Spinal cord central canal of the German shepherd dog: Morphological,histological, and ultrastructural considerations

This study deals with some macroscopical, microscopical, and ultrastructural aspects of the spinal cord central canal of the German shepherd dog. The caudal end of the spinal cord is constituted by the conus medullaris, which may extend to the first sacral vertebra, the terminal ventricle, and the filum terminale. The latter structure is considered as internum (second to third sacral vertebrae) or externum (fifth caudal vertebra), according to its relation to the dura mater. Occasionally, there is a second anchorage which is close to the level of the sixth caudal vertebra. The central canal is surrounded by a ciliated ependymal epithelium, which differs depending upon the levels. The most caudal part of the filum terminale bears a columnar ciliated ependymal epithelium surrounded by two layers of glia and pia mater, which separate the central canal from the subarachnoid space. Microfil injections show a communication between the cavity and the subarachnoid space, as the plastic is able to pass through the ependymal epithelium. At the level of the terminal ventricle there are real separations of the ependymal epithelium, which seem to connect the lumen of the spinal canal with the subarachnoid space. These structures probably constitute one of the drainage pathways of the cerebrospinal fluid. The diameter of the central canal is related to the age of the animal. However, even in very old animals the spinal cord central canal reaches the tip of the filum terminale and remains patent until death. At the ultrastructural level the ependymal cells present villi, located on cytoplasmic projections, cilia, dense mitochondria, and oval nuclei. © 1995 Wiley-Liss, Inc.     

Ultrastructural Study of the Filum Terminate and Caudal Ampulla of the Spinal Cord of Amphioxus (Branchiostoma lanceolatum Pallas)

The filum terminale and caudal ampulla of amphioxus were studied by electron microscopy. The filum terminale consists of ependymal cells whose cilia are directed caudally. Remarkably, nerve fibres course through the filum terminale and caudal ampulla and end on the basal lamina forming neuro-connective structures. Moreover, these nerve boutons are divisible into several classes according to their vesicle content. Boutons containing large dense-cored vesicles are very similar in appearance to the neurosecretory terminals found in the caudal spinal cord of some vertebrates. These observations on nerve fibres suggest that a primitive neurosecretory system similar to the fish urophysis is present in the amphioxus.     

Developmental study of the shortened spinal cord in the adult tiger puffer fish, Takifugu rubripes (Teleostei)

ABSTRACT The spinal cords of vertebrates are generally divided into the cord proper and the minute filum terminale. While the spinal cord extends the entire length of the vertebral canal in the adult tiger puffer, Takifugu rubripes, the cord proper is greatly reduced in length and almost all of the canal is occupied by the filum terminale, which is tape-like rather than thread-like. The dorsal and ventral roots of the spinal nerves extend, respectively, above and below the filum terminale; as a whole, these form a massive cauda equina. Supramedullary cells are found in the rostral half of the medulla oblongata caudal to the cerebellum. In 4-mm long tiger puffers, the spinal cord is cylindrical and supramedullary cells are found in the rostral half of the cord. In 7-mm puffers, the longitudinally arranged ventral roots appear ventrally in the middle portion of the spinal cord. In 15-mm puffers, the dorsal and ventral roots run longitudinally along the spinal cord and have noticeably increased in number. Supramedullary cells are located in the rostral 15% of the cord. In 21-mm puffers, the spinal cord in large part becomes dorsoventrally flattened. In 30-mm puffers, the spinal cord becomes much flatter, and supramedullary cells now are located mainly in the medulla oblongata. These observations indicate that formation of the shortened spinal cord proper is due to at least two developmental processes. First, the elongation of the spinal cord proper is remarkably less than that of the vertebral canal. Second, the bulk of the spinal cord proper is translocated to the cranial cavity, where it is transformed into part of the medulla oblongata.     

Transmission electron microscopic studies of the organization of the ependymocytes in the central canal of the spinal cord of Cercopithecus nigroviridis (Pocock 1907), (Platyrrhina, Cercopithecoidea)

The ependyma of the central canal of the spinal cord of the monkey Cercopithecus nigroviridis was examined by transmission electron microscopy. In the lumbar region and in the filum terminale, many cytoplasmatic protrusions are visible. They are irregular in size and shape and display many microvilli. They are extending into the lumen of the central canal. The basal parts of the ependymocytes occasionally have a very close association with the ependymal blood vessels. The pericapillary space, the pericapillary structures like pericytes and collagen fibrils, and the basal lamina are absent. Opposite branches of the ependymocytes growing together could be observed in the central canal, eventually forming a cytoplasmic unit. Cytoplasmatic extensions of the ependymocytes bridge the lumen of the central canal and melt into each another. Lacunae, such as described by LEONHARDT (1980) in the apical cytoplasm of the ependyma in the rabbit, do also exist in the ependyma coating the central canal of the spinal cord of the monkey Cercopithecus nigroviridis. Some of these lacunae have direct contact to the luminar surface of the central canal, others are separated. Cilia and short microvilli are coating the lacunae. Adjacent ependymal cells form complex interdigitations with each other. Close to their surface on the central canal, there are numerous zonulae adhaerentes. Profiles of the granular and agranular endoplasmatic reticulum are in very close contact to the fine filaments of the zonulae.     

Reissner's fiber and the wall of the central canal in the lumbo-sacral region of the bovine spinal cord

Summary Reissner's fiber (RF) of the subcommissural organ (SCO), the central canal and its bordering structures, and the filum terminale were investigated in the bovine spinal cord by use of transmission electron microscopy, histochemical methods and light-microscopic immunocytochemistry. The primary antisera were raised against the bovine RF, or the SCO proper. Comparative immunocytochemical studies were also performed on the lumbo-sacral region of the rat, rabbit, dog and pig.At all levels of the bovine spinal cord, RF was strongly immunoreactive with both antisera. From cervical to upper sacral levels of the bovine spinal cord there was an increasing number of ependymal cells immunostainable with both antisera. The free surface of the central canal was covered by a layer of immunoreactive material. At sacral levels small subependymal immunoreactive cells were observed. From all these structures sharing the same immunoreactivity, only RF was stained by the paraldehyde-fuchsin and periodicacid-Schiff methods.At the ultrastructural level, ependymal cells with numerous protrusions extending into the central canal were seen in the lower lumbar segments, whereas cells displaying signs of secretory activity were principally found in the ependyma of the upper sacral levels. A few cerebrospinal fluid-contacting neurons were observed at all levels of the spinal cord; they were immunostained with an anti-tubulin serum.The lumbo-sacral segments of the dog, rat and rabbit, either fixed by vascular perfusion or in the same manner as the bovine material, did not show any immunoreactive structure other than RF.The possibilities that the immunoreactive ependymal cells might play a secretory or an absorptive role, or be the result of post-mortem events, are discussed.Supported by Grant I/38259 from the Stiftung Volkswagenwerk, Federal Republic of Germany, and Grant RS-82-18 from the Dirección de Investigaciones, Universidad Austral de ChileThe authors wish to thank Dr. Enrique Romeny from the Valdivia abattoir for kindly providing the bovine spinal cords     

Heterogeneity of astrocytic membranes in the optic nerve and spinal cord of the lizard,Anolis carolinensis

Summary The architecture of astrocytic membranes in the optic nerve and the spinal cord of the lizard, Anolis carolinensis, was investigated by use of the freeze-fracturing technique. Whereas astrocytes in mammals reveal so-called orthogonal arrays of particles (OAPs) in their membranes, astrocytes in lower vertebrates lack these structures. This study demonstrates for the first time OAPs in astrocytes from a submammalian species. They were found commonly in the optic nerve and less frequently in the spinal cord. However, the OAPs in astrocytes of spinal cord were confined to midtrunk levels; the astrocytes in the caudal spinal cord failed to reveal OAPs.Additionally, the ependymal cells around the central canal did not show any OAPs, either in the thoracic or in the caudal spinal cord. They were interconnected by gap and tight junctions, which were not intercalated with each other.The findings support our current working hypothesis according to which the presence and absence of OAPs in astrocytes may be correlated with regenerative incapability or capability of CNS-structures; i.e., whereas the thoracic spinal cord in Anolis carolinensis is known to be incapable of regeneration after injury, the caudal spinal cord is regenerative.     

The caudal spinal cord of coho salmon (Oncorhynchus kisutch): Immunocytochemical evidence of a “caudal serotoninergic system”

Summary The caudal spinal cord of the coho salmon was investigated by means of immunocytochemistry using antisera against serotonin, urotensin I, urotensin II, somatostatin and a urea-extract of bovine Reissner's fiber (AFRU). Populations of serotonin-immunoreactive (IR) neurons were found rostral and dorsal to the urophysis in close spatial association with caudal secretory neurons. Thick, smooth serotonin-IR processes extended toward the external surface of the spinal cord where they displayed conspicuous terminal dilatations. Thin, beaded serotonin-IR fibers appeared to innervate populations of caudal secretory and somatostatin-IR cerebrospinal fluid-contacting neurons. Most caudal neurosecretory cells displayed both urotensin I and urotensin II immunoreactivities; only a minority reacted exclusively with either urotensin I or urotensin II antisera. Urotensin II-IR and somatostatin-IR cerebrospinal fluid (CSF)-contacting neurons were found as an integral component of the central canal wall in the caudal spinal cord and filum terminale; their dendritic processes appeared to contact Reissner's fiber, which displayed a weak AFRU-immunoreactivity while inside the central canal, but became strongly reactive in the interior of the terminal ventricle as it formed the massa caudalis. The distribution of serotoninergic processes points to a regulatory role in the function of caudal secretory and CSF-contacting neurons and to a putative serotonin release into the subarachnoid space and/or meningeal vasculature. It is also suggested that the CSF-contacting neurons of the central canal may participate in a feedback mechanism controlling the secretory activity of the subcommissural organ.Supported by Grant A/1095-1 from the International Foundation for Science, Sweden, to C.Y.; Grant I/63-476 from Volkswagen-Stiftung to E.R.; and Grant S-85-39 from the Dirección de Investigaciones, Universidad Austral de Chile     

Morphological studies of the spinal cord in tetraodontiformes fishes

The spinal cord of two tetraodontiform fishes, the Japanese file fish (Navodon modestus) and the panther puffer (Takifugu pardalis), are unusual among vertebrates in having a markedly abbreviated spinal cord with a long and flattened filum terminale. Only the rostral short part of the cord of both species is cylindrical; the greater part of the cord is markedly flat. The majority of the spinal nerve roots leave the short cylindrical part. The flattened part of the cord contains the central canal, myelinated nerve fibers, and a few motoneurons surrounding the cauda equina, and it is histologically similar to the filum terminale of amphibians and mammals. The spinal cords of other teleosts, the sun-fish and angler, also are abbreviated and possess a filum terminale and cauda equina. These orders possess an enormous head and short trunk. However, the correlation between this body form and an abbreviated cord is not causal, since the tetraodontiform species described here show ordinary body proportions. The spinal cord may be abbreviated in tetraodontiform fishes in general.     

Fine needle aspiration cytodiagnosis of subcutaneous sacrococcygeal myxopapillary ependymoma. A case report.

A tumor located subcutaneously over the coccyx of a 32-year-old woman was diagnosed by fine needle aspiration (FNA) cytology as a myxopapillary ependymoma originating in the soft tissue. The FNA smears showed characteristic papillary structures, consisting of a central mucinous core surrounded by cuboidal-to-columnar cells, and scattered ependymal cells. The excised tumor was connected to neither the filum terminale nor the cauda equina. Histopathologic study confirmed the cytologic findings.     

The shortened spinal cord in tetraodontiform fishes

In teleosts, the spinal cord generally extends along the entire vertebral canal. The Tetraodontiformes, in which the spinal cord is greatly reduced in length with a distinct long filum terminale and cauda equina, have been regarded as an aberration. The aims of this study are: 1) to elucidate whether the spinal cord in all tetraodontiform fishes shorten with the filum terminale, and 2) to describe the gross anatomical and histological differences in the spinal cord among all families of the Tetraodontiformes. Representative species from all families of the Tetraodontiformes, and for comparison the carp as a common teleost, were investigated. In the Triacanthodidae, Triacanthidae, and Triodontidae, which are the more ancestral taxa of the Tetraodontiformes, the spinal cord extends through the entire vertebral canal. In the Triacanthidae and Triodontidae, the caudal half or more spinal segments of the spinal cord, however, lack gray matter and consist largely of nerve fibers. In the other tetraodontiform families, the spinal cord is shortened forming a filum terminale with the cauda equina, which is prolonged as far as the last vertebra. The shortened spinal cord is divided into three groups. In the Ostraciidae and Molidae, the spinal cord tapers abruptly at the cranium or first vertebra forming a cord‐like filum terminale. In the Monacanthidae, Tetraodontidae, and Diodontidae, it abruptly flattens at the rostral vertebrae forming a flat filum terminale. The spinal cord is relatively longer in the Monacanthidae than that in the other two families. It is suggested by histological features of the flat filum terminale that shortening of the spinal cord in this group progresses in order of the Monacanthidae, Tetraodontidae, and Diodontidae. In the Balistidae and Aracanidae, the cord is relatively long and then gradually decreased in dorso‐ventral thickness. J. Morphol. 276:290–300, 2015. © 2014 Wiley Periodicals, Inc.     

Comparative scanning and transmission electron microscopy studies of the ependyma of the central canal in the spinal cord of primates. I. Electron optical image of the ependyma in the central canal of the spinal cord of the callithrix monkey (Callithrix jacchus, Linné 1758)

The ependyma lining the central canal of the spinal cord of adult males and females monkey, Callithrix jacchus, was examined by scanning and transmission electron microscopy. The cross section of the lumen of the central canal are round, oval, or triangular. Light and dark ependymal cells, depending on the density of the cytoplasm, were found. The light ependymal cells are fewer than the dark cells. The ependyma cytoplasm contained numerous mitochondria, filamentous structures, one or more well-developed Golgi-complexes, vesicles of the smooth endoplasmic reticulum, ribosomes, lysosomes, multivesicular bodies, profiles of the rough endoplasmic reticulum, large osmophilic bodies, and microtubules. The nuclei of the ependyma cells usually have a simple, regular round or oval shape. They occupy a relatively large portion of the cell volume and lie in the central or mediobasal position. Some of the nuclei show deep invaginations into the karyoplasm. Most of the mitochondria occupy mainly the supranuclear portion of the apical cytoplasm. There are of the crista-typ. Ribosomes occur free in the cytoplasm, but some attached to the profiles of the rough endoplasmic reticulum or being arranged as polysomes. The filamentous structures are generally prominent cytoplasmic components and are distributed at the apical, lateral, or basal region of the ependymocytes. They are grouped into bundles and arranged in parallel arrays. Some of these bundles reach the plasmamembrane at the free lumina of the central canal, others take contact to the filamentous structures of the zonulae adherentes of the junctional complex below the free surface. The granular endoplasmic reticulum shows specializations. There profiles surrounding granular substances and widely distributed granulations in connection with the nuclear envelope. The functional significance of the deposition of these granulations is still unknown. The luminal surface of the ependymocytes bears many microvilli and cilia. The cilia are regularly arranged in cranio-caudal direction. Each cilium has the typical (9 + 2)-subfibres. The intercellular space at the surface of the ependymal layer shows a single zonula adherens or zonulae adherentes in the row. Tight junctions and gap junctions were not found in the material examined. Cell processes of liquor contacting neurons between adjacent ependyma cells, protruding into the lumen of the central canal, could be observed. The termination of these neurons contains accumulations of mitochondria in the central part, large amounts of vesicles, and small dense bodies. They have short microvilli and some stereocilia at the free surface.(ABSTRACT TRUNCATED AT 400 WORDS)     

Preliminary electron microscopic observations on ependymal cells in the caudal segment of the filum terminale and the ampulla caudalis of Macaca fascicularis and Cercopithecus griseoviridis (primates, Cercopithecidae)

In a previous paper, the concept of the terminal organ (TO) of the subcommissural complex was forwarded. Functionally this complex is a neuro (glio-) hemal organ which serves to discharge the Reissner's secretory material into the systemic circulation. The TO is characterized by structural specializations that make feasible the discharge and chemical decomposition of the secretory material stowed in the massa caudalis (MC). The TO is probably not only the ampulla caudalis (AC); it may comprise even parts of the filum terminale next to the AC. The boundary of the TO is uncertain as yet. It cannot be precluded that the AC, which itself varies in shape and size, is just a receptaculum massae caudalis. The material of the MC escapes from the AC either through apertures of the wall of the AC or of the filum terminale (Neuropori caudalis, slit-shaped gaps). It is also likely that the secretory material becomes chemically decomposed in the AC and is intra- (trans-) cellularly discharged. In this connexion, certain ependymal cells may be of significance. These cells exhibit large, tongue-shaped central projections (temporarily developed?) which bear a considerable number of long microvilli. The significance of these cells probably lies in the enlargement of the cell surface bathing in the CSF which contains the MC. These cells are most abundant in the area of the TO; single, isolated cells of the same type occur in other areas of the ependyma of some primates. This would indicate that the TO does not contain special types of cells not found in other parts of the ependyma, but that the TO differs from other ependymal regions in the density of peculiar cell types.     

Fine structure of the rhombencephalic tela of the bullfrog,Rana catesbeiana

Summary The posterior rhombencephalic tela choroidea of the bullfrog was examined by electron microscopy. This membrane, the pia-ependymal roof of the caudal hindbrain, contains a large central region characterized by cuboidal ependymal cells which surround sizable microscopic apertures — the interependymal pores.Ultrastructurally ependymal cells of this area are characterized by infrequent apical microvilli and cilia. They contain irregularly shaped nuclei and few cytoplasmic organelles that are largely apical in position. The most striking feature is an abundance of cytoplasmic filaments forming an extensive cytoskeleton. Laterally these cells are joined by numerous elaborate desmosomes. The majority of the ependymal cells have a basal lamina consisting of single, double, or triple laminae lying parallel to the basal plasma membrane.Several unusual specializations are seen at the margins of the interependymal pores. The ependymal cells have lateral cytoplasmic processes that form the actual border of each pore. These processes originate from the apical surface of the cell and partially enclose an elaborate network of basal lamina associated with the interependymal pores.These findings demonstrate microscopic apertures in the roof of the fourth ventricle in the bullfrog that are associated with an unusual form of supportive ependyma.     

Distribution of dipeptidyl peptidase II (Dpp II) in rat spinal cord

The histochemical localization of dipeptidyl peptidase II (Dpp II; E.C. 3.4.14.2) activity was demonstrated at the light microscope level in the rat spinal cord. Prominent staining was observed in motoneurons of the ventral horn and in medium to large neurons in the deep laminae of the dorsal horn, the intermediate gray, and in lamina X surrounding the spinal canal. Within neurons, Dpp II was localized largely in cell perikarya and large primary dendrites with no staining observed in cell nuclei. Neurons in the superficial dorsal horn lack Dpp II enzyme activity. Nonneuronal elements which also stained prominently were pericytes associated with blood vessels and ependymal cells lining the lumen of the spinal canal. A few oligodendrocytes and astrocytes were also stained, but they represented a minor component of the total amount of Dpp II activity. Following ventral root injury, Dpp-II-containing motoneurons degenerate; some glial cells in the region of degenerating neurons become Dpp II positive. The localized distribution of Dpp II in spinal cord neurons suggests that this proteolytic enzyme may play a role in the metabolism of an unidentified neuropeptide.     

Early neurogenesis during caudal spinal cord regeneration in adult Gekko japonicus

Gekko japonicus undergoes dramatic changes in the caudal spinal cord after tail amputation. The amputation induces cell proliferation in the caudal ependymal tube. We performed hematoxylin and eosin staining at different time points in the regeneration process to investigate the morphological characterization of the regenerated appendages. The central canal extended to the blastema post-amputation and the cartilage and muscle tissue appeared 3 weeks after injury. We performed the bromodeoxyuridine (BrdU) incorporation assay to detect proliferating cells during the regeneration process. BrdU positive cells were detected in the peri-central canal. Furthermore, nestin and neuron-specific enolase (NSE) immunocytochemistry were applied to detect neural stem/progenitor cells and neurons. Two weeks after injury, nestin-positive cells undergoing proliferation were located outside of the ependymal tube, and NSE positive cells appeared after 3 weeks of amputation. These data suggest that neurogenesis is an early event during caudal spinal cord regeneration in gecko.     

Distribution and characterization of progenitor cells within the human filum terminale

Background

Filum terminale (FT) is a structure that is intimately associated with conus medullaris, the most caudal part of the spinal cord. It is well documented that certain regions of the adult human central nervous system contains undifferentiated, progenitor cells or multipotent precursors. The primary objective of this study was to describe the distribution and progenitor features of this cell population in humans, and to confirm their ability to differentiate within the neuroectodermal lineage.

Methodology/Principal Findings

We demonstrate that neural stem/progenitor cells are present in FT obtained from patients treated for tethered cord. When human or rat FT-derived cells were cultured in defined medium, they proliferated and formed neurospheres in 13 out of 21 individuals. Cells expressing Sox2 and Musashi-1 were found to outline the central canal, and also to be distributed in islets throughout the whole FT. Following plating, the cells developed antigen profiles characteristic of astrocytes (GFAP) and neurons (β-III-tubulin). Addition of PDGF-BB directed the cells towards a neuronal fate. Moreover, the cells obtained from young donors shows higher capacity for proliferation and are easier to expand than cells derived from older donors.

Conclusion/Significance

The identification of bona fide neural progenitor cells in FT suggests a possible role for progenitor cells in this extension of conus medullaris and may provide an additional source of such cells for possible therapeutic purposes.Filum terminale, human, progenitor cells, neuron, astrocytes, spinal cord.     

Adrenergic neurons in the spinal cord of the pike (Esox lucius) and their relation to the caudal neurosecretory system

Summary The lower spinal cord including the caudal neurosecretory system of the pike (Esox lucius) was investigated by means of light and electron microscopy and also with the fluorescence histochemical method of Falck and Hillarp for the visualization of monoamines. A system of perikarya displaying a specific green fluorescence of remarkably high intensity is disclosed in the basal part of the ventrolateral and lateral ependymal lining of the central canal. The area corresponding to the upper half of the urophysis has most cells; their number decreases caudally and cranially. A considerable number of their beaded neurites reach the neurosecretory neurons by different routes but are only occasionally present in the actual neurohemal region. An intensely fluorescent dendritic process is sometimes observed terminating with a bulbous enlargement at the ependymal surface in the central canal. Besides small, electron lucid vesicles in the terminal parts of the axons, the neurons contain numerous large dense-core vesicles which can apparently take up and store 5-hydroxydopa (5-OH-dopa) and 5-hydroxydopamine (5-OH-DA). These neurons are thought to be adrenergic and to contain a primary catecholamine, possibly noradrenaline.The varicosities of the adrenergic terminals are repeatedly observed contiguous to some of the neurosecretory axons, the membrane distance at places of contacts generally ranging from 150–200 Å. Another type of nerve terminals that contain only small empty vesicles, also after pretreatment with 5-OH-dopa or 5-OH-DA, are frequent among the neurosecretory neurons. These axons establish synaptic contacts with membrane thickenings on most of the neurosecretory neurons. Thus it seems that the neurosecretory neurons are innervated by neurons morphologically similar to cholinergic neurons and that part of them receive an adrenergic innervation, which supports the view hat the caudal neurosecretory cells do not constitute a functionally homogeneous population.Supported by the Deutsche Forschungsgemeinschaft and the Joachim-Jungius Gesellschaft zur Förderung der Wissenschaften, Hamburg.Supported by the Swedish Natural Research Council (No. 99-35). This work was in part carried out within a research organization sponsored by the Swedish Medical Research Council (Projects No. B70-14X-56-06 and B70-14X-712-05).Supported by the Deutsche Forschungsgemeinschaft and USPHS Research Grant TW 00295-02.     

Ependyma and meninges of the spinal cord of the mouse

Summary In addition to ependymal epithelial cells, numerous tanycytes are found along the entire central canal of the mouse. These tanycytes are arranged in clusters in the cervical, thoracic and lumbar segments of the spinal cord. In the conus medullaris, tanycytes separate and ensheath bundles of myelinated and unmyelinated axons; their processes take part in the formation of the stratum marginale gliae. In the caudal part of the spinal cord, the ventral wall of the central canal is thin and some areas are reduced to a single-cell thickness. In this region, ependymal cells participate directly in the formation of the stratum marginale gliae.The meninges consist of the intima piae, the pia mater, the arachnoid, a subdural neurothelium and the dura mater. The subarachnoid space appears occluded and opens only around the spinal roots. In the vicinity of the spinal ganglia, the dura mater, the subdural neurothelium and the arachnoid form a cellular reticulum.     

Cytochemical localization of alkaline phosphatase in the ependyma of the rat medulla oblongata

Summary The ependyma of the IVth ventricle and the central canal of the rat medulla oblongata was investigated using the cytochemical technique for alkaline phosphatase (AlPase) which revealed two types of ependymal cells in the medulla. The central canal type of the ependymal cell occupying the dorsal part of the central canal in the lower medulla exhibited intense AlPase activity with light microscopy. These cells had reaction products in all plasma membranes, including the microvilli and the cilia at the luminal cell surface. Some cells appeared to be tanycytes, since the process reached the basement membrane of the parenchymal blood vessel. The ventricular type of ependymal cells, which form the floor of the IVth ventricle and the central canal, contained no reaction products in any structure of the luminal cell surface.The possible relationship between the cerebrospinal fluid and the nervous tissues through the ependymal linings is discussed.     

Morphological changes in the central canal of the cat after kaolin injection into the cisterna magna

40 adult cats were made hydrocephalic by intracisternal injection of 200 mg Kaolin. 34 survived between 24 hours to 4 months. In 19 cases a ventriculostomy was carried out, whereby in 13 animals a contrast filling of the central canal occurred. The contrast medium injected into the ventricles entered the external CSF-space in the lumbo-sacral junction of the filum terminale. Light- and electron-microscopic studies showed adaptive structural changes of the central canal epithelium in the early stages. In later stages massive destructions of ependyma and spinal cord parenchyma were found.