Showing papers on "Pinealocyte published in 2010"

TLR4 and CD14 receptors expressed in rat pineal gland trigger NFKB pathway.

Abstract: Nuclear factor-kappa B (NFKB), a pivotal player in inflammatory responses, is constitutively expressed in the pineal gland. Corticosterone inhibits pineal NFKB leading to an enhancement of melatonin production, while tumor necrosis factor (TNF) leads to inhibition of Aa-nat transcription and the production of N-acetylserotonin in cultured glands. The reduction in nocturnal melatonin surge favors the mounting of the inflammatory response. Despite these data, there is no clear evidence of the ability of the pineal gland to recognize molecules that signal infection. This study investigated whether the rat pineal gland expresses receptors for lipopolysaccharide (LPS), the endotoxin from the membranes of Gram-negative bacteria, and to establish the mechanism of action of LPS. Here, we show that pineal glands possess both CD14 and toll-like receptor 4 (TLR4), membrane proteins that bind LPS and trigger the NFKB pathway. LPS induced the nuclear translocation of p50/p50 and p50/RELA dimers and the synthesis of TNF. The maximal expression of TNF in cultured glands coincides with an increase in the expression of TNF receptor 1 (TNFR1) in isolated pinealocytes. In addition, LPS inhibited the synthesis of N-acetylserotonin and melatonin. Therefore, the pineal gland transduces Gram-negative endotoxin stimulation by producing TNF and inhibiting melatonin synthesis. Here, we provide evidence to reinforce the idea of an immune-pineal axis, showing that the pineal gland is a constitutive player in the innate immune response.

Daily variation of constitutively activated nuclear factor kappa b (nfkb) in rat pineal gland

Abstract: In mammals, the production of melatonin by the pineal gland is mainly controlled by the suprachiasmatic nuclei (SCN), the master clock of the circadian system. We have previously shown that agents involved in inflammatory responses, such as cytokines and corticosterone, modulate pineal melatonin synthesis. The nuclear transcription factor NFKB, detected by our group in the rat pineal gland, modulates this effect. Here, we evaluated a putative constitutive role for the pineal gland NFKB pathway. Male rats were kept under 12 h:12 h light-dark (LD) cycle or under constant darkness (DD) condition. Nuclear NFKB was quantified by electrophoretic mobility shift assay on pineal glands obtained from animals killed throughout the day at different times. Nuclear content of NFKB presented a daily rhythm only in LD-entrained animals. During the light phase, the amount of NFKB increased continuously, and a sharp drop occurred when lights were turned off. Animals maintained in a constant light environment until ZT 18 showed diurnal levels of nuclear NFKB at ZT15 and ZT18. Propranolol (20 mg/kg, i.p., ZT 11) treatment, which inhibits nocturnal sympathetic input, impaired nocturnal decrease of NFKB only at ZT18. A similar effect was observed in free-running animals, which secreted less nocturnal melatonin. Because melatonin reduces constitutive NFKB activation in cultured pineal glands, we propose that this indolamine regulates this transcription factor pathway in the rat pineal gland, but not at the LD transition. The controversial results regarding the inhibition of pineal function by constant light or blocking sympathetic neurotransmission are discussed according to the hypothesis that the prompt effect of lights-off is not mediated by noradrenaline, which otherwise contributes to maintaining low levels of nuclear NFKB at night. In summary, we report here a novel transcription factor in the pineal gland, which exhibits a constitutive rhythm dependent on environmental photic information.

Photoimmunomodulation and melatonin

Abstract: The seasons, and daily physical rhythms can have a profound effect on the physiology of the living organism, which includes immune status. The immune system can be influenced by a variety of signals and one of them is photic stimulus. Light may regulate the immunity through the neuroendocrine system leading to the most recent branch of research the “Photoimmunomodulation”. Mammals perceive visible light (400–700 nm) through some specialized photoreceptors located in retina like retinal ganglion cells (RGC). This photic signal is then delivered to the visual cortex from there to the suprachiasmatic nucleus (SCN) of the hypothalamic region. Melatonin – one of the universally accepted chronobiotic molecule secreted by the pineal gland is now emerging as one of the most effective immunostimulatory compound in rodents and as oncostatic molecule at least in human. Its synthesis decreases with light activation along with norepinephrine and acetylcholine. The changes in level of melatonin may lead to alterations (stimulatory/inhibitory) in immune system. The evidences for the presence of melatonin receptor subtypes on lymphoid tissues heralded the research area about mechanism of action for melatonin. Further, melatonin receptor subtypes-MT1 and MT2 was noted on pars tuberalis, SCN and on lymphatic tissues suggesting a direct action of melatonin in modulation of immunity by photoperiod as well. The nuclear receptors (ROR, RZR etc.) of melatonin are known for its free radical scavenging actions and might be indirectly controlling the immune function.

Modulation of Aanat gene transcription in the rat pineal gland.

Abstract: The main function of the rat pineal gland is to transform the circadian rhythm generated in the suprachiasmatic nucleus into a rhythmic signal of circulating melatonin characterized by a large nocturnal increase that closely reflects the duration of night period. This is achieved through the tight coupling between environmental lighting and the expression of arylalkylamine-N-acetyltransferase, the rhythm-controlling enzyme in melatonin synthesis. The initiation of Aanat transcription at night is controlled largely by the norepinephrine-stimulated phosphorylation of cAMP response element-binding protein by protein kinase A. However, to accurately reflect the duration of darkness, additional signaling mechanisms also participate to fine-tune the temporal profile of adrenergic-induced Aanat transcription. Here, we reviewed some of these signaling mechanisms, with emphasis on the more recent findings. These signaling mechanisms can be divided into two groups: those involving modification of constitutively expressed proteins and those requiring synthesis of new proteins. This review highlights the pineal gland as an excellent model system for studying neurotransmitter-regulated rhythmic gene expression.

'TRPing' synaptic ribbon function in the rat pineal gland: neuroendocrine regulation involves the capsaicin receptor TRPV1.

Abstract: Synaptic ribbons (SRs) are presynaptic structures thought to regulate and facilitate multivesicular release. In the pineal gland, they display a circadian rhythm with higher levels at night paralleling melatonin synthesis. To gain more insight into the processes involved and the possible functions of these structures, a series of experiments were conducted in rodents. We studied the regional distribution of a molecular marker of pineal SRs, the kinesin motor KIF3A in the gland. Respective immunoreactivity was abundant in central regions of the gland where sympathetic fibers were less dense, and vice versa, revealing that intercellular communication between adjacent pinealocytes is enhanced under low sympathetic influence. KIF3A was found to be colocalized to the transient receptor potential channel of the vanilloid receptor family, subtype 1 (TRPV1). The TRPV1 agonist capsaicin increased melatonin secretion from perifused pineals in a dose-dependent manner that was blocked by the competitive TRPV1 antagonist capsazepine. No change in free intracellular calcium was observed in response to TRPV1 ligands applied to pinealocytes responding to norepinephrine, bradykinin and/or depolarization. These data clearly indicate that TRPV1 actively regulates pineal gland function.

d‐Aspartate Oxidase Localisation in Pituitary and Pineal Glands of the Female Pig

Abstract: Recent evidence has shown that d-aspartate modulates hormone secretion in the vertebral neuroendocrine system. Because only d-aspartate oxidase (DDO) can degrade d-aspartate, we determined DDO localisation in the pituitary and pineal glands to elucidate the control mechanisms of local d-aspartate concentration. Brain tissues and pituitary and pineal glands of the female pigs contained a similar DDO activity of 0.38–0.66 U/g protein. However, approximately ten-fold higher concentrations of d-aspartate (0.27–0.35 μmol/g protein) were found in both glands. To determine the distribution of immunoreactive DDO, we made a rabbit polyclonal antibody specific to porcine DDO using a recombinant porcine enzyme. DDO immunoreactivity was found in the cytoplasm of a subgroup of cells in the anterior and intermediate lobes, in a part of nerve processes and terminals in the posterior lobe, and in the cytoplasm of a small group of pinealocytes. We used dual-label immunocytochemistry to determine which pituitary hormones colocalise with DDO, and whether DDO and d-aspartate immunoreactivity is reciprocal. In the pituitary gland, almost all proopiomelanocortin-positive cells colocalised DDO, whereas only growth hormone-positive cells colocalised d-aspartate. d-Aspartate immunoreactivity was not detected where DDO immunoreactivity was found. The present study suggests that DDO plays important roles to prevent undesirable off-target action of d-aspartate by strictly controlling local d-aspartate concentration in the pituitary and pineal glands.

Melatonin reduces oxidative catastrophe in neurons and glia

Abstract: melatonin; reactive oxygen species; reactive nitrogen species; free radicals; oxidative stress; neurons; glia; neurodegenerative diseases Abstract Melatonin, the chief secretory product of the pineal gland, is an uncommonly effective direct free radical scavenger and indirect antioxidant. It detoxifies both reactive oxygen (ROS) and reactive nitrogen species (RNS), both groups of which are abundantly produced in the brain. Endogenously-generated melatonin is discharged from pinealocytes into the rich capillary plexus in the gland and may also be released directly into the cerebrospinal fluid (CSF). In the few species where it has been investigated, CSF levels of melatonin greatly exceed its concentrations in the blood. From both the CSF and the blood melatonin readily enters the brain to protect neurons and glia from molecular damage induced by ROS/RNS. Melatonin's efficacy in reducing molecular damage resulting from toxic oxygen and nitrogen derivatives in both the brain and spinal cord supports the notion that this non-toxic molecule may have utility in forestalling and/or delaying the development and progression of neurodegenerative diseases that have a massive free radical component. The disease models of interest and in which melatonin has been most thoroughly tested include Alzheimer disease, Parkinson disease and to a lesser extent Huntington disease and amyotrophic lateral sclerosis. The experim ental findings summarized herein clearly document that melatonin readily prevents oxidative damage to both neurons and glia. In doing so, it greatly reduces apoptosis of critical cells within the central nervous system.

Calcium concrements in the pineal gland of the Arctic fox (Vulpes lagopus) and their relationship to pinealocytes, glial cells and type I and III collagen fibers.

Abstract: The aim of the present study was to analyze the presence and morphology of the pineal concretions in the Arctic fox and their relationship to pinealocytes, glial cells and collagen fibers. Pineals collected from 7-8 month-old and 3-4 year-old foxes (6 in each age-group) were investigated. Sections of the glands were stained with HE, Mallory's method and alizarin red S as well as subjected to a combined procedure involving immunofluorescent staining with antibodies against antigen S, glial fibril acid protein (GFAP), type I and III collagen and histochemical staining with alizarin red S. The pineal concretions were found in 2 of 6 investigated Arctic foxes aged 3 years and they were not observed in animals aged 7-8 months. The acervuli were present in the parenchyma and the connective tissue septa. They were more numerous in the distal part than in the proximal part of the gland. The acervuli stained with alizarin red S revealed an intensive red fluorescence, what enabled the use of this compound in a combined histochemical-immunofluorescent procedure. A majority of cells in the fox pineal showed positive staining with antibodies against antigen S, a marker of pinealocytes. GFAP-positive cells were especially numerous in the proximal part of the gland. Both antigen S- and GFAP-positive cells were frequently observed close to the concrements. Collagen fibers of type I and III were found in the capsule, connective tissue septa and vessels. Immunoreactive fibers did not form any capsules or basket-like structures surrounding the concrements.

Ca2+-modulated membrane guanylate cyclase in the testes

Abstract: To date, the calcium-regulated membrane guanylate cyclase Rod Outer Segment Guanylate Cyclase type 1 (ROS-GC1) transduction system in addition to photoreceptors is known to be expressed in three other types of neuronal cells: in the pinealocytes, mitral cells of the olfactory bulb and the gustatory epithelium of tongue. Very recent studies from our laboratory show that expression of ROS-GC1 is not restricted to the neuronal cells; the male gonads and the spermatozoa also express ROS-GC1. In this presentation, the authors review the existing information on the localization and function of guanylate cyclase with special emphasis on Ca2+-modulated membrane guanylate cyclase, ROS-GC1, in the testes. The role of ROS-GC1 and its Ca2+-sensing modulators in the processes of spermatogenesis and fertilization are discussed.

Distribution of components of basal lamina and dystrophin-dystroglycan complex in the rat pineal gland: Differences from the brain tissue and between the subdivisions of the gland

Abstract: The pineal gland is an evagination of the brain tissue, a circumventricular neuroendocrine organ. Our immunohistochemical study investigates basal lamina components (laminin, agrin, perlecan, fibronectin), their receptor, the dystrophin-dystroglycan complex (s-dystroglycan, dystrophin utrophin), aquaporins (-4,-9) and cellular markers (S100, neurofilament, GFAP, glutamine synthetase) in the adult rat corpus pineale. The aim was to compare the immunohistochemical features of the cerebral and pineal vessels and their environment, and to compare their features in the distal and proximal subdivisions of the so-called ?superficial pineal gland?. In contrast to the cerebral vessels, pineal vessels proved to be immunonegative to ?1-dystrobrevin, but immunoreactive to laminin. An inner, dense, and an outer, loose layer of laminin as two basal laminae were present. The gap between them contained agrin and perlecan. Basal lamina components enmeshed the pinealocytes, too. Components of dystrophin-dystroglycan complex were also distributed along the vessels. Dystrophin, utrophin and agrin gave a ?patchy? distribution rather than a continuous one. The vessels were interconnected by wing-like structures, composed of basal lamina-components: a delicate network forming nests for cells. Cells immunostained with glutamine synthetase, S100-protein or neurofilament protein contacted the vessels, as well as GFAP- or aquaporin-immunostained astrocytes. Within the body a smaller, proximal, GFAP-and aquaporin-containing subdivision, and a larger, distal, GFAP-and aquaporin-free subdivision could be distinguished. The vascular localization of agrin and utrophin, as well as dystrophin, delineated vessels unequally, preferring the proximal or distal end of the body, respectively.

Pineal-adrenal interactions in domestic male pigeon exposed to variable circadian light regimes and exogenous melatonin.

Abstract: OBJECTIVE This study was aimed to see the histophysiological changes of the pineal and adrenal glands under altered photoperiodic conditions due to the administration of melatonin in the male domestic pigeon, Columba livia Gmelin. METHODS Young adult male domestic pigeons were exposed to long photoperiod (LP; 20 hr light: 4 hr dark), short photoperiod (SP; 4 hr light: 20 hr dark) exogenous melatonin (MEL; 20 microg/100 g body weight/day) was administered for 60 days in the primary breeding and regressive phase. At the end of experiment, adrenal and pineal glands were quickly dissected and processed for histology, ultrastructure study, biochemical, histochemical and immunohistochemical analysis. RESULTS In the primary breeding phase, the number of mitochondria and rough endoplasmic reticulum were increased in the adrenal gland in MEL-LP group, while lipid granules were also increased in the subcapsular zone. In MEL-SP treated group, however, the number of mitochondria decreased. Pinealocytes were increased in size and well-developed Golgi complexes were present near the cell nucleus after induction with MEL-LP treatment during the primary breeding phase. No remarkable changes were noticed in the number of mitochondria. In the regressive phase-I, the adrenocortical cytoplasm showed similar morphological features both in MEL-LP treatment and control groups. In pinealocytes, few rough endoplasmic reticulum and lipid droplets and moderate number of mitochondria were present. In MEL-SP treatment, increased number of mitochondria in the adrenocortical cells and decreased nuclear diameter of the pinealocytes were noticed. Few mitochondria were observed within the pinealocyte cytoplasm. Side chain cleavage enzyme (immunocytochemical) activity was increased in the subcapsular zone in MEL-LP treated group. CONCLUSIONS The present data indicates that the changes in pineal and adrenocortical tissue histophysiology might be due to melatonin rhythm and light/dark regime which act as a modulator in the male domestic pigeon.

Morphological Changes in the Pineal Gland of Rats under Conditions of Long-Term Exposure to Bright Light

Abstract: Changes in the diurnal light cycle affect the morphofunctional state of the pineal gland. The volume of the nucleus, Golgi apparatus, and mitochondria in pinealocytes decreases after 45-day exposure to bright light. After 90 days. the degree of nuclear polymorphism increased, the specific volume of the Golgi apparatus returned to normal, the volume of the granular endoplasmic reticulum decreased, while the volume of lysosomes, free ribosomes, and polysomes increased. These changes reflect plasticity of pinealocytes and adaptation of the gland to long-term 24-h light exposure.

Changes in concentrations of cortisol and melatonin in plasma, expression of synaptophysin, and ultrastructural properties of pinealocytes in goat kids in situations of stress due to early weaning: the effect of melatonin.

Abstract: AIM: To analyse the changes in some histophysiological parameters of the pineal gland of goat kids in situations of stress due to early weaning, and the effect of exogenous treatment with melatonin. METHODS: Twenty-four 6-day-old Verata goat kids were used; 12 suckled their dams throughout the study (non-weaned groups), and the other 12 were removed from their dams and fed a milk replacer (weaned groups). Six goat kids in each group were treated with melatonin, and the other six with doubledistilled pyrogen-free water (Day 0). On Days 28–29, blood samples were collected at 0600, 1000, 1400, 1800, 2200, 0200 and 0600 hours, to determine concentrations of cortisol and melatonin in plasma. On Days 29 and 30, six animals per group (three at 1400 and three at 0200 hours, respectively) were subject to euthanasia and the weight of their pineal glands determined. The structural immunocytochemistry, morphometric analysis, ultrastructural analysis and immunotransmission electron microscopy of the pineal gl...

Melatonin and Sleep: Possible Involvement of GABAergic Mechanisms

Abstract: Pineal melatonin is synthesized and secreted in close association with the light/dark cycle. The temporal relationship between the nocturnal rise in melatonin secretion and the “opening of the sleep gate” (i.e., the increase in sleep propensity at the beginning of the night), coupled with the sleep-promoting effects of exogenous melatonin, support the view that endogenous melatonin is involved in the regulation of sleep. The sleep-promoting and sleep–wake rhythm-regulating effects of melatonin are attributed to its action on MT1 and MT2 melatonin receptors present in the suprachiasmatic nucleus (SCN) of the hypothalamus. Nearly all neurons in the SCN contain γ-aminobutyric acid (GABA), and GABA-driven mechanisms have been shown to play a key role in circadian coupling among regions and neurons in the SCN. Results are reviewed indicating that among the neurochemical effects of melatonin in the SCN, its interaction with the GABAergic system appears to be significant for coupling to sleep mechanisms.

Pineal ribbon synapses: regulated by the gland's central innervation.

Abstract: OBJECTIVE: The pineal gland is part of the circadian clock system and is under the predominant influence of the endogenous oscillator located in the suprachiasmatic nucleus. A polysynaptic pathway involving hypothalamus, spinal cord and sympathetic system regulates the so far best-studied aspect of its neuroendocrine output, i.e., the synthesis and secretion of melatonin. This parameter increases dramatically at night upon sympathetic activation in rats and many other mam mals including man. In addition, parasympathetic, trigeminal, diencephalic and other sites or mechanisms connect the gland, mainly via its stalk, to the nervous system. However, their function for pineal metabolic or morphological features are hardly known. An interesting ultrastructural attribute of the pineal gland are ribbon synapses. These presynaptic structures in pinealocytes are composed of a ribbon and vesicles. They are thought to regulate and facilitate multivesicular release, and display a circadian rhythm with higher levels at night paralleling melatonin synthesis but regulated differently. METHODS: To gain more insight into the roles of both, the non-sympathetic (“central”) innervation and the regulation of pineal ribbon synapses, a surgical transection of the pineal stalk was conducted in rats and the number of synaptic ribbons (SR) were determined by electron microscopy from experimental, shamoperated and control animals. RESULTS: The transection resulted in normal daytime levels but diminished the nocturnal increase of SR numbers when compared to controls or sham-operated rats. CONCLUSION: These data provide first evidence that the central innervation of this neuroendocrine organ plays an important role in SR (up)regulation, and that this pathway is antagonistic to the sympathetic innervation.

Hypothalamus as a possible modulator of the rates of development and aging of mammals

Abstract: The review analyzes the information concerning the possibility to delay aging by slowing down development It is supposed that the rates of development and aging of mammals are modulated by the circadian rhythm generated by the suprachiasmatic nuclei of the hypothalamus Reversible arrest of growth in certain mammal species can be triggered by enhanced somatostatin synthesis with an inhibition of growth hormone, thyroid-stimulating hormone, and melatonin and with a loss of circadian function in the suprachiasmatic nucleus of the hypothalamus

Neurotransmitters and Receptors: Melatonin Receptors

Abstract: Melatonin is a neuromodulator that is synthesized by retinal photoreceptors during the dark period under the control of a circadian pacemaker. Melatonin diffuses to other cells in the retina and binds to specific G protein-coupled receptors to modify their activity. Potential target cells for melatonin within the retina are horizontal cells, bipolar cells, amacrine cells, ganglion cells, retinal pigment epithelial cells, and the photoreceptors themselves. Melatonin inhibits the release of dopamine from amacrine cells and increases the light sensitivity of bipolar and horizontal cells, but also may have direction actions on these cells. The expression of different melatonin receptor subtypes may enable target cells to respond to melatonin by a variety of signaling mechanisms.