Pineal enzymes in chickens: development of daily rhythmicity

Embryonic Development of Avian Pineal Secretory Activity-A Lesson from the Goose Pineal Organs in Superfusion Culture

The embryonic ontogeny of pineal secretory activity in birds has been investigated almost exclusively in chickens. This study aimed to characterize this process in domestic geese. The pineal organs of embryos aged 18–28 days were incubated in superfusion culture under different light conditions for 4–5 days and treated with norepinephrine (NE). Melatonin (MLT) was measured by radioimmunoassay and other indoles by HPLC with fluorescence detection. Additionally, pineal organs were collected from embryos at 14–28 days of age and used to measure catecholamines by HPLC with electrochemical detection. MLT secretion increased with embryo age, most intensively between the 22nd and 24th days of life. The daily changes in MLT secretion under the 12 L:12D cycle occurred on the first day of culture, starting from an embryonic age of 24 days. MLT secretion was controlled by the light-dark cycle in all age groups studied. However, exposure to light during the scotophase did not alter the secretion of MLT. The endogenous oscillator expressed its activity in regulating MLT secretion in the pineal organs of embryos aged 24 days and older but could not generate a rhythm after one cycle. The rhythm of 5-hydroxytryptophan release during the first day of culture was found in the pineal organs of all embryos, while the rhythmic release of N-acetylserotonin and 5-methoxyindole acetic acid started at the age of 24 days. The proportion of released indoles changed with embryo age. NE caused a decrease in MLT secretion and provoked an increase in serotonin release. Incubation of the pineal organs induced the development of MLT secretory machinery and its diurnal rhythmicity. The pineal content of catecholamines increased prominently at the end of embryonic development.

Embryonic Ontogeny of 5-Hydroxyindoles and 5-Methoxyindoles Synthesis Pathways in the Goose Pineal Organ

The aim of this study was to characterize the embryonic ontogeny of 5-hydroxyindoles and 5-methoxyindoles synthesis pathways in the goose pineal organ. The study was performed on embryos aged 14–28 days, which have been incubated under a 12L:12D cycle. The pineal organs were collected for measurements of indole content by HPLC every 6 h on embryonic day (ED) 14, ED 16, ED 18 and ED 22 or every 2 h on ED 24, ED 26 and ED 28. The level of tryptophan showed no significant changes during development and no day-night variations. The content of 5-hydroxytryptophan increased between ED 14 and ED 26. It was significantly higher during scotophase than during photophase starting from ED 14. The serotonin content was low during the early stages of development (ED 14–ED 18) and prominently increased from ED 20. The serotonin levels also showed day-night differences; however, they were less conspicuous than those of 5-hydroxytryptophan. The changes in the level of 5-hydroxyindole acetic acid were similar to those of serotonin. 5-Hydroxytryptophol was measurable from ED 18. Levels of N-acetylserotonin, which were detectable for the first time on ED 16, prominently increased between ED 22 and ED 28 and showed significant day–night differences from ED 20. Melatonin was detectable from ED 18. Like N-acetylserotonin, its content increased rapidly between ED 22 and ED 28, and from ED 20 showed diurnal variations. 5-Methoxyindole acetic acid and 5-methoxytryptophol occurred at measurable levels from ED 18 and ED 26, respectively. The obtained results showed that embryonic development of indole metabolism in the goose pineal organ starts with the beginning of serotonin synthesis. The processes of serotonin acetylation and 5-hydroxyindoles methylation were turned on later. Diurnal rhythmicity develops very early in the embryonic pineal organ of the goose when the eggs are incubated under a 12 h light: 12 h dark schedule. Two processes are responsible for generation of the diurnal rhythms of 5-hydroxyindoles and 5-methoxyindoles: (i) hydroxylation of tryptophan and (ii) acetylation of serotonin.

Circadian melatonin production develops faster in birds than in mammals

The development of circadian rhythmicity of melatonin biosynthesis in the pineal gland starts during embryonic period in birds while it is delayed to the postnatal life in mammals. Daily rhythms of melatonin in isolated pinealocytes and in intact pineal glands under in vivo conditions were demonstrated during the last third of embryonic development in chick embryos, with higher levels during the dark (D) than during the light (L) phase. In addition to the LD cycle, rhythmic temperature changes with the amplitude of 4.5°C can entrain rhythmic melatonin biosynthesis in chick embryos, with higher concentrations found during the low-temperature phase (33.0 vs 37.5°C). Molecular clockwork starts to operate during the embryonic life in birds in line with the early development of melatonin rhythmicity. Expression of per2 and cry genes is rhythmic at least at day 16 and 18, respectively, and the circadian system operates in a mature-like manner soon after hatching. Rhythmic oscillations are detected earlier in the central oscillator (the pineal gland) than in the peripheral structures, reflecting the synchronization of individual cells which is necessary for detection of the rhythm. The early development of the circadian system in birds reflects an absence of rhythmic maternal melatonin which in mammals synchronizes physiological processes of offspring. Developmental consequences of modified development of circadian system for its stability later in development are not known and should be studied.

Epigenetic maternal effects on endogenous rhythms in precocial birds

Development involves interactions between genetic and environmental influences. Vertebrate mothers are generally the first individuals to encounter and interact with young animals. Thus, their role is primordial during ontogeny. The present study evaluated non-genomic effects of mothers on the development of rhythms of precocial Japanese quail (Coturnix c. japonica). First, we investigated the influence of mothering on the ontogeny of endogenous rhythms of young. We compared circadian and ultradian rhythms of feeding activity of quail reared with or without adoptive mothers. More brooded than non-brooded quail presented a circadian and/or an ultradian rhythm. Thus, the presence of the mother during the normal brooding period favors, in the long term, expression of rhythms in the young. Second, we investigated the influence of rhythmic phenotype of the mother on the development of endogenous rhythms of young by comparing quail brooded by circadian-rhythmic adoptive mothers (R) to quail brooded by circadian-arrhythmic adoptive mothers (A). More R-brooded than A-brooded quail expressed circadian rhythmicity, and circadian rhythm clarities were greater in R-brooded than A-brooded quail. Ultradian rhythmicity did not differ between R- and A-brooded quail, nor between R and A adoptive mothers. Thus, the rhythmic phenotypes of quail mothers influence the rhythmic phenotypes of their young. Our results demonstrate that mothers of precocial birds influence epigenetically the ontogeny of endogenous rhythms of the young they raise.

Prehatch entrainment of circadian rhythms in the domestic chick using different light regimes

The onset of circadian rhythms in many animals occurs during prenatal development. We conducted four experiments, using the domestic chick as a model, to assess when these rhythms can first be entrained and the type of light zeitgeber necessary. In Experiment 1, the presence of circadian rhythms was assessed using tonic immobility, an antipredator behavior, whereas in Experiments 2 to 4 body temperature was studied. We demonstrate that (a) circadian rhythms can be entrained during the late stage of the chick's 21-day incubation period (prehatch Days 13-18), (b) only 1 day of light cues [12:12 hr light:dark (12L:12D)] on prehatch Day 13 is necessary for entrainment, and (c) short bouts of light, which simulate the light cues embryos typically experience during natural incubation, can act as zeitgebers although they are not as effective as 12L:12D. The onset of entrainment is earlier than predicted and suggests that the brain structures mediating circadian rhythms mature sooner than proposed by previous research.

Ontogeny of circadian clock gene expression in the pineal and the suprachiasmatic nucleus of chick embryo

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.

Ontogeny of the daily profile of plasma melatonin in European starlings raised under long or short photoperiods

Photoperiodic manipulation of young European starlings suggests that their reproductive physiology is incapable of responding to a short photoperiod until they are fully grown. This study aimed to determine whether the lack of response to a short photoperiod is reflected in the daily profile of plasma melatonin concentrations. Five-day-old starlings taken from nest boxes showed a significant (p < 0.0001) rhythm in plasma melatonin concentrations, with high values during night. In nestlings hand-reared from 5 days of age on a long photoperiod (LD 16:8), equivalent to natural photoperiod at the time, the amplitude of the daily rhythm in melatonin increased significantly (p < 0.01) with age until birds were fully grown (20 days old). In nestlings reared on a short photoperiod (LD 8:16), the daily melatonin profile remained almost identical to that of long photoperiod birds until they were fully grown. However, after 20 days old, the duration of elevated nighttime melatonin began to extend to encompass the entire period of darkness. In contrast, fully grown starlings transferred from a long to a short photoperiod had partially adapted to the short photoperiod after 5 days; by 10 days, the daily melatonin profile was identical to that of birds held chronically on a short photoperiod. Thus, consistent with responses of reproductive physiology, the pineal of young birds appears to be incapable of perceiving, or adapting to, a short photoperiod.

Rhythms of the pineal N-acetyltransferase mRNA and melatonin concentrations during embryonic and post-embryonic development in chicken

Development of a daily rhythmicity in transcription of a gene encoding a rate-limiting enzyme of melatonin biosynthesis, the arylalkylamine-N-acetyltransferase (AA-NAT) was studied by northern blot analysis in pineal glands of 16 and 19-day-old embryos and 1, 4, 8, 11, and 14-day-old chicks. In a parallel experiment, melatonin content in pineal glands and plasma was measured. A significant rhythm of AA-NAT expression was found at embryonic day (ED) 16, the earliest day assayed in this experiment. Expression was low during the daytime and a clear signal was found in the middle of the darktime. The intensity of the signal was increasing during the ontogeny. The nocturnal pineal melatonin concentrations were increasing over the studied period (from ED 19 until post-embryonic day 21). Midnight plasma melatonin concentrations increased from ED19 to PD 3 and oscillated around this value afterwards. Data show that rhythmic expression of AA-NAT mRNA starts very early in development of chicken and plays a major role in melatonin rhythm generation during embryonic development.

Cellular circadian clocks in the pineal

Daily rhythms are a fundamental feature of all living organisms; most are synchronized by the 24 hr light/dark (LD) cycle. In most species, these rhythms are generated by a circadian system, and free run under constant conditions with a period close to 24 hr. To function properly the system needs a pacemaker or clock, an entrainment pathway to the clock, and one or more output signals. In vertebrates, the pineal hormone melatonin is one of these signals which functions as an internal time-keeping molecule. Its production is high at night and low during day. Evidence indicates that each melatonin producing cell of the pineal constitutes a circadian system per se in non-mammalian vertebrates. In addition to the melatonin generating system, they contain the clock as well as the photoreceptive unit. This is despite the fact that these cells have been profoundly modified from fish to birds. Modifications include a regression of the photoreceptive capacities, and of the ability to transmit a nervous message to the brain. The ultimate stage of this evolutionary process leads to the definitive loss of both the direct photosensitivity and the clock, as observed in the pineal of mammals. This review focuses on the functional properties of the cellular circadian clocks of non-mammalian vertebrates. How functions the clock? How is the photoreceptive unit linked to it and how is the clock linked to its output signal? These questions are addressed in light of past and recent data obtained in vertebrates, as well as invertebrates and unicellulars.

Perinatal development of circadian melatonin production in domestic chicks

In contrast to the situation in mammals, in which circadian melatonin production by the pineal gland does not begin until some time after birth, the development of pineal gland rhythmicity is an embryonic event in the precocial domestic fowl. A distinct melatonin rhythm was found in 19-d-old chick embryos maintained under light:dark (LD) 16:8. No significant variation in melatonin levels was detected in embryos exposed to LD 8:16. The melatonin rhythm in the pineal gland and plasma of chick embryos incubated for 18 d in LD 12:12 persisted for 2 d in constant darkness indicating that melatonin production is under circadian control at least from the end of embryonic life. A 1-d exposure to a LD cycle during the first postembryonic day was sufficient to entrain the melatonin rhythm, and previous embryonic exposure to either LD or constant darkness (DD) neither modified this rapid synchronization nor did it affect the melatonin pattern during the two subsequent days in DD. It is suggested that, in contrast to the situation in mammals, the avian embryo has evolved its own early circadian melatonin-producing system because, as a consequence of its extrauterine development, it cannot use the system of its mother.

Synchronization by low-amplitude light-dark cycles of 24-hour pineal and plasma melatonin rhythms of hatchling European starlings (Sturnus vulgaris)

In young European starlings, as in other avian species, high-amplitude 24-hr rhythms in plasma and pineal melatonin are already present around the time of hatching. In chickens this rhythmicity results at least partly from the light sensitivity of the melatonin-producing and -secreting system. In contrast to the chicken, the starling is a hole-nesting bird, and it seemed questionable whether the low light intensities in the nest are sufficient to synchronize perinatal melatonin rhythms. We therefore exposed starling eggs to light cycles roughly simulating those measured in nest-boxes, i.e., an 11-hr phase of complete darkness and a 13-hr phase consisting of 15 min of dim light (10 lux) alternating with 30 min of darkness. For one group the photophase lasted from 0600 to 1900 hr; for the other group the photophase lasted from 1800 to 0700 hr. In approximately 10-hr-old hatchlings of both groups, plasma and pineal melatonin concentrations were high during the dark phase and low during the light phase. We conclude that perinatal low-amplitude light intensity changes of the kind experienced by hatching starlings in the field are sufficient for synchronizing the melatonin-producing and -secreting system in the pineal and possibly other organs.

A role for bursa fabricii and bursin in the ontogeny of the pineal biosynthetic activity in the chicken

The tripeptide bursin (Lys-His-Gly-NH2) is a B cell differentiation hormone derived from the bursa fabricii. The latter is a cloacal diverticulum and the site of B lymphocyte differentiation and selection in aves; also the bursa fabricii is involved in endocrine functions. Herein we demonstrate that in the chicken, the bursa fabricii and bursin are crucial to the ontogeny of both the pineal response to antigenic challenge and pineal circadian synthetic activity. In early embryonically bursectomized chickens, the plasma melatonin response to immunization by porcine thyroglobulin (Tg) was abolished. Also, the amplitudes of both plasma melatonin and pineal N-acetyltransferase (NAT) circadian rhythms were reduced by 50%, whereas the activity of hydroxyindole-O-methyltransferase (HIOMT) remained unchanged. Conversely, administration of either minute amounts (100 pg, 100 fg) or highly dilute (5 x 10(-27) g) bursin, with the exception of a highest dose (100 micrograms), to bursaless embryos induced recovery of normal antigen-induced melatonin response and normal amplitudes of melatonin and NAT rhythms. These findings establish that early in embryonic life, the bursa fabricii and its derived signal (bursin) are essential for normal development of pineal synthetic activity and underline the efficacy of very dilute bursin as an informative signal.

Hydroxyindole-O-methyltransferase gene expression in the pineal gland of chicken embryo: development of messenger RNA levels and regulation by serum

Hydroxyindole-O-methyltransferase (HIOMT), the enzyme which catalyzes the final step of melatonin biosynthesis, constitutes a marker of the functional differentiation of pineal cells. In addition, a day/night rhythm of HIOMT mRNA concentration, previously described in the chicken pineal gland [6], would suggest that HIOMT gene transcription is one output of the circadian system that controls pineal function. The study sought to monitor the developmental expression of HIOMT mRNA in the chick pineal gland and to investigate a possible role of instructive signals in this differentiation process. RT-PCR analysis indicated that HIOMT mRNA is expressed at embryonic day 8 (E8). At E12, HIOMT mRNA became detectable on northern blots and traces of HIOMT activity could be measured. HIOMT mRNA concentration increased 100-fold between E14 and day 10 post-hatch, then levelled off. A day/night rhythm of HIOMT mRNA concentration was readily observed in the pineal gland of 2-day-old chicks. Pineal glands isolated on minimum culture medium at E11 stopped developing HIOMT gene expression. However, the addition of serum to the culture medium restored HIOMT mRNA concentration to the levels observed in vivo. The data suggest that the functional differentiation of melatoninergic cells observed during the second week of embryonic life may be controlled [correction of controled] by serum factors.

Development of regulation of melatonin release in pineal cells in chick embryo

Melatonin release in a pineal cell culture from 13- and 14-day-old chick embryos increased during the dark phase and decreased during the light phase of a 12 h light:12 h dark cycle. When the light-dark cycle was reversed, the pattern of melatonin release in the culture also reversed. 8-Bromo cyclic-AMP stimulated melatonin release in both the light and dark phases. However, no rhythm of melatonin release was detected under constant dark (DD) conditions in a cell culture from 14-day-old chick embryos. In 18-day-old chick embryos, the pineal cell culture expressed a circadian rhythm of melatonin release under DD conditions. These results indicate that mechanisms regulating melatonin synthesis in the avian pineal gland are established during embryonic life.

Influence of maternal melatonin on melatonin receptors in rat offspring

Using quantitative autoradiography, we have studied the influence of maternal plasma melatonin on the expression and density of melatonin receptors in the brain and pituitary of rat offspring. At birth, the same structures displayed melatonin receptors whether the rats were born to and reared by intact or pinealectomized dams. The receptor density was, however, about 20% lower in the group born to pinealectomized dams. At postnatal day 9, when the pups of both groups synthetize rhythmically their own melatonin, this difference was suppressed. These results indicate that melatonin does not appear to be a requirement for the expression of its receptors, but seems to play a stimulatory role in their synthesis.

The pineal organ as a component of the biological clock. Phylogenetic and ontogenetic considerations

In conclusion, several trends are observed in regard to the phylogenetic development of the pineal organ, which are relevant for our understanding of the evolution of biological clock mechanisms. 1. The pineal organ of all vertebrates investigated thus far is capable of producing and releasing melatonin. Melatonin is rhythmically produced and released during darkness and, thus, represents an important neuroendocrine information on the ambient photoperiod. 2. The rhythmic production of melatonin is under control of endogenous oscillators and photoreceptor cells. In several nonmammalian species, these endogenous oscillators and photoreceptors are located within the pineal organ itself. In some avian species, the inherent rhythmicity of the pineal organ appears to be influenced by pacemakers located in other parts of the central nervous system. Their information may be transmitted to the pineal organ via the sympathetic innervation. This innervation develops progressively in the course of phylogeny. In mammals certain pinealocytes express proteins which are specific of retinal and pineal photoreceptors, but these proteins are obviously not involved in photoreception and phototransduction. The mammalian pineal organ lacks not only functioning photoreceptors, but also endogenous oscillators. The photoreceptor cells involved in regulation of the melatonin biosynthesis are located in the retina; the major endogenous oscillator is the suprachiasmatic nucleus (SCN) of the hypothalamus. Information from the retina and the SCN is transmitted to the mammalian pineal organ via a complex neuronal chain, whose last member is the sympathetic innervation originating from the superior cervical ganglion. This innervation is mandatory to maintain the rhythm of the melatonin biosynthesis in the mammalian pineal organ. Interestingly, the effects of noradrenaline, the major neurotransmitter in the sympathetic nerve fibers, displays opposite effects on the melatonin biosynthesis in birds and mammals: it stimulates the melatonin biosynthesis in the mammalian pineal organ, but inhibits the melatonin formation in the chicken. This conversion occurs at the level of the adrenoreceptors. 3. The intrapineal nerve cells giving rise to pinealofugal neuronal projections are reduced in the course of phylogeny. Nevertheless, direct neuronlike connections appear to exist between the pineal organ and the central nervous system of mammals. These projections originate from a population of pinealocytes. Whether such projections are involved in biological clock mechanisms remains an issue not yet resolved. The ontogenetic data reviewed support the notion that, in lower vertebrates, melatonin biosynthesis is primarily controlled by intrapineal photoreceptors, whereas, in mammals, it depends on retinal photoreceptors and the sympathetic innervation of the pineal.(ABSTRACT TRUNCATED AT 400 WORDS)

Hydroxyindole-O-methyltransferase activity in ocular and brain structures of rabbit and hen

Relative activities of hydroxyindole-O-methyltransferase (HIOMT) of some brain and ocular structures of the rabbit and hen were analyzed using different 5-hydroxyindoles, i.e., N-acetylserotonin (NAS), 5-hydroxytryptophol (HTOL), 5-hydroxytryptophan (HTP), 5-hydroxytryptamine (HT), and 5-hydroxy-3-indoleacetic acid (HIAA), as enzyme substrates. Pineal glands of both species, as well as hen retina, are capable of producing, to varying degrees, melatonin, 5-methoxytryptophol, and 5-methoxytryptamine. Hen choroid and iris-ciliary body O-methylated NAS and HTOL, whereas rabbit choroid and, to a much lesser extent, hypothalamus and cerebral cortex all O-methylated only NAS. No measurable HIOMT activity was found in hen brain. NAS was a preferred substrate for HIOMT in the hen tissues, whereas in the rabbit pineal gland NAS and HTOL were equally good substrates for HIOMT. Other tested 5-hydroxyindoles, i.e., HTP, HT, and HIAA, were poor methyl acceptors. Of the tissues examined, the highest HIOMT activity was found in the hen pineal gland, followed by the rabbit pineal gland and hen retina. No significant differences between day and nighttime enzyme activities were observed in the pineal gland and retina of either species. The data suggest that in vertebrates some nervous and ocular tissues possess the potential to produce 5-methoxyindole compounds; however, the HIOMT-catalyzed process shows remarkable substrate-, tissue- and species-dependent variations.

Effects of light on melatonin and two enzymes leading to its production in albino (s(al-c)) and nonalbino chickens

A gene for sex-linked imperfect albinism in the chicken (s(al)) has been associated with increased egg production with an implication that environmental light may play a role. In this study, levels of melatonin and hydroxyindole O-methyltransferase (HIOMT) and N-acetyltransferase (NAT), two enzymes leading to melatonin production, were studied in young albino and nonalbino chickens in relation to the daily light cycle, and after 19 days of constant light or dark. Differences between genotypes were found in the levels of HIOMT activity in the pineals and retinas of birds kept in constant light for 19 days. Other measurements were not significantly different. This study would appear to show that the visual system of imperfect albino chickens reacts differently to light than that of nonalbinos, but not with changes in the daily cycle of plasma melatonin or in NAT activity, which is the enzyme primarily responsible for the control of the melatonin level in the body.

Development of melatonin rhythm in the pineal gland and eyes of chick embryo

A melatonin rhythm was observed in the pineals of 18-day-old chick embryos incubated under a light-dark regime of 18: 6 h. A low pineal melatonin content was found during the light phase of the day. Concentrations started to increase 2 h after dark onset and reached maximum levels after 4 h of darkness. The amplitude of the pineal melatonin rhythm increased considerably after 2 days and night-time concentrations in 20-day-old embryos were more than 5 times higher than in 18-day-old ones. Significant day/night differences in melatonin production were found both in pineals and eyes. Exposure of eggs to 1 h of light during the dark period decreased the high melatonin concentrations in the eyes but not in the pineals of the 20-day-old chick embryo. The results suggest that in this precocial bird at least part of the circadian system may already operate during embryonic life.

The ontogeny of 2-[125I]iodomelatonin binding sites in chicken brain

The characteristics of the binding sites for 2-[125I]iodomelatonin were studied in chicken brain membranes during development. Specific binding, defined using cold melatonin (1 microM), was detected as early as 8-day-old embryos. Scatchard analysis of saturation experiments showed that 2-[125I]iodomelatonin binds to a single class of site at all ages tested (8-day-old embryos to 3-month-old chicks). Binding affinity (Kd) did not change during development (18-31 pM), but the maximal number of binding sites (Bmax) increased until embryonic day 18, and then remained relatively constant until 30 days of age. A further increase in Bmax was seen at 3 months of age. Guanosine 5'-triphosphate (GTP, 1 mM) inhibited 2-[125I]iodomelatonin binding at all ages suggesting that the melatonin binding site is coupled to a guanine nucleotide binding protein at a very early stage of development. Competition experiments with a number of melatonin analogues indicated that the binding site detected in the brain at embryonic day 8 was pharmacologically identical to that observed 15 days after hatching.

Molecular and cellular aspects of hydroxyindole-O-methyltransferase expression in the developing chick pineal gland

The pineal gland influences circadian activity and seasonal breeding through the production of an indolic hormone, melatonin. The terminal step of melatonin biosynthesis is catalyzed by hydroxyindole-O-methyltransferase (HIOMT). Using an antibody directed against HIOMT, we examined the differentiation of the melatoninergic phenotype in the developing chick pineal gland. HIOMT first appeared 4 days before hatch and rose linearly until the 7th day posthatch. This was correlated with an increased immunoreactivity of the 38 kDa enzyme on Western blots and with an accelerated rate of HIOMT biosynthesis as demonstrated by [35S]methionine labeling. Immunocytochemistry revealed a growing number of HIOMT-positive cells between day 2 before hatch and day 15 posthatch. Until hatching HIOMT was expressed almost exclusively in modified photoreceptors. Parafollicular pinealocytes became HIOMT-positive mostly after hatching. Their different timings of functional differentiation emphasize the existence of two populations of melatonin-producing cells in the chick pineal gland.

Structural and functional differentiation of the embryonic chick pineal organ in vivo and in vitro. A scanning electron-microscopic and radioimmunoassay study

The development of sensory structures in the pineal organ of the chick was examined by means of scanning electron microscopy from embryonic day 10 through day 12 post-hatching. At embryonic day 10, the wall of the tubules within the pineal primordium is composed of cells with unspecialized luminal surface. Differentiation of sensory structures starts at embryonic day 12 when pinealocytes and supporting cells can be distinguished. Pinealocytes are recognized by virtue of an inner segment only rarely endowed with a cilium, whereas supporting cells exhibit numerous short microvilli. Further differentiation of the sensory apparatus is achieved by development of an oval-shaped, biconcave swelling at the tip of the cilium, 1 x 2 microns in size, and a collar of long microvilli at the base of the inner segment. Membrane specializations of sensory cilia, however, were not detected. Since during embryonic life new tubules and follicles are continuously formed, all stages of differentiation of sensory structures are found in the chick pineal organ during the second half of the incubation period and the first two weeks after hatching. In 200-microns-thick Vibratome sections of chick-embryo pineal organs cultured in medium BM 86 Wissler for periods up to 13 days the cytodifferentiation parallels the development in vivo. Using an organ-culture system the 24-h release of melatonin into the culture medium was measured by means of radioimmunoassay after solid-phase extraction. At embryonic day 10, the 24-h secretion of melatonin was at the lower range of detection of the RIA (5 pg). The rapid increase in 24-h secretion in melatonin until hatching (approximately 50 micrograms) is approximated by an exponential curve.

Posthatch day/night differences in synaptic ribbon populations of the chick pineal

Pineal synaptic ribbon (SR) populations of the early posthatch white leghorn chick were counted to determine if they demonstrate a rhythm that is in accordance with the light/dark cycle. SRs were counted between day 7 and day 10 and on day 14 of posthatch development, with samples at midlight, middark (14L:10D), and constant darkness. SR populations did not exhibit significant changes on days 7 and 8 under cycled lighting conditions nor on days 9 and 10 under constant darkness. A second experiment demonstrated that the dark:light ratio of SR populations of day 14 chicks, under cycled lighting, was 3.4:1.0, indicating SR rhythmicity by that stage of development. In that a preliminary experiment had demonstrated a 4.2:1.0 dark:light ratio in SR populations in a predominantly day-10 population of chicks, we believe that SR rhythmicity begins on, or near, day 10 of posthatch development. To determine if the invasion of sympathetic fibers from the superior cervical ganglion (SCG) correlates with the initiation of SR light/dark population differences, we employed tyrosine hydroxylase immunofluorescence to reveal the distribution of catecholaminergic fibers in chick pineal follicles. Follicular innervation doubled over the day 7 to day 14 period, during which time light/dark differences in SR populations were established. There is a correlation, in time, between the invasion of the pineal by the sympathetic fibers and the initiation of SR light/dark differences. The circadian rhythm of pineal N-acetyltransferase (NAT) activity, the rate-limiting enzyme in the melatonin pathway, is established earlier (day 2) than the light/dark differences in SR populations (day 10). It is possible that SR rhythmicity is influenced by the ingrowth of the pineal sympathetic innervation, and that SRs respond to an extrapineal oscillator rather than the independent oscillators of the chick pineal responsible for the rhythm of NAT activity and melatonin synthesis.

Ontogeny of light-induced decrease of N-acetyltransferase activity in explanted chick pineal glands

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 21-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 21-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.

Ontogeny of N-acetyltransferase activity rhythm in pineal gland of chick embryo

1. N-acetyltransferase was present in pineal glands of 14-day-old chick embryos though no rhythm either in LL, DD or LD 12:12 was observed in this age. 2. Daily rhythm in pineal NAT activity was found in 18-day-old embryos incubated under LD 12:12 and LD 16:8 but no NAT rhythm was detected in DD or LL. 3. NAT rhythm persists for 2 days in constant darkness and it may be circadian in nature. 4. Presence of melatonin (85 +/- 8 pg/mg tissue) was detected in pineals of 18-day-old chick embryos.

Rhythm development in pineal and circulating serotonin, N-acetylserotonin, and melatonin in Syrian hamsters

The ontogeny of diurnal rhythm patterns in the pineal and serum levels of melatonin, serotonin, and N-acetylserotonin was studied in Syrian hamsters (Mesocricetus auratus) from birth to adulthood. The pineal and blood specimens were collected at 1100 h and 0200 h, and the compounds were measured by radioimmunoassay (RIA) procedures. Pineal melatonin and serotonin did not show any circadian rhythm at day 5 of postnatal age. At this age N-acetylserotonin was undetectable in the light phase but became manifest at night. By 10 days of age pineal serotonin registered an established rhythm pattern, with a higher level during the day. The occurrence of circadian rhythm in pineal melatonin was delayed and manifested first at 25 days of age. At this age, the first detectable daytime level of N-acetylserotonin also occurred. Circadian rhythm in serum melatonin was also established at this age. The serum serotonin did not evince any rhythm pattern throughout the observation period, except at day 17 of postnatal age. The massive concentration of daytime serotonin in the pineal was not reflected in the circulatory system. For serum N-acetylserotonin there was no discernable day-night rhythm in all age groups, except at 25 days of age. The results show that the timing of the appearance of various compounds in the neonatal pineal is variable; the release of the substances does not always reflect their synthesis; the ontogenesis of circadian rhythm is a part of the maturational process; and 25 days of age is a rather critical time in development.

Ontogeny of circadian rhythmicity for melatonin, serotonin, and N-acetylserotonin in humans

The serum concentration of melatonin, serotonin, and N-acetylserotonin were measured by RIA procedures in 28 infants aged 1 week to 9 months. Blood specimens were obtained at 12:00 hr and 24:00 hr. A day-night difference in serum serotonin was present immediately after birth. A significant (P less than 0.001) decrease in serum serotonin concentrations at 12:00 hr and 24:00 hr was observed from the first month of age to the third to ninth month of age. A significant (P less than 0.05) difference in day-night N-acetylserotonin concentration is first seen at age 1-3 months. Serum melatonin concentrations, though detectable, did not show any day-night difference at birth. Melatonin concentrations progressively increased up to the third month of age, and a significant (P less than 0.01) day-night difference appeared thereafter. The results indicate that in humans the circadian organization for serotonin already exists at birth, and the circadian melatonin rhythm develops after birth.

Effects of age, light regimes and food removal on development of daily rhythmicity in chick heart rate

Development of daily rhythms in the chick heart rate was investigated during the post-hatching period. The measurements were made in free-moving chicks at one-hour intervals under different light conditions. Clear daily rhythms were seen 3 days after hatching under LD (12:12 hr.) whereas no daily rhythm was observed under either constant illumination or constant dark. The present study demonstrated that while heart rate increased with age during the post-hatching period, the light-time heart rate increased more rapidly than the dark-time heart rate. It was also found that the daily rhythms in heart rate were not formed after food removal even under LD. These results indicate that the light and feeding play an important role in the development of the daily rhythms in chick heart rate.