. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. CIRCADIAN TIMING AT CELLULAR LEVEL 211 heximide, showing protein synthesis is necessary. RNA synthesis is also required at some times in the cycle. The rat pineal also produces melatonin rhythmically, but the circadian oscillator is not in the pineal. Oscillators in the suprachiasmatic nuclei drive the pineal rhythm (Moore and Klein, 1974). The two are coupled via neural connections of the sym- pathetic nervous system. The neurotransmitter of the sympathetic system, norepi- nephrine, is released and combines with /3-receptor
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. CIRCADIAN TIMING AT CELLULAR LEVEL 211 heximide, showing protein synthesis is necessary. RNA synthesis is also required at some times in the cycle. The rat pineal also produces melatonin rhythmically, but the circadian oscillator is not in the pineal. Oscillators in the suprachiasmatic nuclei drive the pineal rhythm (Moore and Klein, 1974). The two are coupled via neural connections of the sym- pathetic nervous system. The neurotransmitter of the sympathetic system, norepi- nephrine, is released and combines with /3-receptors on the pineal. This activation of the (8-receptors causes c-AMP production, which promotes NAT synthesis. This forced rhythm of the rat pineal, driven by the suprachiasmatic nuclei (SCN), contrasts with the endogenous oscillator in the chicken pineal. Melatonin is also synthesized in the retinas of many vertebrates. Recently, circadian rhythms of melatonin content and NAT activity have been shown in chick retina (Hamm and Menaker, 1980). These rhythms persist in constant darkness and are not abolished by pinealectomy. The levels of NAT and melatonin in the retina are similar to those found in the pineal. Light inactivates NAT activity, as it does in the avian pineal. Melatonin rhythms may promote or modulate rhythms of shedding of outer segment disks from retinal rods. Melatonin rhythms also could affect pigment migration, and photomechanical movements of rods and cones. The suprachiasmatic nuclei of vertebrates Ablation identified the SCN of the mammalian brain as an important circadian oscillator (Moore and Eichler, 1971; Stephen and Zucker, 1972). These bilaterally symmetrical nuclei of the hypothalmus lie just above the optic chiasm (Fig. 7) and receive light information by a retinohypothalmic tract. They control mammalian rhythms such as locomotion and pineal secretion, and are near the top of a hierarchy of oscillators that control mammalian rhythms and integrate the ac
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
