Cytodifferentiation of the Chick Pineal Gland, With Special Reference to the Photosensory and Secretory Elements
TL;DR: Cytodifferentiation of the chick pineal gland throughout the embryonic development was investigated with light and electron microscopy and nuclear invaginations having a large lipid droplet nearby and some aggregations of glycogen are found in the pinealocytes and are transitory changes in structure restricted to certain days of incubation.
Abstract: Cytodifferentiation of the chick pineal gland throughout the embryonic development was investigated with light and electron microscopy. The chick pineal anlage appears first as a small evagination in the diencephalic roof at 60 h of incubation (27–30 somites). Until day 5 of incubation, pineal anlage cells are undifferentiated and appear similar to ventricular ependymal cells. Subsequently, pinealocytes and supporting cells are first distinguishable at 7–8 days, and parafollicular cells are distinguishable at 12 days of incubation. Pigment-containing cells after 6 days and nerve cells after 17 days of incubation gradually increase, especially in the posterior wall of the pineal recess. During embryonic development, the chick pineal gland has both photosen-sory and secretory elements: viz. the former, mitochondria-laden apical protrusions, synaptic ribbons, lamellar whorl-like cilia of the pinealocytes, and adjacent appearance of the pigment-containing cells and the nerve cells; and the latter, dense-cored vesicles of the pinealocytes and dense bodies of the supporting cells. Moreover, nuclear invaginations having a large lipid droplet nearby and some aggregations of glycogen are found in the pinealocytes and are transitory changes in structure restricted to certain days of incubation.
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TL;DR: A new hypothesis of pineal evolution is proposed, in which the old notion 'gradual regression within the sensory cell line' should be replaced with 'changes in fate restriction within the neural lineage of the pineal field'.
Abstract: Pineal evolution is envisaged as a gradual transformation of pinealocytes (a gradual regression of pinealocyte sensory capacity within a particular cell line), the so-called sensory cell line of the pineal organ. In most non-mammals the pineal organ is a directly photosensory organ, while the pineal organ of mammals (epiphysis cerebri) is a non-sensory neuroendocrine organ under photoperiod control. The phylogenetic transformation of the pineal organ is reflected in the morphology and physiology of the main parenchymal cell type, the pinealocyte. In anamniotes, pinealocytes with retinal cone photoreceptor-like characteristics predominate, whereas in sauropsids so-called rudimentary photoreceptors predominate. These have well-developed secretory characteristics, and have been interpreted as intermediaries between the anamniote pineal photoreceptors and the mammalian non-sensory pinealocytes. We have re-examined the original studies on which the gradual transformation hypothesis of pineal evolution is based, and found that the evidence for this model of pineal evolution is ambiguous. In the light of recent advances in the understanding of neural development mechanisms, we propose a new hypothesis of pineal evolution, in which the old notion 'gradual regression within the sensory cell line' should be replaced with 'changes in fate restriction within the neural lineage of the pineal field'.
129 citations
TL;DR: Experimental and molecular aspects are discussed, focusing on the histological and histochemical basis of the function of nonvisual photoreceptors, and a view about functional changes of these photoreCEPTors during pre- and postnatal development as well as about its possible evolution are offered.
Abstract: The role of the nonvisual photoreception is to synchronise periodic functions of living organisms to the environmental light periods in order to help survival of various species in different biotopes. In vertebrates, the so-called deep brain (septal and hypothalamic) photoreceptors, the pineal organs (pineal- and parapineal organs, frontal- and parietal eye) and the retina (of the "lateral" eye) are involved in the light-based entrain of endogenous circadian clocks present in various organs. In humans, photoperiodicity was studied in connection with sleep disturbances in shift work, seasonal depression, and in jet-lag of transmeridional travellers. In the present review, experimental and molecular aspects are discussed, focusing on the histological and histochemical basis of the function of nonvisual photoreceptors. We also offer a view about functional changes of these photoreceptors during pre- and postnatal development as well as about its possible evolution. Our scope in some points is different from the generally accepted views on the nonvisual photoreceptive systems. The deep brain photoreceptors are hypothalamic and septal nuclei of the periventricular cerebrospinal fluid (CSF)-contacting neuronal system. Already present in the lancelet and representing the most ancient type of vertebrate nerve cells ("protoneurons"), CSF-contacting neurons are sensory-type cells sitting in the wall of the brain ventricles that send a ciliated dendritic process into the CSF. Various opsins and other members of the phototransduction cascade have been demonstrated in telencephalic and hypothalamic groups of these neurons. In all species examined so far, deep brain photoreceptors play a role in the circadian and circannual regulation of periodic functions. Mainly called pineal "glands" in the last decades, the pineal organs actually represent a differentiated form of encephalic photoreceptors. Supposed to be intra- and extracranially outgrown groups of deep brain photoreceptors, pineal organs also contain neurons and glial elements. Extracranial pineal organs of submammalians are cone-dominated photoreceptors sensitive to different wavelengths of light, while intracranial pineal organs predominantly contain rod-like photoreceptor cells and thus scotopic light receptors. Vitamin B-based light-sensitive cryptochromes localized immunocytochemically in some pineal cells may take part in both the photoreception and the pacemaker function of the pineal organ. In spite of expressing phototransduction cascade molecules and forming outer segment-like cilia in some species, the mammalian pineal is considered by most of the authors as a light-insensitive organ. Expression of phototransduction cascade molecules, predominantly in young animals, is a photoreceptor-like characteristic of pinealocytes in higher vertebrates that may contribute to a light-percepting task in the perinatal entrainment of rhythmic functions. In adult mammals, adrenergic nerves--mediating daily fluctuation of sympathetic activity rather than retinal light information as generally supposed--may sustain circadian periodicity already entrained by light perinatally. Altogether three phases were supposed to exist in pineal entrainment of internal pacemakers: an embryological synchronization by light and in viviparous vertebrates by maternal effects (1); a light-based, postnatal entrainment (2); and in adults, a maintenance of periodicity by daily sympathetic rhythm of the hypothalamus. In addition to its visual function, the lateral eye retina performs a nonvisual task. Nonvisual retinal light perception primarily entrains genetically-determined periodicity, such as rod-cone dominance, EEG rhythms or retinomotor movements. It also influences the suprachiasmatic nucleus, the primary pacemaker of the brain. As neither rods nor cones seem to represent the nonvisual retinal photoreceptors, the presence of additional photoreceptors has been supposed. Cryptochrome 1, a photosensitive molecule identified in retinal nerve cells and in a subpopulation of retinal photoreceptors, is a good candidate for the nonvisual photoreceptor molecule as well as for a member of pacemaker molecules in the retina. When comparing various visual and nonvisual photoreceptors, transitory, "semi visual" (directional) light-perceptive cells can be detected among them, such as those in the parietal eye of reptiles. Measuring diffuse light intensity of the environment, semivisual photoreceptors also possess some directional light perceptive capacity aided by complementary lens-like structures, and screening pigment cells. Semivisual photoreception in aquatic animals may serve for identifying environmental areas of suitable illumination, or in poikilotermic terrestrial species for measuring direct solar irradiation for thermoregulation. As directional photoreceptors were identified among nonvisual light perceptive cells in the lancelet, but eyes are lacking, an early appearance of semivisual function, prior to a visual one (nonvisual --> semivisual --> visual?) in the vertebrate evolution was supposed.
111 citations
TL;DR: The results strongly suggest that the chicken pineal gland contains at least two types of photoreceptive molecules, pinopsin (major) and chicken red (minor).
56 citations
TL;DR: Using an antibody directed against HIOMT, the differentiation of the melatoninergic phenotype in the developing chick pineal gland was examined and revealed the existence of two populations of melatonin-producing cells in the chick Pineal gland.
30 citations
TL;DR: 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, and the cytodifferentiation parallels the development in vivo.
Abstract: 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, 1×2 μm 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-μm-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 (∼50 μg) is approximated by an exponential curve.
28 citations
Cites background or methods from "Cytodifferentiation of the Chick Pi..."
...Embryological studies have been performed using both morphological and biochemical techniques mainly with the chick pineal organ (Vidmar 1953; Spiroff 1958; Oksche and Vaupel-von Harnack 1965; Campbell and Gibson 1970; Wainwright 1974; Binkley and Geller 1975; Omura 1977; Boya and Calvo 1978, 1980; Calvo and Boya 1978, 1979; M611er 1986, 1987; Oshima and Matsuo 1988)....
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...However, numerous authors (Oksche and Vaupel-von Harnack 1965; Omura 1977; Calvo and Boya 1979; M611er 1986; Oshima and Matsuo 1988) have reported on the development of sensory structures in the chick pineal organ as a general function of embryonic age without paying attention to this fact....
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TL;DR: The findings that are functionally suggestive and those that are important in the design and interpretation of experiments purporting to demonstrate pineal function or activity are discussed in the chapter.
Abstract: This chapter reviews the current state of knowledge of the microscopic structure and composition of the pineal, with emphasis on recent studies. The findings that are functionally suggestive and those that are important in the design and interpretation of experiments purporting to demonstrate pineal function or activity are discussed in the chapter. The mammalian pineal is a solid structure whose cellular constituents are numerically dominated by unique parenchymal cells having distinctive structural and cytochemical characteristics suggesting a primarily secretory and endocrine function. The avian pineal in many species retains a system of lumina lined by ependymal cells or their derivatives. However, some of the parenchymal cells of the avian pineal appear to be secretory and closely positioned anatomically to blood vessels within the organ. The diversity and complexity of pineal structure and composition and the recent advances in knowledge reaffirm the wisdom of avoiding inflexible and narrow concepts of pineal structure and function.
128 citations
TL;DR: The pineal is structurally very diverse among the avian species that have been examined, and a role for this body in controlling gonadal function is indicated, but the evidence is not consistent.
Abstract: The pineal is structurally very diverse among the avian species that have been examined. In some birds, especially owls, the pineal is virtually absent. Sympathetic innervation is provided by projections from the superior cervical ganglia. Several cell types are present in the pineal body, among which are large cells, associated with lamellar bodies, that are commonly considered to be abortive or vestigial photoreceptors. Diurnal cycles of serotonin and melatonin content of the pineal are responsive to photoperiod, and there is a small amount of evidence that the avian pineal may serve as a pacemaker for diurnal rhythms of activity. Pinealectomy indicates a role for this body in controlling gonadal function, but the evidence is not consistent. Indole amines may be the mediators of this presumed endocrine role, but the supporting evidence is not very convincing.
67 citations