Showing papers on "Pinealocyte published in 1985"

Activation of protein kinase C potentiates isoprenaline-induced cyclic AMP accumulation in rat pinealocytes

Abstract: The pineal gland has proven to be an excellent model for the study of adrenergic control systems1. Noradrenaline, released from sympathetic nerve terminals in the pineal gland, regulates a large nocturnal increase in melatonin synthesis by stimulating the activity of arylalkylamine N-acetyltransferase (NAT, EC 2.3.1.87) 30–70-fold1,2. An essential step in both the induction and maintenance of high NAT activity is an increase in intracellular cyclic AMP3,4. Noradrenaline acts via β-adrenoceptors to increase pineal cyclic AMP by activating adenylate cyclase5, and the activation of pineal α1-adrenoceptors6 potentiates β-adrenergic stimulation not only of NAT7,8 but of both cyclic AMP and cyclic GMP9–11. Here we describe investigations designed to test whether α1-adrenergic potentiation of β-adrenergic stimulation of pineal cyclic AMP involves protein kinase C. Our results suggest that kinase activation is involved and the data provide the first demonstration of a synergistic interaction between Ca2+-phospholipid-dependent protein kinase (protein kinase C) and neurotransmitter-dependent stimulation of cyclic AMP.

Photoneural regulation of the mammalian pineal gland.

Abstract: Mammalian pineal function appears to be controlled primarily through the release of noradrenaline from the terminals of nerves whose cell bodies lie in the superior cervical ganglia This is the final segment of the following neural pathway: retina----retinohypothalamic projection----suprachiasmatic nuclei----paraventricular nuclei----intermediolateral cell column----superior cervical ganglia----nervi conarii----pineal gland Noradrenaline acts on pinealocytes through alpha- and beta-adrenoceptors in an atypical manner Beta-Adrenergic activation is an absolute requirement for the stimulation of both cyclic AMP and cyclic GMP production, and by itself produces a sixfold increase in the former and a twofold increase in the latter Alpha-Adrenergic activation potentiates the beta-adrenergic stimulation of cyclic AMP production 10-fold, and that of cyclic GMP production about 200-fold The mechanism of alpha- and beta-adrenergic interaction is being examined, and progress is being made in understanding the adrenergic control of cyclic AMP It appears that alpha-adrenergic agonists act through the alpha 1-subclass of adrenoceptors to stimulate phospholipid turnover and the production of a breakdown product of phosphatidylinositol, diacylglycerol This compound promotes the association of protein kinase C with membranes, which leads to the marked phosphorylation of one protein The precise identity of this protein remains a mystery This interaction leads to a larger cyclic AMP response but does not appear to be involved in the mechanism of potentiation of the cyclic GMP response Changes in chronic neural stimulation produce reciprocal changes in the magnitudes of cyclic AMP and cyclic GMP responses Chronic denervation results in a supersensitive cyclic AMP response and nearly complete disappearance of the cyclic GMP response This is termed 'see-saw' signal processing All the available evidence indicates that melatonin production is regulated by cyclic AMP This nucleotide not only increases the activity of serotonin N-acetyltransferase (more correctly called arylalkylamine N-acetyltransferase) but also stabilizes the enzyme and prevents its inactivation

Atypical synergistic α1- and β-adrenergic regulation of adenosine 3',5'-monophosphate and guanosine 3',5'-monophosphate in rat pinealocytes

Abstract: The adrenergic control of cAMP and 3′,5′-cyclic GMP (cGMP) in dispersed adult rat pinealocytes was investigated. Norepinephrine treatment increased cAMP and cGMP content 60- and 400-fold, respectively; both α- and β-adrenoceptors had to be activated for these responses to occur. β-Adrenergic stimulation alone produced only about 6- and 2-fold increase in cAMP and cGMP content, respectively. α-Adrenergic stimulation, which alone had no effect on either cyclic nucleotide concentration, markedly amplified the β-adrenergic stimulation of both cAMP and cGMP. The relative potency of α-adrenergic agonists and antagonists indicates the α1-subclass of adrenoceptors is involved. A role of α1-adrenoceptors in the control of pineal cAMP is consistent with published evidence of the presence of α1-adrenoceptors on pinealocytes and their role in the regulation of N-acetyltransferase activity and melatonin production. (Endocrinology 116: 2167–2173,1985)

Immunocytochemical demonstration of retinal S-antigen in the pineal organ of four mammalian species.

Abstract: By means of immunocytochemistry retinal S-antigen is selectively demonstrated in retinal photoreceptor cells of the rat and in pinealocytes of the hedgehog, rat, gerbil and cat. Brain areas surrounding the pineal organ are immunonegative. The immunoreactive material is evenly distributed in the perikarya of the cells. Occasionally, inner segments of retinal photoreceptors and processes of pinealocytes are also stained. The outer segments of retinal photoreceptors display a strong immunoreaction. In both pinealocytes and retinal photoreceptors the intensity of the immunoreaction varied considerably among individual cells. The immunocytochemical demonstration of retinal S-antigen in mammalian pinealocytes indicates that these cells still bear characteristics of photoreceptors. This finding is in accord with the concept that mammalian pinealocytes are derived from pineal photoreceptor cells of poikilothermic vertebrates.

Localization of Hydroxyindole-O-Methyltransferase in the Mammalian Pineal Gland and Retina

Abstract: The pineal hormone, melatonin, has been reported to be synthesized in the retina by the enzyme, hydroxyindole-O-methyltransferase (HIOMT). Several laboratories have suggested that melatonin may be involved in photoreceptor outer segment disc shedding, photomechanical movements, and neuromodulation, but the cellular location of the retinal synthesizing enzymes has not been determined yet. Antiserum to HIOMT was obtained from rabbits immunized with bovine pineal extract. The monospecific immunoglobulins to HIOMT were isolated by positive-negative selection using pineal extract-sepharose and brain extract-sepharose affinity chromatography. The purity and specificity of the antibody to HIOMT was confirmed by immunodiffusion, electroblot immunolabeling, SDS-PAGE, and immunoprecipitin titration. Using the peroxidase-antiperoxidase (PAP) technique, HIOMT was localized in the pinealocytes of bovine and human pineal glands obtained during the light period. Rat pineal glands obtained during the dark period exhibited HIOMT immunoreactivity, whereas rat pineal glands obtained during the light period did not. Some pinealocytes of the bovine pineal did not exhibit HIOMT immunoreactivity, suggesting that not all pinealocytes are actively involved in melatonin synthesis. HIOMT was localized in the photoreceptors of bovine, rat, and human retinas, and some labeling also was observed in the inner retina, although the latter showed some species variation. This observation supports the hypothesis that photoreceptors are capable of melatonin synthesis.

Opsin-like immunoreaction in the retinae and pineal organs of four mammalian species

Abstract: Opsin-like immunoreactivity was observed in the retinae and pineal organs of the mouse, rat and guinea pig, and the pineal organ of the cat. In the retina the immunoreaction was restricted to photoreceptor cells, which displayed immunostaining in their perikarya and outer and inner segments. Distinct pinealocytes endowed with characteristic processes were labelled in the pineal organs of the mouse and cat. However, in the cat the number of immunoreactive pinealocytes was very limited. In the pineal organs of the rat and guinea pig immunoreaction was very weak and diffuse. No immunoreaction was observed when the antibody was preabsorbed with purified bovine (rhod)opsin. These findings are in accord with the results of previous studies indicating molecular similarities between retinal photoreceptors and pinealocytes in mammals.

Immunocytochemistry of pineal astrocytes: species differences and functional implications.

Abstract: Immunohistochemical demonstration of glial fibrillary acidic protein (GFAP) was performed in human, sheep, rat and guinea pig pineal bodies to determine if there were species differences. Specialized "basket-like" arrangements of many GFAP-positive astrocytic processes were shown around sheep pinealocytes. Human pineals contained scattered astrocytic cell bodies and a moderate number of GFAP-positive astrocytic processes which, as in sheep, also surrounded pinealocytes, but without the dense basket-like arrangements. In both species GFAP-positive fibers were concentrated at the periphery of pseudolobules and around blood vessels. Rat and guinea pig pineals contained only rare astrocytic cell bodies and few GFAP-positive fibers throughout the glands, but had a concentration of parallel GFAP-positive fibers at the stalk. GFAP-positive fibers in human and sheep pineals may be derived from both intra- and extraglandular sites, whereas in rodents only rare processes appear to be derived from within the gland. Astrocytes may play a role in modulation of pineal indoleamines and norepinephrine, and the species differences observed suggest that this effect may be important in sheep and human pineals but not in rodents.

Eyes--the second (and third) pineal glands?

Abstract: The pineal gland, the retinas and perhaps other tissues as well may in some species produce melatonin that appears in significant quantities in the circulation. In at least one species, Japanese quail, the circadian rhythm in the levels of circulating melatonin reflects contributions from both the pineal and the retinas; in other species circulating melatonin may come exclusively from the pineal or perhaps only from the eyes. Comparative behavioural and physiological data from several bird and lizard species indicate that retinas and pineal glands fulfil similar endocrine roles. Current evidence suggests that in iguanid lizards either retinas or pineal glands, but not both in the same species, have important regulatory influences on circadian organization. This suggests that it should be relatively easy to influence the melatonin-forming ability of a tissue by natural selection, an interpretation bolstered by our finding that the ability to synthesize melatonin has been inadvertently eliminated in the pineal glands of laboratory mice, presumably by the selection involved in producing inbred strains. The genetics of melatonin synthesis in mice is briefly discussed.

Generation of melatonin rhythms.

Abstract: In mammals, information about the environmental photoperiod is relayed from the retina to the suprachiasmatic nuclei (SCN) in the anterior hypothalamus and via the sympathetic nervous system to the pineal gland where it influences the secretion of melatonin. Light plays a dual role: to suppress the release of melatonin and to entrain the circadian rhythm generators in the SCN, which govern the endogenous melatonin rhythm. Under normal daily light-dark cycles melatonin secretion is confined to the dark period. In most photoperiodic species the daily pattern of secretion changes in response to changes in daylength, and this acts as a physiological time cue in the brain for the control of seasonal cycles in reproduction, moulting and other processes. To illustrate the underlying mechanisms that control the melatonin rhythm, results are presented from five experiments in which the blood plasma concentrations of melatonin were measured in Soay rams exposed to a variety of artificial changes in photoperiod including a switch from 16L:8D (16 h light:8 h dark) or 8L:16D to constant darkness, a switch from constant darkness to 1L:23D and a switch from 16L:8D to a 25 h or 23 h light-dark cycle. The results confirm that the melatonin rhythm is generated endogenously and will free-run under constant darkness with a period close to 24 h for at least 10 days. The rhythm can be entrained by exposure to IL:23D with the end of the light period acting as the 'melatonin-on' signal, and phase-shifts in the melatonin rhythm can be induced by phase-shifts in the light-dark cycle. The period for which melatonin concentrations are high each day (melatonin peak) also varies in duration under the different photoperiods, as a result of both the suppressive and the entraining effects of light. Two models explaining the control of melatonin peak duration are discussed.

Changes in the electrical activity of the rat pineal gland following stimulation of the cervical sympathetic ganglia

Abstract: In order to elucidate the role of sympathetic innervation for pineal function, the influence of both unilateral and bilateral electrical stimulation of the superior cervical ganglia on the electrical activity of single cells in the rat pineal gland was investigated. These experiments revealed a clear influence on spontaneous electrical activity of single pinealocytes. About half of the units tested by unilateral stimulation exhibited either a graded continuous augmentation or inhibitions of different magnitude. In addition, 'silent' cells without spontaneous activity could be activated by sympathetic stimulation. Sequential and simultaneous bilateral stimulations showed that only a few cells could be influenced by both ganglia and in these cases the influence seemed to be additive. Some pineal cells do not appear to be under the control of the sympathetic nervous system.

Influence of melatonin and serotonin on the number of rat pineal "synaptic" ribbons and spherules in vitro.

Abstract: Previous studies have shown that the "synaptic" ribbons (SR) and spherules (SS) of the mammalian pineal gland may respond differently under physiological and various experimental conditions. The aim of the present study was to gain insight into the mechanisms that may be responsible for the numerical changes of these organelles during a 24-h cycle. As the possibility exists that the structures are influenced by substances synthesized within the pinealocyte, rat pineal glands were cultured with and without added melatonin or serotonin, using an experimental protocol such that the addition of melatonin and serotonin mimicks the circadian changes of the respective substances within the pineal. The tissue was processed for electron microscopy and the numbers of SR and SS were counted in a unit area of pineal tissue. The results obtained indicate that melatonin added to the incubation medium increases the number of SR in the first half of the night; serotonin decreases SR numbers in the morning. SS numbers, by contrast, decrease following melatonin administration in the afternoon, and increase in the morning following serotonin administration. It thus appears that the numbers of SR and SS are influenced by melatonin and serotonin and that the two structures are regulated by differential, but nevertheless biochemically closely related mechanisms.

Light and Agonist Alter Vasoactive Intestinal Peptide Binding and Intracellular Accumulation of Adenosine 3′,5′-Monophosphate in the Rat Pineal Gland

Abstract: We examined the effects of environmental light and prior treatment with an agonist on vasoactive intestinal polypeptide (VIP) binding and VIP stimulation of cAMP accumulation in the rat pineal gland. VIP binding to pinealocytes and cAMP accumulation in response to VIP were significantly increased in animals kept exposed to constant light compared to those in animals experiencing a dark night before the experiments. Scatchard analysis of [125I]VIP binding indicated the presence of two classes of binding sites: high affinity, low capacity sites and low affinity, high capacity sites. The increased VIP binding to pinealocytes in rats maintained in constant light was attributed to an increase in the number of available VIP receptors at both high and low affinity sites. The affinity of VIP binding to cells was not affected by exposure of the animals to light. VIP stimulation of cAMP accumulation was not inhibited by d,l-propranolol. Prior treatment of pinealocytes with VIP decreased [125I]VIP binding by reducin...

Non-sympathetic synaptic innervation of the pinealocyte of the Mongolian gerbil (Meriones unguiculatus): an electron microscopic study.

Abstract: Direct synaptic innervation of pinealocytes was observed in the superficial pineal gland of the Mongolian gerbil (Meriones unguiculatus) by electron microscopy. This innervation consisted of nerve fibres terminating in boutons with clear transmitter vesicles with a diameter of 40–60 nm. The boutons made synaptic junctions with the cell membrane of the pinealocyte displaying thickenings of both the pre- and postsynaptic membranes. Such boutons persisted in the gland 1 week after removal of both superior cervical ganglia. In contrast, all the sympathetic boutons containing transmitter vesicles with a small dense core disappeared after ganglionectomy. This direct synaptic innervation reveals a neuronal character of the pinealocyte and might underlie reports of action potentials in electrophysiological recordings from the gland.

Mammalian pinealocytes: ultrastructural aspects and innervation.

Abstract: In the mammalian pineal gland it is notoriously difficult to relate structure to function. The pineal-specific cells, the pinealocytes, contain only inconspicuous numbers of secretory granules, and the variable amounts of smooth and rough endoplasmic reticulum also do not point to a particular function. In addition to these widely known cellular components, pinealocytes contain organelles, the so-called 'synaptic' ribbons, histophysiological studies of which provide important insights into the structural and functional complexity of the organ. As synaptic ribbons may be involved in neuronal functions of pinealocytes it is notable that these organelles are structurally heterogeneous. Ribbons fall into at least two categories: rod-like (RSR) and sphere-like (SS) structures. RSR and SS usually do not lie within the same pinealocyte profile and appear to be regulated by different mechanisms. It is conceivable that they are important components of the biological clock system. These findings are related to our knowledge of the innervation of the mammalian pineal gland and to electrophysiological characteristics of pinealocytes.

Ultracytochemical Localization of Calcium in the Superficial Pineal Gland of the Mongolian Gerbil

Abstract: In order to demonstrate fine localization of Ca2+ in the superficial pineal gland of Meriones unguiculatus, the pyroantimonate technique was employed. Control experiments were performed with EGTA and analysis of obtained reaction product using an energy-dispersive x-ray microanalysis. Precipitates of calcium antimonate were formed almost exclusively in swollen clear pinealocytes, in and along their cell membranes, over their nuclei, in mitochondria, the Golgi apparatus, endoplasmic and integrade reticulums. acervuli, in vesicles surrounding synaptic bars, cytoplasmic matrix, and flocculent extracellular material. It has been concluded that the swollen pinealocytes represent a degenerative cell form probably occurring by impairment of plasmalemmal Ca2+-ATPase's ability to eliminate Ca2+ ion from the cell, with consecutive increase of calcium in the cytoplasmic matrix, followed by increase of intramitochondrial Ca2+ concentration, gradual arrest of mitochondrial function, depolymerization of cytoskeletal microtubuli, loss of the cell form, and cell death. Decrease of function of pinealocyte plasmalemma seems to be related to aging.

Distribution of dopamine-beta-hydroxylase-like immunoreactivity in the rat pineal organ.

Abstract: The aim of the present investigation was to study the distribution in the rat pineal gland of dopamine-β-hydroxylase (DBH) which is essential for the formation of the melatonin synthesis-regulating substance noradrenaline (NA). In 5- and 8-month-old male Sprague-Dawley rats DBH-like immunoreactivity (DBH-LI) was studied using polyclonal antibodies against DBH and the indirect immunofluorescent technique. DBH-LI was mainly located in pincal nerve fibres coming from the superior cervical ganglia. The intensity of the staining reaction was considerably lower than in non-pineal noradrenergic nerve fibres and the impression was gained by comparison of DBH-LI specimens with glyoxylic acid-treated sections that only approximately one third of the NA-containing intrapineal nerve fibres exhibited DBH-LI. There were no detectable differences in DBH-LI with regard to time of day and age of the animals. These results sugest that NA synthesis may be relatively low in intrapineal sympathetic nerve fibers and that the NA required for the regulation of pineal melatonin synthesis may, to a large degree, stem from the circulation. In addition to nerve fibres, some rare intrapineal cell bodies exhibited DBH-LI; in 5-month-old rats their numbers did not reveal significant differences between day and night. These cells do not appear to represent pinealocytes. They may be a special population of noradrenergic nerve cells perhaps belonging to an as yet unknown intrapineal regulatory system.

Ultrastructure of the Rat Pineal Stalk

Abstract: The ultrastructure of the rat pineal stalk was described. The pineal stalk contained few pinealocytes, glial cells and numerous nerve fibers. The last were mostly non-myelinated axons, although a few myelinated ones were also observed. Glial cells showed many filaments, mostly in the processes which presented a longitudinal orientation. Other more lamellar processes were found enclosing the axons. The pineal stalk became wider as it reached the body of the gland. Ultrastructurally, this wide region resembled more the pineal body. Bundles of non-myelinated nerve fibers were seen around the pineal stalk.

Does the Manatee Have a Pineal Body

Abstract: The brain of an adult, female manatee (Trichechus manatus) was prepared for histological examination of the region of the diencephalon and mesencephalon, where the pineal body typically would be located. Careful examination of hematoxylin-eosin stained, interrupted serial microtomy sections revealed that this animal has a tubular epiphyseal recess apparently lacking organic pineal differentiation. There was no cytological evidence of pinealocytes in the vicinity of the atypical pineal rudiment.

Impact of psychosocial stress on pineal structure of male gerbils (Meriones unguiculatus, cricetidae).

Abstract: Stress responses were investigated in 5-month-old male gerbils Breeders having no pubescent litters served as controls The first experimental group never left their parents' cage and were thereby fought by higher-ranking males; the second and third groups were stressed for a week by four daily 1-minute encounters with trained fighters, the second group during daytime, the third during the dark period The first and second groups developed signs of gonadal regression, the third did not The adrenals of the first group weighed the same as those of controls; the adrenals of both other groups were increased in weight In the adrenal medulla of all experimental groups, a large number of cells were densely packed with noradrenaline-containing vesicles In each experimental group the pineal changes included a remarkable decrease in nuclear size of pinealocytes, an increased number of colloidal cysts, and a reduction of that portion of the plasmalemma that is lined by subsurface cisterns All these changes are interpreted in terms of pineal activation, as are the increased number of membrane whirls found in the first group The third group exhibited an additional decrease in the size of mitochondria and in the number of "synaptic" structures This finding and the day-night differences in the gonadal response indicate that stress interferes with the metabolic cyclicity of the pineal gland However, it remains indiscernible whether the pineal stress reaction signals a general activation of the gland or a change in it's temporal activity patterns

Formation of autophagosomes in the pinealocytes of the rat and mongolian gerbil (Meriones unguiculatus): a lysosome wrapping mechanism?

Abstract: Autophagosome formation in rat and gerbil pinealocytes is described. It starts with the setting up of a tubular acid phosphatase-rich cisterna which gradually wraps around cytoplasmic areas to be catabolized. In light of obtained findings, it seems that the autophagosome formation in pinealocytes is a type of lysosome wrapping mechanism.

Ultrastructural Studies on the Pinealocyte Mitochondria During the Daytime and at Night

Abstract: Rat pinealocytes were found to contain mitochondria in three configurational states and they were calculated during their maximum (11:00) and minimum (23:00) serotonin content under various conditions of lighting (LD 12:12 and D 24). Their proportions were found to change in the circadian rhythm. Analysis of these results indicated the existence of correlation between pinealocyte bioenergetics and melatonin biosynthesis and its lack in relation to serotonin. Cell groupings with mitochondria in the same configurational state were observed, which suggests the existence of functionally differentiated zones within the pineal gland. In this context, the biochemically demonstrated circadian rhythm in the pineal gland secretion results from the synchronization at the organ level arising from the resultant function of individual pinealocytes.

Postnatal development of "synaptic" ribbons and spherules in the guinea pig pineal gland.

Abstract: Previous studies have shown that the functionally enigmatic pineal "synaptic" ribbons are structurally a heterogeneous group of organelles consisting of rodlike ribbons sensu stricto, spherules, and intermediate forms. As ribbons and spherules react differently under various experimental conditions, these organelles were studied qualitatively and quantitatively during the postnatal period in guinea pigs. It was found that the pinealocytes were highly differentiated at birth and contained all three forms of "synaptic" structures. Ribbons and intermediate forms were more abundant than spherules and exhibited a striking increase in number on postnatal days 1 and 2; this increase was followed by a distinct trough and by a second peak at days 12 and 13, after which their numbers declined to reach adult levels by day 20. The spherules were small in number at birth and did not show the large immediate postnatal increase observed for the ribbons and intermediate forms. Instead there was a steady numerical increase up to day 12 (absolute number) or day 15 (relative numbers), followed by a decrease to adult level by day 20. Whereas during the early postnatal period (days 1 to 3) the majority of pinealocytes were characterized by ribbons and intermediate forms, with increasing age spherule-bearing pinealocytes increased in number. As ribbons and spherules were usually not found in the same pinealocyte, the present findings are interpreted to mean that ribbons and spherules characterize different types of pinealocytes showing an inverse numerical development postnatally. Developmentally intermediate forms behave like ribbons.

Melatonin formation in different parts of the guinea-pig pineal complex as assessed over 24 hours.

Abstract: There is morphological evidence that the pineal gland is not a uniformly built organ but rather a complex. In the guinea-pig the gland is 6--7 mm in length and dumbbell-shaped, the proximal part coming into intimate contact with central commissural fibres. The aim of the present 24-hour study was to examine in male guinea-pigs whether the proximal, intermediate and distal areas of the gland are involved in melatonin formation and to compare their rhythmicities. Levels of melatonin in serum and the whole pineal gland as assessed by RIA show day/night ratios of 1 : 1.25 and 1 : 3.3, respectively. Serotonin N-acetyltransferase activity was found to exhibit ratios of 1 : 1.75 (Experiment I) and 1 : 4.4 (Experiment II). All three pineal regions are involved in melatonin formation, and to the same extent. Whether the rhythms in the different regions are identical could not be clarified as the curves obtained exhibited striking oscillations and the day/night differences were rather small. As the extrapineal portion of the habenular commissure was found to contain melatonin there is a possibility that melatonin may be taken up when the commissural fibres pass through the pineal parenchyma.

The pineal body of the dog.

Abstract: A technique is described for finding the pineal body of the dog. The posterior half of the skull is cut a little behind the parietofrontal suture, through the occipital condyles. The cerebral hemispheres and cerebellum are carefully sliced, disclosing the pineal at the frontal edge of the colliculi. Two types of cells are present, those with completely round nuclei, and others with vesicular and variably shaped nuclei. In the histological pattern, ependymal cells were observed on the edges, pinealocytes and glial cells within the gland.

Stereologic studies on mitochondrial configuration in the rat pinealocytes.

Abstract: Stereologic studies were performed on rat pinealocytes. In the morphometric analysis the following parameters were taken into consideration: the volume density of the outer and inner membranes, surface areas of the outer and inner membranes, inner membrane to outer membrane surface area ratio, volumes of the outer and inner compartments, and partition coefficients of these compartments. Visual analysis demonstrated three mitochondrial configurational states. Based on the mitochondrial criteria, the existence of three pinealocyte types may be demonstrated. The authors believe that these are the cells in three different functional states.

Seasonal rhythms of indoleamine levels in the rat pineal gland

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