Showing papers on "Pinealocyte published in 2005"

The human pineal gland and melatonin in aging and Alzheimer's disease.

Abstract: The pineal gland is a central structure in the circadian system which produces melatonin under the control of the central clock, the suprachiasmatic nucleus (SCN). The SCN and the output of the pineal gland, i.e. melatonin, are synchronized to the 24-hr day by environmental light, received by the retina and transmitted to the SCN via the retinohypothalamic tract. Melatonin not only plays an important role in the regulation of circadian rhythms, but also acts as antioxidant and neuroprotector that may be of importance in aging and Alzheimer's disease (AD). Circadian disorders, such as sleep-wake cycle disturbances, are associated with aging, and even more pronounced in AD. Many studies have reported disrupted melatonin production and rhythms in aging and in AD that, as we showed, are taking place as early as in the very first preclinical AD stages (neuropathological Braak stage I-II). Degeneration of the retina-SCN-pineal axis may underlie these changes. Our recent studies indicate that a dysfunction of the sympathetic regulation of pineal melatonin synthesis by the SCN is responsible for melatonin changes during the early AD stages. Reactivation of the circadian system (retina-SCN-pineal pathway) by means of light therapy and melatonin supplementation, to restore the circadian rhythm and to relieve the clinical circadian disturbances, has shown promising positive results.

Mechanisms regulating melatonin synthesis in the mammalian pineal organ.

Abstract: The day/night rhythm in melatonin production is a characteristic feature in vertebrate physiology. This hormonal signal reliably reflects the environmental light conditions and is independent of behavioral aspects. In all mammalian species, melatonin production is regulated by norepinephrine, which is released from sympathetic nerve fibers exclusively at night. Norepinephrine elevates the intracellular cAMP concentration via beta-adrenergic receptors and activates the cAMP-dependent protein kinase A. This pathway is crucial for regulation of the penultimate enzyme in melatonin biosynthesis, the arylalkylamine N-acetyltransferase (AANAT); cAMP/protein kinase A may, however, act in different ways. In ungulates and primates, pinealocytes constantly synthesize AANAT protein from continually available Aanat mRNA. During the day-in the absence of noradrenergic stimulation-the protein is immediately destroyed by proteasomal proteolysis. At nighttime, elevated cAMP levels cause phosphorylation of AANAT by protein kinase A. This posttranslational modification leads to interaction of phosphorylated AANAT with regulatory 14-3-3 proteins, which protect AANAT from degradation. Increases in AANAT protein are paralleled by increases in enzyme activity. Stimulation of the cAMP/protein kinase A pathway may also activate pineal gene expression. In rodents, transcriptional activation of the Aanat gene is the primary mechanism for the induction of melatonin biosynthesis and results in marked day/night fluctuations in Aanat mRNA. It involves protein kinase A-dependent phosphorylation of the transcription factor cyclic AMP response element-binding protein (CREB) and binding of phosphorylated CREB in the promoter region of the Aanat gene. In conclusion, a common neuroendocrine principle, the nocturnal rise in melatonin, is controlled by strikingly diverse regulatory mechanisms. This diversity has emerged in the course of evolution and reflects the high adaptive plasticity of the melatonin-generating pineal organ.

Rhythmic serotonin N-acetyltransferase mRNA degradation is essential for the maintenance of its circadian oscillation.

Abstract: Serotonin N-acetyltransferase (arylalkylamine N-acetyltransferase [AANAT]) is the key enzyme in melatonin synthesis regulated by circadian rhythm. To date, our understanding of the oscillatory mechanism of melatonin has been limited to autoregulatory transcriptional and posttranslational regulations of AANAT mRNA. In this study, we identify three proteins from pineal glands that associate with cis-acting elements within species-specific AANAT 3' untranslated regions to mediate mRNA degradation. These proteins include heterogeneous nuclear ribonucleoprotein R (hnRNP R), hnRNP Q, and hnRNP L. Their RNA-destabilizing function was determined by RNA interference and overexpression approaches. Expression patterns of these factors in pineal glands display robust circadian rhythm. The enhanced levels detected after midnight correlate with an abrupt decline in AANAT mRNA level. A mathematical model for the AANAT mRNA profile and its experimental evidence with rat pinealocytes indicates that rhythmic AANAT mRNA degradation mediated by hnRNP R, hnRNP Q, and hnRNP L is a key process in the regulation of its circadian oscillation.

The melatonin-cytokine connection in rheumatoid arthritis

Abstract: Melatonin up regulates cytokine production and immune function A substance from pineal gland extracts, which lightens the skin melanocytes of amphibians and fishes, was isolated in 1958 and called melatonin (MLT, N -acetyl-5-methoxytryptamine).1 In both diurnal and nocturnal species, the absence of light at night stimulates MLT biosynthesis. Electrical signals originating from the retina reach the suprachiasmatic nuclei which, in turn, send inputs via the paraventricular nuclei to the spinal cord and then to the superior cervical ganglia. The fibres terminate at the pinealocytes.2 Absence of light results in increased norepinephrine release and activation of α1 and β-adrenergic receptors on the pinealocytes. This triggers a series of intracellular responses, resulting in activation of the enzymes N -acetyltransferase (EC 2.3.1.87) and hydroxyindole- O -methyl transferase (EC 2.1.1.4), which convert serotonin into MLT.2 The circadian nocturnal release of MLT has a profound influence on the internal environment of the organism, with diverse physiological effects. The main function of MLT seems to be that of synchronising the organism in the photoperiod and it may have a role in reproduction, metabolism, seasonality, thermoregulation, and immunity. Animal studies have shown that binding of MLT to specific receptors in antigen activated T helper (Th) cells results in an up regulation of cytokine production and immune function.3 In general, the immunoenhancing action of MLT seems restricted to T dependent antigens and to be most pronounced in immunodepressed situations. For example, MLT may completely counteract thymus involution and the immunological depression induced by stress or glucocorticoid treatment,4 or restore depressed immunological functions after soft tissue trauma and haemorrhagic shock.5 MLT may also rescue haematopoiesis in mice treated with cancer chemotherapeutic compounds.6 This effect apparently involves the endogenous release of granulocyte/macrophage colony stimulating factor and MLT-induced opioid cytokines.3,6,7 The …

Melatonin synthesis and melatonin-membrane receptor (MT1) expression during rat thymus development: role of the pineal gland.

Abstract: To gain insight into the relationship between thymus and pineal gland during rat development, the melatonin content as well as the activity and expression of the two key enzymes for melatonin biosynthesis, i.e. N-acetyltransferase (NAT) and hydroxyindole-O-methyltransferase (HIOMT), were studied in the thymus at fetal and postnatal stages. Moreover, melatonin-membrane receptor (MT1) expression was also analyzed. We found both the expression and activity of thymic NAT and HIOMT at 18 days of fetal life. Additionally, there is production of melatonin in the thymus as well as MT1 expression at this fetal age. These results show values higher in day-time than at night-time. The pineal gland begins to produce significant levels of melatonin around postnatal day 16, and this synthesis shows a circadian rhythm with high values during the dark period; therefore the nocturnal serum melatonin may inhibit thymic melatonin production. To document this, we report an increased melatonin content of the thymus in pinealectomized rats compared with sham-pinealectomized. In conclusion, these results show, for the first time, the presence of the biosynthetic machinery of melatonin and melatonin production in developing rat thymus and that the pineal gland may regulate this process.

The rhythm and blues of gene expression in the rodent pineal gland.

Abstract: In all vertebrates, melatonin is rhythmically synthesized in the pineal gland and functions as a hormonal message, encoding for the duration of night. In rodents, the nocturnal rise and fall of the arylalkylamine N-acetyltransferase (AA-NAT) activity controls the rhythmic synthesis of melatonin. This rhythm is centered around the transcriptional regulation of the AA-NAT by two norepinephrine-inducible transcription factors, the activator CREB (Ca2+/cAMP-response element binding protein) and the inhibitor ICER (inducible cAMP early repressor). CREB is activated by phosphorylation, which is one of the fastest responses in pinealocytes upon adrenergic stimulation, occurring within minutes. ICER in turn accumulates only after several hours, a time gap resulting from the required de novo protein synthesis upon adrenergic stimulation. However, these molecular components of neuroendocrine signaling in the rodent pineal gland are supplemented by the impact of a variety of neurotransmitters and neuromodulators, and by translational and post-translational mechanisms. By molecular crosstalk, those different inputs on pinealocytes seem to fine-tune the shape of the melatonin signal, by interacting at various levels with the NE/cAMP/pCREB/ICER pathway. In addition, these alternate signaling routes may be important in acute “emergency” situations. Together, concerted signaling events in the rodent pineal gland help to generate a stable and reliable hormonal message of darkness for the body, that, however, can be altered rapidly upon sudden and unexpected “error” signals.

Reactive changes of interstitial glia and pinealocytes in the rat pineal gland challenged with cell wall components from gram-positive and -negative bacteria

Abstract: Lipopolysaccharide (LPS), the major proinflammatory component of gram-negative bacteria, is well known to induce sepsis and microglial activation in the CNS. On the contrary, the effect of products from gram-positive bacteria especially in areas devoid of blood-brain barrier remains to be explored. In the present study, a panel of antibodies, namely, OX-6, OX-42 and ED-1 was used to study the response of microglia/macrophages in the pineal gland of rats given an intravenous LPS or lipoteichoic acid (LTA). These antibodies recognize MHC class II antigens, complement type 3 receptors and unknown lysosomal proteins in macrophages, respectively. In rats given LPS (50 microg/kg) injection and killed 48 h later, the cell density and immunoexpression of OX-6, OX-42 and ED-1 in pineal microglia/macrophages were markedly increased. In rats receiving a high dose (20 mg/kg) of LTA, OX-42 and OX-6, immunoreactivities in pineal microglia/macrophages were also enhanced, but that of ED-1 was not. In addition, both bacterial toxins induced an increase in astrocytic profiles labelled by glial fibrillary acid protein. An interesting feature following LPS or LTA treatment was the lowering effect on serum melatonin, enhanced serotonin immunolabelling and cellular vacuolation as studied by electron microscopy in pinealocytes. The LPS- or LTA-induced vacuoles appeared to originate from the granular endoplasmic reticulum as well as the Golgi saccules. The present results suggest that LPS and LTA could induce immune responses of microglia/macrophages and astroglial activation in the pineal gland. Furthermore, the metabolic and secretory activity of pinealocytes was modified by products from both gram-positive and -negative bacteria.

Molecular components and mechanism of adrenergic signal transduction in mammalian pineal gland: regulation of melatonin synthesis.

Abstract: Rhythmic neural outputs from the hypothalamic suprachiasmatic nucleus (SCN), which programme the rhythmic release of norepinephrine (NE) from intrapineal nerve fibers, regulate circadian rhythm of melatonin synthesis. Increased secretion of NE with the onset of darkness during the first half of night stimulates melatonin synthesis by several folds. NE binds to both alpha1- and beta-adrenergic receptors present on the pinealocyte membrane and initiates adrenergic signal transduction via cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) generating pathways. The NE-induced adrenergic signal transduction switches 'on' melatonin synthesis during the early hours of night by stimulating expression of the rate-limiting enzyme of melatonin synthesis, N-acetyltransferase (AA-NAT) via cAMP-protein kinase A (PKA)-cAMP response element binding protein (CREB)-cAMP response element (CRE) pathway as well as by increasing AA-NAT activity via cAMP-PKA-14-3-3 protein pathway. Simultaneously, adrenergically-induced expression of inducible cAMP early repressor (ICER) negatively regulates aa-nat gene expression and controls the amplitude of melatonin rhythm. In the second half of night, increased release of acetylcholine from central pinealopetal projections, inhibition of NE secretion by SCN, withdrawal of adrenergic inputs and reversal of events that took place in the first half lead to switching 'off' of melatonin synthesis. Adrenergic signal transduction via cGMP-protein kinase G (PKG)-mitogen activated protein kinase (MAPK)-ribosomal S6 kinase (RSK) pathway also seems to be fully functional, but its role in modulation of melatonin synthesis remains unexplored. This article gives a critical review of information available on various components of the adrenergic signal transduction cascades involved in the regulation of melatonin synthesis.

Pineal circadian clocks gate arylalkylamine N‐acetyltransferase gene expression in the mouse pineal gland

Abstract: In mammals it has been thought that the circadian clock localizes only in the suprachiasmatic nucleus of the hypothalamus. Recent studies have revealed that certain brain regions and peripheral tissues may also have intrinsic circadian clocks. However, the roles played by 'peripheral circadian clocks' have not been fully elucidated. In this study, we investigated their function using mouse pineal glands, and found that expression of the arylalkylamine N-acetyltransferase (Aa-Nat, EC 2.3.1.87, the rate-limiting enzyme of melatonin synthesis) gene after adrenergic receptor stimulation depended on the time of day even in vitro (gating). Phase-dependent Aa-Nat responses were observed in both melatonin-proficient and melatonin-deficient mouse pineal glands. Phosphodiesterases are unlikely to suppress Aa-Nat induction because a phosphodiesterase inhibitor itself had no effect on the mRNA levels. Puromycin was ineffective in inducing Aa-Nat mRNA levels in either the presence or absence of isoproterenol, suggesting that newly synthesized proteins may not be necessary to gate the Aa-Nat responses. We also discovered circadian dependence of the expression of Period1-luminescence in Period1-luciferase transgenic mouse pineal glands: circadian clocks may be functional in culture. Aa-Nat mRNA levels showed no significant circadian rhythms in the absence of isoproterenol, thus suggesting that Aa-Nat mRNA levels are induced by adrenergic mechanisms, not by a pineal circadian clock. Our results suggest that the pineal circadian clock may determine timing when Aa-Nat gene expression can respond to inputs from the master circadian clock in the suprachiasmatic nucleus, e.g. adrenergic stimulation.

Features of the Circadian Clock in the Avian Pineal Gland

Abstract: The effects of different environmental factors on the circadian rhythm of melatonin release by chicken pineal glands were analyzed in 5-day experiments in vitro. Periodic, brief 4-h illumination at around midnight resulted in phase inversion in 2 days. Exposure to repeated 41 degrees C temperature elevation at around midnight caused no phase shift in the basic melatonin rhythm. Repeated inversion of the polarity of the magnetic field also affected rhythmic melatonin release. Additionally, expressions of Per1, Per2, Per3, Bmal1, Bmal2, Clock, Cry1, and Cry2 clock genes were simultaneously detected in single chicken pineal glands.

Post-hatching development of the turkey pineal organ: histological and immunohistochemical studies.

Abstract: Objective The study was performed to analyze structural changes of the turkey pineal during the post-hatching development. Material and methods The pineals were collected from male turkeys at the age of 1 day, 2, 8, 22, 56 weeks and subjected to histological investigations including morphometrical analyses. The pinealocytes were identified immunohistochemically using antiserum against hydroxyinolo-O-methyltransferase (HIOMT). Results and conclusions Independently of age, the pineal consisted of a narrow proximal part and a club-shaped top. The narrow part extended into the stalk attached to the diencephalon. The pineal parenchyma was formed by the follicles, surrounded by the connective tissue. The caudal part of the organ contained the pineal lumen, which prolonged into the stalk lumen. Up to the age of two weeks the stalk lumen was open to the third ventricle, later--closed. The proximal part of the stalk showed age-dependent reduction. During the investigated period of life, the pineal increased in size due to creation of new follicles, enlargement of the follicles and development of the stroma. In immature turkeys, the follicular wall was formed by elongated cells bordering the lumen and sparse, peripherally localized, round cells. This pseudostratified organization was transformed during ontogenesis into thick, multilayer structure (characteristic for 22- and 56-week-old turkeys) composed by the layer of elongated cells and several layers of round cells, located peripherally. The rudimentary-receptor and secretory pinealocytes were demonstrated based on HIOMT-immunoreactivity. The secretory pinealocytes were sparse in young birds and predominated in mature turkeys. Intra-pineal calcified concrements occurred in 56-week-old turkeys.

Dopamine receptor activation in bovine pinealocyte via a cAMP-dependent transcription pathway.

Abstract: D 1 - and D 2 -dopamine receptors in the bovine pineal gland were previously identified and characterized. The data indicate that the density of D 1 -dopamine receptors far exceeded that of D 2 -dopamine receptors. In our previous study, the mRNA for both the D 1 - and D 2 -dopamine receptors which elucidated the status of dopamine and its possible involvement in the pineal function was identified. A selective D 1 -agonist enhanced N-acetyltransferase (NAT) activity and increased the melatonin level, whereas, a selective D 2 -agonist inhibited NAT activity and decreased the melatonin level. An attempt has been made in the present study to clarify the mechanism of dopamine in controlling melatonin production in bovine pineal. The level of intracellular cyclic 3',5'-adenosine monophosphate (cAMP) was determined after a 2-hr incubation of bovine pinealocytes with selected combinations of drugs. SKF 38393, a selective D 1 -agonist, enhanced intracellular level of cAMP, and its effect was blocked by SCH 23390, a D 1 -selective antagonist. In contrast quinpirole, a selective D 2 -agonist, inhibited forskolin-stimulated intracellular level of cAMP while its effect was blocked by a D 2 -selective antagonist, spiperone. In addition, the dopamine-dependent phosphorylation of the transcription factors, cAMP responsive element-binding protein (CREB) was investigated. Immunoblots showed that SKF 38393 enhanced CREB phosphorylation and the stimulatory effect was abolished by SCH 23390 whereas quinpirole inhibited forskolin-stimulated phosphorylated CREB production and the inhibitory effect was prevented by spiperone. Taken together with our previous data, the results indicate that activation of D 1 -dopamine receptor in bovine pinealocyte stimulates NAT activity and enhances melatonin level whereas activation of D 2 -dopamine receptor leads to an inhibitory effect and these stimulatory and inhibitory effects act, in part, via a cAMP-dependent transcription mechanism.

Proteasomal proteolysis in the adrenergic induction of arylalkylamine-N-acetyltransferase in rat pinealocytes.

Abstract: In this study, we investigated the effect of proteasomal inhibition on the induction of arylalkylamine-N-acetyltransferase (AA-NAT) enzyme in cultured rat pinealocytes, using two proteasome inhibitors, MG132 and clastolactacystin β-lactone (c-lact). Addition of c-lact or MG132 3 h after norepinephrine (NE) stimulation produced a significant increase in AA-NAT protein level and enzyme activity. However, when the proteasome inhibitors were added before or together with NE, significant reductions of the NE-induced aa-nat mRNA, protein, and enzyme activity were observed. A similar inhibitory effect of MG132 on aa-nat transcription was observed when cells were stimulated by dibutyryl cAMP, indicating an effect distal to a post-cAMP step. The inhibitory effect of MG132 on adrenergic-induced aa-nat transcription was long lasting because it remained effective after 14 h of washout and appeared specific for aa-nat because the induction of another adrenergic-regulated gene, MAPK phosphatase-1, by NE was not affecte...

Vitamin A is a necessary factor for sympathetic-independent rhythmic activation of mitogen-activated protein kinase in the rat pineal gland.

Abstract: The circadian clock in the suprachiasmatic nucleus (SCN) controls day-to-day physiology and behavior by sending timing messages to multiple peripheral oscillators. In the pineal gland, a major SCN target, circadian events are believed to be driven exclusively by the rhythmic release of norepinephrine from superior cervical ganglia (SCG) neurons relaying clock messages through a polysynaptic pathway. Here we show in rat an SCN-driven daily rhythm of pineal MAPK activation that is not dependent on the SCG and whose maintenance requires vitamin A as a blood-borne factor. This finding challenges the dogma that SCG-released norepinephrine is an exclusive mediator of SCN-pineal communication and allows the assumption that humoral mechanisms are involved in pineal integration of temporal messages.

Cell culture models for oscillator and pacemaker function: recipes for dishes with circadian clocks?

Abstract: Primary cell cultures of avian pinealocytes and the mammalian suprachiasmatic nucleus (SCN), immortalized cell lines derived from the SCN (SCN2.2), and fibroblasts derived from mice and rats have been employed as in vitro models to study the cellular and molecular mechanisms underlying circadian biological clocks. This article compares and contrasts these model systems and describes methods for avian pinealocyte cultures, immortalized SCN2.2 cells, and mouse fibroblast culture. Each of these culture models has advantages and disadvantages. Avian pinealocytes are photoreceptive, contain a circadian pacemaker, and produce rhythms of an easily assayed endocrine output—melatonin. However, the molecular mechanisms underlying pinealocyte function are not understood. SCN2.2 cells express metabolic and molecular rhythms and can impose rhythmicity on cocultured cells as well as rat behavior when transplanted into the brain. Yet, the entrainment pathways are not experimentally established in these cells. Fibroblast cultures are simple to produce and express molecular clock gene rhythms, but they express neither physiological rhythmicity nor pacemaker properties. The relative merits of these culture systems, as well as their impact on understanding circadian organization in vivo, are also considered.

Tachykinins and tachykinin-receptors in the rat pineal gland

Abstract: High-pressure liquid chromatography of extracts of rat pineal glands, followed by radio immunological analysis with antibodies against tachykinins, demonstrated the presence of substance P, neurokinin A and neurokinin B in the superficial rat pineal gland. Immunohistochemistry on perfusion-fixed rat brain sections showed substance P and neurokinin A to be present in nerve fibers located both in the perivascular spaces as well as intraparenchymally between the pinealocytes. After extracting total RNA, followed by reverse transcription and polymerase chain reaction amplification with primers specific for NK1-, NK2- and NK3-receptors, agarose gel analysis of the reaction products showed the presence of mRNA encoding all three neurokinin receptors. Immunohistochemical analysis showed NK1 receptor to be located in the interstitial cells of the gland. This location was confirmed by use of in situ hybridization using radioactively labeled antisense oligonucleotide probes. Double immunohistochemical stainings showed that the NK1-immunoreactive cells were not a part of the macrophages or antigen-presenting cells of the gland. Our study suggests that tachykinins, after release from intrapineal nerve fibers, are involved in an up to now unknown function, different from that of melatonin synthesis.

Immunohistochemical demonstration of opioids and tachykinins in human pineal gland.

Abstract: The human pineal gland secretes melatonin in a circadian rhythm manner. The rhythm of melatonin synthesis is primarily controlled by the noradrenergic sympathetic system originating from the superior cervical ganglion. Several neurotranmitters/neuropeptides have been reported to influence the production of melatonin in the pineal glands of many mammalian species. Both opioid peptide, a pain suppressing peptide and substance P, a pain inducing peptide were also reported to be present in the pineal gland of several kinds of mammals. However, few studies have been demonstrated in humans. Therefore, in the present study, the immunohistochemical investigation was performed in the human pineal gland by using antisera raised against leu-enkephalin, met-enkephalin and beta-endorphin to demonstrate an opioidergic system; and antisera raised against substance P, neurokinin A, and neurokinin B to study a tachykinin system. A high amount of leu- and met-enkephalin immunoreactivities were observed in intrapineal neuronal-like cells while very few were presented in nerve fibers. This result suggests a local regulatory function or paracrine opioidergic control in human pineal. Substance P- and neurokinin A-immunoreactivities, but not neurokinin B were observed in the human pineal gland. They are located mostly in nerve fibers but a few in neuronal-like cells. The tachykininergic control of human pineal is mainly from the nerve fibers which have their perikaryal origin outside the gland. Some of the nerve fibers might originate from neurons in the brain and/or from a peripheral ganglion.

The expression of α-internexin and peripherin in the developing mouse pineal gland

Abstract: The mammalian pineal gland contains pinealocytes, interstitial glial cells, perivascular macrophages, neurons and neuron-like cells The neuronal identity of neurons and neuron-like cells was an enigma α-Internexin and peripherin are specific neuronal intermediate filament proteins and are expressed differentially in the CNS and PNS We investigated the development of immunoreactivity and expression patterns of mRNAs for α-internexin and peripherin in the mouse pineal gland to determine the neuronal identity of these cells Both α-internexin- and peripherin-immunoreactive cells were readily visualized only after birth Both proteins were at the highest level on the postnatal day 7 (P7), rapidly declined at P14, and obtained their adult level at P21 Both protein and mRNA of α-internexin are expressed in some cells and nerve processes, but not all, of adult mouse pineal gland Less number of peripherin immunoreactive or RNA-expressing cells and nerve processes were identified Accumulations of α-internexin and peripherin proteins were also found in the cells from the aged pineal gland (P360) We concluded that some cells in the developing mouse pineal gland may differentiated into neurons and neuron-like cells expressing both α-internexin and/or peripherin only postnatally, and these cells possess dual properties of CNS and PNS neurons in nature We suggested that they may act as interneurons between the pinealocyte and the distal neurons innervating the pinealocytes, or form a local circuitry with pinealocytes to play a role of paracrine regulatory function on the pinealocytes

N-bromoacetyltryptamine strongly and reversibly inhibits in vitro melatonin secretion from mammalian pinealocytes.

Abstract: OBJECTIVES: Cell-permeable and specific inhibitors of melatonin secretion are sill lacking among tools of the pineal research Recently, a large effort has been made in the development of arylalkylamine N-acetyltransferase inhibitors, but in most cases the new drugs were tested exclusively using cell-free assays or non-pineal cells The aim of the present study was to characterize the effect of N-bromoacetyltryptamine (BAT), the first synthesized cell-permeable inhibitor of arylalkylamine N - acetyltransferase, on melatonin secretion from rat and pig pineal glands METHODS: The studies were performed in the superfusion cultures of rat and pig pineal explants Melatonin secretion was determined by radioimmunoassay (RIA) RESULTS: BAT strongly inhibited the non-stimulated and norepinephrine - stimulated melatonin secretion from the pig and rat pineal explants, with ED50 03 - 07 microM The adrenergic stimulation did not modify significantly the inhibitory potency of BAT on the melatonin release The decline in melatonin secretion induced by the BAT - treatment was biphasic in both rat and pig pinealocytes, with an initial rapid phase followed by a slow one The half-time of BAT-induced decline in the non - stimulated and norepinephrine-stimulated melatonin secretion was ca 25 - 35 minutes The inhibitory effect of BAT was reversible in pinealocytes of both investigated mammals CONCLUSIONS: The results show that BAT is a potent and reversible inhibitor of the melatonin secretion in the mammalian pineal gland and open the way for the use of this inhibitor in investigations on the pinealocyte physiology performed in vitro

Demonstration of PACAP-immunoreactive intrapineal nerve fibers in the golden hamster (Mesocricetus auratus) originating from the trigeminal ganglion.

Abstract: By using immunohistochemistry, a network of nerve fibers containing pituitary adenylate-cyclase activating polypeptide (PACAP) was demonstrated in the pineal gland of the golden hamster, a photoperiodic species often used in pineal and circadian rhythm research. The nerve fibers are present in the capsule from where they permeate into the pineal perivascular spaces and parenchyma. Immuno-electron microscopy showed the PACAPergic nerve terminals, with clear transmitter vesicles, to terminate in the interstitial spaces between the pinealocytes or in the perivascular spaces. Some of the PACAPergic nerve terminals made synapse-like contacts with the pinealocytes. The origin of the PACAP-containing nerve fibers innervating the pineal gland of the hamster was investigated by combined retrograde tracing with fluorogold and immunohistochemistry for PACAP. A 2% fluorogold solution was injected iontophoretically into the superficial pineal gland and the animals were allowed to survive for 1 wk. After perfusion fixation of the rats, the location of the tracer was investigated in the brain, the parasympathetic sphenopalatine, and otic ganglia, as well as in the sensory trigeminal ganglia. The tracer was found in perikarya of all the investigated ganglia. However, co-localization with PACAP was found only in the trigeminal ganglion.

Morphological and biochemical study of the pineal gland of pregnant and non-pregnant female vizcachas (Lagostomus maximus maximus).

Abstract: OBJECTIVES: The morphological and biochemical aspects of the pineal gland of pregnant and non-pregnant female vizcachas were investigated to examine whether there is a relationship between the pregnancy and this gland. METHODS: Pregnant and non-pregnant adult female vizcachas were used. The ultrastructure of type I cell (dark and light pinealocytes) was studied. Pineal and serum melatonin were investigated by radioimmunoassay. Radiometric methods were applied to investigate the arylalkylamine-N-acetyltransferase (AA-NAT) and hydroxyindole-O-methyltransferase (HIOMT) activities. RESULTS: The morphological study showed the existence of dark and light pinealocytes. The differences between both cells are slight. However, the appearance of dark pinealocytes suggests that they have a high activity. These cells were more abundant in the pineal gland of pregnant females. The pineal melatonin levels and the AA-NAT activity were higher in the pregnant females. Serum melatonin and HIOMT activity did not show significant differences. CONCLUSION: Our results suggest that the morphological and biochemical changes in the pineal gland of pregnant vizcachas are associated with the gestation. However, the relation between the pineal gland and the pregnancy is complex and further studies are necessaries to clearly establish it.

Ultrastructural and Morphometric Study of the Pineal Complex in Indian Major Carp Catla Catla in Response to Continuous Light and Darkness

Abstract: The present communication deals with the ultrastructurai and morphometric study of the pineal complex in a hitherto unstudied Indian major carp Catia catla . In this fresh water teleost, the pineal complex is a discrete structure composed of a distal 'end vesicle' (EV), a long connecting 'pineal stalk' (PS), and a convoluted 'dorsal sac' (DS). Light microscopic study demonstrated that the parenchyma of the EV contains two types of cells, viz., 'light cells', and 'dark cells'; of which only 'light cells' exhibit significant annual cyclic variations in the nuclear diameter. Consequently, attempts have been made to employ transmission electron microscopy for identification and characterization of the photosensory cellular components of the pineal complex in the carps following exposure to continuous illumination (LL; 24L) or continuous darkness (DD : 24D) for 30 days during the different phases of an annual reproductive cycle. The study also indicated the presence of two types of cells which shared the features of photoreceptorand supporting cells in the EV of the pineal complex respectively. Significant changes were noted in the size and shape of various sub-cellular organelles in the photoreceptor-, but not in the supporting cells of the pineal EV following exposure to LL or DD schedules. While an increase in the nuclear diameter was noted in the photoreceptor cells of EV in the carp held under DD in each part of the annual gonadal cycle, significant regressive changes occurred in the photoreceptor cells of the EV in LL group offish but only during the preparatory and the pre-spawning phases of theannual cycle. Commonly, it was found that an increase in the number of secretory granules, synaptic vesicles and synaptic ribbons, and hypertrophy of mitochondria occurred in the pinealocytes of carps held under DD, while regressive changes in the parenchymal cells of EV resulted in the pineal complex following exposure to LL. It was interesting to note that morphometric and uitrastructurai changes in response to altered lighting conditions were demonstrable only in the EV, but not in the PS and DS of the pineal complex. Thus, it appeared conclusive that the pineal complex in Catla catla is directly associated with photoreception, and the EV is the only part of pineal complex that performs the alleged function. However, the etiology of differential responsiveness of the EV photoreceptor cells to LL in different parts of annual reproductive functions remains unknown.

Age-related histological changes in the pineal gland (epiphysis cerebri) of the dog

Abstract: The histological changes with the progress of age in the pineal gland of dogs were studied. Twenty dogs of both sexes clinically healthy were used. Two dogs from different ages were chosen from 2 days of age up to 4 years of age. The size and shape of the pineal gland showed no or little change with the progress of age. The pineal recess of the newly born dogs consisted of arrow cleft remained unchanged up to maturity. The changes were classifiedinto3stages. The first one, the parenchyma was highly cellular with either randomly distributed cells or cords-like structure. The main cellular elements were the pinealocytes and few glial cells. The mitotic figure was predominant. From the second stage onward, the number of pinealocytes decreased and the number of both glial and pyknotic cells increased. The glial filaments appeared long and branched at 4 months old dogs. The pigmented cells appeared at 2 days old dogs and became more with the advances of age. In conclusion, the decrease in the number of pinealocytes in our results could be attributed to either the pinealocytes undergoes differentiation to other cells similar to glial cells, due to change in nuclear morphology and the presence of large numbers of glial filaments, or by pyknosis in which the pinealocytes degenerated. The last suggestion augmented by wide separation of the cells from2years old dog onward.

Ultrastructural organization of epiphysis in rats under the action of electromagnetic fields and during mammary carcinogenesi.

Abstract: Experiments conducted by the authors, as well as clinical studies, show that in addition to hormonal mis-balance, development of mammary gland cancer is significantly influenced by the action of low frequency electromagnetic fields on epiphysis By reducing the production of melatonin it increases the risk of development of mammary gland tumors The review of scientific literature indicates that pinealocytes are the main morphological substrate responsible for functional activity of pineal cells When estimating large specific weight of lipids, many researchers point to the dependence of their presence in epiphysis on the level of melatonin It is thought that hormones of pineal cells are deposited in the form of lipid drops The most characteristic feature in the structure of pinealocytes is the presence of large number of various size complexes in their bodies and appendices According to many authors this could be the form of depositing the secretory products of pinealocytes, such as melatonin, biological amines, etc Ultrastructure characteristic of pinealocytes described in the review provides deeper understanding of the fine structure morpho-physiology of epiphysis, enable to point out the peculiarities of its functionality under the influence of electromagnetic fields and discover the organizational structure of pineal body at a time of the mammary gland tumor development

Comparative biochemical observations on rat pineal gland and serum

Abstract: The comparative biochemistry of the pineal gland and the serum in 24 rats is reported in the present study. Glucose, urea, alkaline and acid phosphatases, aspartate and alanine aminotransferases, calcium and phosphorous values were estimated and these values were represented in terms of milligrams of protein. Glucose and urea values were about three and forty six times higher in the pineal tissue than in serum. The activity of phosphatases, aminotransferases were also higher in the pineal. The higher value of glucose and alkaline phosphatase activity is indicative high level of energy metabolism going on in the pinealocytes. The calcium: phosphorus ratio in the pineal gland and serum were 1.68:1.00 and 1.00:1.01 respectively. The present study indicates that the pineal gland represents a glandular tissue having high metabolism and cannot be considered as brain sand or vestige.