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At least 145 records · Page 8Linked to original sources
PubMed1999

Circadian and seasonal changes of synaptic bodies in different parts of the rabbit pineal gland.

In the mammalian pineal gland, synaptic bodies (SBs) are poorly understood organelles. Previous studies in rabbits have shown that the organelles are rather heterogeneous in shape, are few in number during the day and increase in number at night. No studies are currently available on seasonal changes in this species and it is unknown whether the biological rhythms are identical in the proximal, intermediate and distal parts of the elongated pineal. To this end, a study was made of 84 rabbits kept under natural lighting conditions to examine numerical variations of the different types of SBs in the proximal, intermediate and distal regions of pineal glands procured at different timepoints of a 24-hour cycle and in each of the four annual seasons. In the present study, rod-like, sphere-like, ovoid, rectangular and triangular SB profiles were distinguished; the first two types being the most abundant. In addition to the well-known circadian changes, with low numbers of SB profiles during the day and high numbers at night, we found pronounced season-related differences as well as differences related to pineal regions. In autumn and winter, nighttime SR profile numbers were significantly higher than in spring and summer. With respect to regional differences it was found that the amplitude of the circadian rhythm increased in a proximo-distal direction in the gland. In autumn the strongly enhanced nocturnal increase was restricted to the distal region of the gland, whereas in winter it was seen in both the distal and the intermediate regions. The regional differences are probably related to the fact that the postganglionic sympathetic fibres, which regulate pineal function, enter the gland distally and proceed rostrally to the proximal region. Taken together, the results show that day- and nightlength are structurally coded in the pineal gland by means of SB numbers. Provided the SBs of the mammalian pineal gland are involved in synaptic processes, the results suggest that synaptic processes are enhanced at night as well as in autumn and winter.

Animals↗
PubMed1990

Circadian variations of adrenergic receptors in the mammalian pineal gland: a review.

Pineal adrenergic receptor numbers show circadian variations in both rat and Syrian hamster. In the rat pineal beta-adrenergic receptor density reaches peak values either late in the light phase or at middark; the differences in the circadian phase seem related to the light:dark cycle to which the animals are exposed. No circadian rhythm of pineal alpha-adrenergic receptors is documented in intact rats. In the Syrian hamster pineal beta-adrenergic receptor density is high throughout the light phase and drops to minimal values at the time of the nocturnal peak of melatonin production. The circadian rhythm of pineal alpha-adrenergic receptor numbers runs parallel to the beta-adrenergic receptor variation, but is less pronounced. In the rat, pineal melatonin production is rapidly induced by beta-adrenergic agonists at any time during a 24-hour period, even when the pinealocyte beta-adrenergic receptor number is lowest (early in the light phase). In contrast, the Syrian hamster pineal seems most responsive to beta-adrenergic agonists in the late night while being less responsive during the day when beta-adrenergic receptor density is high. Interestingly, the human pineal gland is also not especially responsive to adrenergic stimulation during the light phase, possibly making the Syrian hamster pineal a better model than the rat pineal for determining neural/pineal interactions in humans. Comparison of the circadian variations in pineal adrenergic receptors leads to the conclusion that the functional differences between rat and hamster pineal are probably not explicable in terms of the adrenergic receptors, but are caused most likely by (a) intracellular mechanism(s) beyond the adrenergic receptors.

Animals↗
PubMed1997

Phototransduction cascade and circadian oscillator in chicken pineal gland.

The chicken pineal gland has an endogenous circadian oscillator that controls the diurnal oscillation of N-acetyltransferase activity responsible for melatonin rhythm. It has been speculated that the chicken pineal cell contains a photoreceptive molecule that receives the environmental light signal and transmits the signal to the oscillator for resetting the phase. In spite of several lines of evidence suggesting the similarity between retinal and pineal photon-signal transducing proteins, the identity of the photoreceptive molecule had been an open question. In 1994, we isolated a pineal cDNA encoding a novel photoreceptive molecule and named it "pinopsin." The protein expressed in 293EBNA cells bound 11-cis-retinal to form a blue-sensitive pigment with an absorption maximum at about 470 nm. A putative G-protein interaction site of pinopsin shared a relatively high similarity in amino acid sequence to that of rhodopsin, implying that pinopsin functionally couples with transducin or transducin-like G-protein(s) in the pineal cells. We have cloned a cDNA for chicken pineal transducin alpha-subunit, and the deduced amino acid sequence contained a potential site to be ADP-ribosylated by pertussis toxin (PTX). Therefore, the transducin-mediated pathway could be blocked by PTX, though previous studies showed that treatment of the cultured chicken pineal cells with PTX had no effect on the light-induced phase-shift of the oscillator. Accordingly, it is unlikely that transducin mediates the light-input pathway to the oscillator, which may involve PTX-insensitive G-protein(s) or some unidentified component(s). The G-protein coupled receptor-mediated signaling processes regulating melatonin synthesis are discussed.

Adenosine Diphosphate Ribose↗
PubMed1987

Cellular and molecular mechanisms controlling melatonin release by mammalian pineal glands.

1. The pineal gland is regulated primarily by photoperiodic information attaining the organ through a multisynaptic pathway initiated in the retina and the retinohypothalamic tract. 2. Norepinephrine (NE) released from superior cervical ganglion (SCG) neurons that provide sympathetic innervation to the pineal acts through alpha1- and beta 1- adrenoceptors to stimulate melatonin synthesis and release. 3. The increase in cyclic AMP mediated by beta 1-adrenergic activation is potentiated by the increase in Ca2+ flux, inositol phospholipid turnover, and prostaglandin and leukotriene synthesis produced by alpha 1-adrenergic activation. 4. Central pinealopetal connections may also participate in pineal control mechanisms; transmitters and modulators in these pathways include several neuropeptides, amino acids such as gamma-aminobutyric acid (GABA) and glutamate, and biogenic amines such as serotonin, acetylcholine, and dopamine. 5. Secondary regulatory signals for pineal secretory activity are several hormones that act on receptors sites on pineal cells or at any stage of the neuronal pinealopetal pathway.

Adrenergic Fibers↗
PubMed1996

Effect of calcium on melatonin secretion in chick pineal gland I.

Melatonin is the neurohormone which is synthesized by the pineal gland and secreted rhythmically. The role of calcium in the activation of melatonin production remains unknown. In this study, we demonstrated that calcium input participates in the regulation of chick pineal gland. Pineal glands from Gallus domesticus were perifuse with Krebs medium (controls) or with Krebs medium plus drugs (ethylene glycol tetraacetic acid (EGTA) or calcium ionophore A23187). When EGTA was added to the perifusion medium, free extracellular calcium concentrations were dramatically decreased and melatonin synthesis was decreased. On the other hand, when the calcium ionophore A23187 was added to the perifusion medium, chick pineal glands exhibited a marked increase in secretion of melatonin. No effects were observed when chick pineal glands were treated with drugs during or after the time of the natural peak levels. We propose that calcium input from extracellular medium and output from intracellular calcium reserves are primary mechanisms in the activation of melatonin synthesis in the chick pineal gland.

Animals↗
PubMed1989

On thymidine incorporation by the cultured chick pineal gland.

Explanted chick pineal glands exhibited a cycle in thymidine incorporation when cultured either under a cycle of illumination or in constant darkness. This cycle appeared to be entrained to the light cycle under which the birds were maintained. The incorporation reflected gene replication in a small fraction of the cell population that was largely, but not entirely, located in the stroma of the gland. Glands cultured with colchicine for 28 h contained a very small number of cells showing metaphase chromosomes.

Animals↗
PubMed1988

Morphological changes of the adrenal gland following soft-laser irradiation of the pineal gland.

We present the results obtained in the adrenal gland of white rats (average weight 220 g) following irradiation of the pineal gland with laser light. Irradiation was carried out with a 5 mW Politec 750 Helium-Neon laser. Total irradiation time was 5 min, with rest intervals of 1 min for every minute of irradiation. Pineal gland irradiation was done under "open sky", i.e., directly at the gland. The effects of the suprarenal gland were studied 3, 7 and 10 d postirradiation. Morphological signs of an increasing activity have been observed in all layers of the cortex and in the medulla of the gland. The highest increase was found 7 d after irradiation in the fascicular zone and in the medulla, and after 3 d in the glomerular and reticular zone. We suggest that laser light induces an inhibitory effect observed at the suprarenal gland. This effect is similar to that found following pinealectomy, showing once again that the pineal gland exerts control on the suprarenal gland, mediated by luminous stimuli.

Adrenal Glands↗
PubMed1979

Release and specific binding of prostaglandins in bovine pineal gland.

Incubated bovine pineal glands released prostaglandin E-and prostglandin F-like material (304 +/- 20 and 582 +/- 56 pg/mg dry tissue wt/h, respectively) and the release was increased 2.2 2.9-fold by adding 10(-4)-10(-6)M of norepinephrine to the medium. Binding assays revealed the existence of high affinity binding of 3H-prostaglandin E2 (3H-PGE2) and 3H-prostaglandin F1 alpha (3H-PGF2 alpha) in low speed supernatants of pineal homogenates. Binding was increased by increasing Ca++ concentration in medium up to 2 mM, was heat labile and was depressed following incubation with trypsin. In subcellular fractionation studies maximal 3H-PG binding was found in the 27000 x g pellet. Scatchard analysis of 3H-PGE2 binding revealed the presence of a single population of binding sites with a Kd= 1.2 nM and a binding site concentration of 1-2 pmoles/g protein. A single population of binding sites for 3H-PGF2 alpha was also detected with a Kd= 1.7 nM and a similar binding site concentration. Non-radioactive PGE1 and PGE2 were almost equally effective to compete for 3H-PGE1 binding sites (ED50= 5 and 2 nM, respectively). Unlabeled PGF1 was relatively ineffective to compete for 3H-PGE2 binding (ED50 greater than 1000 nM) but displaced effectively 3H-PGF2 alpha binding (ED20=1.2 nM).

Animals↗
PubMed1988

Enkephalin-like immunoreactivity in neurons in the human pineal gland.

Adult human pineal glands were prepared for immunohistochemical analysis using antisera against Leu-enkephalin, neuropeptide Y, dopamine-beta-hydroxylase and vasoactive intestinal polypeptide. The material shows small neurons located in septae and along the capsule of the gland which exhibit enkephalin-like immunoreactivity. The neurons have fairly extensive dendritic arbors and immunoreactive axons are present in the septae and beneath the capsule, particularly in a perivascular location, and occasionally extend into lobules of the gland among parenchymal cells. No consistent immunoreactivity was observed with other antisera but bundles of axons exhibiting dopamine-beta-hydroxylase or neuropeptide Y-like immunoreactivity are observed in some of the material in a perivascular location.

Adult↗
PubMed1989

On the uptake and incorporation of thymidine by cultured chick pineal glands.

Cultured chick pineal glands showed a marked cycle in the incorporation of thymidine into DNA. They also accumulated exogenous thymidine in one, or more, endogenous thymidine pool(s). However, there was no significant variation in ability to take up thymidine during incubation with either standard medium or media of increased thymidine content. We could not eliminate the possibility of variation in size of a quantitatively minor, but metabolically extremely important, thymidine pool which "channels" precursor directly into DNA.

Animals↗
PubMed2001

Characterisation of P2Y(1)-like receptor in cultured rat pineal glands.

The rat pineal gland possesses P2 receptors which potentiate the effect of noradrenaline-induced N'-acetyl-5-hydroxytryptamine (N'-acetyl-5-HT) production. In the current study, this receptor was characterised according to agonist selectivity and signal transduction mechanisms. 2-MethylthioATP (2MeSATP), 2-chloroATP (2-ClATP), adenosine 5'-O-2-thiodiphosphate, (ADPbetaS), ATP and ADP, but not UTP, potentiated noradrenaline-induced N'-acetyl-5-HT production in a concentration-dependent manner. 2MeSATP neither induced the production of adenosine 3':5'-cyclic monophosphate (cyclic AMP), nor inhibited its formation when the glands were stimulated by forskolin. The phospholipase C inhibitor 1-[6-[[(17beta)-3-Methoxyestra-1,3,5(10)-trien-17-yl]amino]hexyl]-1H-pyrrole-2,5-dione (U73122), but not the inactive analogue, 1-[6-[[(17beta)-3-Methoxyestra-1,3,5(10)-trien-17-yl]amino]hexyl]-2,5-pyrrolidinedione (U73343), blocked the 2MeSATP effect. The P2 receptor antagonist pyridoxalphosphate-6-azophenyl-2',4'-dissulphonic acid (PPADS), which inhibits phospholipase C-coupled P2Y(1) receptors, blocked the 2MeSATP effect. In conclusion, our data strongly suggest that the P2-like receptor that is present in rat pinealocytes and which is responsible for the potentiation of noradrenaline-induced N'-acetyl-5-HT production is a P2Y(1)-like receptor, coupled to a G protein which stimulates phospholipase C.

Adenosine Diphosphate↗
PubMed1991

Differential effects of electrical stimulation, blockade of neuronal amine uptake and activation of alpha 2-adrenoceptors on the release of endogenous noradrenaline and 5-hydroxytryptamine from the isolated rat pineal gland.

Isolated rat pineal glands were incubated in vitro and the release of endogenous noradrenaline or 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) was determined by HPLC with electrochemical detection. In the absence of test drugs, the spontaneous outflow of noradrenaline was about 10 fmol/10 min and electrical stimulation (5 Hz, 1500 pulses) evoked the release of about 70 fmol noradrenaline. Nomifensine enhanced the spontaneous outflow of noradrenaline about threefold and the electrically evoked release of noradrenaline about sixfold. In the presence of nomifensine, the alpha 2-adrenoceptor antagonist yohimbine markedly increased the electrically evoked release of noradrenaline, whereas the alpha 1-adrenoceptor antagonist prazosin had no effect. Clonidine inhibited the electrically evoked release of noradrenaline by about 65%, and this was antagonized by yohimbine in a competitive manner. In the absence of drugs, the initial spontaneous outflow of 5-HT was (compared with noradrenaline) very high 64 pmol/10 min). It declined by 80% within 1 h of incubation in vitro. The outflow of 5-HIAA amounted initially to 38 pmol 10 min and declined by 40% within 1 h of incubation. Addition of L-tryptophan (10 mumol/l) after 1 h of incubation in vitro largely enhanced the outflow of 5-HT and 5-HIAA within 30 min of incubation (about ten- and fourfold, respectively). When L-tryptophan was present from the onset of incubation the initial outflow of 5-HT and 5-HIAA was only slightly elevated, but the decline was largely attenuated. Neither omission of calcium nor addition of nomifensine, clonidine or yohimbine significantly affected the spontaneous outflow of 5-HT or 5-HIAA.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Prolonged treatment with glucocorticoid dexamethasone suppresses melatonin production by the chick pineal gland and retina.

The chick pineal gland and retina synthesize melatonin in a circadian rhythm with high levels during the night. The rhythmic changes in the hormone production result predominantly from the fluctuation in the activity of serotonin N-acetyltransferase (AA-NAT), a penultimate and key regulatory enzyme in melatonin biosynthesis. The aim of this study was to analyze the effects of an acute and prolonged in vivo treatment with a glucocorticoid dexamethasone (4 mg/kg, ip) on the nocturnal increase in AA-NAT activity in chick pineal gland and retina. In acute experiments, dexamethasone (single dose)-injected chicks were killed after 2 h, while in prolonged experiments the glucocorticoid was given once daily for 7 days and the animals were killed 26-32 h after the last injection. Acute administration of dexamethasone did not affect AA-NAT activity in the chick pineal gland and retina. In the pineal glands and retinas of chicks that were treated with dexamethasone for one week and then killed at the end of the light phase of the 12:12 h light-dark cycle, AA-NAT activity was significantly higher than the enzyme activity found in tissues isolated from the vehicle-treated (control) animals. In addition to that, the nocturnal increase in pineal and, to a lower extent, retinal AA-NAT activity was significantly lower in dexamethasone-treated birds when compared with the respective control groups. It is suggested that prolonged treatment of animals with dexamethasone reduces the amplitude of the rhythmic melatonin production, a phenomenon which may affect chronobiological processes being under control of this hormone.

Animals↗
PubMed1996

Sudden death due to a glial cyst of the pineal gland.

Asymptomatic cysts of the pineal gland are found frequently by radiological examination of the brain or at postmortem examination. Symptomatic cysts are rare, and may require surgical intervention. Sudden death due to a cystic lesion of the pineal gland is very rare. A case of a 22 year old man who collapsed and died unexpectedly is reported. Postmortem examination revealed a glial cyst of the pineal gland and evidence of chronic obstructive hydrocephalus. Deaths from colloid cysts and pineal gland cysts are rare, but should be considered where no other cause of death is evident, especially with a history of headaches. Their small size, and their possible rupture on dissection can make them difficult to detect if a careful examination is not undertaken.

Adult↗
PubMed1980

Presence of AVT-, alpha-MSH-, LHRH- and somatostatin-like compounds in the rat pineal gland and their relationship with the UMO5R pineal fraction. An immunocytochemical study.

Using antibodies against AVT, alpha-MSH, LHRH and somatostatin, immunoreactive cells were detected in the rat pineal gland. All of these antibodies stain the same cells, which also react immunocytochemically when an antibody against the UMO5R sheep pineal fraction, a fraction that presents antigonadotropic properties in vivo, is used. Relatively more immunoreactive cells are present in the pineals of young rats than in the pineals of adult animals. Comparison of the results obtained with different potent antibodies against each of the peptides, and a study of the staining properties of the antibodies in the pineal after solid phase absorption to different peptides or to different sheep pineal fractions, led to the proposal that the immunoreactivity found in the rat pineal is not due to the presence of AVT, alpha-MSH, LHRH or somatostatin, but to a cross-reaction of each of these antibodies with (an) unidentified compound(s). This compound is synthetized in the pineal gland, as was demonstrated using cultured pineals. The UMO5R and the Prot. 4 fractions of the sheep pineal seem to be chemically related to this unknown compound, the possible endocrine nature of which is discussed.

Aging↗
PubMed2001

Microglia play a role in mediating the effects of cytokines on the structure and function of the rat pineal gland.

The role of the pineal gland in regulating immune function has been extensively investigated. However, there is little information about possible feedback mechanisms of immunological factors on pineal gland neuroendocrine functions. Therefore, experiments were designed to test the effects of cytokines (interferon-gamma, IFN-gamma, interleukin-1 beta, IL-1 beta; tumor necrosis factor-alpha, TNF-alpha; transforming growth factor-beta 1, TGF-beta 1) on pinealocytes and the role of pineal microglia in mediating these cytokine effects in the pineal gland of the rat. Our studies showed that IFN-gamma enhanced 5-hydroxytryptamine (5-HT) content (measured by high-performance liquid chromatography, HPLC) and increased pinealocyte process length in pineal cultures. IL-1 beta treatment decreased 5-HT content in both cell and organ culture, but exhibited no effect on pinealocyte process length. 5-HT content and process length were decreased by TNF-alpha treatment. IFN-gamma and IL-1 beta exhibited no significant effect in the absence of microglia in cell cultures. In contrast, TNF-alpha caused a further decline in 5-HT content even in the absence of microglia in the cultures. The effects of TNF-alpha were probably due to toxic effects, since an increased number of pyknotic nuclei were observed in treated cultured explants. TGF-beta 1 treatment caused aggregation of pinealocytes in cultures and suppressed process length and 5-HT content. In conclusion, cytokine effects on pinealocytes may be mediated by microglia (IFN-gamma and IL-1 beta) or act directly on pinealocytes (TNF-alpha). The presence of IL-1 beta and TGF-beta 1 protein in the pineal gland and the suppressive effect of TGF-beta 1 on pinealocytes in cultures further suggest that endogenous cytokines play regulatory roles in response to peripheral homeostatic changes.

Animals↗
PubMed1990

Vasoactive intestinal peptide stimulates melatonin release from perifused pineal glands of rats.

The rat pineal gland is known to release melatonin in response to noradrenergic stimulation. The effect of vasoactive intestinal peptide (VIP), one of the neuropeptides present in the pineal, was examined on perifused rat pineal glands. VIP stimulated melatonin release with a dose-dependent effect above 10(-7) M. In regard of kinetic characteristics, the pattern of melatonin release after VIP stimulation was similar to that after isoproterenol stimulation. 10(-6) M VIP-stimulated melatonin release was not altered when the pineal glands were treated with 10(-5) M propranolol (a beta-adrenergic antagonist) or 10(-5) M prazosin (an alpha 1-adrenergic antagonist). Thus VIP has a noradrenergic-independent effect on melatonin secretion. Conversely, this VIP effect is greatly inhibited by the specific action of a VIPergic antagonist. This suggests that VIP acts on melatonin synthesis through its own binding sites. This study demonstrates that melatonin secretion from rat pineal glands may be elicited through a VIPergic system which is independent of the well-known noradrenergic system.

Animals↗