Showing papers on "Pinealocyte published in 1983"

Melatonin is a potent modulator of dopamine release in the retina

Abstract: Melatonin, a hormone originally discovered in the pineal gland1, has also been found in the retina of several vertebrate species2–5. The enzyme system for melatonin synthesis also exists in the retina2,3,6–8, where the activity of one such enzyme, (serotonin N-acetyltransferase) varies with changes in light intensity in a circadian pattern3,8. As the activity of dopamine containing amacrine neurones of the retina is influenced by changes in illumination9–12 it was of interest to determine the effect of melatonin and its precursors, serotonin and N-acetylserotonin, on the release of 3H-dopamine from rabbit retina. I report here that picomolar concentrations of melatonin (IC50 9pM) selectively inhibited the calcium-dependent release of 3H-dopamine from rabbit retina, but not from striatum. Melatonin, was 1,000 times more potent than its precursor N-acetylserotonin in inhibiting the release of 3H-dopamine in retina, while the putative neurotransmitter serotonin13, was inactive. It is suggested that the light-dependent production of melatonin could play a physiological role in modulating the activity of dopamine-containing neurones in the retina.

The Pineal Gland and Mammalian Photoperiodism

Abstract: The mammalian pineal gland appears to be a major endocrine component in the regulation of photoperiodic responses. The circadian pattern of secretion of the pineal hormone, melatonin, is regulated by

Circadian Rhythms of Pineal Function in Rats

Abstract: In pineal glands melatonin is synthesized daily. Melatonin synthesis in rats kept in most light-dark cycles occurs during the subjective night. This rhythm, which persists in constant dark, is a circadian rhythm which may be a consequence of another circadian rhythm in the pineal gland, of N-acetyltransferase activity (NAT). The NAT rhythm has been studied extensively in rats as a possible component of the system timing circadian rhythms. The NAT rhythm is driven by neural signals transmitted to the pineal gland by the sympathetic nervous system. Environmental lighting exerts precise control over the timing of the NAT rhythm. In rats, there is enough data to describe a daily time course of events in the pineal gland and to describe a pineal "life history." Hypothetical schemes for generation of the NAT rhythm and for its control by light are presented.

Evidence for Pineal Gland Modulation of the Neuroendocrine-Thyroid Axis

Abstract: Experiments with rats and hamsters have provided evidence for an inhibitory action of the pineal gland on the neuroendocrine-thyroid axis. While maintenance of these animals in short photoperiod results in reduced levels of circulating thyroxin (T4), pinealectomy restores the levels to normal. Recent studies suggest that an active pineal gland produces a substance which inhibits thyrotrophin-releasing hormone release from the hypothalamus. Several investigators have concluded that endogenous melatonin, produced in the pineal gland, could account for the inhibitory action of the pineal gland on blood T4 levels. Although melatonin administration has been reported to inhibit blood T4 levels in both rats and hamsters, under certain experimental conditions melatonin administration can be demonstrated to have a counter-antithyrotrophic effect resulting in increased blood levels of T4 and thyrotrophin. Assay of blood levels of melatonin of rats and hamsters under various experimental conditions will be necessary to distinguish physiological from pharmacological effects of melatonin. Lesion studies as well as studies with melatonin implants in the brain, suggest that the site of action is in the anterior hypothalamus. The effects of melatonin on the neuroendocrine-thyroid axis are similar to its effects on the neuroendocrine-gonadal axis, leading to the hypothesis of a common site of action for the thyroid and gonadal effects of melatonin. Although many pineal 'factors' have been postulated to account for the action of this gland, an action of melatonin on the serotonergic system of the brain stem could account for the data.

Circadian variations in pinealocytes of the Chinese hamster, Cricetulus griseus. A quantitative electron-microscopic study.

Abstract: Circadian morphological variations of pinealocytes in the superficial pineal of the Chinese hamster (Cricetulus griseus) were studied using quantitative electron-microscopic techniques. The volume of the nucleus and cytoplasm of pinealocytes exhibited similar circadian variations, with the maximum around the middle of the light period and the minimum during the first half of the dark period. Synaptic ribbons in pinealocytes were classified into three groups, type-1, −2 and −3 synaptic ribbons, which appeared as rods, round or irregular bodies and ring-shaped structures, respectively; a synaptic ribbon index was determined for the respective types. The synaptic ribbon index was expressed as the number of synaptic ribbons in the pinealocyte profile representing the cell size. The type-1 synaptic ribbon index, which was smallest during the second half of the light period, was increased during the dark period. The length of straight or slightly curved rods showed a 24-h change similar to that of the type-1 synaptic ribbon index; the length of the rods was maximal during the first half of the dark period and minimal at the end of the light period. There was no apparent circadian variation in the type-2 synaptic ribbon index. The type-3 synaptic ribbon index was higher during the light period than during the dark period; the index attained zero 3h after the onset of darkness and, thereafter, increased gradually.

Serotonin axons of the ependyma and circumventricular organs in the forebrain of the guinea pig. An immunohistochemical study.

Abstract: The distribution of supraependymal nerve fibers (SEF) containing serotonin (5-HT) was investigated immunohistochemically in the forebrain of the guinea pig The highest densities of immunoreactive axons were found in the pars centralis and the inferior horn of the lateral ventricle and also in the superior part of the third ventricle Because of the special development of the choroid plexus in these ventricular regions, it is suggested that 5-HT SEF might be involved in the regulation of the composition of the cerebrospinal fluid The ependyma lining the circumventricular organs located in the forebrain, was not observed to receive a significant 5-HT-SEF innervation In the pituitary gland, a loose but constant network of 5-HT axons, resembling those which course in the anterobasal hypothalamus, arcuate nucleus and internal layer of the median eminence, was observed in the neural lobe In the epiphysis, immunoreactive 5-HT was detected in all pinealocytes (the entire cell was filled with reaction product) and in fibers running between them

“Synaptic” ribbons and spherules of the guinea pig pineal gland: Inverse day/night differences in number

Abstract: The present study deals with the functionally enigmatic "synaptic" ribbons and spherules of guinea pig pinealocytes. Whereas the ribbons have been shown to exhibit a 24-hr rhythmicity with low numbers during the day and high numbers at night, very little of a definitive nature is known about the spherules. Sixteen male guinea pigs of the Hartley strain were perfusion fixed, 8 between 0900-1100 hr, and 8 between 2100-2300 hr. The ribbons and spherules were counted in the pineal parenchyma of the proximal, intermediate, and distal regions. In confirmation of earlier studies, it was found that "synaptic" ribbons are equally abundant in the proximal, intermediate, and distal regions of the gland, during both the day and the night, and that they increase significantly in number at night when compared with daytime values. The spherules, by contrast, are more abundant proximally and are present in greater numbers during the day than at night. As ribbons and spherules are usually not found in one and the same pinealocytic profile, and based on previous electrophysiological studies, it is proposed that the ribbons are morphological markers of nocturnally active pinealocytes, whereas spherules characterize diurnally active pinealocytes.

Glial fibrillary acidic (GFA) protein-containing cells in the human pineal gland.

Abstract: The development of human pineal astrocytes was studied in a prospective autopsy series of 115 cases with an age range of 24 weeks of gestation to 91 years. Pineal glands selected from cases with postmortem intervals of one to 24 hours were fixed in Bouin's fluid and immunostained using the peroxidase-antiperoxidase technique and an antiserum against human glial fibrillary acidic (GFA) protein. In adults, scattered, mostly angular and strongly-positive cells and processes were present. A few primary processes emanated from each astrocyte which abruptly subdivided into several secondary ones, creating a pervasive interstitial network of fibers which surrounded almost every individual pinealocyte. Astrocytic endfeet formed a limiting lamina at the periphery of the gland and a barrier between perivascular spaces and the pineal parenchyma. At 24 weeks of gestation, occasional punctate staining, mainly around vessels, was present in the pineal body, while in the surrounding white matter there was already pronounced astrocytic differentiation. Around 32 weeks of gestation, well-formed astrocytes and a weakly staining network of their processes appeared in differentiated areas of the pineal gland. Both astrocytes and their interstitial network of processes became more prominent with advancing age. There was no astrocytic hypertrophy or hyperplasia around calcified deposits. Rosenthal fibers stained negatively for GFA protein. These findings emphasize the significance of the astrocytic participation in the structure of the human pineal gland throughout life.

Postnatal development of cell types in the rat pineal gland.

Abstract: The morphological development of the rat pineal gland has been studied from 1 to 60 days of age. During the first days, undifferentiated cells (pinealoblasts) with scanty cytoplasm and frequent mitotic figures were observed. The differentiation of cell types (Types I and II pinealocytes) began on the third day after birth and was completed by days 15-20. At 3 days of age, nerve fibres were first observed, both in the connective spaces and in the parenchyma. After 5 days, an important hypertrophy of pinealocytes began, mostly Type I, which continued until 60 days of age. After 45 days, all the ultrastructural features described in the adult pineal gland were already present. The findings are discussed.

β-Adrenergic Receptor Control of Rat Pineal Hydroxyindole-O-Methyltransferase

Abstract: The nature of the postsynaptic adrenergic receptor on rat pinealocytes which controls hydroxyindole-O-methyltransferase (HIOMT) activity was studied. This enzyme is involved in the synthesis of the pineal hormone melatonin. Adrenergic drugs were administered continuously for a 7-day period to rats in which neural stimulation of the pineal gland was blocked by either superior cervical ganglionectomy or exposure to constant light. l-Isoproterenol, a beta-adrenergic agonist, prevented the fall in enzyme activity that occurs when neural stimulation is interrupted; d-isoproterenol was ineffective. The potency order of different adrenergic agonists was d,l-isoproterenol greater than l-norepinephrine greater than l-epinephrine. Terbutaline, a selective beta 2-adrenergic agonist, was ineffective. The selective alpha 1-adrenergic agonists phenylephrine and methoxamine and the alpha 2-agonist clonidine were also ineffective. High doses of the beta-adrenergic blocker propranolol antagonized the effect of isoproterenol and caused a fall in HIOMT activity in normal rats housed under normal diurnal lighting. This in vivo evidence is consistent with the hypothesis that the neural control of pineal HIOMT is mediated via a beta-adrenergic receptor.

Inverse correlation between "synaptic" ribbon number and the density of adrenergic nerve endings in the pineal gland of various mammals.

Abstract: The number of "synaptic" ribbons was inversely correlated with the density of the adrenergic nerve endings of the pineal gland compared among a diverse group of species including the fox, cat, rat, cotton rat, white-footed mouse, Djungarian hamster, ground squirrel, and chipmunk. The concentration of norepinephrine paralleled the number of adrenergic nerve terminals in the pineal glands of the cotton rat, rat, and ground squirrel, the only species in which norepinephrine concentrations were measured. The number of ribbon fields paralleled numbers of "synaptic" ribbons in all species examined. Adrenergic nerve endings were observed primarily within the perivascular spaces, although some endings also were found among parenchymal cells. Adrenergic nerve endings forming synaptic junctions with pinealocytes were not observed in any of these species, nor was there any physical association between these nerve endings and "synaptic" ribbons.

Innervation of the avian pineal organ. A comparative study.

Abstract: The innervation of the pineal organ was studied in 26 avian species under particular consideration of comparative aspects. A population of nerve cells and their pinealofugal (afferent) fiber systems were stained by means of the acetylcholinesterase method, while catecholamine-containing pinealopetal (efferent) fibers were demonstrated with the use of the glyoxylic acid method. Afferent axons were mainly found in the postero-proximal portion of the organ, and the patterns of their distribution were classified into three groups according to the characteristic densities of the reaction product. The number of acetylcholinesterase-positive neurons in the avian pineal organs examined in this study varied extremely from species to species, ranging from 0 to 362. Catecholamine-containing nerve fibers penetrating the antero-lateral walls of the pineal follicles accompanied blood vessels and were arranged more densely in the distal portion of the organ, in contrast to the distribution of the acetylcholinesterase-positive nerve fibers. Three-dimensional reconstruction of the distributional patterns of both types of neural projections was performed for the pineal organ of every avian species examined. In avian species possessing a relatively conspicuous afferent projection, such as Passeriformes, Nycticorax, and Milvus, terminals of catecholamine-containing nerve fibers were observed exclusively in the interfollicular and perivascular tissues. In Galliformes, which display only few pineal afferents, catecholamine-containing fibers terminate not only in the interfollicular space, but also in the neuroepithelial parenchyma. The regional differences in the innervation in the avian pineal organ suggest that the pinealocytes ranging from more sensory-like to more secretory-like elements are arranged in a mosaic-like pattern.

Cerebrospinal fluid-contacting neurons, sensory pinealocytes and Landolt's clubs of the retina as revealed by means of an electron-microscopic immunoreaction against opsin.

Abstract: Opsin-immunoreactive sites of hypothalamic cerebrospinal fluid (CSF)-contacting neurons, pinealocytes and retinal cells were studied in various vertebrates (Carassius auratus, Phoxinus phoxinus, Triturus cristatus, Bombina bombina, Rana esculenta) by means of postembedding immuno-electron microscopy with the use of the protein A-gold labeling method. The retina of the rat served as a general reference tissue for the quality of the immunocytochemical reaction.

24-hour-variation of pineal gland volume, pinealocyte nuclear volume and mitotic activity in male Sprague-Dawley rats.

Abstract: In two experiments carried out on two alternate days, the 24-hrhythmicity of pineal gland volume, pinealocyte nuclear size in cortex and medulla and mitotic actty were studied in male Sprague-Dawley rats, to assess to what extent morphological parameters reflect the pronounced day/night differences in pineal melatonin formation. Pineal volume exhibited statistically significant changes in the second experiment only, with a distinct trough at 6 p.m. Karyometry revealed highly variable patterns. In the first experiment, pinealocyte nuclear changes lacked parallelism in cortex and medulla. The cortex exhibited a bimodal curve with peaks at noon of the first day and at 6 a.m. of the second day, and two troughs at 6 a.m. and midnight respectively of the first day. The medulla showed no clear-cut rhythmicity. In the second experiment, cortex and medulla reacted similarly, nuclear size decreasing from 6 a.m. to 6 p.m., remaining low thereafter. Mitotic activity of pinealocytes is low (on average 23 mitotic figures/gland). In both experiments statistically significant differences existed between certain times, pointing in the direction of 24-hrhythmicity, but whereas the curve exhibited a peak at midnight in the first experiment, mitotic activity in the second experiment showed a trough at midnight. It is concluded that for as yet unexplained reasons morphological parameters do not appear to accurately reflect circadian rhythmicity of pineal melatonin formation.

Evolution of Pineal Control of Endocrine Function in Lower Vertebrates

Abstract: Pineal bodies, and other associated parietal structures, are remarkably varied among vertebrates These organs apparently assumed, in the primitive vertebrates, a principal role in integration of photic information. The pineal photoreceptor cell seems to have evolved into the secretory pinealocyte that is found in most of the higher vertebrates. Along with the evolution of the photoreceptor element into the pinealocyte, there is a concomitant shift in the neural connection of the pineal organ. The pinealo-fugal, sensory innervation gives way to an autonomic, pinealo-petal motor innervation. Thus, direct photosensitivity was superceded by indirect, optically-mediated control of the now secretory pineal gland. Even though pineal organs display such unusual plasticity and diversity across groups, responsivenses to light remains a constant feature. Photoperiod may modify the diurnallyrhythmic patterns of melatonin secretion across seasons and invoke appropriate “programs” which permit an animal to anticipate seasonal changes. Thus, melatonin may be a key molecule, attuned to photoperiodicity, which has been selected through evolution to effect adaptation to annual events.

CSF-contacting pinealocytes in the pineal recess of the Mongolian gerbil: a correlative scanning and transmission electron microscope study.

Abstract: The pineal recess of the Mongolian gerbil was studied using correlative scanning and transmission electron microscopy. The surface of the pineal recess can be subdivided into three distinct zones: (1) central, (2) transitional, and (3) peripheral. In the gerbil, the deep pineal gland is located deep to the central and transitional zones. The ependyma of the peripheral zone is densely ciliated and resembles that of the main ventricular lining. Ependymal cells of the transitional zone are sparsely ciliated but possess numerous microvilli on their apical surfaces. Supraependymal neurons were identified in the transitional zones. These cells appear to make a synaptic-like contact with the underlying ependymal cells. Of the three zones, the central zone demonstrated the greatest amount of morphological variability. Although a number of supraependymal structures could be identified in the central zone, the most remarkable feature was the presence of protruding cells that possessed no significant surface features. Employing correlative transmission electron microscopy, the protruding cells were shown to be CSF-contacting pinealocytes. The number of CSF-contacting pinealocytes present in the central zone varied from one cell to large clusters that covered the entire zone. The results of this investigation demonstrate the presence of a direct contact and the potential for interaction between the deep pineal gland and the CSF of the pineal recess in the gerbil.

The pineal organ of Raja clavata: Opsin immunoreactivity and ultrastructure

Abstract: The pineal organ of Raja clavata was studied by light and electron microscopy, including the immunocytochemical antiopsin reaction. The pineal organ of the ray consists of three portions: (i) a large proximal pineal, (ii) a long tube-like connecting stalk, and (iii) a short distal terminal enlargement. This latter end-vesicle lies in the deep connective tissue layers of the braincase. All portions of the pineal are composed of pinealocytes, intrinsic neurons, ependymal/glial cells, and bundles of nerve fibers embedded in thin neuropil formations. The inner segments of the pinealocytes protrude into the lumen in all parts of the organ and usually contain basal bodies and numerous mitochondria. Often, two outer segments were found to arise from the basal bodies of a single inner segment. By means of light-microscopic immunocytochemistry the outer segments showed a strong antiopsin reaction. The axons of the pinealocytes form ribbon-containing synapses on dendrite-like profiles, which appear to belong to the intrinsic pineal neurons. There are other axo-dendritic synapses established by presynaptic terminals lacking ribbons and containing granular and synaptic vesicles. Pineal neurons may contain granular vesicles approximately 60-100 nm in diameter; their processes contribute to the bundles of unmyelinated axons. The fine structural organization of the pineal organ and the opsin immunoreactivity of the outer segments of the pinealocytes indicate a photoreceptive capacity of the organ. The double outer segments represent a peculiar multiplication of the photoreceptor structures.

distribution of monoamine-containing nerve fibers in the pineal organ of untreated and sympathectomized dogs. Fluorescence- and immunohistochemical studies.

Abstract: Monoamine (noradrenaline and serotonin)-containing nerve fibers distributed in the pineal organ of the dog were studied by means of histochemistry (formaldehyde-induced fluorescence) and immunohistochemistry (peroxidase-antiperoxidase-PAP method) with the use of a serotonin antiserum. With the fluorescence-histochemical technique a dense network of blue-green fluorescent fibers was demonstrated in the pineal organ. Most of these fibers formed a perivascular plexus and their branches penetrated into the intercellular spaces of the parenchymal cells. Since these fibers completely disappeared ten days after bilateral removal of the superior cervical ganglia, it was confirmed that they are noradrenergic post-ganglionic sympathetic nerve fibers. A few yellow-fluorescent fibers were detected in the proximal part of the organ after ganglionectomy. By the use of the PAP method, intensively immunoreactive parenchymal cells and nerve fibers were demonstrated. The distribution pattern of these fibers was similar to that of the fluorescent sympathetic fibers. After almost all immunopositive fibers had been abolished by sympathectomy, some serotonin-containing fibers remained. The latter could be traced back to a system of serotonin fibers in the epithalamic region. These findings suggest that 1) the sympathetic noradrenergic fibers in the pineal organ of the dog take up serotonin which is released from the pinealocytes, and 2) this organ receives a dual monoamine innervation via peripheral noradrenergic and central serotonergic nerve fibers.

The influence of different 5-methoxyindoles on the process of protein/peptide secretion characterized by the formation of granular vesicles in the mouse pineal gland. An in vitro study.

Abstract: The effects of different 5-methoxyindoles on the process of protein/peptide secretion characterized by the formation of granular vesicles (GV) have been studied in mouse pinealocytes maintained in explant culture. All 5-methoxyindoles studied clearly influence the number of granular vesicles in the pinealocytes. Comparing all present results it appeared that, in this system, melatonin was the least effective of all 5-methoxyindoles tested in stimulating secretion. 5-Methoxyindole-3-acetic acid, irrespective of the duration of the experiment and of the presence of noradrenaline, increased the number of GV. For all other 5-methoxyindoles, 5-methoxytryptamine, 5-methoxytryptophan, 5-methoxytryptophol and melatonin, it appeared that the effects depend on the duration of application and on the presence or absence of noradrenaline in the medium. Moreover, depending on the experimental conditions and the 5-methoxyindole tested, antagonistic as well as synergistic effects between 5-methoxyindoles and noradrenaline were observed. The present results, which suggest that the 5-methoxyindoles are also active in the pineal gland itself, demonstrate that, as far as the formation of granular vesicles is concerned, there exists a very complex mechanism of regulation, involving the sympathetic innervation and the 5-methoxyindoles (which are themselves under the influence of this innervation). The physiological significance of this system is discussed in relation to a proposed working hypothesis.

Effects of melatonin on synaptic ribbons in pinealocytes of the Chinese hamster, Cricetulus griseus. A quantitative electron-microscopic study.

Abstract: The effects of melatonin on synaptic ribbons (SR) in pinealocytes of the Chinese hamster (Cricetulus griseus) were examined. SR were classified into types 1, 2 and 3, which appear as rods, round or irregular bodies and ring-shaped structures, respectively; a synaptic ribbon index (SR index) was determined for the three types. Administration of two doses of 1.5 mg/kg melatonin at noon and 3 p.m. causes an increase in the type-1 and type-2 SR indices 3 h after the second injection in hamsters kept under alternating light and dark conditions (lights on from 7 a.m. to 7 p.m.). Likewise, in animals that are exposed to extended light for 5 h and receive two doses of melatonin at 7 p.m. and 10 p.m., an increase in the type-1 and type-2 SR indices occurs 3 h after the second injection. The increase in the type-2 SR index induced by melatonin administration to hamsters exposed to extended light is greater than the increase in the type-1 SR index under the same experimental conditions. Type-2 SR index, but not type-1 SR index, increases following bilateral superior cervical ganglionectomy. An increase in type-1 and type-2 SR indices occurs at 6 p.m. in ganglionectomized animals administered two doses of melatonin 6 h (noon) and 3 h (3 p.m.) before the time of sacrifice. No significant change is observed in type-3 SR index in animals subjected to any of the above treatments. The results indicate that exogenous melatonin may act directly on pinealocytes of the Chinese hamster to cause an increase in size and/or number of the type-1 and type-2 SR. Type 3-SR may have a role different from that of type-1 and type-2 SR; type-1 and type-2 SR may be functionally related.

Aspects of Evolution of the Pineal Organ

Abstract: The pineal organ is an ancient derivative and integral component of the brain. (Recent comprehensive reviews have been published by Kappers and Pevet, 1979; Leonhardt, 1980; Vollrath, 1981; Oksche and Pevet, 1981.) Phylogenetically it has changed from a ‘third eye’ endowed with photoreceptor cells to an endocrine gland influenced by visual stimuli from the retina (Fig. 1). The pineal organ has the capacity to translate photic (and apparently also other sensory and neural) information into a neuroendocrine response (cf. Wurtman et al., 1968. In a subsequent step this neuroendocrine message acts on various target organs. The unusual anatomical and physiological characteristics of the pineal organ make it an interesting subject of analysis both in brain research and endocrinology. In evolutionary terms the pineal organ displays features of a photoreceptor, biological clock, and endocrine gland (cf. Oksche and Pevet, 1981). It is a member of the group of circumventricular organs (Vigh and Vigh-Teichmann, 1981) and a component of the photoneuroendocrine systems (Oksche and Hartwig, 1979). The pinealocyte can be considered as a paraneuron (Ueck and Wake, 1979) originating from a special type of cerebrospinal fluid (CSF)-contacting neuron (Vigh and Vigh-Teichmann, 1981; see for references) displaying both sensory and secretory properties (i.e. a sensoneuroendocrine cell).

On the occurrence of a myeloid body in pinealocytes of the white-footed mouse, Peromyscus leucopus - An electron-microscopic study

Abstract: The fine-structural features of pinealocytes of the white-footed mouse, Peromyscus leucopus, were examined. A single population of pineaocytes was observed in both superficial and deep components of the gland. Cells in both locations are characterized by the presence of an indented nucleus exhibiting a prominent nucleolus. The usual organelles in the perikaryon are the Golgi complexes, mitochondria, endoplasmic reticulum, polysemes, microtubules and dense-core vesicles. In addition the perikaryonal cytoplasm often contains a single myeloid body. These bodies are usually lenticular in shape, are formed of an array of flattened membranous cisternae, and are not bounded by a limiting membrane. This organelle usually lies in the vicinity of the nucleus and is infrequently associated with lipid bodies. Complex forms were also observed. The cisternae are continuous with elements of the endoplasmic reticulum at points along their expanded rims. The outer surface of the cisternal membrane exhibits a granularity or fuzziness. The cisternae may be fenestrated. Pinealocyte processes with an abundance of clear vesicles, and some dense-core vesicles and vesicle-crowned rodlets are present in the parenchyma.

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

Abstract: 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 cytoplasm, 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.