Influence of continuous light and darkness on the secretory pinealocytes of<Emphasis Type="Italic">Heteropneustes fossilis</Emphasis>

In an earlier study onHeteropneustes fossilis, evidence of secretory activity in the pinealocytes had been demonstrated at the electron microscopic (EM) level and it was found to exist in two phases: a secretory phase (light cells) and a storage phase (dark cells). In the present investigation,H. fossilis was subjected to artificial photoperiods of continuous illumination and continuous darkness for a period of ten days and the effect on the secretory pinealocytes was studied at the EM level. Marked results were observed within the short period of ten days emphasizing the role of environmental photoperiod on the secretory activity of the pinealocytes. During continuous illuminated phase, both light and dark cells were observed: the light cells showed intense secretory activity and dark cells a storage one. During the dark phase both types of cells were present but in different metabolic states and neither of the cells demonstrated synthetic nor storage activity. Light cells were metabolically active but not secretory active and dark cells showed a necrotic condition. Phagocytotic activity of the dark cells was also seen. Intense neural activity was also observed during exposure to both the artificial photoperiods. The results highlight the role of light on the secretory activities of the pinealocytes of the catfish pineal organ.     

Cerebrospinal fluid-contacting area in the pineal recess of the vole (Microtus agrestis), Guinea Pig (Cavia cobaya), and rhesus monkey (Macaca mulatta)

Summary The ventricular lining in the pineal recess of the vole (Microtus agrestis), guinea pig (Cavia cobaya) and Rhesus monkey (Macaca mulatta) was investigated light and electron microscopically. Deep in the pineal recess of all three species the ependymal lining exhibits interruptions. A varying proportion of pinealocytes penetrates through this ependymal area, so that the surface of the protruding cells is directly exposed to the cerebrospinal fluid (CSF). At their base, these cells are anchored in the hypependymal tissue by means of processes. It is conjectured that these pinealocytes are engaged in secreting pineal substances into the CSF, as various physiological findings appear to indicate.     

The pineal gland of the gerbil,Meriones unguiculatus

Summary Electron microscopy was employed in a study of the pineal gland of the Mongolian gerbil (Meriones unguiculatus). It was determined that the gerbil pineal gland contains pinealocytes and glial cells with the pinealocytes being the predominant cell type. The pinealocytes contain numerous organelles traditionally considered as being either synthetic or secretory in function such as an extensive Golgi region, smooth (SER) and rough (RER) endoplasmic reticulum, secretory vesicles and microtubules. Other cytoplasmic components are also present in the pinealocytes (synaptic ribbons, subsurface cisternae) for which no function has been assigned. Dense-cored vesicles are rare. Vacuolated pinealocytes are present and appear to be intimately associated with the formation of the pineal concertions. Evidence presented supports the proposal that the concretions form within the vacuoles. Once the concretions reach an enlarged state, the vacuolated pinealocytes break down and the concretions are thus extruded into the extracellular space where they apparently continue to increase in size. The morphology of the glial cells was interpreted as indicative of a high synthetic activity. The glial cells contain predominantly the rough variety of endoplasmic reticulum and form an expansion around the wide perivascular area.Supported by NSF grant PCM 77-05734     

Photoreceptor-like outer segments in the pineal organ of the lovebird,Uroloncha domestica (Aves: Passeriformes)

Summary In the pineal organ of the lovebird, Uroloncha domestica, bulbous, cup-shaped and elongated outer segments of photoreceptor-like pinealocytes are demonstrated by scanning electron microscopy. These scarce outer segments, 4–11 m in length, extend into the pineal lumen. The present structural observations speak in favor of photosensitive pinealocytes in the pineal organ of Uroloncha domestica. The relation of the photoreceptor-like pinealocytes to acetylcholinesterase-positive nerve cells and a nervous connection between the pineal and the brain indicate that the pineal organ of this passeriform species may be the site of neuroendocrine and photoreceptive functions.Supported by a fellowship from the Japan Society for the Promotion of Science to M. UeckSupported by a grant from the Ministry of Education of Japan to K. Wake and by a grant of the Deutsche Forschungsgemeinschaft to M. Ueck     

Surface ultrastructure of the olfactory rosette of an air-breathing catfish,Heteropneustes fossilis (Bloch)

The surface architecture of the olfactory rosette ofHeteropneustes fossilis (Bloch) has been studied by scanning electron microscopy. The olfactory rosette is an oval structure composed of a number of lamellae arranged pinnately on a median raphe. The raphe is invested with epithelial cells and pits which represent goblet cell openings. On the basis of cellular characteristics and their distribution the lateral surface of each olfactory lamella is identified as sensory, ciliated non-sensory and non-ciliated non-sensory epithelium. The sensory epithelium is provided with receptor and supporting cells. The ciliated non-sensory epithelium is covered with dense cilia obscuring the presence of other cell types. The non-ciliated non-sensory epithelium is with many polygonal areas containing cells.     

The pineal region in the opossum,Didelphis virginiana

Summary In the pineal region of the opossum, Didelphis virginiana, two types of cells predominate: 1) pinealocytes, and 2) fibrous astrocytes. Pinealocytes are characterized by the presence of prominent Golgi bodies, numerous clear and dense-cored vesicles, sensory cilia (9+0), vesicle-crowned rods, and condensation of a material that was always associated with the rough endoplasmic reticulum. In addition, two other cell types are occasionally seen. These include 1) neuron-like cells, and 2) darker staining cells of unknown identity. The endoplasmic reticulum of the darker staining cells is typically expanded and filled with an amorphous substance. Although the pineal region is small in size, the present findings suggest that pinealocytes in this species are metabolically active cells displaying a secretory function. Moreover, the presence of sensory cilia (9+0) and vesicle-crowned rods indicates that pinealocytes of the opossum are phylogenetically related to the photoreceptor cells found in the pineal organ of lower vertebrates.     

Immunocytochemical and electron-microscopic investigations of the pineal organ in adult agamid lizards,Uromastix hardwicki

Summary Lacertilian species display a remarkable diversity in the organization of the neural apparatus of their pineal organ (epiphysis cerebri). The occurrence of immunoreactive S-antigen and opsin was investigated in the retina and pineal organ of adult lizards, Uromastix hardwicki. In this species, numerous retinal photoreceptors displayed S-antigen-like immunoreactivity, whereas only very few pinealocytes were labeled. Immunoreactive opsin was found neither in retinal photoreceptors nor in pinealocytes. Electron microscopy showed that all pinealocytes of Uromastix hardwicki resemble modified pineal photoreceptors. A peculiar observation is the existence of a previously undescribed membrane system in the inner segments of these cells. It is evidently derived from the rough endoplasmic reticulum but consists of smooth membranes. The modified pineal photoreceptor cells of Uromastix hardwicki were never seen to establish synaptic contacts with somata or dendrites of intrapineal neurons, which are extremely rare. Vesiclecrowned ribbons are prominent in the basal processes of the receptor cells, facing the basal lamina or establishing receptor-receptor and receptor-interstitial type synaptoid contacts. Dense-core granules (60–250 nm in diameter) speak in favor of a secretory activity of the pinealocytes. Attention is drawn to the existence of receptor-receptor and receptor-interstitial cell contacts indicating intramural cellular relationships that deserve further study.Supported by the Deutsche Forschungsgemeinschaft (Ko 758/31) and the Deutscher Akademischer Austauschdienst (Senior DAAD Research Fellowship to M.A.H.)     

Twenty-four-hour changes in pinealocytes,capillary endothelial cells and pericapillary and intercellular spaces in the pineal gland of the mouse

Summary Semiquantitative electron-microscopic observations on the pineal gland of dd-mice were carried out to determine whether 24-h rhythms exist in pinealocytes, pericapillary and intercellular spaces and capillary endothelial cells. Nuclear and cytoplasmic areas of pinealocytes and the area of condensed chromatin in pinealocytes showed inversely related circadian rhythms; the former two increased, whereas the latter decreased, during the light period. The extent of pericapillary and wide intercellular spaces exhibited 24-h changes, with an increase and decrease occurring during the light period and the dark period, respectively. The cross-sectional area of endothelial cells decreased and the number of fenestrae increased during the light period; this was reversed during the dark period. The results suggest that the increase in the nuclear and cytoplasmic areas of pinealocytes, the area of pericapillary and wide intercellular spaces and the number of fenestrae, and the decrease in the area of condensed chromatin and endothelial cells during the light period may be related to an increase in synthetic activity of pinealocytes in the mouse.     

Electron microscopic studies of the corpuscles of Stannius of an airbreathing teleost (Heteropneustes fossilis)

The ultrastructure of the corpuscles of Stannius (CS) ofHeteropneustes fossilis reveals a homogenous cellular composition characterized by only one cell type, with large secretory granules and abundant ribosomal endoplasmic reticulum. These cells are comparable to the type 1 cell described in the CS of other teleosts; type 2 cells, whose presence is ubiquitous in the CS of freshwater species are absent inH. fossilis. Our data on the CS ofH. fossilis demonstrate that not all freshwater species possess type 2 cells in their CS and these are not essential for life in freshwater.     

Induction of c-fos protein-like immunoreactivity in the rat and hamster pineal gland after the onset of darkness

Summary Induction of c-fos protein (FOS) after the onset of darkness was studied immunocytochemically in the rat and hamster pineal gland. The animals were kept on a 12:12 h light-dark cycle. Before the dark period no FOS staining was seen in either rat or hamster pineal cells. Five hours after the onset of darkness 342±18 pinealocytes/0.2 mm² (mean±SD) displayed FOS-like immunoreactivity in the hamster pineal gland; in the rat pineal gland only 5±2 pinealocytes/0.2 mm² showed a faint staining. Two hours later the density of FOS positive cells was decreased to 60±11/0.2 mm² in the hamster but increased to 519±103/0.2 mm² in the rat pineal gland. Three hours before the beginning of the light period no FOS positive cells were detected in either animal. Both the rat and hamster pineal gland showed a transient and temporally defined expression of c-fos protein in the middle of the dark period. This may be related to a more active functional state of pinealocytes, which is reflected in a peak of melatonin synthesis during the darkness.     

Paraneuronal pseudobranchial neurosecretory cells in scorpion catfish Heteropneustes fossilis: an environment scanning electron microscope and transmission electron microscope study

Yadav, L., Sengar, M., Zaccone, D. and Gopesh, A. 2011. Paraneuronal pseudobranchial neurosecretory cells in scorpion catfish Heteropneustes fossilis: an environment scanning electron microscope and transmission electron microscope study. —Acta Zoologica (Stockholm) 00 : 1–8. Pseudobranchial neurosecretory system (PNS), found in the gill region of certain groups of teleosts, falls under the category of the ‘diffuse neuroendocrine system’ (DNES). The cells belonging to the system share morpho‐functional features with the paraneuronal cells observed in respiratory tract and airway surfaces of higher vertebrates. On the basis of the experimental observations, a role in condition of hypoxia has been recorded for this system. In an attempt to elucidate the ultrastructure of pseudobranchial neurosecretory cells, present investigation was undertaken using environment scanning electron microscope (ESEM) and TEM in an air‐breathing catfish, Heteropneustes fossilis. The external morphology of PNS under ESEM appeared as a mass of cells supplied with nerves and blood capillaries. Each cell mass is made up of numerous pear‐shaped neurosecretory cells, confirmed by neurosecretion‐specific acid violet stain. The TEM investigation of the cells revealed the presence of different sizes of dense‐cored vesicles in the cytoplasm, which was observed as granular cytoplasm under light microscope. Presence of large number of mitochondria in the cytoplasm confirmed active involvement of these cells in the physiology of fishes. Although lacuna prevails regarding the exact function of this system of fish, its probable role in hypoxic condition and surfacing behavior are speculated.     

Nucleolus-like bodies in the pineal gland of the Djungarian hamster (Phodopus sungorus)

Summary Light- and electron-microscopic observations on the pineal gland of Phodopus sungorus revealed intracytoplasmic inclusions resembling nucleolus-like bodies similar to those found in other regions of the central nervous system. Bernhard's EDTA method was used to confirm that these inclusions were nucleolus-like bodies. These structures were rarely found in pinealocytes of sexually active longday animals, whereas large numbers of them were observed in pinealocytes of sexually quiescent short-day animals. Nucleolus-like bodies may therefore be involved in pineal secretion.     

Peptidergic cells in the mammalian pineal gland. Morphological indications for a paracrine regulation of the pinealocyte

Several neuropeptides are present in the mammalian pineal gland. Most of these peptides, eg neuropeptide Y, vasoactive intestinal peptide, and peptide histidine isoleucine, are located in nerve fibres innervating the gland. In some mammalian species, neuropeptides are also found in cells scattered in the pineal parenchyma. In the rat, bipolar cells immunoreactive for somatostatin are present, just as cells containing mRNA encoding somatostatin can be detected in the gland by in situ hybridisation. In the pineal gland of the European hamster, many cells are immunoreactive for enkephalin. Ultrastructural cytochemical analysis of these cells reveals a pinealocyte morphology. Processes from the opioidergic pinealocytes terminate in the parenchyma between the non-immunoreactive pinealocytes. Some of the processes contain small clear and large dense core vesicles and end in club shaped swellings which make synapse-like contacts with other pinealocytes. The ultrastructural morphology suggests that the opioidergic cells exert a paracrine regulation on other pinealocytes.     

Induction of c-fos protein-like immunoreactivity in the rat and hamster pineal gland after the onset of darkness

Induction of c-fos protein (FOS) after the onset of darkness was studied immunocytochemically in the rat and hamster pineal gland. The animals were kept on a 12:12 h light-dark cycle. Before the dark period no FOS staining was seen in either rat or hamster pineal cells. Five hours after the onset of darkness 342 +/- 18 pinealocytes/0.2 mm2 (mean +/- SD) displayed FOS-like immunoreactivity in the hamster pineal gland; in the rat pineal gland only 5 +/- 2 pinealocytes/0.2 mm2 showed a faint staining. Two hours later the density of FOS positive cells was decreased to 60 +/- 11/0.2 mm2 in the hamster but increased to 519 +/- 103/0.2 mm2 in the rat pineal gland. Three hours before the beginning of the light period no FOS positive cells were detected in either animal. Both the rat and hamster pineal gland showed a transient and temporally defined expression of c-fos protein in the middle of the dark period. This may be related to a more active functional state of pinealocytes, which is reflected in a peak of melatonin synthesis during the darkness.     

Pinealocytes contacting the cerebrospinal fluid of the suprapineal recess in the Mongolian gerbil (Meriones unguiculatus)

Summary The pineal system of the Mongolian gerbil (Meriones unguiculatus) was investigated by light and electron microscopy, special attention being paid to the sites of contact with the ventricular system. The results reveal that the pineal system of this species has a specific topographical relationship to the suprapineal recess of the third ventricle. The dorsal side of the proximal part of the pineal system forms the floor and the caudal wall of this recess. Here, a consistent and relatively large area lacks an ependymal lining, enabling pinealocytes to come into direct contact with the cerebrospinal fluid (CSF). This area is assumed to be the morphological correlate of a close functional interrelationship between the pineal tissue and the CSF.     

The pineal organ as a folded retina: immunocytochemical localization of opsins

The most simple pineal complex (the pineal and parapineal organs of lampreys), consists of saccular evaginations of the diencephalic roof, and has a retina-like structure containing photoreceptor cells and secondary neurons. In more differentiated vertebrates, the successive folding of the pineal wall multiplies the cells and reduces the lumen of the organ, but the pattern of the histological organization remains similar to that of lampreys; therefore, we consider the histological structure of the pineal organ of higher vertebrates as a 'folded retina'. The cell membrane of several pineal photoreceptor outer-segments of vertebrates immunoreact with anti-retinal opsin antibodies supporting the view of retina-like organization of the pineal. Some other pineal outer segments do not react with retinal anti-opsin antibodies, a result suggesting the presence of special pineal photopigments in different types of pinealocytes that obviously developed during evolution. The chicken pinopsin, detected in the last years, may represent one of these unknown photopigments. Using antibodies against chicken pinopsin, we compared the immunoreactivity of different photoreceptors of the pineal organs from cyclostomes to birds at the light and electron microscopic levels. We found pinopsin immunoreaction on all pinealocytes of birds and on the rhodopsin-negative large reptilian pinealocytes. As the pinopsin has an absorption maximum at 470 nm, these avian and reptilian immunoreactive pinealocytes can be regarded as green-blue light-sensitive photoreceptors. Only a weak immunoreaction was observed on the frog and fish pinealocytes and no reaction was seen in cyclostomes and in the frontal organ of reptiles. Some photoreceptors of the retina of various species also reacted the pinopsin antibodies, therefore, pinopsin must have certain sequential similarity to individual retinal opsins of some vertebrates.     

Morphometric analysis of the pineal complex of the golden hamster over a 24-hour light:dark cycle: II. The deep pineal in untreated and optically enucleated animals

The deep pineal gland of golden hamsters was morphometrically analyzed and quantitatively compared with the superficial pineal under a 14:10 lighting regime and following blinding. The deep pineal comprised 6-10% of the total pineal parenchymal tissue. Pinealocytes of the deep gland were smaller than the cells of the superficial pineal and showed a greater percent volume of Golgi bodies, rough endoplasmic reticulum, and dense-cored vesicles. Twenty-four-hour rhythms in nucleoli and Golgi bodies were found in deep pinealocytes. These rhythms were out of phase with comparable rhythms in the superficial pineal gland, suggesting that distinct subpopulations of pinealocytes are present within the respective parts. Blinding resulted in decreased nuclear and nucleolar volume, while the amount of smooth endoplasmic reticulum, Golgi bodies, dense bodies, and dense-cored vesicles increased significantly. Marginal increases were seen in mitochondria and lipid droplets. The greater abundance of those organelles involved in synthesis and secretion suggests enhanced cellular activity after blinding. Many of the morphological responses are similar to alterations in the pinealocytes of the superficial pineal following optic enucleation.     

The pineal organ of Raja clavata: Opsin immunoreactivity and ultrastructure

Summary 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 dendritelike 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.This investigation was supported by grants from the Deutsche Forschungsgemeinschaft to A. Oksche (Ok 1/24; 1/25: Mechanismen biologischer Uhren)On leave from the 2nd Department of Anatomy, Semmelweis OTE, Budapest, Hungary     

The epiphysis (pineal body) and the APUD system

Light and electron microscopic studies were conducted on 10 humans who died of the different cardiac diseases; and 20 guinea pigs pineal glands. Pinealocytes or secretory cells of the pineal gland have morphological likeness with the APUD system cells. They have a well-developed endoplasmic reticulum, Golgi complex, mitochondrial component and in cytoplasm dense-core vesicles are discovered. However the pinealocytes have a neuron-like structure and they are not separate cells as apudocytes, but they are a principal component of the pineal parenchyma in which pinealocytes are in tight interactions with glia, blood vessels and nerve terminations. Analysis of morphological and functional similarity and difference between pinealocytes and apudocytes allows to consider pineal gland as an APUD organ. A circadian rhythmicity of some secretory vesicles in pinealocytes of the guinea pig has been established.     

The influence of luteinizing hormone-releasing hormone (LHRH) on the process of protein and/or peptide secretion characterized by the formation of granular vesicles in mammalian pinealocytes

In the present study, the effect of LHRH on the process of protein and/or peptide secretion characterized by the formation of granular vesicles has been studied by means of an in vitro system in the pinealocytes of three different species of rodents. LHRH has a strong influence on the activity of this process. However, this effect varies with the presence of noradrenaline (NA) in the medium and is not identical in the individual species studied. In the rat and mouse, for example, LHRH induces an increase in the number of granular vesicles when the pinealocytes are cultured in a NA-free medium, while, in contrast, in the hamster this stimulatory effect is found exclusively in the presence of NA. Moreover, in the pinealocytes of the mouse, in the presence of NA, LHRH shows an inhibitory effect on protein secretion. These results clearly demonstrate that LHRH, at least under the present in vitro conditions, acts on the synthetic activity of the pineal gland, and demonstrates the importance of pineal protein and/or peptide "hormones" in pineal endocrinology.