Comparative histology of pineal calcification.

The pineal organ (pineal gland, epiphysis cerebri) contains several calcified concretions called "brain sand" or acervuli (corpora arenacea). These concretions are conspicuous with imaging techniques and provide a useful landmark for orientation in the diagnosis of intracranial diseases. Predominantly composed of calcium and magnesium salts, corpora arenacea are numerous in old patients. In smaller number they can be present in children as well. The degree of calcification was associated to various diseases. However, the presence of calcified concretions seems not to reflect a specific pathological state. Corpora arenacea occur not only in the actual pineal tissue but also in the leptomeninges, in the habenular commissure and in the choroid plexus. Studies with the potassium pyroantimonate (PPA) method on the ultrastructural localization of free calcium ions in the human pineal, revealed the presence of calcium alongside the cell membranes, a finding that underlines the importance of membrane functions in the production of calcium deposits. Intrapineal corpora arenacea are characterized by a surface with globular structures. Meningeal acervuli that are present in the arachnoid cover of the organ, differ in structure from intrapineal ones and show a prominent concentric lamination of alternating dark and light lines. The electron-lucent lines contain more calcium than the dark ones. There is a correlation between the age of the subject and the number of layers in the largest acervuli. This suggests that the formation of these layers is connected to circannual changes in the calcium level of the organ. The histological organization of the human pineal is basically the same as that of mammalian experimental animals. Pineal concretions present in mammalian animal species are mainly of the meningeal type. Meningeal cells around acervuli contain active cytoplasmic organelles and exhibit alkaline phosphatase reaction in the rat and mink, an indication of a presumable osteoblast-like activity. Using Kossa's method for the staining of calcium deposits, a higher calcium concentration was detected in the rat pineal than in the surrounding brain tissue. Since in parathyroidectomised rats calcified deposits are larger and more numerous than in controls, the regulation of the production of acervuli by the parathyroid gland has also been postulated. In most of submammalian species, the pineal organs (pineal-, parapineal organ, frontal organ, parietal eye) are photoreceptive and organized similarly to the retina. Acervuli were found in the pineal of some birds. The pineal organs of lower vertebrates (fish, amphibians, reptiles) exhibit a high calcium content by ultrastructural calcium histochemistry (PPA-method). However, concrements are not formed. The accumulation of Ca2+ seems to depend on the receptor function of the organ. Comparing pineal and retinal photoreceptors in the frog, the photoreceptor outer segments of pinealocytes as well as retinal cones and rods show a large amount of Capyroantimonate deposits. In dark adapted animals calcium ions are present in both sides of the photoreceptor membranes of the outer segment, whereas calcium is shifted extra-cellularly following light adaptation. Overviewing the data available about the pineal calcification, we can conclude that a multifactorial mechanism may be responsible for the calcification. The pineal of higher vertebrates is not just a simple endocrine gland, rather, its histological organization resembles a folded retina having both hormonal and neural efferentation. Mammalian pinealocytes preserve several characteristics of submammalian receptor cells and accumulate free Ca2+ on their membranes (1). In the thin walled retina and in the similarly organized pineal of submammalian species, the diffusion of extracellular calcium is probably easy and there is a lesser tendency to form concrements. (ABSTRACT TRUNCATED)

Actual problems of the cerebrospinal fluid-contacting neurons.

Cerebrospinal fluid (CSF)-contacting neurons form a part of the circumventricular organs of the central nervous system. Represented by different cytologic types and located in different regions, they constitute a CSF-contacting neuronal system, the most central periventricular ring of neurons in the brain organized concentrically according to our concept. Because the central nervous system of deuterostomian echinoderm starfishes and the prochordate lancelet is composed mainly of CSF-contacting-like neurons, we hypothesize that this cell type represents ancient cells, or protoneurons, in the vertebrate brain. Neurons may contact the ventricular CSF via their dendrites, axons, or perikarya. Most of the CSF-contacting nerve cells send their dendritic processes into the ventricular cavity, where they form ciliated terminals. These ciliated endings resemble those of known sensory cells. By means of axons, the CSF-contacting neurons also may contact the external CSF space, where the axons form terminals of neurohormonal type similar to those known in the neurohemal areas. The most simple CSF-contacting neurons of vertebrates are present in the terminal filum, spinal cord, and oblongate medulla. The dendritic pole of these medullospinal CSF-contacting neurons terminates with an enlargement bearing many stereocilia in the central canal. These cells are also supplied with a 9 x 2 + 2 kinocilium that may contact Reissner's fiber, the condensed secretory material of the subcommissural organ. The Reissner's fiber floating freely in the CSF leaves the central canal at the caudal open end of the terminal filum in lower vertebrates, and open communication is thus established between internal CSF and the surrounding tissue spaces. Resembling mechanoreceptors cytologically, the spinal CSF-contacting neurons send their axons to the outer surface of the spinal cord to form neurosecretory-type terminals. They also send collaterals to local neurons and to higher spinal segments. In the hypothalamic part of the diencephalon, neurons of two circumventricular organs, the paraventricular organ and the vascular sac, of the magnocellular neurosecretory nuclei and several parvocellular nuclei, form CSF-contacting dendritic terminals. A CSF-contacting neuronal area also was found in the telencephalon. The CSF-contacting dendrites of all these areas bear solitary 9 x 2 + 0 cilia and resemble chemoreceptors and developing photoreceptors cytologically. In electrophysiological experiments, the neurons of the paraventricular organ are highly sensitive to the composition of the ventricular CSF. The axons of the CSF-contacting neurons of the paraventricular organ and hypothalamic nuclei terminate in hypothalamic synaptic zones, and those of magno- and parvocellular neurosecretory nuclei also form neurohormonal terminals in the median eminence and neurohypophysis. The axons of the CSF-contacting neurons of the vascular sac run in the nervus and tractus sacci vasculosi to the nucleus (ganglion) sacci vasculosi. Some hypothalamic CSF-contacting neurons contain immunoreactive opsin and are candidates to represent the "deep encephalic photoreceptors." In the newt, cells derived from the subependymal layer develop photoreceptor outer segments protruding to the lumen of the infundibular lobe under experimental conditions. Retinal and pineal photoreceptors and some of their secondary neurons possess common cytologic features with CSF-contacting neurons. They contact the retinal photoreceptor space and pineal recess, respectively, both cavities being derived from the third ventricle. In addition to ciliated dendritic terminals, there are intraventricular axons and neuronal perikarya contacting the CSF. Part of the CSF-contacting axons are serotoninergic; their perikarya are situated in the raphe nuclei. Intraventricular axons innervate the CSF-contacting dendrites, intraventricular nerve cells, and/or the ventricular surface of the ependyma. (ABSTRACT TRUNCATED)

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.

Immunoreactive excitatory amino acids in the parietal eye of lizards, a comparison with the pineal organ and retina.

The fine structure of the organ and the localization of the excitatory amino acids glutamate and aspartate were studied in the parietal eye of lizards by postembedding immunoelectron microscopy. The parietal eye contains cone photoreceptor cells, secondary neurons, and ependymal and lens cells. The photoreceptors form long inner and outer segments, some of them being paired as "twin-photoreceptors" by zonulae adherentes. Perikarya of neurons bear sensory cilia (containing 9x2+0 pairs of tubules) extending into the intercellular space. No neurohormonal terminals are present in the parietal eye. A higher immunoreactivity to glutamate than to aspartate is found in the photoreceptors and in the secondary neurons of the parietal eye. Glutamate immunogold labeling is more intense in the axonal processes of photoreceptors and neurons and in most of the nerve fibers of the parietal nerve running to the brain stem. Weak aspartate and glutamate immunoreactivity can be detected in the ependymal and lens cells. A similar distribution of immunoreactive amino acids is found in the photoreceptors, secondary neurons, and ependymal glial elements of the pineal organ, and retina of the lateral eye of the same animals. Immunoreactive glutamate accumulates in the axons of photoreceptors and secondary neurons of the parietal eye suggesting that this excitatory amino acid acts as a synaptic mediator in the neural efferentation of the organ. Thus, the efferent light-conducting pathway of the parietal organ is similar to that of the pineal organ and lateral eye retina. As the Mullerian cells of the retina, the ependymal and lens cells of the parietal eye and the ependymal-glial cells of the pineal organ may play a role in the metabolism and/or elimination of excitatory amino acids released by photoreceptors.

Similar fine structural localization of immunoreactive glutamate in the frog pineal complex and retina.

The distribution of immunoreactive glutamate was compared in the pineal complex (pineal and frontal organs) and retina of frogs (Rana esculenta, R. arvalis, R. ridibunda, R. catesbeiana, Bufo viridis, Bombinator igneus) by postembedding immuno-electron microscopy. Similar to retinal photoreceptors (rods and cones), bipolars and ganglion cells, the rod- and cone-like photoreceptors and the neurons of the pineal and frontal organs exhibited glutamate immunoreactivity. Synaptic terminals of photoreceptor cells on secondary neurons of the pineal complex and retina were strongly immunoreactive. The pineal tract and the fibers of the frontal nerve also displayed glutamate immunoreactivity. There was no essential difference in the immunoreactivity of the retinal and pineal elements among the species studied. The similar histology of the pineal complex and retina of the frog and the high correlation of their binding sites of antiglutamate immunosera allow us to assume that glutamate performs a similar role in the pineal complex as is already known for the retina. The high immunoreactivity of the presynaptic region of pinealocytic processes and axons of secondary neurons suggests the role of a neurotransmitter for this excitatory amino acid in the efferent pathways of the pineal complex.

Development of the photoreceptor outer segment-like cilia of the CSF-contacting pinealocytes of the ferret (Putorius furo).

The postnatal development of the pineal organ of the ferret (Putorius furo) was investigated electron-microscopically with special interest given to the cerebrospinal fluid (CSF)-contacting pinealocytes and their large, vesiculated cilia. In the pineal of the newborn ferrets, there is a lumen--a pineal ventricle--which is a diverticle of the third ventricle of the diencephalon. The luminal surface of the pineal is bordered by ependymal cells and CSF-contacting pinealocytes. A sensory, 9 x 2 + 0 type cilium arises from the free surface of the pinealocytes and thickens in the first week. There are mitotic figures in the wall of the pineal ventricle, being reduced to a pineal recess during the second and third postnatal week. In two week-old animals, vesicles appear in the cilia of the pinealocytes. The vesicles may form rows and fill the enlarged cilium at the third week. Near the basal bodies, a proximal connecting piece remains narrow and free of vesicles. In older animals, there are multivesicular and dense bodies in the pineal cilia. The reduction of the pineal ventricle closes the CSF-contacting cilia in the intercellular spaces. Axon-like processes of pinealocytes form synaptic ribbon-containing terminals on secondary pineal neurons. Axons of pineal neurons enter the fiber bundles of the pineal tract running to the habenular nuclei. All these structures do not differ from the light conducting pathway of the submammalian pineals. The ultrastructure of the cilia investigated resembles that of the developing outer segments of the retina and represents a preserved light perceiving structure of the mammalian pinealocytes. Further studies are necessary to elucidate whether the early differentiation of the cilia and synapses indicates a timing of the circadian light rhythmicity in young ferrets by direct pineal photosensitivity.

Two components of the pineal organ in the mink (Mustela vison): their structural similarity to submammalian pineal complexes and calcification.

The pineal complex in the mink (Mustela vison) consists of a larger ventral and a smaller dorsal pineal. Both organs contain pinealocytes, neurons, glial cells, nerve fibers and synapses in an organization characteristic of nervous tissue. The cellular elements are arranged circularly around strait lumina. These lumina correspond to the photoreceptor spaces of submammalian pineals. A 9 + 0-type cilium marks the receptory pole of the pinealocytes which may form an inner-segment-like dendrite terminal in the pineal lumina. The cilia correspond to outer segments which form photoreceptor membrane multiplications in the pineal of submammalians and in certain insectivorous and mustelid mammals (bat, hedgehog, ferret). Axonal processes of the pinealocytes contain synaptic ribbons and terminate on intrapineal neurons of both organs. This pattern represents a neural efferentation of the pineal nervous tissue. The axonal processes of pinealocytes also form neurohormonal endings which pierce the perivascular limiting glial membrane in the ventral as well as in the dorsal pineal. The upper pineal ("epipineal") of the mink may correspond to the parapineal, frontal, or parietal organs of submammalian pineal complexes. Both pineals are encapsulated by the meningeal tissue of the brain stem. Afferent vasomotor axons of the meninges innervate smooth muscle cells of pineal arterioles. There are corpora arenacea in the pineal arachnoid and in the pineal nervous tissue, primarily in the ventral pineal. The localization of calcium ions detected around the membrane of pineal cells by pyroantimonate cytochemistry suggests membrane activity as the source of the calcium ions. The accumulation of calcium by the pinealocytes may be due to their neurosensory character. The mink is the first animal described to have both intrapineal and meningeal concrements like the human pineal.

Immunocytochemistry and calcium cytochemistry of the mammalian pineal organ: a comparison with retina and submammalian pineal organs.

Morphologically the mammalian pineal organ is a part of the diencephalon. It represents a neural tissue histologically ("pineal nervous tissue") and is dissimilar to endocrine glands. Submammalian pinealocytes resemble the photoreceptor cells of the retina, and some of their cytologic characteristics are preserved in the mammalian pinealocytes together with compounds demonstrable by cyto- and immunocytochemistry and participating in photochemical transduction. In our opinion, the main trend of today's literature on pineal functions--only considering the organ as a common endocrine gland--deviates from this structural and histochemical basis. In mammals, similar to the lower vertebrates, the pinealocytes have a sensory cilium developed to a different extent. The axonic processes of pinealocytes form ribbon-containing synapses on secondary pineal neurons, and/or neurohormonal terminals on the basal lamina of the surface of the pineal nervous tissue facing the perivascular spaces. Ribbon-containing axo-dendritic synapses were found in the rat, cat, guinea pig, ferret, and hedgehog. In the cat, we found GABA-immunoreactive interneurons, while the secondary nerve cells, whose axons enter the habenular commissure, were GABA-immunonegative. GABA-immunogold-labeled axons run between pinealocytes and form axo-dendritic synapses on intrapineal neurons. There is a similarity between the light and electron microscopic localization of Ca ions in the mammalian and submammalian pineal organs and retina of various vertebrates. Calcium pyroantimonate deposits--showing the presence of Ca ions--were found in the outer segments of the pineal and retinal photoreceptors of the frog. In the rat and human pineal organ, calcium accumulated on the plasmalemma of pinealocytes and intercellularly among pinealocytes. The formation of pineal concrements in mammals may be connected to the high need for Ca exchange of the pinealocytes for their supposed receptor and effector functions.

Cytochemistry of CSF-contacting neurons and pinealocytes.

Gamma aminobutyric acid (GABA)-immunoreactive neurons of the paraventricular organ of the bony fish Coregonus albus send dendrites into the third ventricle. Their axons run to the synaptic zone of the infundibular lobe. The dendrites may take up some chemical information from the third ventricle, while the axons communicate it to the neuropil of the hypothalamus perhaps to modify its activity according to the state of the CSF. Serotonin-immunoreactive CSF-contacting neurons in the spinal cord of the hagfish Myxine glutinosa from dendrite terminals in the central canal and bear stereocilia like known mechanoreceptors. The Reissner's fiber runs above the stereocilia and flows out from the central canal through its caudal opening. Possibly, the fiber keeps open this aperture and ensures the flow of the CSF, which may serve as a mechanoreceptory input for the CSF-contacting neurons. In the pineal recess of hedgehog, CSF-contacting pinealocytes develop enlarged cilia corresponding to the photoreceptor outer segments of submammalian pinealocytes. Potassium pyroantimonate cytochemistry shows a similar localization of calcium ions in the mammalian pinealocyte as in the submammalian photoreceptor ones. Pineal calcifications are present in some birds (goose, duck) and may be connected to the photoreceptory Ca-exchange of the pineal organ. Axonic processes of pinealocytes form synapses on secondary neurons in mammals (hedgehog, rat, cat). Such neurons are also present in human pineals. Axons of these neurons constitute a pinealofugal pathway. In the cat, some of the intrinsic pineal neurons are GABA-immunoreactive, they form axodendritic and axo-axonic synapses (inhibitory?) on immunonegative neurons and pinealocytes, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative ultrastructure and opsin immunocytochemistry of the retina and pineal organ in fish.

The pineal organ and retina were compared in developing charr and cisco, further in adult cisco, eel, creek chub, dace, zebrafish and black moli by opsin immunocytochemistry. In prehatching charr embryos, retinal rods and cones and pinealocytes displayed well-developed outer segments and formed synapses. Differentiation of the retina started centrally but was more advanced in the dorso-caudal retina than rostroventrally. The pineal organ differentiated earlier distally than proximally. In the cisco, the pineal organ and retina differentiated around hatching. In charr embryos, further in the larval and adult species studied, opsin immunoreactivity was found in retinal rods, accessory cones and many "rod-like" pinealocytes, a result indicating the presence of rhodopsin and/or porphyropsin. Retinal principle cones, long and short cones and some "cone-like" pinealocytes were opsin-immunonegative; they are thought to represent red- and/or u.v./violet-sensitive elements. The pineal organ may be involved in negative phototaxic behavior. Both the retina and pineal organ appear to be suitably differentiated to detect light in the larval and embryonic charr.

Immunocytochemical demonstration of serotonin-immunoreactive cerebrospinal fluid-contacting neurons in the paraventricular organ of pigeons and domestic chickens.

The paraventricular organs (PVO) of the pigeon and domestic chicken contain at least three types of serotonin-immunoreactive (serotonin-ir) CSF-contacting neurons. Type 1 neurons were predominant. They had two bipolar extending processes. The somata were mostly found in the pars hypendymalis. Type 2 neurons were characterized by thin and long apical processes. Their perikarya were found in the pars distalis of the PVO or the more lateral area of this organ. Type 3 neurons were considerably smaller and had round somata. They were mostly bipolar with thin and short dendritic processes and thin basal processes. A small number of this type was conspicuous along the cranial peripheral region of the PVO. In addition to the PVO area, aggregations of small, bipolar serotonin-ir CSF-contacting neurons were shown in the most caudal wall of the third ventricle of both species, distributed medially or paramedially. Immunoelectron microscopy revealed many dense granules in apical ventricular processes and perikarya. Synaptic connections were frequently observed on basal processes.

Ultrastructure and opsin immunocytochemistry of the pineal complex of the larval Arctic charr Salvelinus alpinus: a comparison with the retina.

The fine structure and opsin immunocytochemistry of the pineal and parapineal organs of the salmonid fish Salvelinus alpinus, the landlocked Arctic charr, were studied and compared with the retina in various developmental stages, from prehatching to two-month-old. For opsin immunocytochemistry two polyclonal antibovine rhodopsin and the monoclonal antichicken opsin antibodies OS-2 (detecting blue and green pigments) and OS-1 (detecting green and red pigments) were used. Histologically, the pineal organ consists of nervous tissue like that of the retina. It is composed of photoreceptor pinealocytes, which formed axon terminals containing synaptic ribbons, on the dendrites and perikarya of secondary pineal neurons. Already in prehatching embryos, both the pineal and retinal photoreceptors display well-developed outer segments and form synaptic terminals. The distal part of the pineal organ differentiates earlier than its proximal stalk. The differentiation of the retina starts centrally, but the caudal and dorsal retinae are differentiated earlier than the rostral and ventral ones. At the end of the larval period, the lateral retina is still undifferentiated. In all stages studied, (rhod)opsin immunoreactivity was found in the outer segments of the pineal organ and rod-type retinal photoreceptors, a finding speaking in favour of the presence of the opsin of a rhodopsin/porphyropsin. Cone-type retinal photoreceptors identified morphologically in the pre- and posthatching stages were opsin-immunonegative with the four primary antisera used. This result suggests that in the charr the opsins of cone visual pigments differ in their chemical nature from those of rhodopsin/porphyropsin. The parapineal organ was opsin immunonegative. Using the monoclonal antibody OS-2 opsin immunoreactivity was also detected in inner segments, perikarya, and pedicles of rod-type photoreceptors of both retina and pineal organ of embryos and 1- to 4-day-old larvae. This may indicate a high level of opsin gene expression during photoreceptor growth around hatching. The well-developed pineal organ and its opsin content are discussed in connection with the photonegative behaviour of the larval charr.

GABA-immunoreactive intrinsic and -immunonegative secondary neurons in the cat pineal organ.

The pineal organ of the cat was studied by postembedding gamma-aminobutyric acid (GABA) immunocytochemistry. Two polyclonal rabbit GABA antisera were used with light microscopic peroxidase and electron microscopic immunogold techniques. A considerable number of intrinsic neurons are scattered in the proximal portion of the pineal organ. Some of the nerve cells were GABA-immunoreactive; other neurons as well as pinealocytes and glial/ependymal cells were immunonegative. A few GABA-immunoreactive neurons behave like CSF-contacting neurons by penetrating the ependymal lining of the pineal recess. GABA-immunoreactive neurons were more frequently found in the subependymal region. Small bundles of thin immunoreactive unmyelinated and thick immunoreactive myelinated nerve fibers occurred in the proximal pineal, especially near the habenular commissure. There were synapses of various types between GABA-immunoreactive and -immunonegative fibers. Myelinated immunoreactive axons seemed to loose their sheaths after entering the organ. Axon-like processes of pinealocytes terminated on dendrites of immunonegative neurons present near the posterior and habenular commissures. The axons of these neurons were found to join the commissural fibers and may represent a pinealofugal pathway conducting information originating from pinealocytes. The pinealocytic axons forming ribbon-containing synapses on dendrites of secondary neurons speak in favor of the sensory-cell nature of the pinealocytes. The pinealopetal myelinated GABA-immunoreactive axons and the intrinsic "GABA-ergic" neurons are proposed to inhibit the action of intrapineal neurons on which the pinealocytic axons terminate.

Opsin immunocytochemical characterization of different types of photoreceptors in the frog pineal organ.

The pineal organ of the frog, Rana esculenta and R. temporaria, was studied by opsin immunocytochemistry using two polyclonal antibovine rhodopsin and the monoclonal antichicken opsin antibodies OS-2 (detecting blue and green pigments) and COS-1 (detecting green and red pigments). Four types of photoreceptor cells were distinguished. The large outer segments of the numerous electron-dense photoreceptor cells ("large pineal rods") were immunoreactive with the rhodopsin and OS-2 antibodies, but reacted weakly with antibody COS-1. Some electron-dense photoreceptors with smaller outer segments ("small pineal rods") were found that were strongly OS-2-immunoreactive but moderately rhodopsin-positive. The long outer segments of the oil droplet containing photoreceptors ("large pineal cones") were only immunoreactive with the COS-1 antibodies. The small electron-lucent photoreceptors ("small pineal cones") were immunonegative with all the opsin antisera used. These results confirm the presence of the opsin of a (green-sensitive) rhodopsin in the "large rod" photoreceptors. A blue-sensitive pigment is supposed to be present in the "small rod" photoreceptors, and a red-sensitive one in the oil droplet-containing "large cones". The opsin-immunonegative "small cone" is discussed to contain a (UV-blue?) photopigment that differs essentially in its antigenic sites from the other pigments. The presence of four types of photoreceptors equipped with the opsins of apparently different photopigments strengthens the view that the frog pineal organ is capable of measuring different ranges of the light spectrum.

A comparison of the ultrastructure and opsin immunocytochemistry of the pineal organ and retina of the deep-sea fish Chimaera monstrosa.

The pineal organ and retina of the rat-fish Chimaera monstrosa were compared by electron microscopy and immunocytochemistry using antisera against colour-specific opsins and paying special attention to pineal CSF-contacting neurons and retinal Landolt's clubs. In the retina, a large number of Landolt's clubs and two types of rod-like photoreceptors were found. The outer segments of the numerous electron-dense "tall rods" displayed strong immunoreactivity with the monoclonal OS-2 antibodies--first of all detecting green- and blue-sensitive pigments. These results point out the presence of a chrysopsin-like photopigment. A weak cross-reactivity with the COS-1 and rhodopsin antisera indicates that the photopigment in question has certain amino acid sequence homologies with red and green photopigments. The outer segments of the few electron-lucent "broad rods" reacted with the OS-2 antiserum intensely but weakly with the COS-1 antiserum, a result suggesting the presence of a (blue?) photopigment differing from that of the tall rods. Since in the pineal organ the outer segments of the photoreceptor cells were opsin-immunonegative with all four antisera used, it is suggested that they contain an essentially different (UV-blue?) pigment. The pineal CSF-contacting neurons and retinal Landolt's bipolars were found to be principally similar in cytology. Their ciliated (receptor) dendrite terminals protruding into the photoreceptor space lacked photoreceptor membranes and were opsin-immunonegative. They are supposed to perceive information (on ionic properties?) from the fluid of the pineal lumen and retinal photoreceptor space. On the other hand, by their synaptic connections the CSF-contacting neurons and Landolt's bipolars are considered to be secondary neurons of the light-perceiving pathway of both organs.

Meningeal calcification of the rat pineal organ. Finestructural localization of calcium-ions.

The surface of the pineal organ of the rat is covered by a leptomeningeal tissue, the continuation of the corresponding meningeal layers of the diencephalon. The pineal leptomeninx consists of stratified arachnoid and of pia mater cells which follow the vessels into the pineal nervous tissue. The pineal arachnoid contains electron-lucent and electron dense cells differing from each other in their cytoplasmic components. Corpora arenacea of various size and density occur among these arachnoid cells and can grow into the pineal organ alongside pia mater tissue. Acervuli often form groups in circumscribed meningeal "calcification foci". Concrements are absent or rare in the 1- and 2-month-old animal, while they are usually present in the 4- and 6-month-old rats. The electronmicroscopic localization of Ca-ions was studied in 2- and 4-month-old rats by potassium pyroantimonate cytochemistry. In the 4-month-old animals, arachnoid cells containing a varying amount of Ca-pyroantimonate deposits were found first of all around corpora arenacea, but there were also cells free of deposits in the close vicinity of the acervuli. Deposits were preferentially localized to the cytoplasm of electron dense arachnoid cells and to the cell membrane of electron-lucent cells. Most of the precipitates occurred in locally enlarged intercellular spaces. Here, microacervuli were found in 4-month-old animals suggesting that a calcium-rich environment was responsible for the appearance of the concrements. Intermediate stages between the small acervuli and large concentric corpora arenacea may indicate an appositional growth of the acervuli in the calcification foci.(ABSTRACT TRUNCATED AT 250 WORDS)

Pineal corpora arenacea produced by arachnoid cells in the bat Myotis blythi oxygnathus.

There are corpora arenacea among the cell layers of the arachnoid on the dorsal surface of the pineal organ of the bat (Myotis blythi oxygnathus). The pineal arachnoid consists of electron lucent cells connected by cell injunctions to flat sheets and sandwiched on both sides by electron-dense cell rows. Among the superficial cell layers, collagen fibrils form loose bundles. In the electron-lucent cells, pinocytotic vesicles, rough surfaced endoplasmic reticulum, active Golgi areas and granular vesicles of various sizes can be found. Electron dense cells display fewer cytoplasmic organelles than the light ones. Lying between and below the hemispheres and cerebellum the pineal arachnoid does not contact the dura mater directly, therefore it continues on its both sides into arachnoid trabeculae. Corpora arenacea occur in lacunar enlargements of the arachnoid, first of all in the thickened dorsal portion of the pineal leptomeninx. The acervuli are insulated by collagen fibrils and exhibit concentric layers of various density. Needle-shaped structures resembling hydroxyapatite crystals were found in these concentric layers. There was no sign of formation of acervuli in the pinealocytes or elsewhere in the pineal nervous tissue proper. These findings confirm that view that corpora arenacea can be produced by the pineal arachnoid. The formation of acervuli is accompanied by secretory and resorptive phenomena of arachnoid cells.

The cerebrospinal fluid-contacting neuron: a peculiar cell type of the central nervous system. Immunocytochemical aspects.

Cerebrospinal fluid (CSF)-contacting neurons are located periventricularly or inside the brain ventricles; they contact the CSF via their dendrites, perikarya or axons. Most of these neurons form ciliated dendrite terminals in the internal CSF as do retinal and pineal photoreceptors in the optic ventricle and pineal recess. The peculiar localization, polarization and synaptic connections of the CSF-contacting neuronal elements suggest receptor and integrative functions. The present review pays special attention to vitamin A (retinoids) immunoreactivity in CSF-contacting neurons as compared with that present in retinal and pineal photoreceptor cells, common neurons, glial and adenohypophysial cells. The immunoreactivity of the dark-adapted photoreceptor outer segments was strong, but decreased after illumination, suggesting the functioning of vitamin A as the chromophore of the retinal and pineal photopigments. Retinoid immunoreaction was also found in the endoplasmic reticulum, nuclei, nucleoli and mitochondria of the cell types studied. This cytological localization suggests that vitamin A compounds may be involved in the function of these organelles. The CSF-contacting neurons contain varying amounts of bioactive materials. The intracellular distribution of immunoreactive serotonin (5-HT), substance P (SP) and gamma-aminobutyric acid (GABA) is compared with that of immunoreactive vitamin A. Immunogold labeling for SP was demonstrated in dense-core vesicles of preoptic neurons; 5-HT marking was found on the dense-core vesicles of subependymal CSF-contacting neurons of the paraventricular organ, while GABA immunoreaction was localized in the cytoplasm of distal infundibular CSF-contacting neurons. The CSF-contacting neurons are considered to synthesize and release their bioactive substances at transmitter synapses, and/or at neurohormonal terminals into the external CSF in accord with information received by their dendrites from the internal CSF and by afferent fiber connections from various brain areas.

Immunoelectron microscopy of rhodopsin and vitamin A in the pineal organ and lateral eye of the lamprey.

Rhodopsin- and vitamin A-immunoreactive sites were studied in the pineal organ of the larval and adult brook lamprey (Lampetra planeri Bloch), as well as in the retina of the larval lateral eye, at the electron microscopic level. In the pineal organ, several types of photoreceptor cells could be distinguished by their morphology and the immunoreactivity of their outer segments. The different kinds of photoreceptor cells were located at different levels of the pineal organ according to their distance from the "pineal window". The most superficial level, the so-called pellucida, appears to represent an exclusively "cone-type" area containing slender, rhodopsin-immunonegative (UV-blue-sensitive?) photoreceptors only. The second level, the pineal retina, contained predominantly rod-type photoreceptors, i.e., large, strongly rhodopsin-immunopositive (green-sensitive) photoreceptors medially, and few, small, weakly rhodopsin-immunopositive (blue-green-sensitive?) cells bilaterally. At the deepest level, the pineal atrium, there were both rod- and cone-type photoreceptor cells, the latter possibly representing red-sensitive elements. Vitamin A immunoreactivity was found in the outer segments of the pineal photoreceptor cells, in the cytoplasm and mitochondria of inner segments and perikarya, as well as in nuclear euchromatin and compact nucleoli. A similar gold labelling of organelles was observed in the ependyma and pineal neurons. The vitamin A immunoreaction of the outer segments suggests retinoids are present as chromophores of the photopigments. In the peripheral retina of the larval lateral eye, vitamin A immunoreactivity was found in some organelles of the undifferentiated photoreceptor cells, neurons, pigment epithelium and Müllerian cells. The localization of immunoreactive vitamin A in nuclei, nucleoli and cytoplasm including mitochondria appears to strengthen the case for an interaction of retinoids in the function of these organelles.

The pinealocyte forming receptor and effector endings: immunoelectron microscopy and calcium histochemistry.

The pinealocytes--the main cellular elements of the pineal organ--are polarized, displaying a (photo)receptor and an axonic effector cell pole. The receptor endings are of two main types: they bear rod-type or cone-type outer segments characterized by the presence of immunoreactive opsin-, S-antigen- and vitamin A-binding sites. The effector pole may form ribbon-containing synapses on the secondary pineal neurons, and/or neurohormonal terminals on the basal lamina of the pineal nervous tissue. Applying potassium pyroantimonate (PPA) to electron-microscopic histochemistry, we found in the frog that both effector terminals and photoreceptor outer segments contained a large amount of Ca-pyroantimonate deposit similar to retinal cones and rods. Rods and rod-like pinealocytes contained more deposits than cones. The higher concentration of calcium on the cell membranes of dark pinealocytes in the rat may be connected with their rod-like character. In the frog, a high amount of calcium seemed to be concentrated in the photoreceptor effector terminals, especially around their synaptic ribbons, and in myeloid bodies of the pineal ependyma and retinal pigment epithelium. Calcium was richly found in or around corpora arenacea in the human and rat pineal. It is suggested that the formation of concrements may be connected with the high demand of Ca-exchange of pinealocytes for their receptor and effector membrane functions. In the rat, lymphocytes were found to migrate through the wall of the vena magna of Galen and to closely contact pinealocytes, presumably to receive immunological information as an additional pineal output.