Development of day-night rhythmicity in "synaptic" ribbon numbers in the pinealocytes of posthatch chicks kept under either natural photoperiodic conditions or continuous illumination (original) (raw)
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Experientia, 1995
The chick pineal gland exhibits circadian rhythms in melatonin synthesis under in vivo and in vitro conditions. A daily rhythm of melatonin production was first detectable in pineal glands isolated from chick embryos at embryonic day 16 and incubated under a LD cycle. All pineal glands isolated from 17-day-old and older embryos were rhythmic while no gland isolated at embryonic day 14 and 15 exhibited a daily rhythm in melatonin synthesis. Melatonin production in static cultures of embryonic pineal cells was rhythmic over 48 h if the cells were kept under a LD cycle. When embryonic pineal cells were incubated in constant darkness the rhythm in melatonin production was damped within 48 h. These results suggest that chick pineal cells from embryonic day 16 onwards are photosensitive but that the endogenous component of the melatonin rhythm is not completely developed at that age. A soluble analogue of cAMP stimulated and norepinephrine inhibited melatonin synthesis in cultured embryonic pineal cells. These findings indicate that the stimulatory and inhibitory pathways controlling melatonin synthesis in the mature pineal gland are effective in pineal cells isolated from chick embryos at least 2 days before hatching.
Development of melatonin rhythm in the pineal gland and eyes of chick embryo
Experientia, 1992
The action of the brain factor is independent of that of the hormones released by the endocrine glands. Ecdysterone present in the incubation medium at a concentration of 10 -6 M does not affect the activation of PSG by the brain factor, nor does 10 -6 M juvenile hormone II. It is noteworthy that in our system 10-6 M juvenile hormone II inhibits the incorporation of [3H]-uridine into RNA of PSG by at least 30 % during 3 h incubation in vitro, and this inhibition was abolished by the brain factor. It seems that at least a part of the observed effect of brain implantation reported earlier 3 should be ascribed to a direct, hormone-independent action of brain tissue factor(s). More work is needed on the isolation and structure of brain factor, which may show some similarities to other insect neuropeptides 16-18.
Experientia, 1995
The chick pineal gland exhibits circadian rhythms in melatonin synthesis under in vivo and in vitro conditions. A daily rhythm of melatonin production was first detectable in pineal glands isolated from chick embryos at embryonic day 16 and incubated under a LD cycle. All pineal glands isolated from 17-day-old and older embryos were rhythmic while no gland isolated at embryonic day 14 and 15 exhibited a daily rhythm in melatonin synthesis. Melatonin production in static cultures of embryonic pineal cells was rhythmic over 48 h if the cells were kept under a LD cycle. When embryonic pineal cells were incubated in constant darkness the rhythm in melatonin production was damped within 48 h. These results suggest that chick pineal cells from embryonic day 16 onwards are photosensitive but that the endogenous component of the melatonin rhythm is not completely developed at that age. A soluble analogue of cAMP stimulated and norepinephrine inhibited melatonin synthesis in cultured embryonic pineal cells. These findings indicate that the stimulatory and inhibitory pathways controlling melatonin synthesis in the mature pineal gland are effective in pineal cells isolated from chick embryos at least 2 days before hatching.
Circadian Signaling in the Chick Pineal Organ
Chronobiology International, 2003
The chick pineal organ is recognized to contain an endogenous circadian oscillator as well as having direct photic input pathways and the capability of synthesizing melatonin. Despite its interesting circadian cell biology, far less is known about the chick pineal as compared to mammalian pineal glands. The goals of our research were to identify and characterize novel components of the circadian system in this photoneuroendocrine organ. Using a subtractive screening strategy of a nocturnal chick pineal cDNA library, we identified numerous genes whose expression in the chick pineal has never been reported. Among these, we focused our attention on a homologue to the regulatory subunit of the mammalian serine=threonine protein phosphatase (STPP) 2A. The expression of this gene in the chick pineal is highly circadian both in vivo and in vitro. Analysis of the PP2A enzyme in this tissue revealed that it is predominantly cytosolic in localization, sensitive to classical PP2A inhibitors, and far more active during the subjective night. Interestingly, the acute pharmacological inhibition of PP2A leads to elevated phosphoCREB levels and concomitant melatonin secretion, indicating that this enzyme participates at some level in the control of nocturnal pineal melatonin synthesis. In a second aspect of our research, we examined the mechanisms underlying the circadian rhythmicity of cyclic GMP in the chick pineal. This signaling molecule is poorly understood, despite its well-known, highamplitude circadian rhythms and the presence of many cGMP-dependent targets in this tissue. Our work has shown that although both soluble (sGC) and membrane-bound 617 (mGC) forms of guanylyl cyclase are present, the primary contributor to the circadian rhythms of cGMP is the mGC-B enzyme, which is activated only by the natriuretic peptide CNP. As pharmacological blockade of mGC-B (but not sGC) suppresses nocturnal cGMP levels, we conclude that CNP-dependent mechanisms are involved. Hence, the circadian clock in the chick pineal appears to drive either CNP secretion or mGC-B expression (or synthetic efficiency) in order to elevate nocturnal cGMP. Conversely, light may inhibit cGMP by uncoupling this drive. These data provide new strategies for understanding both photic input pathways (presumed to depend on cGMP) and cGMP-dependent cellular function in the chick pineal organ.
Brain research, 2003
Avian circadian rhythms are regulated by a multiple oscillatory system consisting of the pineal, the suprachiasmatic nucleus (SCN) and the eye. In the present study, ontogeny of circadian clock in the pineal and the SCN of chick embryo was examined using Per2 expression as a marker. A daily rhythmicity of Per2 expression was first detectable at embryonic day (ED) 18 in the pineal and at ED 16 in the SCN under light -dark (LD) cycles. The amplitude of the rhythmicity increased during the development. In contrast, little expression was observed during the development in constant darkness. These results suggest that although circadian clock matures by the end of the embryonic life in chicken, LD cycles are required for the expression of the Per2. D
Electrophysiological evidence for circadian rhythmicity in a mammalian pineal organ
Journal of Neural Transmission, 1980
Long-term electrophysiological recordings from the guinea-pig pineal organ show that three types of intrinsic cells can be distinguished: (i) Cells showing constant firing rates over periods of up to 24 hours. (ii) Cells which are highly active during the day and show a low firing rate during the night. (iii) Cells which exhibit low activity during the day and enhanced activity during the night; these cells can be strongly inhibited by 1 rain of light given during the night. Both the light-and darkness-activated cells show activity patterns which closely follow season-dependent differences in day-and night-lengths. In addition, both cell types show an oscillatory pattern in maintained activity. 0300-9564/80/004 7/0181/~ 02.00
Ontogeny of Light-Induced Decrease of N-Acetyltransferase Activity in Explanted Chick Pineal Glands
Journal of Pineal Research, 1990
The ontogeny of chick pineal serotonin N-acetyltransferase (NAT) activity was investigated in explanted chick pineal glands at 4, 10 and 21 d of age. Nocturnal levels of the enzyme and the response of the enzyme to light exposure were determined in pineal glands maintained in short-term culture at each age. The results indicate that nocturnal NAT activity was increased in the glands from older birds. Nocturnal levels of NAT activity at the time of the initiation of the experiment were threefold greater in glands from 2 1-d-old birds as compared to that in glands from 4-day-old chicks. The response to light was similar in all three ages examined; light induced a significant decrease in NAT activity within 60 min in explanted glands from 4-d-old chicks and within 180 min in the glands from the 10-and 2 1 -d-old chicks. A paradoxical transient increase in enzyme activity occurred immediately (within 5 min) following light exposure which was significant in the glands from the youngest chicks, and present, but more variable, in the older chicks. These data indicate that the nocturnal enzyme activity is greater in glands from older birds, but that light exposure of explanted glands initiates a transient rise followed by a decrease in NAT activity at all three ages.
Role of the Pineal in the Circadian System of Birds
American Zoologist, 1976
SYNOPSIS. Pinealectomy of sparrows abolishes the free running rhythm of locomotor activity in constant darkness. Without their pineals, sparrows still entrain to light-dark cycles and show other signs that they retain part, but not all, of the circadian system. Interruption of either the neural input to the pineal or its neural output, or both, does not abolish the free running rhythm. Rhythmicity can be restored to a pinealectomized bird by implanting the pineal of a donor into the anterior chamber of its eye. A model of the circadian system controlling locomotor behavior is proposed to account for these facts. We suggest that the avian pineal contains a self-sustained oscillator, and as a consequence, produces a rhythmic hormonal output. Circadian fluctuations of this hormone entrain a damped oscillator located elsewhere, which in turn drives the locomotor activity. Each oscillator has separate access to environmental light cycles. The behavior of a pinealectomized bird is determined exclusively by its damped oscillator. It does not free run because it lacks the self-sustained oscillator which, however, can be restored by transplantation. The transplanted pineal continues its self-sustained circadian hormonal output which entrains the damped oscillator and restores the system to its normal state.
Proceedings of the National Academy of Sciences, 2000
Endogenous circadian rhythms have been described in a wide range of organisms from prokaryotes to man. Although basic circadian mechanisms at the molecular level are genetically fixed, certain properties of circadian rhythms at the organismic level can be modified by environmental conditions and subsequently retained for some time, even in organisms shielded from 24-hr environmental variations. To investigate the capacity of animals to acquire and store photoperiodic information, we examined activity and melatonin rhythms in house sparrows during synchronization to two different photoperiods and during subsequent prolonged darkness. Under constant environmental conditions, intact animals continued to have long feeding activity times when previously exposed to long days and short feeding activity times when previously exposed to short days. Correspondingly, significantly different durations of elevated melatonin in the plasma directly reflected the differences in night length during synchronization as well as during prolonged darkness. Additionally, we found a significant difference in the amplitude of the nocturnal melatonin signal, which also was conserved in prolonged darkness. To investigate whether the photoperiodic experience of an intact animal can be ''memorized'' by an isolated component of its circadian pacemaking system, we have investigated in vitro melatonin release during continuous darkness from explanted pineal glands of house sparrows after in vivo synchronization to two distinct photoperiods. Differences in the durations of elevated melatonin occurred during the first two cycles in culture and a difference in melatonin amplitude was detectable during the first night in culture. Our data indicate that photoperiodic patterns imposed on sparrows during in vivo synchronization can be maintained as an internal representation of time within the isolated pineal gland. Hence, the pineal gland, as one of the most significant components of the songbird circadian pacemaker, not only has the capacity to autonomously produce circadian rhythms of melatonin release but also is capable of storing biologically meaningful information experienced during previous cycles.