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At least 199 records · Page 11Linked to original sources

PubMed1990

Melatonin production by the guinea pig pineal gland in vitro.

The fluid bathing pineal glands isolated from guinea pigs was collected serially and its melatonin content was estimated. Production was found to be high (500 pg/5 min) soon after isolation of the gland: it declined exponentially to a maintained lower level (50 pg/5 min) with a half-time of 16-20 min. A rapid increase could be produced by exposure of the gland to the beta-adrenoceptor agonist orciprenaline or by stimulating it electrically. The time course and the extent of the responses to either form of stimulation were similar in glands that had been taken in the morning, at dusk or in mid-dark: the prestimulation peak was lower from glands taken at dusk. Thus the pineal gland of the guinea pig is capable of responding rapidly to stimulation of its beta-adrenoceptors at any time. These responses parallel the depolarization observed intracellularly in this species when the pineal gland is stimulated electrically or exposed to beta-adrenoceptor agonists.

Animals↗

PubMed1975

A diurnal rhythm in melanocyte-stimulating hormone content of the rat pituitary gland and its independence from the pineal gland.

Resting pituitary melanocyte-stimulating hormone (MSH) content was studied in adult rats kept under a controlled 14 h light-10 h dark regimen. A diurnal rhythm was found in pituitary MSH levels, showing peak values at 4.00-6.00 p.m., and low values during darkness and the beginning of the light period. The normally occurring fall in pituitary MSH content between 6.00 p.m. and midnight was also found in rats exposed to a prolonged photoperiod. Sympathetic denervation of the pineal gland by superior cervical ganglionectomy, as well as pinealectomy, did not block the rhythm in pituitary MSH, and had no effect on pituitary MSH content. In addition, melatonin administered i.v. did not affect pituitary MSH levels, either when MSH activity was tested on the Anolis skin in vitro, or when the in vivo assay with hypophysectomized frogs (Rana pipiens) was used. It was concluded that the diurnal rhythm in pituitary MSH content is not directly related to the light-dark cycle and is not controlled by pineal melatonin or any otherpineal factor.

Animals↗

PubMed2002

The anatomy and innervation of the mammalian pineal gland.

The parenchymal cells of the mammalian pineal gland are the hormone-producing pinealocytes and the interstitial cells. In addition, perivascular phagocytes are present. The phagocytes share antigenic properties with microglial and antigen-presenting cells. In certain species, the pineal gland also contains neurons and/or neuron-like peptidergic cells. The peptidergic cells might influence the pinealocyte by a paracrine secretion of the peptide. Nerve fibers innervating the mammalian pineal gland originate from perikarya located in the sympathetic superior cervical ganglion and the parasympathetic sphenopalatine and otic ganglia. The sympathetic nerve fibers contain norepinephrine and neuropeptide Y as neurotransmitters. The parasympathetic nerve fibers contain vasoactive intestinal peptide and peptide histidine isoleucine. Recently, neurons in the trigeminal ganglion, containing substance P, calcitonin gene-related peptide, and pituitary adenylate cyclase-activating peptide, have been shown to project to the mammalian pineal gland. Finally, nerve fibers originating from perikarya located in the brain containing, for example, GABA, orexin, serotonin, histamine, oxytocin, and vasopressin innervate the pineal gland directly via the pineal stalk. Biochemical studies have demonstrated numerous receptors on the pinealocyte cell membrane, which are able to bind the neurotransmitters located in the pinealopetal nerve fibers. These findings indicate that the mammalian pinealocyte can be influenced by a plethora of neurotransmitters.

Animals↗

PubMed1996

Diurnal variation of the adenylyl cyclase type 1 in the rat pineal gland.

Nocturnal melatonin production in the pineal gland is under the control of norepinephrine released from superior cervical ganglia afferents in a rhythmic manner, and of cyclic AMP. Cyclic AMP increases the expression of serotonin N-acetyltransferase and of inducible cAMP early repressor that undergo circadian oscillations crucial for the maintenance and regulation of the biological clock. In the present study, we demonstrate a circadian pattern of expression of the calcium/calmodulin activated adenylyl cyclase type 1 (AC1) mRNA in the rat pineal gland. In situ hybridization revealed that maximal AC1 mRNA expression occurred at midday (12:00-15:00), with a very low signal at night (0:00-3:00). We established that this rhythmic pattern was controlled by the noradrenergic innervation of the pineal gland and by the environmental light conditions. Finally, we observed a circadian responsiveness of the pineal AC activity to calcium/calmodulin, with a lag due to the processing of the protein. At midday, AC activity was inhibited by calcium (40%) either in the presence or absence of calmodulin, while at night the enzyme was markedly (3-fold) activated by the calcium-calmodulin complex. These findings suggest (i) the involvement of AC1 acting as the center of a gating mechanism, between cyclic AMP and calcium signals, important for the fine tuning of the pineal circadian rhythm; and (ii) a possible regulation of cyclic AMP on the expression of AC1 in the rat pineal gland.

Adenylyl Cyclases↗

PubMed1982

Alterations in the spontaneous activity of cells in the guinea pig pineal gland and visual system produced by pineal indoles.

The indoles serotonin (SER), melatonin (MEL), 5-methoxytryptophol (5-MTL) and 5-hydroxytryptophol (5-HTL) were administered during daytime microelectrophoretically to 240 cells in the pineal gland of the guniea-pig. The action of SER and 5-HTL was predominantly depressant on the electrical activity, MEL and 5-MTL caused an excitation in most of the units. Although MEL and 5-MTL caused fairly similar reactions on average, they appear to act on different cells. The effects of microelectrophoretically applied MEL and 5-MTL on the spontaneous or evoked activity in the visual system (retinal ganglion cells, optic tract, lateral lateral geniculate body, superior colliculus) of the guinea-pig were also investigated. Of the 76 cells tested in the visual system 25 of the ON- and OFF-cells increased the rate of discharge when the two indoles were applied. Cells in the optic layer of the superior colliculus showed no measurable response to the application of the two substances. 5-HTL caused no effect on cells in the visual system.

Animals↗

PubMed2003

Effect of a synthetic pineal tetrapeptide (Ala-Glu-Asp-GLy) on melatonin secretion by the pineal gland of young and old rats.

The pineal gland contains many peptides known to be implicated in melatonin production. We examined the effects of a synthetic pineal tetrapeptide Ala-Glu-Asp-Gly on melatonin secretion by the pineal gland. The tetrapeptide effects on pineal gland melatonin secretion were studied in young (9 weeks) and old (27 months) male Wistar rats using a perifusion device. Pineal tetrapeptide at the concentrations used (10(-4) to 10(-6) M) had no significant effect upon melatonin secretion whatever the age of the animals, young or old. We also looked at the effect of the tetrapeptide on pineal melatonin stimulated by a beta-adrenergic agonist, isoproterenol. We found that isoproterenol-induced melatonin increase was not modified by the tetrapeptide. Our results suggest that the pineal tetrapeptide Ala-Glu-Asp-Gly, does not seem to play a role, at least in vitro, in the control of melatonin secretion by the rat pineal gland.

Adrenergic beta-Agonists↗

PubMed1991

Retinoids and carotenoids in bovine pineal gland.

The retinoids and carotenoids in bovine pineal gland were analyzed by high-performance liquid chromatographic methods. The major retinoid observed was all-trans retinol, with an average level of 579 pmol/g wet tissue. In agreement with a previous report, retinal was not detected; however, we could not detect any retinyl ester in bovine pineal gland. Methods similar to those used in studying metabolism of vitamin A in the bovine eye were used to study the esterification and isomerization reactions of retinoids in the pineal gland. Neither esterification nor isomerization reactions occurred. These results suggest that the key retinoids and enzymes involved in visual function are absent in the bovine pineal gland. The major carotenoid, which has not previously been reported in pineal gland, was beta-carotene at an average level of 1830 pmol/g wet tissue.

Animals↗

PubMed1977

Effect of melatonin implants on gonadal weights and pineal gland fine structure of the golden hamster.

Weekly subcutaneous implants of melatonin in a beeswax pellet prevented the testicular regression which normally occurs in hamsters exposed to short photoperiod for 8 weeks. Normal (14L:10D) hamster testes were indistinguishable from the testes of melatonin-treated (1L:23D) hamsters. The exogenous melatonin had varied effects on the fine structure of the golden hamster pineal gland. Pineal ocyte nuclear characteristics of melatonin-treated hamsters (smaller average diameter, less polymorphism, and more heterochromatin) as well as apparent reductions in the amounts of hypertrophic SER and lipid moieties seemed to indicate that melatonin caused inhibition of pineal gland activity, and in this respect counteracted the effects of short photoperiod. However, an apparent increase in the number of large mitochondria, membrane whorls and dense-cored secretory vesicles in pinealocytes of melatonin-treated hamsters suggests enhanced pineal gland activity.

Animals↗

PubMed1998

Effects of ethylene glycol tetraacetic acid, A23187 and calmodulin, calcium activated neutral proteinase antagonists on melatonin secretion in perifused chick pineal gland.

We have recently described, using perifused pineal glands, that calcium influx participates in the activation of chick pineal gland. This study shows that the loss of perifused chick pineal gland activity is a complex process which seems to involve the release of calcium from intracellular stores, calmodulin and calcium-activated neutral protease (CANP). Pineal glands were perifused with Krebs medium (controls) or with Krebs medium plus the drugs ethylene glycol tetraacetic acid (EGTA; calcium chelator), A23187 (calcium ionophore), EGTA plus A23187 (extra-intra cellular calcium chelation), trifluoperazine and CGS9343B (calmodulin inhibitors), and E-64 (CANP inhibitor) at the time of the natural peak of melatonin release. When EGTA or A23187 were added to the perifusion medium, no effects were observed. On the other hand, when the calcium chelator EGTA plus A23187 (free extra and intracellular calcium levels were dramatically decreased), trifluoperazine, CGS 9343B or E-64 were added to the perifusion medium melatonin synthesis increased significantly and was sustained for 8 h. We propose a prominent role for calcium output from intracellular stores in regulating melatonin production primarily by acting on Ca-calmodulin and calcium-activated neutral protease.

Animals↗

PubMedDate not supplied

Identification of serotonin 5HT2 receptors in bovine pineal gland.

The concentration of serotonin in the pineal gland is extremely high, which prompted speculation that in addition to serving as a precursor of melatonin, serotonin may have an independent function of its own. By using [3H]-spiperone as a ligand, and ketanserine as a selective serotonin 5HT2 receptor antagonist, we have identified 5HT2 receptor in the bovine pineal gland, revealing a single population of binding sites with a dissociation equilibrium constant (Kd) value of 1.26 +/- 0.41 nM and a receptor density (Bmax) value of 193 +/- 38.85 fmol/mg protein. In displacement experiments, the concentrations of the drugs required to inhibit 50% of the specific binding of [3H]-spiperone in descending order of potency were methysergide greater than ritanserin greater than pirenperone greater than pipamperone greater than ketanserin greater than cyproheptadine greater than M-trifluoromethylphenyl-piperazine greater than prazosin greater than 5-methoxy-N-N-dimethyltryptamine hydrogen oxalate greater than 1-(3-chlorophenol) piperazine greater than serotonin. In the rat pineal gland, [3H]-spiperone revealed a low affinity serotonin binding site with a Kd value of 25.77 +/- 10.7 nM and a Bmax value of 1244 +/- 472 fmol/mg protein. The results of these studies are interpreted to indicate that the bovine pineal gland possess serotonin 5HT2 receptor. However, the rat pineal gland possess a serotoninergic binding site of unknown nature.

Animals↗

PubMed2004

The nicotinic receptor in the rat pineal gland is an alpha3beta4 subtype.

The rat pineal gland contains a high density of neuronal nicotinic acetylcholine receptors (nAChRs). We characterized the pharmacology of the binding sites and function of these receptors, measured the nAChR subunit mRNA, and used subunit-specific antibodies to establish the receptor subtype as defined by subunit composition. In ligand binding studies, [3H]epibatidine ([3H]EB) binds with an affinity of approximately 100 pM to nAChRs in the pineal gland, and the density of these sites is approximately 5 times that in rat cerebral cortex. The affinities of nicotinic drugs for binding sites in the pineal gland are similar to those at alpha3beta4 nAChRs heterologously expressed in human embryonic kidney 293 cells. In functional studies, the potencies and efficacies of nicotinic drugs to activate or block whole-cell currents in dissociated pinealocytes match closely their potencies and efficacies to activate or block 86Rb+ efflux in the cells expressing heterologous alpha3beta4 nAChRs. Measurements of mRNA indicated the presence of transcripts for alpha3, beta2, and beta4 nAChR subunits but not those for alpha2, alpha4, alpha5, alpha6, alpha7, or beta3 subunits. Immunoprecipitation with subunit-specific antibodies showed that virtually all [3H]EB-labeled nAChRs contained alpha3 and beta4 subunits associated in one complex. The beta2 subunit was not associated with this complex. Taken together, these results indicate that virtually all of the nAChRs in the rat pineal gland are the alpha3beta4 nAChR subtype and that the pineal gland can therefore serve as an excellent and convenient model in which to study the pharmacology and function of these receptors in a native tissue.

Animals↗

PubMed2003

Development of rhythmic melatonin secretion from the pineal gland of embryonic mummichog (Fundulus heteroclitus).

The pineal gland of vertebrates produces and secretes the hormone melatonin in response to changes in the light-dark cycle, with high production at night and low production during the day. Melatonin is thought to play an important role in synchronizing daily and/or seasonal physiological, behavioral, and developmental rhythms in vertebrates. In this study, the functional development of the pineal melatonin-generating system was examined in the mummichog, Fundulus heteroclitus, an euryhaline teleost. In this species, the pineal gland contains an endogenous oscillator, ultimately responsible for timing the melatonin rhythm. Oocytes from gravid females were collected and fertilized in vitro from sperm collected from mature males. Skull caps containing attached pineal glands were obtained from F. heteroclitus embryos at different embryonic stages and placed in static or perfusion culture under various photoperiodic regimes. Rhythmic melatonin secretion from pineal glands of embryonic F. heteroclitus embryos exposed to a 12L:12D cycle in static culture was observed at five days post-fertilization. The ontogeny of circadian-controlled melatonin production from F. heteroclitus pineal glands exposed to constant darkness for five days was also seen at day five post-fertilization. These data show that early development of the pineal melatonin-generating system in this teleost occurs prior to hatching. Pre-hatching development of the melatonin-generating system may confer some selective advantage in this species in its interactions with the environment.

Animals↗

PubMed1984

Sympathetic reinnervation of the pineal gland after postganglionic nerve lesion does not restore normal pineal function.

The activity of the enzyme serotonin N-acetyltransferase (NAT) in the rat pineal gland exhibits a large circadian rhythm, with peak activity occurring at night. This rhythm is dependent on stimulation of the pineal gland by neurons whose cell bodies are in the superior cervical ganglia and whose axons reach the gland via the internal carotid nerves (ICNs). Two days after both ICN were cut, crushed, or frozen, nighttime NAT activity was decreased by 90%. The remaining low level of enzyme activity was not affected by decentralization of the superior cervical ganglia. Thus, this enzyme activity did not depend on the activity of neurons in these ganglia. Bilaterally lesioning the ICN also abolished the neuronal uptake of norepinephrine in the pineal, further indicating that the sympathetic innervation of the gland had been destroyed. Three months after crushing both ICNs, nighttime NAT activity was only 20% of control values. However, in these animals, bilateral decentralization of the superior cervical ganglion reduced this low level of NAT activity by 90%. Thus, NAT activity, although low, was again dependent on sympathetic nerve stimulation. In contrast to this rather small recovery of nocturnal NAT activity, the norepinephrine uptake capacity of the gland recovered to 60% of control values. A similar discrepancy between the extent of recovery of NAT activity and of norepinephrine uptake was observed when the ICNs were frozen rather than crushed. To determine to what extent the sympathetic nerves that had reinnervated the pineal gland in these lesioned animals were capable of regulating NAT activity, their cervical sympathetic trunks were stimulated electrically at 5 Hz for 3 hr during the daytime.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetyltransferases↗

PubMed1990

Alpha-2 adrenergic activity of bromocriptine and quinpirole in chicken pineal gland. Effects on melatonin synthesis and [3H]rauwolscine binding.

In the pineal gland and retina of chickens, serotonin N-acetyl-transferase (NAT) activity and melatonin content are modulated by different receptors, alpha-2 adrenergic receptors in pineal gland and D2-dopamine receptors in retina. The effect of two D2-dopamine receptor agonists, bromocriptine and quinpirole (LY 171555), on melatonin synthesis in these tissues was investigated. Systemic administrations of bromocriptine and quinpirole decreased nocturnal NAT activity and melatonin content of both pineal gland and retina. Bromocriptine was equipotent in the two tissues, whereas quinpirole was approximately 100-fold more potent in retina than in pineal gland. In pineal gland, the suppressive effects of bromocriptine and quinpirole on NAT activity were blocked by yohimbine, a selective alpha-2 adrenergic receptor antagonist, but not by spiperone, a D2-dopamine receptor antagonist. In contrast, bromocriptine- and quinpirole-induced decreases of the enzyme activity in retina were antagonized by spiperone, and not affected by yohimbine. The nocturnal increase of NAT activity of pineal glands in vitro was inhibited with an order of potency clonidine greater than bromocriptine greater than quinpirole. Additionally, bromocriptine and quinpirole displaced the specific binding of [3H]rauwolscine, an alpha-2 adrenergic receptor antagonist, to membranes from chicken pineal gland, with potencies comparable to those observed for inhibition of NAT activity in vitro. It is suggested that bromocriptine and quinpirole, in addition to their D2-dopaminergic activity, can stimulate alpha-2 adrenergic receptors in pineal gland of chicken.

Animals↗

PubMedDate not supplied

Occurrence of D-aspartic acid in rat brain pineal gland.

We found a high concentration (1030 pmol per pineal gland) of D-aspartic acid (D-Asp) in the pineal gland of 6-week-old Sprague-Dawley (SD) rats. The content of D-Asp decreased with age, being 210 and 33 pmol per pineal gland in 28- and 45-week-old rats respectively. The proportion of D-Asp [(D-Asp/total Asp) x 100] also decreased with age, declining from 66% to 10% between 6 and 45 weeks after birth. The proportion of D-Asp did not differ between the sexes. The concentration of D-Asp was higher at night (at 2.00 a.m. 2830 +/- 485 pmol per pineal gland) than during the day (at 10.00 a.m. 1030 +/- 200 and at 3:00 p.m. 682 +/- 194 pmol per pineal gland), suggesting that biosynthesis of D-Asp in the pineal gland occurs at night. D-Asp was found to be distributed in the cytosol of pinealocytes, but its biological role remains unclear.

Aging↗

PubMed2006

Immunocytochemical characterization of Delta-opioid and Mu-opioid receptor protein in the bovine pineal gland.

Opioidergic innervation has been identified in the mammalian pineal gland. Recently, opioid receptors in bovine pineal glands have been characterized; the activation of these receptors leads to the stimulation of melatonin synthesis. In this study, the precise localization of opioid receptors in bovine pineal glands was determined by an immunohistochemical technique using antibodies raised against delta-opioid and mu-opioid receptors. Immunoreactivity of these two receptors was present at a moderate level in pinealocytes. A double-labeling study has shown that delta-opioid receptors are localized predominantly with mu-opioid receptors in the same pinealocytes. These immunopositive pinealocytes are often located in a group; however, some of them are dispersed individually. In addition, both types of receptors were found in glial cells and processes. A small number of delta-receptor-immunoreactive nerve fibers were observed in the perivascular space and intraparenchyma of the pineal gland. Mu-opioid receptor immunoreactivity was found in a number of nerve fibers throughout the gland, and in terminal-like dots on pinealocytes. There was immunocolocalization between delta-opioid receptors or mu-opioid receptors and leu-enkephalin in some nerve fibers. The results of this study indicate that the modulatory effect of the opioid system on melatonin secretion in pineal glands might act via opioid receptors on pinealocytes, whereas receptors located on nerve fibers might modulate the release of opioid peptides.

Animals↗

PubMed1990

[Sagittal MR images of normal pineal glands after Gd-DTPA injection].

We evaluated normal pineal glands on Gd-DTPA enhanced MR images on a 1.5 Tesla superconducting unit. On enhanced sagittal MR images with a 3-mm slice thickness, pineal glands were identified as solid or cystic structures. The solid and cystic pineal glands were divided into two subgroups according to the degree of enhancement. The solid pineal glands showed diffuse or subtle enhancement and cystic ones showed peripheral enhancement either completely or incompletely. Of the 50 patients, 19 (38%) had solid pineal glands and 31 (62%) had cystic ones. In male, 7 out of 11 (63%) showed solid pineal glands and in female, 27 out of 39 (70%) showed cystic ones.

Adolescent↗

PubMed1990

Postnatal development of the dog pineal gland. Light microscopy.

The light microscopical morphology of the dog pineal gland from the first postnatal day to maturity is described. In the first postnatal week, the pineal parenchyma shows immature cells and many mitotic figures. In this week, pigmented cells are observed for the first time, both in the pineal gland and in extrapineal nodules. Throughout the second week, the pineal parenchyma shows a cordonal pattern that disappears progressively in the following stages. From the 20-30th day onward, it is feasible to discern the cell types characteristic for the adult pineal gland. In the adult animals, the length of the pineal gland axes almost quadruplies that of the pineal gland in neonatal stages. The light microscopical features of the adult dog pineal gland are also described.

Age Factors↗