The fine structure of ependymal processes in the teleost optic tectum

Regional differences in the ependyma of the optic tectal ventricle of adult zebrafish with structures referring to brain hydrodynamics

Classical electron microscopic morphological studies provide detailed ultrastructural information, which may lend insights into cellular functions. As a follow-up to our morphological investigation of the adult zebrafish (Danio rerio) optic tectum, in this study, we have analyzed the ependymal structures lining the surfaces of the tectal ventricle: the torus, tegmental surface of the valvula cerebelli and the periventricular gray zone of the optic tectal cortex. We used toluidine blue stained plastic (semithin) sections for light microscopy and scanning electron microscopy. Our morphological findings of gated entrances and/or egresses indicate that, at least in the adult zebrafish brain, there may be a bidirectional direct flow communication between the ventricular cerebrospinal fluid and the parenchymal interstitial fluid.

Pharmacological and Morphological Evidence of AMPK-Mediated Energy Sensing in the Lower Brain Stem Ependymocytes to Control Reproduction in Female Rodents

Ependymocytes are one of the energy-sensing cells that regulate animal reproduction through their responsiveness to changes in extracellular glucose levels and the expression of pancreatic-type glucokinase and glucose transporter 2, which play a critical role in sensing blood glucose levels in pancreatic β-cells. Molecular mechanisms underlying glucose sensing in the ependymocytes remain poorly understood. The AMP-activated protein kinase (AMPK), a serine/threonine kinase highly conserved in all eukaryotic cells, has been suggested to be an intracellular fuel gauge that detects cellular energy status. The present study aims to clarify the role AMPK of the lower brainstem ependymocytes has in sensing glucose levels to regulate reproductive functions. First, we will show that administration of 5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside, an AMPK activator, into the 4th ventricle suppressed pulsatile LH release in female rats. Second, we will demonstrate the presence of AMPK catalytic subunit immunoreactivities in the rat lower brainstem ependymocytes. Third, transgenic mice were generated to visualize the ependymocytes with Venus, a green fluorescent protein, expressed under the control of the mouse vimentin promoter for further in vitro study. The Venus-labeled ependymocytes taken from the lower brainstem of transgenic mice revealed that AMPK activation by 5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside, an AMPK activator, increased in vitro intracellular calcium concentrations. Taken together, malnutrition-induced AMPK activation of ependymocytes of the lower brainstem might be involved in suppression of GnRH/LH release and then gonadal activities.

Windows of the brain: Towards a developmental biology of circumventricular and other neurohemal organs

We review the anatomical and functional features of circumventricular organs in vertebrates and their homologous neurohemal organs in invertebrates. Focusing on cyclostomes (lamprey) and urochordates (ascidians), we discuss the evolutionary origin of these organs as a function of their cell type specification and morphogenesis.

Development of vimentin and glial fibrillary acidic protein immunoreactivities in the brain of gray mullet (Chelon labrosus), an advanced teleost

Previous studies in teleosts have revealed the presence of the intermediate filaments vimentin (Vim) and glial fibrillary acidic protein (GFAP) in glial cells of the spinal cord and/or some brain regions, but there is no comprehensive study of their distribution and developmental changes in fishes. Here, the distribution of Vim and GFAP immunoreactivities was studied in the brain of larvae, juveniles, and adults of an advanced teleost, the gray mullet (Chelon labrosus). A different sequence of appearance was observed for expression of these proteins: Vim levels decreased with age, whereas GFAP increased. In general, both immunoreactivities were expressed early in perikarya and endfeet of ependymocytes (tanycytes), whereas expression in radial processes appeared later. In large larvae, the similar expression patterns of Vim and GFAP suggest that some of these glial cells contain both proteins. Subependymal radial glia cells were observed mainly in the optic tectum, exhibiting Vim and GFAP immunoreactivity. The only immunoreactive cells with astrocyte-like morphology were observed in the optic chiasm of the adult, and they were positive for both GFAP and Vim. The perivascular processes of glial cells showed a different distribution of Vim and GFAP during development and had a caudorostral sequence of appearance of immunoreactivities similar to that observed for ependymal and radial glia cells. Several circumventricular organs (the organon vasculosum hypothalami, saccus vasculosus, and area postrema) exhibited highly specialized Vim- and/or GFAP-expressing glial cells. The glial cells of the midline septa of several brain regions were also Vim and/or GFAP immunoreactive. In the adult brain, tanycytes retain Vim expression in several brain regions. As in other vertebrates, the regions with Vim-immunoreactive ventricular and midline glia may represent areas with the capability of plasticity and regeneration in adult brain.

Evidence for the c-ret protooncogene product (c-Ret) expression in the spinal tanycytes of adult rat

Expression of the protein product of c-ret (c-Ret) in the spinal cord of the adult rat was examined immunohistochemically at both electron and light microscopic levels. In the cervical, thoracic and lumbar segments of the spinal cord, a large number of c-Ret immunoreactive cells were found in both ependymal and subependymal layers of the central canal. These cells were ovoid or triangular in shape and had a well developed single cytoprocess which protruded into the central canal. None of the neuropeptides and neuronal markers examined, including substance P, CGRP, galanin, neuropeptide Y, tyrosine hydroxylase, methionine-enkephalin, choline acetyltransferase and glially fibrilally acidic protein, was present in these c-Ret immunoreactive cells in the spinal cord. Ultrastructurally, a desmosome-like structure was found between the apical part of the cytoprocess and the ependymal cell. These morphological observations indicated that c-Ret positive cells are spinal tanycytes. The present results suggest that spinal tanycytes in the rat express a trophic factor receptor and may respond to GDNF in the cerebrospinal fluid.

Structural changes, related to reproduction, in the hypothalamus and in the pars tuberalis of the rhesus monkey: Part I. The hypothalamus. Part II. The pars tuberalis

Certain cells lining a circumscribed area of the III ventricle of the rhesus monkey differ from those cells which constitute the characteristic ependymal lining of the brain. The specialized cells studied comprise a number of types which differ in their structure, ultrastructure and staining affinities; all demonstrate features which are generally associated with active secretion and/or absorption. A group of such cells, which form a limited area of the latero-ventral walls of the anterior hypothalamus, have long processes which extend to the walls of the blood vessels in the median eminence. The evidence indicates that many of these cells, here described as Type B or tanycyte cells, secrete their products into the primary capillary network of the pituitary portal system. Another group of cells, here described as Type C and C' cells are found in a slightly more posterior position lining the floor of the ventricle; as yet there are no indications that these may secrete into blood vessels in the median eminence. Some of the specialized cells lining the III ventricle (Types B and C') showed changes in relation to reproductive activity: No such changes were observed in Type C cells nor in the characteristic ependymal cells (Type A) found elsewhere. Studies on normal and experimental male and female monkeys showed that Type B tanycyte cells differed in males and females and altered during the menstrual cycle in the female. Following ovariectomy these cells showed regressive changes but returned to a normal appearance after a single injection of oestradiol. In view of the close spatial relationship of the tanycyte ependyma to cells of the pars tuberalis it was interesting to note that pars tuberalis cells also altered in relation to the menstrual cycle. The evidence presented accords with the view that certain cells which line the III ventricle of the brain and have prolongations extending to pituitary blood vessels, thus linking the cerebrospinal fluid and the blood system in the region of the pituitary, may play a role in the regulation of pituitary function and thereby constitute an important neuro-endocrine system.

Tanycytes in the sunfish brain: NADPH-diaphorase histochemistry and regional distribution

NADPH-diaphorase histochemistry has been shown to be a useful method for identifying cells that synthesize and release nitric oxide, which is implicated in the modulation of a variety of neural functions, including synaptic transmission, cerebral blood flow, and excitotoxicity. In the sunfish brain, NADPH-diaphorase histochemistry stains tanycytes specifically and almost exclusively, allowing for a thorough examination of the morphology and distribution of this type of cell. Tanycytes are nonciliated, process-bearing ependymal and extraependymal cells that contact the ventricular surface via apical processes, and the pial surface via basal processes. Ependymal tanycytes are located at the ventricular surface, and project basal processes into the parenchyma of the brain. Extraependymal tanycytes are found away from the ventricular matrix. Some extraependymal tanycytes are small, bipolar, and tend to be associated with bundles of basal processes. Isolated extraependymal tanycytes are larger, darkly stained, and multipolar. Their basal processes terminate in specialized endfeet on blood vessels, neuronal somata, or the pial surface. Specialized types of tanycytes are found in the optic tectum, the epineurial septum between axonal bundles along the midline in the medulla, and in restricted regions on the pial surface in the medulla. The only NADPH-diaphorase-positive neurons are found in the commissural nucleus of area ventralis telencephali. Injection of horseradish peroxidase into the ventricles shows that tanycytes lining the third and fourth ventricles are capable of taking up the tracer and transporting it into their basal processes. Tanycytes are unevenly distributed in the brain. There is a rough rostrocaudal gradient of cell density: tanycytes are sparse in the telencephalon and dense in the isthmus and medulla, although cell density is low in the spinal cord. Not all ventricular linings contain tanycytes: cell density is low in the medial ventricle of the telencephalon and in the infundibular recess, and high along the fourth ventricle. The function of tanycytes in the sunfish is not known. The association of tanycytes with both the ventricles and blood vessels raises the possibility that they play some role in sampling the biochemical constituents of both compartments and communicating the information to neural elements. It is proposed that tanycytes react to the biochemical composition in the ventricle and plasma by increasing or decreasing nitric oxide synthesis and release, which in turn influence neuronal activity or cerebral blood flow.

Astroglial pattern in the spinal cord of the adult barbel (Barbus comiza)

The distribution and the structural, ultrastructural and immunohistochemical characteristics of the astroglial cells in the spinal cord of the adult barbel (Barbus comiza) have been studied by means of metallic impregnations (Golgi and gold-sublimate), immunohistochemical (GFAP and vimentin) and electron microscopic techniques. GFAP-positive cells were mainly distributed in the ependyma and in the periependymal region, but they have also been observed at subpial level in the anterior column. The ependymocytes were heterogeneous cells because they showed different immunohistochemical characteristics: GFAP-positive, vimentin-positive or non-immunoreactive cells. The radial astrocytes showed only GFAP immunoreactivity, and their processes ended at the subpial zone forming a continuous subpial glia limitans. Desmosomes and gap junctions between somata and processes of radial astrocytes were numerous, and a relationship between radial astroglial processes and the nodes of Ranvier was also described. The perivascular glia limitans was poorly developed and it was not complete in the blood vessels of the periependymal zone; in this case, the basal lamina was highly developed. An important characteristic in the barbel spinal cord was the existence of a zone with an abundant extracellular space near the ependyma. The presence of radial astroglial somata at subpial level, the existence of vimentin-positive ependymocytes and the abundant extracellular space in the periependymal zone is discussed in relation to the regeneration capacity and the continuous growth showed by fish. Moreover, the abundance of gliofilaments and desmosomes leads us to suggest that mechanical support might be an important function for the astroglial cells in the barbel spinal cord.

Pathology associated with meningoencephalitis during bacterial kidney disease of salmonids

The neural pathology associated with spontaneous cases of bacterial kidney disease (BKD), in five species of commercially reared salmonids, was investigated histopathologically and with immunofluorescence. Patterns of localisation of the causative organism of BKD within the central nervous system suggest that haematogenous spread to the meninges, particularly the tela choroidea posterior, the tela choroidea and vascularised capsule of the saccus dorsalis and epiphysis of the epithalamus, and the saccus vasculosus of the hypophysis, appears to be a frequent route by which the central nervous system becomes infected. Retrograde extension from the posterior uvea to the floor of the diencephalon along the epineurium and perineurium of the optic nerve also may be a mechanism of neural invasion. Extension appeared to occur from these sites into adjacent areas of the meninges, the neural parenchyma and ventricles. Demonstration of bacteria within salmonid ependymal cells, as well as the apparent ability of salmonid ependymal cells to respond metaplastically suggest a similarity to mammalian type III ependymal cells (tanycytes). Based on this study, it is apparent that teleosts can survive protracted severe brain damage. This, combined with the apparent similarities of neural response to infection between the salmonids used in this study and higher vertebrates, suggests that teleosts may be a useful lower vertebrate model for studying the pathogenesis and sequelae of bacterial meningitis.

Fine structural organization of the ependymal region of the paraventricular nucleus of the rat thalamus and its relation with projection neurons

The ependymal lining of the diencephalic third ventricle is known to exhibit significant variation in zonal architecture and the relations of neurites to the ventricular surface in different regions remains obscure. The present study explores the fine structural organization of the ependymal region of the thalamic paraventricular nucleus. Methodology was developed for tracing neurites of cells retrogradely labelled with horseradish peroxidase based on our recent observation that paraventricular neurons projecting to the amygdaloid complex cluster near the ventricle and emit numerous dendrites extending toward the ependymal surface. A relatively uniform population of cuboidal 'pale' ependymocytes dominates the ventricular lining of the thalamic paraventricular nucleus, although a few 'dark' ependymocytes are interspersed. The subependymal region displays a variety of glial elements. Dendrites of thalamic paraventricular projection neurons terminate in proximity to the ependymal layer from which they are generally separated by thin cytoplasmic processes of putative astrocytes, and few indent the basal portion of ependymal cells. Thin 'terminal' (i.e., serially traced) horseradish peroxidase-labelled dendrites filled with lipid and lysosome-like dense bodies were often enveloped by astrocyte membrane whorls. This feature may constitute a reactive glial response in horseradish peroxidase-labelled dendritic terminals. A distinctive arrangement of tortuous astrocyte leaflets was insinuated between the basal portion of ependymocytes in a zone exhibiting numerous caveolae, apparently isolating neurites from direct contact with the cerebrospinal fluid. These findings indicate that the ependymal region of the thalamic paraventricular nucleus is not characterized by those features of the basal third ventricle suspected to confer neuroendocrine interaction between neurons and cerebrospinal fluid. The structural arrangement between ependymocytes and thalamic paraventricular projection cells indicate a specialized relation of these neurons with the ependymal interface, but apparently not directly with the overlying cerebrospinal fluid.

Primary culture of astrocytic glial cells from rainbow trout, Salmo gairdneri L., brain

A method is described for the preparation and maintenance of rainbow trout brain astrocytes in primary culture. A dissociated cell suspension was prepared from brains from young fish by mechanical sieving through nylon guazes, and the cells cultured in polylysine-treated plastic tissue culture flasks at 22 degrees C. The resultant cultures were characterised by specific immunofluorescent staining using glial fibrillary acidic protein (GFAP) for astrocytes and Thy 1 for fibroblastic cells. The cultures were greater than 95% astrocytes with fibroblasts the only other cell type present. These highly enriched astrocyte cultures provide a unique system for various neurochemical, neurophysiological and biochemical studies of fish neural cells. Polyunsaturated fatty acid metabolism will be an area of particular interest.

Radial glia and astrocytes in developing and adult telencephalon of the lizard Gallotia galloti as revealed by immunohistochemistry with anti-GFAP and anti-vimentin antibodies

The development of radial glia and astrocytes in the telencephalon of the lizard Gallotia galloti was studied by immunohistochemistry with anti-vimentin and anti-GFAP antibodies. Vimentin appears at embryonic stage 32 (E32) in the proliferative zone of the lateral ventricle and subpial end-feet in the marginal zone. At E34-35 the staining intensity for vimentin in all radial glia is maximal. It then decreases and disappears in most structures in adult animals. GFAP appears at E35 in the end-feet in the marginal zone and its intensity increases until adulthood, particularly in radial and sinuous fibers and in fibers that originate from the sulci and invade the ventral striatum and the septum. In contrast, the reaction is weak in the cortex, in the anterior dorso-ventricular ridge, and in the amygdala nuclei. Radial glia is still present in the adult, and the composition of its intermediate filaments changes during development from vimentin to GFAP. No GFA-positive cell bodies except those of ependymal glia were detected in telencephalon.

Glial fibrillary acidic protein and vimentin immunohistochemistry in the developing and adult midbrain of the lizard Gallotia galloti

The distribution of glial fibrillary acidic protein (GFAP)- and vimentin-containing cells was studied by immunohistochemistry in the midbrain of the lizard Gallotia galloti. At embryonic stage 32 (E32), vimentin immunoreactivity appeared first in cell bodies located in the ventricular walls, in radial fibers, and subpial end-feet and increased in these structures until E34/E35. Faint GFAP immunoreactivity gradually appeared in the same structures between E34 and E37, and this increased until adulthood, whereas vimentin immunoreactivity decreased after E35, becoming limited to a few end-feet and fibers in the adult, mainly in the tegmentum. Thus, in developing Gallotia midbrain a shift from vimentin-containing to GFAP-containing intermediate filaments begins around E36 or E37. At E40, in addition to the cell bodies in the ependymal area, dispersed GFAP-positive cells, possibly immature astrocytes appeared. These cells showed the same shift. In the adult lizard, GFAP-positive radial glia are still present and coexist with GFAP-positive astrocytes, which are prefentially located in the marginal optic tract and the oculomotor nuclei, but are absent in the fasciculus longitudinalis medialis. Optic tectum, pretectum, tegmentum, and isthmic nuclei are the areas richest in GFAP-positive radial fibers: these were much less abundant in the deep mesencephalic nuclei. Thus, in this lizard, GFAP-positive astrocytes display a clear cut regional distribution: they are present in mesencephalon, whereas they are absent in telencephalon.

Organization of astrocytes in the visual pathways of the goldfish: an immunohistochemical study

We have used antisera directed against glial cytoskeletal proteins to examine the distribution and organization of astrocytes in the visual pathways of the goldfish. We describe two different types of cells, which may be distinguished by their unique cytoskeletal proteins. Antibodies raised against a 48 Kd optic nerve protein react with stellate astrocytes in the optic nerve but virtually no glial cells in the brain (although blood vessels and the meninges in the brain were stained). The optic nerve astrocytes form a dense meshwork of processes through which the optic fibers pass. The intraorbital and intracranial segments of the nerve are divided into fascicles, each bounded by a glia limitans, which extend across the optic chiasm. Astroglial cells in the brain bind antibodies raised against a 50 Kd brain cytoskeletal protein. These antibodies show a very limited cross-reactivity with optic nerve cells. Brain astrocytes have filiform profiles and most appear to be deployed as radial glia. The glial fabric of the brain, as revealed by these antibodies, is far more loosely woven than that of the optic nerve. There is a sharp boundary between the two types of glial cells, immediately behind the optic chiasm. Glial processes in the optic tracts arise from cells in the preoptic area, whereas those in the optic tectum arise from cells that reside locally. In the optic tract, a glia limitans was often difficult to discern, whereas in the tectum one was always evident and composed of endfeet at the pial extremities of radial glial processes. These findings are discussed both in the context of previous observations by other workers as well as with regard to their possible functional implications.

Peripheral nerve grafts to the frog optic tectum: a morphological study of foreign axon regeneration in the central nervous system

The proximal stump of a transected mandibular nerve was grafted onto the rostrodorsal surface of the optic tectum in adult Rana pipiens to investigate the morphologic characteristics of nonspecific axonal regeneration in a highly organized region of central nervous system (CNS). Within the first 3 weeks postgraft surgery (WPS), the nerve-tectum interface became firmly established. Concomitant with this was an invasion of the host tectum by a small number of fine "pioneerlike" axons from the nerve. By 6 WPS there developed a concerted instreaming of a large number of peripheral fibers. Once within the CNS, the foreign axons distributed themselves throughout the rostrocaudal extent of the tectum, but primarily its dorsal aspect within superficial layers 8 and 9. Presence of intact optic fibers at the time of mandibular fiber invasion served somewhat to restrict the regenerating aberrant axons in their course through layer 9. This restriction could be avoided by removal of the optic input either before or during peripheral ingrowth. However, once peripheral fibers had entered and established themselves in the host environment, no subsequent manipulation of the retinotectal projection had any effect. The aberrant growth pattern, which appeared remarkably stable after 6 WPS, consisted of a plexus of medium- and fine-caliber peripheral axons. Many of these fibers had numerous branches and "en passant" varicosities, the latter encompassing a variety of shapes and sizes. Terminal swellings and arborizations were also found. When comparing the regeneration of optic and mandibular nerve fibers in the tectum, two distinctions were made. Whereas optic axons revealed a fascicular and layered organization, mandibular axons showed a highly segregated and disordered growth pattern. These characteristic differences were maintained even when the two fiber systems were allowed to coregenerate into the same target tectum. Thus, each of the two groups of axons interacts with the tectal substrate in a distinct manner, apparently independent of the other.

Spinal tanycytes in the adult rat: a correlative Golgi gold-toning study

In Golgi impregnated transverse sections through the cervical spinal cord of the 7-12-week-old adult rat, numerous tanycytes were observed radiating from the ependyma into the gray matter that surrounds the central canal. The tail processes of these tanycytes terminated as foot processes in association with blood vessels. Spinal tanycytes were classified into ependymal (E) and subependymal (S) types on the basis of the shape and position of the soma. The soma of the E tanycyte was shaped as a column and was entirely located within the ependyma. In contrast, the soma of the S tanycyte was flask shaped, with the widest portion of the flask located subependymally and the elongated portion extending through the ependyma ultimately reaching the luminal surface. Selected Golgi impregnated sections were gold toned and deimpregnated for direct correlative analysis at the ultrastructural level. Gold-toned tanycytes contained the fine clusters of gold particles underlying the plasma membrane of the cell body and coarse clusters of gold particles throughout the tail and foot processes. The apical surface of tanycytes was characterized by numerous microvilli and large cytoplasmic protrusions that evaginated from the apical surface into the lumen of the central canal. At the luminal surface, adjacent tanycytes were joined laterally by junctional complexes with punctate tight junctions and zonulae adhaerentes associated with fibrils and microtubules. In contrast, gap junctions, hemidesmosomes, and puncta adhaerentia were found between adjacent tail processes of tanycytes. The foot processes interdigitated with one another and abutted the basal lamina around the perivascular space of blood vessels. The basal lamina was continuous around the lateral walls of foot processes and filled the spaces between membranous infoldings of the lateral walls. These basal membrane labyrinths were continuous with the basal lamina of the blood vessel and may provide an extensive surface relation between the perivascular space and the neighboring extracellular compartment. The findings of the present study support the contention that tanycytes may modify the composition of substances moving between the perivascular and extracellular spaces.

Aging changes in the optic tectum of the guppy Poecilia (Lebistes) reticulatus

Histological surveys of the brains of guppies throughout their lifespan showed no overall loss of tissue with advancing age. Brain and body increased in size at a similar rate throughout adult life in male fish. In old females after the age of two years, brain growth apparently ceased, although body growth continued at a low rate. In both sexes there was a loss of neurones from the stratum griseum periventriculare in the midbrain roof in old age; the decrease in size was significant. The midbrain is a major correlative center concerned with spatial orientation. How far neuronal loss may contribute to functional behavioral disorder in old age is unknown, but a loss of orientation could render the older fish more susceptible to predation.

Functional anatomy of the tectum mesencephali of the goldfish. An explorative analysis of the functional implications of the laminar structural organization of the tectum

The present paper is aimed at an exploration of the possible functional significance of the laminar organization of the goldfish tectum at both the cellular and the synaptic level. For this purpose (1) the data concerning the structure of the teleostean tectum are surveyed, (2) a conceptual framework of the intratectal connectivity in the goldfish is proposed, (3) the electrophysiological data concerning the teleosteam tectum are surveyed and (4) the degree of correlation between the structural and physiological data available is discussed. Apart from the retina, tectal afferents originate from at least 10 other brain centers. At least 5 of these projections appear to be topographically organized. Tectal afferents, neurons as well as synapses reveal a characteristic intratectal lamination pattern. Tectal efferents project to at least 10 brain centers, and have until now been shown to arise from 6 cell types. The structural data surveyed allow the construction of a conceptual framework of tectal circuitry on the basis of 3 starting points. (1) The existence of at least 8 presynaptic zones or laminae, each containing a characteristic set of presynaptic structures (afferents and axons of interneurons). (2) The fact that the tectal postsynaptic structures (somata and dendrites of tectal neurons) each have a characteristic location, extension and synaptic density, which determines the relative importance of the different presynaptic zones for each cell type. (3) The laminar specificity hypothesis, which implies that presynaptic structures that coexist in a particular presynaptic zone terminate without preference on all types of postsynaptic structures within that zone. The conceptual framework of tectal circuitry is quantified in terms of connectivity index and connective importance. Analysis of the framework constructed leads to a detailed description of the intratectal pathways involved in the processing of the 4 main streams of tectal input (i.e. visual, toral, telencephalic and 'deep' input). It was concluded that the laminar organization of the tectum is primarily relevant for multimodal integration and that the tectal cell types each receive a characteristic sample out of the multimodal information available in the different tectal layers.(ABSTRACT TRUNCATED AT 400 WORDS)

Comparative study of the glial fibrillary acidic protein in vertebrates by PAP immunohistochemistry

Glial fibrillary acidic protein (GFA) has been visualized by direct peroxidase antiperoxidase (APA) immunohistochemistry in various vertebrates (cyclostomes, teleosts, amphibians, reptiles, birds, and several placental mammals). In this study GFA-immunoreactivity (GFA-I) was observed in all species examined except in cyclostomes and amphibians. Two types of immunoreactive elements were observed: astrocytes and long processes without visible somata. Astrocytic cells with GFA-I were first found in the snake, and more cells were in birds where the pattern of distribution was similar to that of mammals. Within mammals, few differences in the manner of localization were observed among different species, except in the corpus callosum and the ependymal and subependymal layers. Long straight processes were observed in the lower submammalians--the lamprey, carp, and turtle. They radiated through the neuropil from the ventricular wall and followed nerve fiber bundles in the white matter. An uncommon feature was observed in the turtle brain, which possessed very intense GFA-I within the ependymal layer. The presence of GFA-containing profiles in the ependyma of adult animals is discussed in relation to GFA-positive structures seen in the human brain during ontogeny or under certain pathological conditions.

Morphology of radial glia, ependymal cells, and periventricular neurons in the optic tectum of goldfish (Carassius auratus)

There are three populations of cells in the deep layers of the optic tectum in a normal adult goldfish: the periventricular neurons, the ependymal cells, and the radial glia. The characteristic morphological features which distinguish the three cell populations are examined at light and electron microscopic levels in the present work. A radial glial cell has a deeply invaginated nucleus located in a subependymal layer. Its cytoplasm contains mitochondria with 35-nm dark granules and 20-nm microtubules but no intermediate filaments. Its prominent radial process extends through the superficial tectal layers. In contrast, the processes of ependymal cell ramify and interweave within the ependymal region. The cytoplasm of an ependymal cell contains prominent bundles of intermediate filaments but not microtubules. Its soma lies at or near the ventricular surface. A periventricular neuron has a round nucleus and a smooth dendrite which extends toward the superficial tectal layers. Its cytoplasm contains microtubules and agranular mitochondria. Axosomatic and axodendritic synapses are found on periventricular neurons. The morphological characteristics of these cell types are considered in relation to previous descriptions of teleost tectal cytology and with regard to the atypical natures of the cytoskeletal elements of the ependymal and radial glial cells.

Inverse prominence of ependyma and capillaries in the spinal cord of vertebrates: a comparative histochemical study

Spinal cords of 15 species representing six classes of vertebrates and the protochordate amphioxus were examined with histochemical methods for esterase, ATPase, LDH, PAS, and PAS-phosphorylase. Ependymal and glial cell processes were demonstrated and resembled heavy metal impregnations. Capillaries also were shown. The prominence of glycogen-rich ependymal structures in the spinal cord of nonmammalian vertebrates, and the increase in intramedullary blood vessels in placental mammals, suggest an inverse relationship between the relative development of the ependyma and of the blood supply. The marsupial opossum has sparseness of both ependyma and capillaries, but exhibits an extensive pattern of branched glial processes in both white and gray matter.

The structure of the inferior lobe of the teleost hypothalamus

Electron microscopic and Golgi studies on the inferior lobes of sunfish and goldfish are described. The inferior lobe consists primarily of a nucleus ventricularis of densely packed cells surrounding the lateral recess of the third ventricle, and a peripherally situated nucleus diffusus consisting mostly of scattered neurons. A cell-sparse zone of dense neuropil is located between the two cellular areas. Neurons of both nuclei have spiny dendrites and axons which originate from basal dendrites. In some cases axons are found to send a collateral into the cell-sparse zone. Neurons of the nucleus diffusus possess collaterals that extend a considerable distance within the nucleus itself. The ultrastructure of cells of both nuclei reveals cytoplasmic organelles typical of most neurons. Synapses containing dense-cored and clear vesicles are present on the spines and shafts of the dendrites of both neuronal types. In only rare cases synapses were observed on the soma of neurons of the nucleus ventricularis. Possible anatomical substrates involved in the control of feeding and aggression in teleosts are considered in light of the present findings. Morphological similarities of the inferior lobes and related areas in various fishes and amphibians are discussed and their possible significance for the understanding of the evolution of hypothalamic mechanisms is considered.

Cytoarchitecture of the optic tectum in the nurse shark

The cytoarchitecture of the optic tectum of the nurse shark is described and related to the arrangements of afferents from retina, telencephalon and contralateral tectum. Its lamination is not pronounced when compared to tecta of most other non-mammalian species but more comparable to those of mammals. The absence of highly differentiated cells such as pyramidal and true horizontal cells is perhaps correlated with the poor differentiation in general, including the apparent partial overlap of inputs. Some neurons near the midline were found to possess dendrites extending into the contralateral tectum.

Calcium-containing structures in vertebrate glial cells. Ultrastructural and microprobe analysis

Electron probe microanalysis has revealed that vesicular or cisternal structures containing electron-dense material in frog ependymal glial cells contain deposits of calcium and phosphorus. The so-called "osmiophilic particles" in human astrocytes also contain calcium. It is suggested that these organelles are storage sites of calcium.