian rhythms of temperature selection and locomotion in lizards.
ABSTRACT The existence of a circadian rhythm of behavioral temperature selection has been demonstrated in lizards (Podarcis sicula) held on a thermal gradient in constant darkness. This rhythm becomes temporarily abolished during 1 week following parietalectomy and 2-3 weeks following pinealectomy. Parietalectomy does not affect the locomotor rhythm, while pinealectomy invariably lengthens the freerunning period of this rhythm. These results support the contention of separate control systems for the temperature selection rhythm and the locomotor rhythm. As neither rhythm is definitively abolished by parietalectomy and pinealectomy, other pacemaking components exist elsewhere in the circadian system of Podarcis sicula which can control both rhythms.
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ABSTRACT: In mammals both the regulation of circadian rhythms and photoperiodic responses depend exclusively upon photic information provided by the lateral eyes; however, nonmammalian vertebrates can also rely on multiple extraocular photoreceptors to perform the same tasks. Extraocular photoreceptors include deep brain photoreceptors located in several distinct brain sites and the pineal complex, involving intracranial (pineal and parapineal) and extracranial (frontal organ and parietal eye) components. This review updates the research field of the most recent acquisitions concerning the roles of extraocular photoreceptors on circadian physiology and behavior, particularly photic entrainment and sun compass orientation.Chronobiology International 08/2004; 21(4-5):501-19. DOI:10.1081/CBI-120039813 · 2.88 Impact Factor
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ABSTRACT: The lizard Iguana iguana when kept in constant ambient temperature displays 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 pinealectomy completely abolishes the rhythm of body temperature. However, the rhythm of locomotor activity is only slightly affected by parietalectomy plus pinealectomy. Our results demonstrate that the pineal complex is centrally involved in the generation and control of the circadian rhythm of body temperature but is only marginally involved in locomotor rhythmicity. Plasma melatonin levels are not significantly reduced by parietalectomy, whereas pinealectomy dramatically lowers the level and completely eliminates the circadian rhythm of melatonin in the circulation. Isolated parietal eye, pineal, and retina all synthesize melatonin with robust circadian rhythmicity when maintained for >/=4 d in culture, although in the intact animal all or almost all of the circulating melatonin comes from the pineal. The circadian system of I. iguana is composed of multiple circadian oscillators that reside in different tissues and have specific and different roles.The Journal of Neuroscience : The Official Journal of the Society for Neuroscience 02/1998; 18(3):1105-14. · 6.75 Impact Factor
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ABSTRACT: The daily rhythm of behavioral thermoregulation in sleepy lizards (Tiliqua rugosa) was studied in laboratory thermal gradients under a 12L:12D photoperiod in autumn and spring. In both seasons, lizards showed distinctive daily rhythms of behavioral thermoregulation, selecting their highest body temperatures during the late photophase and lowest ones during the late scotophase or early photophase. When lizards were subjected to a period of constant darkness at both seasons, this rhythm persisted and free-ran with a period of 24.7 h, indicating that it is an endogenous circadian rhythm. Furthermore, the expression of this circadian rhythm varies seasonally in the amplitude of its free-running rhythm and in the phase at which the minimum T-b is selected during 12L:12D. The seasonal variation in the expression of the circadian rhythm of behavioural thermoregulation in Tiliqua rugosa lizards is likely to reflect seasonal changes in the neural regulation of this rhythm.Herpetologica 09/2006; 62(3):259-265. DOI:10.1655/0018-0831(2006)62[259:CROBTI]2.0.CO;2 · 1.07 Impact Factor