Recent advances in pineal cytochemistry. Evidence of the production of indoleamines and proteinaceous substances by rudimentary photoreceptor cells and pinealocytes of Amniota

Temporal organization of the brain: Neurocognitive mechanisms and clinical implications

The synchrony between the individual brain and its environment is maintained by a system of internal clocks that together reflect the temporal organization of the organism. Extending the theoretical work of Edelman and others, the temporal organization of the brain is posited as functioning through "re-entry" and "temporal tagging" and binds the wide range of possible times to a unified cognitive experience which is held in unison with the outside world. Dysfunction in this system is reflected in the temporal discord seen in cases of aging, sleep disorder, jet-lag, and shift-work, as well as in mental disorders and drug-induced changes in consciousness. The extent to which neuroendocrine structures contribute to the neurocognitive mechanisms which underlie consciousness has so far not been explored. Therefore, neuroendocrine mechanisms contributing to the temporal organization of the brain are reviewed. It is concluded that time-and its neuroendocrine correlate melatonin-is a binding principle for organizing conscious experience.

Influence of continuous light and darkness on the secretory pinealocytes of Heteropneustes fossilis

In an earlier study on Heteropneustes fossilis, evidence of secretory activity in the pinealocytes had been demonstrated at the electron microscopic (EM) level and it was found to exist in two phases: a secretory phase (light cells) and a storage phase (dark cells). In the present investigation, H. fossilis was subjected to artificial photoperiods of continuous illumination and continuous darkness for a period of ten days and the effect on the secretory pinealocytes was studied at the EM level. Marked results were observed within the short period of ten days emphasizing the role of environmental photoperiod on the secretory activity of the pinealocytes. During continuous illuminated phase, both light and dark cells were observed: the light cells showed intense secretory activity and dark cells a storage one. During the dark phase both types of cells were present but in different metabolic states and neither of the cells demonstrated synthetic nor storage activity. Light cells were metabolically active but not secretory active and dark cells showed a necrotic condition. Phagocytotic activity of the dark cells was also seen. Intense neural activity was also observed during exposure to both the artificial photoperiods. The results highlight the role of light on the secretory activities of the pinealocytes of the catfish pineal organ.

Structural and ultrastructural characteristics of human pineal gland, and pineal parenchymal tumors

We have studied 20 pineal parenchymal tumors (PPT) and 4 normal or cystic pineal glands both by light and electron microscopy and immunohistochemistry with antibodies against glial markers [glial fibrillary acidic protein (GFAP) and protein S-100] or neural/neuroendocrine markers [neurofilaments (NF), synaptophysin and chromogranin A]. Light microscopy revealed the cellular organization of pinealocytes in the normal gland and in different morphological types of pineal tumors (typical pineocytomas, PPT with intermediate differentiation, mixed PPT exhibiting elements of both pineocytoma and pineoblastoma and pineoblastomas). Immunohistochemistry showed the presence of GFAP and protein S-100 in interstitial cells in non-neoplastic pineal gland. Cell processes were labeled with anti-synaptophysin and anti-NF antibodies. No immunoreactivity was found for chromogranin A in non-neoplastic pineal gland. In pineocytomas, GFAP and protein S-100 were observed in interstitial cells. Synaptophysin and NF were present in the large rosettes of pineocytomas. Synaptophysin, NF and chromogranin A were present in pineocytomas with a lobular arrangement of cells. Anti-chromogranin A immunoreactivity was also seen in lobular areas of some PPT with intermediate differentiation. Analysis of normal human pineal gland by electron microscopy showed the presence of vesicle-crowned rodlets (VCR or synaptic ribbons), fibrous filaments (F), paired twisted filaments but few dense-core vesicles (DCV) in normal pinealocytes. Tumoral pineal cells appeared to differentiate either towards a neurosensory pathway characterized by the presence of sensory cells elements (VCR and F), or towards a neuroendocrine pathway, with the occurrence of many DCV. Immunogold labeling demonstrated the presence of chromogranin A in neurosecretory granules.

Morphofunctional aspects of the mammalian pineal gland

The primary aim of this review is to present the current state of knowledge of the ultrastructure of the mammalian pineal gland, with emphasis on its functional aspects. Basic ultrastructural features of the mammalian pinealocytes are presented with special attention paid to ultrastructural aspects of pineal secretion.

[Pineal body in vertebrates: a model for investigations of receptor and effector mechanisms of neuronal systems]

Cell and molecular biological investigations have greatly contributed to our understanding of receptor and effector mechanisms in sensory, neuronal, and endocrine cells. A fascinating aspect of this line of research is how such mechanisms have evolved and how they interact with each other. As shown in this contribution, the vertebrate pineal organ is an interesting model to study these problems, because it undergoes a conspicuous transformation during phylogeny, comprises two well-characterized receptor mechanisms (photoreception and adrenoreception), and acts upon its targets via neuronal and neuroendocrine signals.

Complex relationships between the pineal organ and the medial habenular nucleus-pretectal region of the mouse as revealed by S-antigen immunocytochemistry

S-antigen-immunoreactive pinealocytes located in the deep portion of the pineal organ of inbred and wild pigmented mice give rise to long, beaded processes penetrating into the habenular and pretectal regions. In addition, the medial habenular nuclei and the pretectal area contain S-antigen-immunoreactive perikarya, which resemble pinealocytes in size, shape and immunoreactivity and are considered as "pinealocyte-like" epithalamic cells. Immunoblotting techniques reveal that a single protein band of approximately 48 kDa molecular weight accounts for this immunoreactivity. As shown with the use of the electron microscope, the majority of the S-antigen-immunoreactive processes is closely apposed to immunonegative neuronal profiles and perikarya of the habenular and pretectal regions. S-antigen-immunoreactive processes and perikarya of both pinealocytes of the deep pineal organ and pinealocyte-like epithalamic cells may form the postsynaptic element in conventional synapses involving axons provided with clear synaptic vesicles. Thus, certain mammalian pinealocytes may receive and transmit signals via point-to-point connections resembling neuro-neuronal contacts. These results challenge the concept that the mammalian pineal organ exerts its influence exclusively via the release of melatonin into the general circulation. Furthermore, they provide evidence (i) that neuronal circuits not involving the sympathetic system participate in the regulation of pineal functions in mammals, and (ii) that intimate histogenetic and functional relationships exist between the pineal organ and the habenular-pretectal nuclei in mammals.

Localization of serotonin-like immunoreactivity in the eyestalk of the prawn Palaemon serratus (Crustacea, Decapoda, Natantia)

A serotonin-like substance in the organ of Bellonci in the eyestalks of embryos, larvae, and adults of the prawn Palaemon serratus was visualized by the use of two specific antisera against serotonin (5-hydroxytryptamine; 5-HT) in combination with peroxidase-antiperoxidase (PAP). The organ of Bellonci, characterized by compact onion bodies distally and degenerating onion bodies proximally, was the only site of the serotonin-like substance in adults, as well as during development in embryos and larvae. Variations in the content of the 5-HT analogue in the adult were detected during the molting cycle. There was more immunoreactivity in specimens fixed at night than in those fixed in daytime. Likewise, colchicine and nialamide injections enhanced the immunoreactivity of the serotonin-like substance. Extirpations of the medulla externa X organ (MEX), a neurosecretory cell group of the optic ganglion medulla externa, produced the same effect.

Neurohypophyseal hormone-like peptides in the ovine pineal gland using reverse-phase liquid chromatography and radioimmunoassay

A method is described for the determination of the neurohormone contents of ovine pineal tissue by radioimmunoassay (RIA) after successive fractionation on gel filtration in formic acid and reverse-phase liquid chromatography (HPLC). This method gives a good resolution for the neurohormones vasopressin, vasotocin and oxytocin, without a significant interference of aspecific cross-reacting of peptides with the RIA. An acid extract from ovine pineal tissue was found to contain amounts of immunoreactive AVP- and OXT-like peptides, whereas an AVT-like peptide was not detectable over background levels after HPLC with post-column RIA. It is concluded from our results that an AVT-like peptide is not present in ovine pineal tissue, and the pineal AVP- and OXT-like peptides appeared to be associated to neurophysin molecules.

Pineal melatonin rhythms in the lizard Anolis carolinensis: II. Photoreceptive inputs

The pineal organ of the lizard Anolis carolinensis acts as a transducer of photoperiodic information, since light can affect the pineal melatonin rhythm (PMR). The synthesis and secretion of melatonin may be a major mechanism whereby a circadian pacemaker within the pineal can control circadian clocks located elsewhere. An investigation into potential routes by which light could affect the PMR showed that (1) removal of the photosensory parietal eye did not affect the PMR as compared to controls under either a light-dark (LD) 12:12 cycle and a constant temperature (32 degrees C) or an LD 12:12 cycle and a daily temperature cycle (32 degrees C/20 degrees C); (2) removal of both the parietal eye and the lateral eyes did not affect the PRM of anoles held in LD 12:12 (constant 32 degrees C); (3) the PMR of blinded anoles re-entrained to a 10-hr shift in the phase of the LD cycle as rapidly as that of sighted anoles; (4) blocking light penetration to the brains of anoles, but leaving the lateral eyes exposed, blocked the ability of anoles to re-entrain to a 10-hr shift in the phase of an LD cycle. The data support the hypothesis that light directly affects the PMR in Anolis and that other potential photic inputs (parietal eye, lateral eyes) play little or no role. This conclusion is supported by previous neurophysiological and ultrastructural studies showing that the lizard pineal possesses functional photoreceptors.

Ultrastructural demonstration of exocytosis in the pineal gland

Granular vesicles are present in pinealocytes and in rudimentary photoreceptor cells of many vertebrates, sometimes in large amounts. Their dense cores have been shown to store proteinaceous compounds, but the way they are released remains speculative. The aim of this study was to demonstrate whether or not exocytosis is the mechanism by which secretory products stored within granular vesicles are released. Therefore, a method has been used allowing a clear ultrastructural study of secretory products by exocytosis, even in tissues in which this process of secretion is quite rare and/or very slow. Exocytotic figures have been clearly demonstrated in the three species studied: golden hamster, snake, and parakeet. Nevertheless, they were never commonly observed as it was the case in neurohypophysis, even in such animals as the parakeet and snake, in which granular vesicles are very numerous. The possible reasons of this observation are discussed.

Pineal-retinal molecular relationships: distribution of "S-antigen" in the pineal complex

The immunocytochemical localization of S-antigen, a specific protein first discovered in retinal photoreceptors, was studied in the pineal complex of vertebrates (eel, pike, frog, lizard, passerines, mouse, hamster) using monoclonal antibody immunofluorescence. S-antigen immunoreactivity was demonstrated concurrently in retinal photoreceptors and in most pineal phototransducers of all species, i.e. in pineal cells of the receptor series (cone-like, modified photoreceptor cells, pinealocytes) and in cone-like photoreceptors of the frog frontal organ and lizard parietal eye. The labelling was distributed either in all compartments of these cells, or restricted to outer segments. The functional significance of the S-antigen as well as some phylogenetic and ontogenic implication of this marker are discussed.

Ultrastructure of the pineal gland of the brush mouse (Peromyscus boylei): influence of long and short photoperiod

The ultrastructure of the pineal gland of wild-captured brush mice (Peromyscus boylei) was examined. A homogeneous population of pinealocytes was present in the pineal gland of this species. The Golgi apparatus, granular endoplasmic reticulum, mitochondria, lysosomes, dense-core vesicles, vacuoles containing fluocculent material, clear vesicles, microtubules and glycogen particles were consistent components of the pinealocyte cytoplasm; infrequently-observed organelles included centrioles, "synaptic" ribbons, subsurface cisternae, multivesicular bodies, lipid droplets and annulate lamellae-like structures. Quantitative comparison of pinealocyte ultrastructure revealed larger cross-sectional areas of cytoplasma, nucleus, Golgi apparatus, granular endoplasmic reticulum, mitochondria and vacuoles containing flocculent material as well as higher number of dense-core vesicles in the animals kept in short photoperiod (LD 8 : 16) as compared to those in animals kept in long photoperiod (LD 16 : 8). These observations suggest that restricting the amount of light to which animals are exposed activated the pinealocytes of brush mice.

Influence of testosterone on protein/peptide secretion as characterized by the formation of granular vesicles in rat and mouse pinealocytes. An in vitro study

In the present study, using an in vitro system, the effect of testosterone on protein/peptide secretion in mouse and rat pinealocytes as characterized by the formation of granular vesicles (GV) has been studied. In both species testosterone induces a significant increase in the number of GV. This effect, however, is observed only when the pineals are cultured in a noradrenaline-free medium. These results clearly demonstrate that testosterone, at least under these in vitro conditions, is involved in the regulation of protein/peptide secretion, and point to the importance of pineal proteic/peptidic "hormones" in pineal endocrinology.

Ultrastructure of the pineal gland of the eastern chipmunk (Tamias striatus)

The ultrastructure of the pineal gland of the wild-captured eastern chipmunk (Tamias striatus) was examined. A homogenous population of pinealocytes was the characteristic cellular element of the chipmunk pineal gland. Often, pinealocytes showed a folliclelike arrangement. Mitochondria, Golgi apparatus, granular endoplasmic reticulum, lysosomes, centrioles, dense-core vesicles, clear vesicles, glycogen particles, and microtubules were consistent components of the pinealocyte cytoplasm. The extraordinary ultrastructural feature of the chipmunk pinealocyte was the presence of extremely large numbers of "synaptic" ribbons. The number of "synaptic" ribbons in this species exceeded by a factor of five to 30 times that found in any species previously reported. In addition to pinealocytes, the pineal parenchyma contained glial cells (oligodendrocytes and fibrous astrocytes). Capillaries of the pineal gland of the chipmunk consisted of a fenestrated endothelium. Adrenergic nerve terminals were relatively sparse.

Comparison of some peptidic and proteic ovine pineal fractions with a bovine pineal E5 fraction

Using rather simple and mild extraction and separation methods, three ovine pineal fractions (XM 300 R-PP7.2' and PP7.2 S) were obtained, which contain peptidic/proteic substances and which show fluorescence characteristics of indoles. The ovine fractions were compared with the bovine pineal E-5 fraction. The ovine fractions are chemically sensitive to normal laboratory light and stable in red light (lambda greater than 600 nm). Immunologically, these fractions and the bovine E 5 fraction are stable. From the results of radioimmunological experiments it was concluded that the bovine pineal E 5 fraction as well as the ovine pineal fraction XM 300 R-PP7.2 and PP7.2S may contain (a) peptide(s) ending by the same carboxy terminal tripeptide Pro-Arg-Gly(NH2).

Effect of castration and adrenalectomy on the ultrastructure of pinealocytes in the female garden dormouse (Eliomys quericnus L.) under different conditions of lighting and temperature during the normal period of hibernation

The ultrastructure of the female garden dormouse pinealocyte has been studied during the period of hibernation in normal, castrated, castrated and adrenalectomized hibernant animals and non-hibernant ones living under a L-D = 10-14 photoperiodicity or continuous lighting. Continuous illumination on the one hand, and gonad and adrenalectomy on the other, have similar effects on the ultrastructure of pinealocytes. Especially a striking reduction of liposomes, an increased development of the Golgi apparatus and of cisterns formed by the rough endoplasmic reticulum were observed. The observations suggest that the liposomes are involved in a perhaps indoleaminergic antigonadotropic secretory process whereas the peculiar dilated cisterns of the rough endoplasmic reticulum may be related with a pineal polypeptidergic gonadotropic secretory process.

Ultrastructure of the pineal organ of the killifish, Fundulus heteroclitus, with special reference to the secretory function

The pineal organ of the killifish, Fundulus heteroclitus, was investigated by electron microscopy under experimental conditions; its general and characteristic features are discussed with respect to the photosensory and secretory function. The strongly convoluted pineal epithelium is usually composed of photoreceptor, ganglion and supporting cells. In addition to the well-differentiated photosensory apparatus, the photoreceptor cell contains presumably immature dense-cored vesicles (140-220 nm in diameter) associated with a well-developed granular endoplasmic reticulum in the perinuclear region and the basal process. These dense-cored vesicles appear rather prominent in fish subjected to darkness. The ganglion cell shows the typical features of a nerve cell; granular endoplasmic reticulum, polysomes, mitochondria and Golgi apparatus are scattered in the electron-lucent cytoplasm around the spherical or oval nucleus. The dendrites of these cells divide into smaller branches and form many sensory synapses with the photoreceptor basal processes. Lipid droplets appear exclusively in the supporting cell, which also contains well-developed granular endoplasmic reticulum and Golgi apparatus. Cytoplasmic protrusions filled with compact dense-cored vesicles (90-220 nm in diameter) are found in dark-adapted fish. The origin of these cytoplasmic protrusions, however, remains unresolved. Thus, the pineal organ of the killifish contains two types of dense-cored vesicles which appear predominantly in darkness. The ultrastructural results suggest that the pineal organ of fish functions not only as a photoreceptor but also as a secretory organ.