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PubMed1999

Interstitial glial cells of the gerbil pineal gland display immunoreactivity for the metabotropic glutamate receptors mGluR2/3 and mGluR5.

Recent studies have strengthened the hypothesis that neuroactive amino acids such as L-glutamate play an important role in the physiology of the mammalian pineal gland. In particular, there is now considerable evidence that L-glutamate is liberated from electron-lucent microvesicles of pinealocytes for a paracrine modulation of melatonin synthesis and release which may at least partially be mediated by the metabotropic glutamate receptor mGluR3. In order to expand our incomplete knowledge of possible pineal target cells and signal transduction mechanisms which are involved in glutamate-dependent intercellular communication, we have performed an immunohistochemical study of the gerbil pineal gland with antibodies directed against the metabotropic glutamate receptors mGluR2/3 and mGluR5. Using microwave irradiation of cryostat sections prior to immunostaining, strong immunoreactivity for both receptor subtypes was constantly observed in a subpopulation of pineal cells. Interestingly, these mGluR-positive cells could be identified as interstitial glial cells since they were labeled by antibodies against the intermediate filament protein vimentin in double immunofluorescence histochemistry. This indicates that interstitial glial cells in the gerbil possess the capacity to express at least two metabotropic glutamate receptors coupled to different intracellular signal transduction pathways. Therefore, it can be concluded that the glutamatergic communication system of the pineal gland may not only enable paracrine crosstalk among pinealocytes but probably also relies on interactions between pinealocytes and interstitial cells analogous to neuronal-glial signaling.

Animals↗

PubMedDate not supplied

Vasotocin release from the pineal gland of newborn mammals: the involvement of GABA mechanisms.

The arginine vasotocin (AVT) levels were bioassayed in the pineal extracts from 20-day-old kittens and from 10-day-old rat pups and in the cerebrospinal (CSF) samples taken from 20-day-old kittens. The animals received daily (between the postnatal day 2 and the day of sacrifice) the selective GABA receptor antagonist picrotoxin (5 X 10(-7) mg) or the specific GABA agonist valproic acid (10(-5) mg). Picrotoxin was found to produce a decrease of the pineal AVT levels in newborn kittens and rats, and an increase of the AVT amount of the CSF samples from kittens. Valproic acid had opposite effects, producing an increase of pineal AVT in both species and a decrease of AVT levels in the kittens CSF samples below the sensitivity limit of the bioassay method. The result suggests that not only in adult, but also in newborn mammals, the inhibitory feed-back loop between the brain and the pineal gland is GABA-mediated and that the GABA-ergic mechanisms are involved in regulating the release of AVT from the pineal gland.

Animals↗

PubMed2000

Photoperiodic information acquired and stored in vivo is retained in vitro by a circadian oscillator, the avian pineal gland.

Endogenous circadian rhythms have been described in a wide range of organisms from prokaryotes to man. Although basic circadian mechanisms at the molecular level are genetically fixed, certain properties of circadian rhythms at the organismic level can be modified by environmental conditions and subsequently retained for some time, even in organisms shielded from 24-hr environmental variations. To investigate the capacity of animals to acquire and store photoperiodic information, we examined activity and melatonin rhythms in house sparrows during synchronization to two different photoperiods and during subsequent prolonged darkness. Under constant environmental conditions, intact animals continued to have long feeding activity times when previously exposed to long days and short feeding activity times when previously exposed to short days. Correspondingly, significantly different durations of elevated melatonin in the plasma directly reflected the differences in night length during synchronization as well as during prolonged darkness. Additionally, we found a significant difference in the amplitude of the nocturnal melatonin signal, which also was conserved in prolonged darkness. To investigate whether the photoperiodic experience of an intact animal can be "memorized" by an isolated component of its circadian pacemaking system, we have investigated in vitro melatonin release during continuous darkness from explanted pineal glands of house sparrows after in vivo synchronization to two distinct photoperiods. Differences in the durations of elevated melatonin occurred during the first two cycles in culture and a difference in melatonin amplitude was detectable during the first night in culture. Our data indicate that photoperiodic patterns imposed on sparrows during in vivo synchronization can be maintained as an internal representation of time within the isolated pineal gland. Hence, the pineal gland, as one of the most significant components of the songbird circadian pacemaker, not only has the capacity to autonomously produce circadian rhythms of melatonin release but also is capable of storing biologically meaningful information experienced during previous cycles.

Animals↗

PubMed1979

Ultrastructural localization of monoamines in nerve fibers of the pineal gland in golden hamsters.

Nerve terminals in the pineal glands of control, parachlorophenylalanine (PCPA)-, reserpine- and nialamide-administered hamsters were studied with glutaraldehyde-dichromate (GD) and formaldehyde-glutaraldehyde-dichromate (FGD) techniques in the electron microscope. In control pineals treated with the FGD or GD technique, clusters of electron dense reactive particles with a diameter of 20-30 nm, and mainly located in the perivascular space, were identified as dense cores of the small granulated vesicles (SGVs) in the pineal nerve fibers. After the administration of PCPA, the reactive cores were greatly decreased in number in the FGD-treated pineal blocks, whereas a lot of clusters of reactive cores were observed in the perivascular space in GD-treated specimens. After reserpine treatment, no reactive structures were revealed by GD or FGD technique. Reactive cores appeared to be increased in number and in electron density in GD- or FGD-treated pineals of hamsters after administration of nialamide. From the observations, it is concluded that the dense cores of SGVs in the pineal nerve fibers contain both primary catecholamines and 5-hydroxytryptamine although it was not determined whether both amines are located in the same or separate vesicles.

Animals↗

PubMed1984

Pineal gland morphology in rats with experimentally induced protein-calorie malnutrition.

The morphology of the pineal gland was studied in protein-calorie-malnourished (PCM) rats. Twenty-day-old male Sprague-Dawley rats were placed in a 14:10 photoperiod and fed either an 8% low protein diet (LPD) or a standard laboratory diet (SLD) containing 27% protein for 30 d. At 50 d of age, rats from both animal groups were sacrificed at 0900 h and at 2400 h, and the pineal glands were immersion-fixed for either light or electron microscopic analysis. The cytoplasm and nuclei of the pinealocytes from the SLD-fed rats were consistently larger than those of the animals maintained on the LPD. Additionally, the lipid droplets were larger and more prominent in the controls at both 0900 h and 2400 h. Even though the size of these inclusions did not vary among animals given the same diet as a function of the time of sacrifice, they were more numerous in both the well-fed and malnourished rats during the dark phase of the photoperiod. In contrast neither diet nor sampling time affected the size or number of pinealocyte mitochondria. These morphological observations lend further support to the premise than PCM impairs the cellular activity of the pinealocytes.

Animals↗

PubMed1993

Immunocytochemical demonstration of nerve growth factor (NGF) receptor in the pineal gland: effect of NGF on pinealocyte neurite formation.

Nerve growth factor receptor immunoreactivity (NGFRI) in the pineal gland was examined both light and electron microscopically using the monoclonal antibody 192IgG. NGFRI was located on sympathetic fibers and on perivascular cells resembling macrophage/microglia. A pineal gland dispersed cell culture model confirmed the presence of NGFRI in cells that exhibited processes of varying lengths and were distributed among pinealocytes and other flat cells. Pinealocytes in dispersed cell culture were identified immunocytochemically by their expression of S-antigen, their round shape and small size and their tendency to extend neurites in the direction of the flat cells in culture. The length of pinealocyte neurites showed a significant increase when cultured in the presence of NGF (25 ng/ml), suggesting that trophic factors, mediated by these macrophage/microglial cells, are important to the morphogenesis of these neuroendocrine cells. Neurotrophic activation of these neuroendocrine macrophage/microglia may have neuro-immunomodulatory implications leading to expression of proteins encoded by the major histocompatibility complex.

Animals↗

PubMed1983

Prostanoid profile in specific brain areas, pituitary and pineal gland of the male rat. Influence of experimental conditions.

Using chromatographic separation and specific radioimmunoassays, we were able to detect the prostanoids PGD2, PGF2 alpha, PGE2, 6-keto-PGF1 alpha and thromboxane B2 in selected brain areas, pituitary and pineal glands of adult male rats. Our results suggest regional differences in the biosynthetic capacity of homogenates. Higher amounts were produced by the pituitary and pineal gland (33 and 28 ng/mg protein, respectively). In the hypothalamus, the median eminence was the most active part (24 ng/mg protein). The sum of the 5 prostanoids in whole hypothalamus was higher after 15 min incubation (10 ng/mg protein), than at zero time (2.7 ng) or after immediate freezing of the tissue (1.2 ng). We confirm the predominance of PGD2 after incubation of the homogenates in each of the 8 areas in the brain, pituitary and pineal gland. However, PGD2 was not predominant when the prostanoid profile was estimated immediately after homogenization or when the hypothalamus was immediately frozen in liquid nitrogen. The ratio PGD2/PGF2 alpha was 2.7, after 15 min incubation, 0.9 at zero time and 0.8 for the hypothalamus immediately frozen. Furthermore, PGD2 predominance was not observed when intact tissues were incubated without homogenization.

Animals↗

PubMed1999

An intrinsic neuronal-like network in the rat pineal gland.

Recent studies have shown that in rat pineal glands kept in vitro action potential-producing cell clusters are demonstrable. To test whether the clusters interact, multiple-unit recordings were carried out simultaneously from different clusters, with or without electrical stimulation. Clusters with rhythmic burst activity exhibit highly synchronized firing and electrical stimulation of one cluster elicits an immediate response in another one, apparently involving synapses but not gap junctions. It is hypothesized that the interacting clusters form a network. As the firing is affected by norepinephrine, acetylcholine and Ca2+, the network may monitor the interstitial concentrations of these substances and spread this information in the gland, to modulate melatonin secretion.

Animals↗

PubMed1997

Melatonin secretion of the rat pineal gland in response to norepinephrine in different types of the anovulatory syndrome.

Earlier experimental results show the role of altered pineal function in the development of the constant estrous-anovulatory (CEA) state induced by neonatal androgen sterilization (NA) or in the spontaneously developed anovulatory syndrome in the aging rat (AG-CEA state). Since norepinephrinergic (NE) innervation of pineal gland represents the main stimulus for melatonin secretion in mammals, in the present experimental series, the reactivity of pineal tissue to NE was investigated in in vitro perifusion system in rats suffering from NA-CEA or AG-CEA state, using the model of pineal body deprived from neural inputs. The data indicate that the 'melatonin deficiency' observed in the 2 types of anovulatory syndrome (NA-CEA and AG-CEA states) is due to disturbance of norepinephrinergic innervation of the pineal gland rather than to deficient secretory capacity of pineal tissue.

Animals↗

PubMed1998

Potential role of kallikrein in diurnal rhythms and perivascular distribution in rat pineal glands.

Kallikrein hydrolyzes various biologically active peptides, other than kininogens, such as vasoactive intestinal polypeptide (VIP), in vitro. Since kallikrein and VIP have been immunohistochemically shown to be present in the perivascular areas of the pineal gland, this study was designed to determine their topographic proximity in these glands, using immunohistochemical and immunoelectron microscopic double staining methods. Furthermore, since this gland is well-known to have a circadian rhythm, the kallikrein content was measured every 4 h, using a synthetic substrate, Pro-Phe-Arg-MCA, and an enzyme-linked immunosorbent assay (ELISA) to determine whether kallikrein has a circadian rhythm. The immunoreactivities of kallikrein and VIP were highly localized in the perivascular extracellular spaces and were virtually identical in distribution. The kallikrein content changed every 4 h and was high under light and low under dark conditions. The change was more evident when the synthetic substrate was used, and this rhythm was subtle on ELISA. VIP is also said to have a circadian rhythm in the pineal glands, being low under light and high under dark conditions, i.e., opposite to that of kallikrein. Since kallikrein degrades VIP in vitro, it is reasonable to speculate that pineal gland kallikrein is involved in the processing of VIP and possibly other biologically active peptides in the perivascular areas with a discernible circadian rhythm.

Animals↗

PubMedDate not supplied

Histaminergic and noradrenergic control of cyclic AMP formation in the pineal gland and cerebral cortex of three avian species: cock, duck, and goose.

The goal of the present study was to examine the effects of forskolin (FOR), histamine (HA), L-noradrenaline (NA), isoprenaline (ISO) and dopamine (DA) on cyclic AMP formation in whole pineal glands and cerebral cortical slices of cock, duck and goose. HA (100 muM) and FOR (10 muM) potently increased cyclic AMP production in the pineal glands of all studied avian species, showing a synergistic interaction when applied together. HA at the dose of 1 mM significantly stimulated adenylyl cyclase activity in the membrane preparations of cock pineal glands while lower concentrations were ineffective. HA markedly enhanced cyclic AMP formation in cerebral cortex of cock (an effect being potentiated for FOR), but did not affect the nucleotide production in this brain structure of duck and goose. DA (100 muM) had no effect, NA (100 muM) only moderately (5-22% increased, where ISO (10muM) significantly (by 50-90%) enhanced cyclic AM_ synthesis in avian cerebral cortex. Propranolol (1 muM) antagonized all these effects, while preincubation with yohimbine and prazosin significantly enhanced NA action in cortical slices of duck and goose.

Adenylyl Cyclases↗

PubMed1989

Neuroendocrine mediated effects of electromagnetic-field exposure: possible role of the pineal gland.

Reports from recent epidemiological studies have suggested a possible association between extremely low frequency (ELF; including 50- or 60-Hz) electric- and magnetic-field exposure, and increased risk of certain cancers, depression, and miscarriage. ELF field-induced pineal gland dysfunction is a possible etiological factor in these effects. Work in our laboratory and elsewhere has shown that ELF electromagnetic-field exposure can alter the normal circadian rhythm of melatonin synthesis and release in the pineal gland. Consequences of reduced or inappropriately timed melatonin release on the endocrine, neuronal, and immune systems are discussed. Laboratory data linking ELF field exposure to changes in pineal circadian rhythms in both animals and humans are reviewed. The authors suggest that the pineal gland, in addition to being a convenient locus for measuring dyschronogenic effects of ELF field exposure, may play a central role in biological response to these fields via alterations in the melatonin signal.

Animals↗

PubMed1992

Neuropeptide Y (NPY) and C-flanking peptide of NPY in the pineal gland of normal and ganglionectomized sheep.

The present immunohistochemical study describes the presence and distribution of nerve fibers containing neuropeptide Y (NPY), and C-Flanking Peptide Of NPY (CPON) in the pineal gland of the sheep. Nerve fibers were detected by using a series of antisera directed against NPY or against CPON. Many positive immunoreactive nerve fibers were identified in the pial capsule of the pineal, in connective septae and in the parenchyma between pinealocytes. The intraparenchymal fibers were particularly evident and created an extensive network throughout the gland. Nerve fibers immunoreactive for all the peptides were also observed in the posterior commissure and in the stria medullaris thalami. No NPY- or CPON-positive neurons were found in the pineal gland. In order to study the site of origin of NPY- and CPON-immunoreactive nerve fibers, the superior cervical ganglia were bilaterally removed in a series of animals. Sympathetic denervation was checked by using an antiserum against tyrosine hydroxylase (TH). Nearly all TH-immunoreactive elements disappeared in the pineal glands of animals sacrificed 15 days after surgery. Also the density of NPY- and CPON-immunoreactive nerve fibers decreased in the animals after the ganglionectomy. However, a number of nerve fibers still remained in the gland. These data indicate that some NPY- and CPON-immunoreactive nerve fibers of the sheep pineal gland derive from an extrasympathetic origin. The very dense innervation of the sheep pineal gland with nerve fibers containing NPY and CPON strongly indicates a functional role for this family of peptides in the pineal gland of this species.

Animals↗

PubMed1991

Effect of different photoperiods on the diurnal rhythm of 5-methoxytryptamine in the pineal gland of golden hamsters (Mesocricetus auratus).

This study tested the photo-dependency of the rhythmic synthesis of 5-methoxytryptamine (5-MT) in the pineal gland of golden hamsters. After pargyline administration, pineal 5-methoxytryptamine and melatonin were measured by HPLC in male golden hamsters kept under short and long photoperiod. In both photoperiodic regimes, a clear 5-MT rhythm was observed which fitted a sinusoidal function with high values occurring during the daytime and low values occurring during the night-time. The duration of the low night-time levels was clearly proportional to the length of the dark phase. A marked rhythm of melatonin synthesis was also seen with low daytime levels and high night-time values. An inverse relationship between 5-MT and melatonin levels was observed. Thus, after pargyline administration, the rhythms of 5-MT and melatonin in the pineal gland of golden hamsters are photoperiod-dependent and show a reciprocal relationship.

5-Methoxytryptamine↗

PubMed1979

The projection of the calcified pineal gland on slightly rotated AP films as a reliable landmark. A CT study.

The projection of the pineal gland between the two outer tables of the skull in the AP film has been reconstructed on the basis of the CT print of the head, with and without lateral rotation. In this experimental approach it is proven that rotation up to 5 degrees does not influence the position of the pineal gland on the AP film. The range of the normal position of the pineal in the frontal plane is defined and the normal distribution is given.

Calcification, Physiologic↗

PubMed2005

Features of the circadian clock in the avian pineal gland.

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.

Animals↗

PubMed1983

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

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

Animals↗

PubMed1999

Immunoreactivity for multiple GABA transporters (GAT-1, GAT-2, GAT-3) in the gerbil pineal gland.

In order to further elucidate the role of gamma-aminobutyric acid (GABA) within the mammalian pineal gland, an immunocytochemical study was performed aimed at providing information on the occurrence and localization of the plasma-lemmal GABA transporters GAT-1-3 in the gerbil pineal organ. Whereas all three transporter subtypes were regularly present in this endocrine tissue, their cellular distribution differed. The analysis of serial semi-thin sections showed that pinealocytes as well as interstitial glial cells contain immunocytochemically detectable amounts of GAT proteins, indicating that both pineal parenchymal cell types participate in GABA reuptake. These results lend additional support to the hypothesis that GABA serves important physiological functions in the pineal gland.

Animals↗