Microscopic focus on ependymal cells of the spinal cord of the one-humped camel (Camelus dromedarius): Histological, immunohistochemical, and transmission microscopic study

The current study was designed to give a complete microscopic description of the ependymal cells of the one-humped camel (Camelus dromedarius) using histological, immunohistochemical, and transmission microscopic descriptions of the ependymal cells of the fresh 35 spinal cord samples immediately after their slaughtering. In our findings, the central canal of the spinal cord was lined by multilayered stratified cuboidal or columnar ependymal cells. The ependymal cells had an irregular striated border at their free surface. The ependymal cells do not exhibit a basement membrane. The simple oval nucleus was occupied a large part of the cell with spherical mitochondria. The apical surface of the ependymal cells possesses long cilia; each cilium was bounded by an evagination of the luminal plasma membrane. Some ependymal cells had minute finger-like projections on their luminal plasma membrane. In the perinuclear zone of ependymal cells, many cristiform mitochondria, free ribosomes, and Golgi complexes usually occur. Vacuoles with homogenous and clear fluid were observed. The lateral surface of the adjacent ependymal cells exhibits several tight junctions represented by zonulae occludens and adherens. There were many desmosomes between the neighboring ependymal cells. A perinuclear whorl of filaments fills the lateral part of these ependymal cells. The ependymal cells revealed a clear immunohistochemical reaction with proliferating cell nuclear antigen and nestin stain. There were no obvious differences between the different segments of the spinal cord. Our data concluded that the ependymal cells display clear differences in anatomy as well as ultrastructure that may reflect their distinct functional activity.

Autoradiography and inmmunolabeling suggests that lizard blastema contains arginase-positive M2-like macrophages that may support tail regeneration

BACKGROUND

The regenerating blastema of the tail in the lizard Podarcis muralis contains numerous macrophages among the prevalent mesenchymal cells. Some macrophages are phagocytic but others are devoid of phagosomes suggesting that they have other roles aside phagocytosis.

METHODS

The presence of healing macrophages (M2-like) has been tested using autoradiographic, immunohistochemical and ultrastructural studies.

RESULTS

Autoradiography shows an uptake of tritiated arginine in sparse cells of the blastema and in the regenerating epidermis. Bioinformatics analysis suggests that epitopes for arginase-1 and -2, recognized by the employed antibody, are present in lizards. Immunofluorescence shows sparse arginase immunopositive macrophages in the blastema and few macrophages also in the apical wound epidermis. The ultrastructural study shows that macrophages contain dense secretory granules, most likely inactive lysosomes, and small cytoplasmic pale vesicles. Some of the small vesicles are arginase-positive while immunolabeling is very diffuse in the macrophage cytoplasm.

CONCLUSIONS

The presence of cells incorporating arginine and of arginase 1-positive cells suggests that M2-like macrophages are present among mesenchymal and epidermal cells of the regenerative tail blastema. M2-like macrophages may promote tail regeneration differently from the numerous pro-inflammatory macrophages previously detected in the scarring limb. The presence of M2-like macrophages in addition to hyaluronate, support the hypothesis that the regenerative blastema of the tail in lizards is an immuno-privileged organ where cell proliferation and growth occur without degenerating in a tumorigenic outgrowth.

Labelling of individual ependymal areas in lateral ventricles of human brain: ependymal tables

Different types of ependymal areas were studied and labelled in the human brain lateral ventricle. Periventricular structures were included in coining the names of the ependymal areas because they represent a basic and stable part of brain nerve structures suitable for the sake of clarity of localization of the ependyma. The labelling of individual ependymal areas was composed from letters: "Lv" (lateral ventricle); "E" (ependymal area) and letters for abbreviations of the closest periventricular structure, e.g. the septum pellucidum is "sp". The labelling for ependymal area over the septum pellucidum is thus "LvE-sp". The studied types of ependymal areas were arranged in so‑called ependymal tables for cornu anterius, pars centralis, cornu inferius and cornu posterius of the human lateral ventricle. Labelling of individual ependymal areas allows for better localization and characterisation of these areas in future studies carried out by various methods (e.g. morphological, biological, molecular) and will prevent from using misnomers with different types of ependymal areas in norm as well as in pathology (Tab. 5, Fig. 6, Ref. 22). Text in PDF www.elis.sk.

On the origin of the term ependyma

The term ependyma is considered as a translation of the expression integumentum ventriculorum cerebri or Überzug der Hirnhöhlen [the lining of the brain ventricles] in German used by the Wenzel brothers (1812). The first documented usage of this term is found in the work of the German anatomist Karl Ernst Bock from the year 1839, but nobody has ever claimed authorship of the word. Formulations such as "so-called" are used in connection with the term, avoiding any reference to a specific originator. The term first started being used in anatomical literature written in German. In its subsequent history, various interpretations of the meaning of the term have emerged, and certain attempts have also been made to change its formal aspect.

[STRUCTURAL ORGANIZATION OF THE PROCESSES OF EPENDYMO- CYTES LINING THE LATERAL VENTRICLES OF THE RAT BRAIN]

The aim of this study was to examine the structural organization of processes of ependymocytes lining the lateral ventricles of the rat brain using vimentin immunocytochemistry and confocal laser microscopy. The study was performed on adult male rats (n = 3). It was found that most typical ependymocytes had basal processes, while 1/3 of these cells had none. Some vimentin-immunopositive tanycyte-like cells with long processes appoaching blood vessels, were found inside the ependymal lining In some typical ependymocytes, cytroskeleton wa s formed by intermediate filaments of mixed type containing both vimentin and glial fibrillary acidic protein.

FLAIR images at 7 Tesla MRI highlight the ependyma and the outer layers of the cerebral cortex

OBJECTIVES

Fluid-attenuated inversion recovery (FLAIR) imaging is an important clinical 'work horse' for brain MRI and has proven to facilitate imaging of both intracortical lesions as well as cortical layers at 7T MRI. A prominent observation on 7T FLAIR images is a hyperintense rim at the cortical surface and around the ventricles. We aimed to clarify the anatomical correlates and underlying contrast mechanisms of this hyperintense rim.

MATERIALS AND METHODS

Two experiments with post-mortem human brain tissue were performed. FLAIR and T2-weighted images were obtained at typical in vivo (0.8mm isotropic) and high resolution (0.25mm isotropic). At one location the cortical surface was partly removed, and scanned again. Imaging was followed by histological and immunohistochemical analysis. Additionally, several simulations were performed to evaluate the potential contribution from an artifact due to water diffusion.

RESULTS

The hyperintense rim corresponded to the outer - glia rich - layer of the cortex and disappeared upon removal of that layer. At the ventricles, the rim corresponded to the ependymal layer, and was not present at white matter/fluid borders at an artificial cut. The simulations supported the hypothesis that the hyperintense rim reflects the tissue properties in the outer cortical layers (or ependymal layer for the ventricles), and is not merely an artifact, although not all observations were explained by the simulated model of the contrast mechanism.

CONCLUSIONS

7T FLAIR seems to amplify the signal from layers I-III of the cortex and the ependyma around the ventricles. Although diffusion of water from layer I into CSF does contribute to this effect, a long T2 relaxation time constant in layer I, and probably also layer II-III, is most likely the major contributor, since the rim disappears upon removal of that layer. This knowledge can help the interpretation of imaging results in cortical development and in patients with cortical pathology.

Postnatal deletion of Numb/Numblike reveals repair and remodeling capacity in the subventricular neurogenic niche

Neural stem cells are retained in the postnatal subventricular zone (SVZ), a specialized neurogenic niche with unique cytoarchitecture and cell-cell contacts. Although the SVZ stem cells continuously regenerate, how they and the niche respond to local changes is unclear. Here we generated nestin-creER(tm) transgenic mice with inducible Cre recombinase in the SVZ and removed Numb/Numblike, key regulators of embryonic neurogenesis from postnatal SVZ progenitors and ependymal cells. This resulted in severe damage to brain lateral ventricle integrity and identified roles for Numb/Numblike in regulating ependymal wall integrity and SVZ neuroblast survival. Surprisingly, the ventricular damage was eventually repaired: SVZ reconstitution and ventricular wall remodeling were mediated by progenitors that escaped Numb deletion. Our results show a self-repair mechanism in the mammalian brain and may have implications for both niche plasticity in other areas of stem cell biology and the therapeutic use of neural stem cells in neurodegenerative diseases.

Role of androgens and glucocorticoids in the regulation of diazepam-binding inhibitor mRNA levels in male mouse hypothalamus

In peripheral organs, gonadal and adrenal steroids regulate diazepam-binding inhibitor (DBI) mRNA expression. In order to further investigate the involvement of peripheral steroid hormones in the modulation of brain DBI mRNA expression, we studied by semiquantitative in situ hybridization the effect of adrenalectomy (ADX) and castration (CX) and short-term replacement therapy on DBI mRNA levels in the male mouse hypothalamus. Cells expressing DBI mRNA were mostly observed in the arcuate nucleus, the median eminence and the ependyma bordering the third ventricle. In the median eminence and the ependyma bordering the third ventricule, the DBI gene expression was decreased in ADX rats and a single injection of corticosterone to ADX rats induced a significant increase in DBI gene expression at 3 and 12 h time intervals without completely restoring the basal DBI mRNA expression observed in intact mice. In the arcuate nucleus, ADX and corticosterone administration did not modify DBI mRNA expression. CX down-regulated DBI gene expression in the ependyma bordering the third ventricle. The administration of dihydrotestosterone (3-24 h) completely reversed the inhibitory effect of CX. In the median eminence and arcuate nucleus, neither CX or dihydrotestosterone administration modified DBI mRNA levels. These results suggest that the effects of glucocorticoids on the hypothalamo-pituitary-adrenocortical axis and androgens on the hypothalamo-pituitary-gonadal axis are mediated by DBI.

Microscopic Stucture of the Lamina Terminalis: Implications for Microsurgical Third Ventriculostomy

OBJECTIVE

The neurosurgical approach through the lamina terminalis (LT) is a commonly used technique for management of the third ventricle region pathology. Furthermore, LT fenestration is a recommended procedure during surgery of ruptured intracranial aneurysms. Though the LT is a rudimentary structure in adult human brain, its neurosurgical significance is eliciting increasing interest. The aim of the presented study is to characterize the LT histologically, with special attention to the previously recommended area of LT fenestration and to the localization and structure of the organum vasculosum lamina terminalis (OVLT).

METHODS

The study was performed on tissue sampled from eight formalin-fixed brains. Paraffin sections taken from various levels of the LT were routinely stained with hematoxylin and eosin (H&E) and by immunohistochemical methods.

RESULTS

The LT in the inferior part bordering the optic recess and immediately above the optic chiasm exhibited paucicellular, mainly fibrillar, glial tissue with scanty neural elements and small vessels. At about halfway along the length of the LT an area of loose structure, with an increased number of glial cells, small neurons and thin-walled vessels corresponding to the OVLT was observed. In the majority of examined cases the OVLT was poorly developed and was therefore sometimes overlooked. The superior segment of the LT near the anterior commissure disclosed again paucicellular and slightly loosened fine fibrillar tissue.

CONCLUSIONS

The results of the present microscopic study confirm the opinion that the inferior segment of the LT is the most convenient place for safe incision. Its thinnest middle part immediately above the optic recess is composed mainly of gliotic tissue. Above, prominent loosened tissue and the rather rudimental structure of the OVLT seem to be additional favorable factors for a safe fenestration of the LT.

Anatomy and physiology of the leptomeninges and CSF space

The arachnoid membrane and pia mater are the two membranous layers that comprise the leptomeninges. Cerebrospinal fluid is made within the ventricular system by cells of the choroid plexus and ependyma. This chapter describes in detail the normal anatomic structure and physiologic interactions of the cerebrospinal fluid and leptomeningeal space that are critical to our understanding and treatment of leptomeningeal metastases.

Synthesis of transthyretin by the ependymal cells of the subcommissural organ

Transthyretin (TTR) is a protein involved in the transport of thyroid hormones in blood and cerebrospinal fluid (CSF). The only known source of brain-produced TTR is the choroid plexus. In the present investigation, we have identified the subcommissural organ (SCO) as a new source of brain TTR. The SCO is an ependymal gland that secretes glycoproteins into the CSF, where they aggregate to form Reissner's fibre (RF). Evidence exists that the SCO also secretes proteins that remain soluble in the CSF. To investigate the CSF-soluble compounds secreted by the SCO further, antibodies were raised against polypeptides partially purified from fetal bovine CSF. One of these antibodies (against a 14-kDa compound) reacted with secretory granules in cells of fetal and adult bovine SCO, organ-cultured bovine SCO and the choroid plexus of several mammalian species but not with RF. Western blot analyses with this antibody revealed two polypeptides of 14 kDa and 40 kDa in the bovine SCO, in the conditioned medium of SCO explants, and in fetal and adult bovine CSF. Since the monomeric and tetrameric forms of TTR migrate as bands of 14 kDa and 40 kDa by SDS-polyacrylamide gel electrophoresis, a commercial preparation of human TTR was run, with both bands being reactive with this antibody. Bovine SCO was also shown to synthesise mRNA encoding TTR under in vivo and in vitro conditions. We conclude that the SCO synthesises TTR and secretes it into the CSF. Colocalisation studies demonstrated that the SCO possessed two populations of secretory cells, one secreting both RF glycoproteins and TTR and the other secreting only the former. TTR was also detected in the SCO of bovine embryos suggesting that this ependymal gland is an important source of TTR during brain development.

The sensory circumventricular organs of the mammalian brain

The brain's three sensory circumventricular organs, the subfornical organ, organum vasculosum of the lamina terminalis and the area postrema lack a blood brain barrier and are the only regions in the brain in which neurons are exposed to the chemical environment of the systemic circulation. Therefore they are ideally placed to monitor the changes in osmotic, ionic and hormonal composition of the blood. This book describes their. General structure and relationship to the cerebral ventricles Regional subdivisions Vasculature and barrier properties Neurons, glia and ependymal cells Receptors, neurotransmitters, neuropeptides and enzymes Neuroanatomical connections Functions.

The distribution and morphological characteristics of serotonergic cells in the brain of monotremes

The distribution and cellular morphology of serotonergic neurons in the brain of two species of monotremes are described. Three clusters of serotonergic neurons were found: a hypothalamic cluster, a cluster in the rostral brainstem and a cluster in the caudal brainstem. Those in the hypothalamus consisted of two groups, the periventricular hypothalamic organ and the infundibular recess, that were intimately associated with the ependymal wall of the third ventricle. Within the rostral brainstem cluster, three distinct divisions were found: the dorsal raphe nucleus (with four subdivisions), the median raphe nucleus and the cells of the supralemniscal region. The dorsal raphe was within and adjacent to the periaqueductal gray matter, the median raphe was associated with the midline ventral to the dorsal raphe, and the cells of the supralemniscal region were in the tegmentum lateral to the median raphe and ventral to the dorsal raphe. The caudal cluster consisted of three divisions: the raphe obscurus nucleus, the raphe pallidus nucleus and the raphe magnus nucleus. The raphe obscurus nucleus was associated with the dorsal midline at the caudal-most part of the medulla oblongata. The raphe pallidus nucleus was found at the ventral midline of the medulla around the inferior olive. Raphe magnus was associated with the midline of the medulla and was found rostral to both the raphe obscurus and raphe pallidus. The results of our study are compared in an evolutionary context with those reported for other mammals and reptiles.

Increased number of BrdU-labeled neurons in the rostral migratory stream of the estrous prairie vole

In the mammalian forebrain, most neurons originate from proliferating cells in the ventricular zone lining the lateral ventricles, including a discrete area of the subventricular zone in which neurogenesis continues into adulthood. The majority of the cells generated in the anterior portion of the subventricular zone (SVZa) are neuronal precursors with progeny that migrate to the olfactory bulb (OB) along a pathway known as the rostral migratory stream (RMS). The list of factors that influence the proliferation and survival of neurons in the adult brain remains incomplete, but previous studies have implicated neurotrophins in mammals and estrogen in birds. This study examined the effect of estrus induction on the proliferation of SVZa neurons in female prairie voles. Prairie voles, unlike many other rodents, are induced into estrus by chemosensory cues from a male. This olfactory-mediated process results in an increase in serum estrogen levels and the consequent induction of behavioral estrus (sexual receptivity). Female prairie voles induced into estrus by male exposure had a 92% increase in BrdU-labeled cells in the SVZa compared to females exposed to a female. Double-label immunocytochemical studies demonstrated that 80% of the BrdU-labeled cells in the RMS displayed a neuronal phenotype. Ovariectomized females exposed to a male did not show an increase in serum estrogen or BrdU labeling in the RMS. Conversely, ovariectomized females injected with estrogen were sexually receptive and had more BrdU-labeled cells in the RMS than oil-injected females. These data suggest that, in female prairie voles, estrus induction is associated with increased numbers of dividing cells in the RMS, possibly via an estrogen-mediated process.

RF penetration in ultra high field MRI: challenges in visualizing details within the center of the human brain

PURPOSE

The purpose of this work is to discuss radio frequency (RF) penetration and its relevance to imaging the human head and to acquire images containing intricate structures located at the center of the brain with ultra high field MRI (UHFMRI).

METHOD

A simple plane wave analysis of RF penetration was performed based on Maxwell equations as a function of frequency up to 900 MHz. Gradient-recalled images were acquired at 8 T (340 MHz) using an RF resonator operating in quadrature. Typical acquisition parameters were as follows: TR = 750 ms, TE = 17 ms, slice thickness = 2 mm, FOV = 20 x 20 cm, matrix = 1,024 x 1,024. The specific absorption rate was well below 1 W/kg.

RESULTS

A simple analytical treatment, for a plane wave up to 900 MHz, reveals a lack of decreasing penetration depth with frequency beyond 200 MHz. Gradient-recalled echo images acquired from the human head displayed good contrast, homogeneity, and resolution. Importantly, excellent structural detail was observed on the resulting MR images, demonstrating that RF penetration is not a problem at 8 T. Images reveal excellent detail including the red nucleus, anterior commissure, fornix, mamillary body, pineal gland, and ependymal lining of the fourth ventricle.

CONCLUSION

Structures located at the center of the human brain can be clearly visualized at 8 T with no detectable loss in signal intensity arising from RF penetration. The ability to examine these structures with UHFMRI will provide a powerful new modality for diagnostic radiology.

[Characteristics of the ependyma in various parts of the subcommissural organs in rats]

In this work the authors have researched ependyma of some parts of subcommissural organ of rats by optic microscopy. 4% formaldehyde was injected in vivo in carotid arteries. After immolation their brains were extracted together with brain meninges and embedded in celiodine. Celoidine blocks have been sliced and then coloured by Nissle's method. Horizontal and frontal brain dissections were performed with a purpose to acquire a good sight into the subcommissural organ. On the basis of optic microscopy of the examined material, numerous morphological variations in the size and appearance of subcommissural organ were determined as well as the presence of many layers of ependymal cells close to the posterior commissura.

Localization of a G protein Gi2 in the cilia of rat ependyma, oviduct and trachea

In previous studies, the localization of a pertussis toxin-sensitive G protein was demonstrated in ependymal cilia, but the identification of the subtype of G protein was inconsistent. To clarify this issue, we studied the localization of Goalpha, Gi1alpha, Gi3alpha and Gi2alpha in the ciliated ependymal cells and in the cilia of some other tissues of rats using specific antibodies. The cilia of the ependymal cells that line the ventricular cavity of the brain were intensely immunoreactive for Gi2alpha, but not for Goalpha, Gi1alpha or Gi3alpha. Immunoblot analysis demonstrated higher levels of Gi2alpha in the ependymal cilia-rich pellet than in the motor area of the parietal cortex. At the ultrastructural level, the immunoreactivity specific for Gi2alpha was found predominantly in the cilia, but rarely in the microvilli or the basal bodies of ependymal cells. In cross-sections, the immunoreactivity specific for Gi2alpha was observed only in cell membranes, in particular, in the inner electron-dense leaflet of the trilaminar structure. In addition to that in the ependymal cilia, such specific localization of Gi2alpha was observed in the motile cilia in other tissues, including the oviduct and trachea. By contrast, the stereocilia in the ductus deferens were not immunopositive for Gi2alpha. These findings suggest that Gi2 might play an important role in the signal transduction in ciliary membrane-associated function(s) of the ependymal cells, oviduct and trachea.

Central innervation of the rat ependyma and subcommissural organ with special reference to ascending serotoninergic projections from the raphe nuclei

The subcommissural organ (SCO) and the cerebral ependyma receive serotoninergic innervation, but little is known about their origin in the raphe nuclei. Application of the retrograde tracer cholera toxin subunit B (ChB) in the third ventricle resulted in uptake in ependymal axons and backfilling of perikarya in the dorsomedian part of the dorsal raphe nucleus, immediately under the caudal aqueduct. By using dual staining with antisera against serotonin and ChB, a portion of the retrogradely labeled neurons was observed to co-store serotonin. Phaseolus vulgaris-leucoagglutinin (PHA-L) was injected into different raphe nuclei to fill the neurons in the same areas where the retrogradely labeled neurons were found. PHA-L injection in the midline of the dorsal raphe nucleus gave rise to ascending axonal processes in the mesencephalic central gray, from where they entered the periventricular strata and the third ventricular ependyma. In the cerebral ependyma, large numbers of positive fibers were consistently found in the ventral part of the lateral ventricles and in the dorsal part of the third ventricle. A large number of PHA-L-immunoreactive fibers were observed in the hypendymal layer of the lateral part of the SCO. Terminal fibers near the ependymal cells were also observed. In all cases, the PHA-L injections labeled innervating fibers both within the ependyma and in the SCO, whereas injections into the median raphe nucleus or in other raphe nuclei (i.e., the raphe pallidus and the raphe pontis) labeled fibers neither in the SCO nor in the ependyma. This study shows that a specific group of predominantly serotoninergic neurons innervates both the ependyma and the SCO and is probably involved in cerebrospinal fluid regulation.

Specific potentialities of embryonic rat serotonergic neurons to innervate different periventricular targets in the adult brain

During the development of the central nervous system, neurons are directed by both genetic and environmental factors to differentiate and form connections with their targets. We took advantage of the abundant homogeneous serotonergic innervations of the ependyma forming the supra- and subependymal plexuses to investigate possible commitment of embryonic neurons to innervate specific targets during axogenesis in the rat. The origin of the supraependymal innervation was determined by retrograde transport of cholera toxin (CT) from the ventricles. The supraependymal plexuses of the fourth ventricle mainly originated from neurons in the dorsocaudal region of the raphe dorsalis (DRN), while the rostral DRN and raphe centralis (CRN) contained perikarya projecting into the third ventricle. This suggested the existence, along the rostrocaudal axis of the raphe, of different neuronal subsets able to form distinct supraependymal plexuses in the third or fourth ventricle. To determine whether serotonergic neurons were committed to innervate specific areas of the ependyma, different embryonic metencephalic segments (rostral, median, or caudal) from 14-day-old rat embryos were independently grafted into the third or fourth ventricle of an adult brain in which the serotonergic neurons had been previously destroyed. The distinctive patterns of re-innervation specific to each of grafted segments indicate that subsets of embryonic serotonergic neurons are indeed committed to innervate certain restricted ependymal areas of the adult brain, presumably in response to different neurotropic and/or neurotrophic cues.

Tropism of serotonergic neurons towards glial targets in the rat ependyma

During development, recognition mechanisms between neurons and their targets are necessary for the formation of the neuronal network. Neural connections are synaptic or non-junctional. Both types of communication can be found between neurons and glial elements in the periventricular walls. Serotonergic fibers form synaptic contacts on the specialized ependymocytes of the subcommissural organ, a structure which forms the roof of the third ventricle at its junction with the aqueduct. A network of non-junctional fibers containing both GABA and serotonin spread between the cilia of the classical ependymocytes in the ventricles. These anatomical, morphological and biochemical features suggest a tropism and specific recognition mechanisms between glial elements and serotonergic neurons. This hypothesis can be tested by the study of the innervation of the subcommissural organ and the classical ependyma by grafted embryonic neurons after a chemical destruction of the serotonergic endogenous innervation. Solid implants or cell suspensions prepared from embryonic metencephalon were transplanted to either the third ventricle or the periventricular gray matter in 5,7-dihydroxytryptamine denervated rats. Grafted serotonergic neurons were able to reinnervate the classical ependyma and the subcommissural organ. The fibers forming the supraependymal plexus were non-junctional and contained both serotonin and GABA while those innervating the subcommissural organ formed synaptic contacts and contained only serotonin. The signals capable of inducing the ependymal innervation were specific for serotonergic neurons since catecholaminergic neurons present in the grafts were unable to innervate either classical or specialized ependymocytes. These results demonstrate that glial cells are targets for serotonergic neurons and that the morphological and biochemical characteristics of the serotonergic innervation are closely related to the target cell phenotype.

A method for finding stereotaxic coordinates from brain sections

A method for finding the stereotaxic coordinates of brain areas from actual brain sections is presented. It uses a digitizer connected to a computer to gather coordinates from photographs of brain sections. The coordinates are mathematically translated and rotated to yield stereotaxic atlas coordinates of the areas digitized.

Distribution of intraventricularly injected horseradish peroxidase in cerebrospinal fluid compartments of the rat spinal cord

The circulation of the cerebrospinal fluid along the central canal and its access to the parenchyma of the spinal cord of the rat have been analyzed by injection of horseradish peroxidase (HRP) into the lateral ventricle. Peroxidase was found throughout the central canal 13 min after injection, suggesting a rapid circulation of cerebrospinal fluid along the central canal of the rat spinal cord. It was cleared from the central canal within 2 h, in contrast with the situation in the brain tissue, where it remained in the periventricular areas for 4 h. In the central canal, HRP bound to Reissner's fiber and the luminal surface of the ependymal cells; it penetrated through the intercellular space of the ependymal lining, reached the subependymal neuropil, the basement membrane of local capillaries, and appeared in the lumen of endothelial pinocytotic vesicles. Furthermore, it accumulated in the labyrinths of the basement membrane contacting the basolateral aspect of the ependymal cells. In ependymocytes, HRP was found in single pinocytotic vesicles. The blood vessels supplying the spinal cord were classified into two types. Type-A vessels penetrated the spinal cord laterally and dorsally and displayed the tracer along their external wall as far as the gray matter. Type-B vessels intruded into the spinal cord from the medial ventral sulcus and occupied the anterior commissure of the gray matter, approaching the central canal. They represented the only vessels marked by HRP along their course through the gray matter. HRP spread from the wall of type-B vessels, labeling the labyrinths, the intercellular space of the ependymal lining, and the lumen of the central canal. This suggests a communication between the central canal and the outer cerebrospinal fluid space, at the level of the medial ventral sulcus, via the intercellular spaces, the perivascular basement membrane and its labyrinthine extensions.

Vasopressinergic neurons in periependymal and periventricular areas of the rostral third ventricle of the rat

On the lateral wall of the rostral third ventricle, an area separates the ependyma from the neurosecretory PVN neurons. Since VP from the latter discharges into the vasculature, the above area may be regarded as constituting an interface between the ventricular and vascular compartments of the CNS. As VP release into the two compartments is integrated, the interface region has been explored for possible existence of a neural infrastructure that would allow such an integration. Immunohistochemical staining for VP following colchicine treatment reveals the presence of an elaborate vasopressinergic network in the interface region that is divisible into a medial periependymal and a lateral periventricular area. A closer examination indicates that the ependymal, periependymal, periventricular and PVN areas (in that order medio-laterally) are all interconnected through this network. The medial area appears to be receptive in nature, while the connectivity of the lateral area points to an effector function. All in all, such a neural network would provide a sound morphological basis for integration of neuroendocrine mechanisms modulating VP release into the ventricular and vascular compartments of the CNS.

A stereological study of the ependyma of the mouse spinal cord. With a comparative note on the choroid plexus ependyma

Applying different stereological techniques, the total ependymal volume in the spinal cord of mice was estimated to be 83 x 10(6) microns cubed, the number of cells to be 163,000 and the mean ependymal cell volume to be 510 microns cubed. Compared to choroid plexus cells in the third ventricle, the ependymal cells in the spinal cord contained a smaller mitochondrial volume (9.8% versus 4.6% of cell volume) and less rough endoplasmic reticulum (2.1% versus 0.4%). These findings indicate that the metabolic activity of the ependyma in the spinal cord is lower than that in the choroid plexus. Compared to liver and exocrine pancreatic cells, ependymal cells in both locations must be considered to have a rather low metabolic activity.

Postnatal neurogenesis in the olfactory bulbs of a lizard. A tritiated thymidine autoradiographic study

Autoradiographically labelled cells were observed in the olfactory bulbs of perinatal, young and adult specimens of the lizard Podarcis hispanica following intraperitoneal injection of tritiated thymidine (5 muCi/g b.wt). After survival times of 7, 18 and 28 days labelled cells were found in the granular layer of both main and accessory bulbs. A few labelled cells were observed in the ependyma, mitral and glomerular layer. In the main olfactory bulb, one week of survival time resulted in labelling of cells in the innermost part of the granular layer. Longer survival times (up to 4 weeks), resulted in labelling of cells mainly in the outermost part of the granular layer. This spatio-temporal gradient was not observed in the accessory bulb. Nevertheless, longer survival times resulted in greater number of labelled cells located in the dorsal and ventral parts of the granular layer of the accessory bulb.

Sub/supraependymal axonal net in the brains of sharks and probable targets in parasynaptic relationship

A sub/supraependymal system of varicose axons in the tectal midline ridge formation of shark brains is described. Lengths of axons and their terminals are seen freestanding in the cerebrospinal fluid (CSF) as well as in close contiguity with the large CSF-contacting and supraependymal mesencephalic trigeminal neurons of the midline ridge formation. The relationship of axonal varicosities and terminals to both CSF and supraependymal somata is such as to suggest a nonsynaptic association. This finding is discussed in the context of its utility in testing the concept of parasynaptic modulation in vertebrate brains. The topographical arrangement described is one in which the essential operational elements of parasynaptic activity can be identified in a neuronal assemblage whose functional association is known.

Correlated electrophysiology and morphology of the ependyma in rat hypothalamus

The ependyma lines the ventricular system of the vertebrate brain and spinal cord. Although its embryology and morphology have been studied extensively, little is known of its physiological properties, particularly in mammals. Tanycytes are modified ependymal cells that are found predominantly lining the floor of the third ventricle, overlying the median eminence. Their processes accompany and enwrap neuroendocrine axons that course from hypothalamic nuclei to terminals in the median eminence, but the significance of this interaction is not yet understood. Intracellular recording and injection techniques were used to study ependymal cells and tanycytes of the rat in the hypothalamic slice preparation after differentiating their respective regions morphologically. With extracellular [K+] = 6.24 mM, the mean membrane potential (+/- SD) for common ependyma was -79.9 +/- 1.40 mV and for tanycytes, -79.5 +/- 1.77 mV. Input resistances (Rin) were very low (much less than 1 M omega). Single-cell injection of Lucifer yellow revealed dye coupling among 2-70 ependymal cells and 5-48 tanycytes. In both freeze-fractured replicas and thin sections, large numbers of gap junctions were found between adjacent ependymal cells and between adjacent tanycytes. The observations of numerous gap junctions, extensive dye coupling and low input resistance demonstrated that both populations are strongly coupled networks. Perhaps for this reason, attempts to uncouple these cells using sodium propionate or CO2 were unsuccessful. Electrical stimulation of the arcuate nucleus did not elicit any detectable synaptic response in impaled tanycytes, so that the functional significance of synaptoid contacts between neuroendocrine neurons and the postsynaptic tanycytes is not yet apparent. Ependymal cells and tanycytes demonstrated a near-Nernstian response to changes in extracellular [K+] between 3 and 20 mM. This finding, as well as their high negative resting potential, low Rin, extensive coupling and absence of spontaneous electrical excitability demonstrate that ependymal cells possess numerous glial characteristics and may therefore have similar functions. In the hypothalamus, ependyma probably take up K+ released from adjacent endocrine neurons and shunt it to the ventricular space.

[The morphology and incidence of supraependymal structures in the cerebral ventricle system in sheep]

The morphology and distribution of supraependymal structures in the ventricular system of sheep of both sexes were studied by common histological methods. Seven forms of supraependymal structures were distinguished according to shape; they are most frequent and most variable in the infundibular region of the third cerebral ventricle. In the ewes their occurrence in this region depends on the status of the ovarian cycle and in the rams it depends on the year season. The most frequent forms are hemi-spherical to spherical light-coloured protrusions and the so-called blebs: in the ewes they occur during anoestrus and, to a minor extent, during proestrus, and in rams in the "rest" period. In the winter reason (the rest period) the rams have button-like formations on ependyma surface in the infundibular region, and in summer there are finger-like protrusions. No such structures occur in the ewes. A larger part of the supraependymal structures are believed to be products of ependyma secretion which, in the infundibular region but nowhere else, is associated with sex: with the ovarian cycle in the ewes and with the year season in the rams.

Ependyma of the central canal of the rat spinal cord: a light and transmission electron microscopic study

Ependymal cells of the rat central canal were examined with a view to identifying features that distinguish them regionally and from their counterparts elsewhere in the ventricular system. The results revealed that the lining consisted for the most part of a pseudostratified layer of uniformly organised cuboidal to columnar ependymal cells present in largest numbers in lumbar and sacral segments and in the conus. Two cell variants were identified on the basis of the presence or absence of a radially directed cytoplasmic process originating from the base of the cell. The tanycytic form of ependymal cell was encountered along the entire length of the central canal but with increased frequency in caudalmost segments. Ependymal cells were largely similar in ultrastructural appearance along the length of the cord. Although they were also similar in appearance and orientation to their counterparts in the ventricles they did exhibit some unique features. The most notable were the prominent junctional complexes and associated filaments present along the lateral border of the cells near their apex and the abundance of intermediate filaments in tanycytes. The central canal of the filum differed most markedly from other segments of the cord and resembled in structure the primitive ependymal tube of the caudal cord in lower vertebrates. Ependymal cells of the cord were not sufficiently dissimilar morphologically from their counterparts in the ventricles to account for differences in proliferative capacity in response to localised injury. A factor that merits further study is the difference in numbers of tanycyte ependymal cells in the two locations for they may be the reactive elements that proliferate in response to injury.

Physical effects of the choroid plexus on the cochlear nuclei in man

Relatively deep invaginations on the surface of the dorsal cochlear nucleus (DCN) inside the fourth ventricle lateral recess were observed just below the choroid plexus. The ependymal cells and neurons in the affected areas of the DCN manifest coarse inclusions in their cytoplasm. The inclusions are rounded granules, approximately 2 micron in diameter, relatively evenly spread through cytoplasm of these cells. The inclusions are not lipofuscin or known, non-viral cytoplasmic bodies specific for certain diseases accompanied by degeneration of the nervous tissue. The inclusions are, however, observed in cells with relatively high lipofuscin content. The change in transportation of the nutrients and metabolites between the affected areas in the DCN, cerebrospinal fluid, and capillaries as well as metabolic impairments in the DCN may be a reason for the observed accumulation of inclusions and lipofuscin. These pathological changes may also be a reason for certain hearing disorders.

Neurohemal contact in the internal zone of the rabbit median eminence

The concept of neurosecretion as the mechanism by which neural control of adenohypophyseal function is accomplished was based on the observation that long capillary loops penetrate deeply into the supraopticohypophyseal tract as it passes through the median eminence internal zone. However, neural contact upon these capillary loops has not been demonstrated in the mammalian median eminence. The present transmission electron microscopic investigation of the rabbit median eminence demonstrates neurohemal contact in the median eminence internal zone. Axons containing small lucent vesicles 53.3 +/- 3.28 nm in diameter (mean +/- SEM) or small lucent and large granular vesicles with a mean diameter of 122.4 (+/- 3.28 nm) in their terminals make neurohemal contact with capillary loops in the internal zone and form a cuff about them. These terminals resemble terminals found in the external zone. Intravenous injection of the false neurotransmitter 5-hydroxydopamine (5-OH-DA) renders small lucent vesicles granular in both the external and internal zone. The effect of 5-OH-DA injection is abolished by concurrent reserpine administration. Whereas large granular vesicles in many terminals become lucent after reserpine administration, in others they remained electron dense. Viewed in the light of previous studies our findings suggest that the internal plexus arises from the external plexus and invaginates the neuropil carrying connective tissue and parvicellular axon terminals of aminergic and peptidergic systems from the external zone into the internal zone, that some elements making neurohemal contact with long capillary loops are terminals of the noradrenergic reticular infundibular tract arising outside the hypothalamus in the brainstem, and that long capillary loops form a system of repeating microvascular modules which markedly increase the surface available for neurohemal contact.

Subchoroidal approach to the third ventricle. Microsurgical anatomy

The third ventricle can be approached by performing a few surgical maneuvers: (a) dividing the ependyma on the inferolateral aspect of the choroid plexus of the lateral ventricle; (b) separating leptomeningeal bundles within the tela chorioidea, and (c) dividing the roof of the third ventricle along the stria medullaris. Main landmarks are the thalamostriate vein and the direct lateral vein. Small subependymal veins or neural branches of the posterior medical choroidal artery, or both, occasionally cross the access route. The third ventricle is seen through both the opening in the roof and the foramen of Monro. A wider exposure can be obtained by cutting the terminal segment of the thalamostriate vein.

Morphology of the organum vasculosum of the lamina terminalis (OVLT) of the sheep

Examination of the ventricular surface of the organum vasculosum of the lamina terminalis (OVLT) of sheep with the scanning electron microscope revealed an elongated protuberance occupying most of the frontal wall of the third ventricle below the level of the anterior commissure. This protuberance lacked ciliated ependymal cells. Examination of horizontal sections with the transmission electron microscope revealed an apparent lack of regularly apposed ependymal cells, suggesting that ependyma is either greatly modified or absent. The surface was composed of numerous intertwining cell processes with some scattered cells situated on this surface. The body of this structure was composed of many cell processes separated by a network of extracellular channels sometimes extending to the ventricular surface. Towards the base of this protuberance, a plexus of blood vessels was observed. Some of these vessels exhibited fenestrated endothelium. Neuronal processes were also apparent in this region. These unusual anatomical features suggest a specific function for this brain region in sheep.

Caudal spinal cord of the teleost Sternarchus albifrons resembles regenerating cord

The morphology of spinal cord in the caudal-most spinal segments of normal adult Sternarchus albifrons is different from that of more rostral adult cord. The caudal segments are strikingly similar to the regenerating spinal cord observed after amputation of the tail in Sternarchus. In the caudal-most vertebral segment of normal spinal cord, ependymal cells are radially enlarged and are more numerous than in more rostral adult cord. Large processes of the ependymal cells extend into the central canal, which also contains a prominent Reissner's fiber. Invaginations of the outer surface of the spinal cord, with the associated basal lamina, are common. Lateral to the immediate ependymal layer, extracellular spaces contain longitudinally oriented neurites. Cell bodies and cell processes filled with dense-cored vesicles occur throughout the caudal-most segment of spinal cord, and are especially concentrated in the ventral half, interspersed with numerous capillaries. In all these respects the caudal-most segments of normal adult spinal cord in Sternarchus closely resemble regenerating spinal cord of Sternarchus. In both regions, at least some of the ependymal cells retain the ability to divide and generate new neurons and glial cells.

Reissner's fiber in the sacral cord and filum terminale of the possum Trichosurus vulpecula: a light, scanning, and electron microscopic study

The ending of Reissner's fiber (RF) and structural features associated with gaps or fissures in the rostral part of the filum were investigated using light, scanning, and transmission microscopic techniques in young and mature possums of both sexes. To the best of the author's knowledge the report contains results of the first successful application of the SEM for a study of RF in the spinal cord. Some new observations suggest that while the bulk of RF is formed by the subcommissural organ and moved caudally, additional secretory products may be added by ependymal cells in the sacral and possibly other regions of the spinal cord. Evidence is provided in support of the view that RF may pass through gaps in the ependymal lining in the rostral part of the dorsal wall of the filum terminale and caudal end of the sacral cord to reach the periependymal loose tissue and possibly the subarachnoid space. The region of the gap shows the surface of the ependyma facing the lumen of the filum to be covered with microvilli and cilia, and to be in direct continuity with the external surface of the ependyma covered with basement membrane with glial processes and collagen fibers in close proximity. The present results confirm and extend observations reported by Wislocki et al. ('56).

Supra-ependymal serotoninergic nerves in mammalian brain: morphological, pharmacological and functional studies

Supra-ependymal nerves in mammals (mainly rats) have been shown to contain serotonin (5-hydroxytryptamine, 5-HT) by combined Falck-Hillarp fluorescence histochemistry, ultrastructural monoamine cytochemistry and pharmacology as well as by immunohistochemistry and autoradiography. Supra-ependymal 5-HT cells do not occur. At least in rats, virtually all supra-ependymal nerves contain 5-HT and in our opinion the occasionally described non-5-HT supra-ependymal nerve cells and their processes contribute little to the supra-ependymal nerve plexus (with the possible exception of those cells above the median eminence). The cells of origin of the supra-ependymal 5-HT nerves are situated in raphe nuclei. The axons and terminals (varicosities) contain small and large dense core vesicles in both of which 5-HT is stored. A co-transmitter has not been found among the candidates investigated so far (leu- and met-enkephalin, substance P and gamma-aminobutyric acid (GABA)). The nerves possess uptake mechanisms specific for 5-HT and possibly GABA. Occasionally desmosome-like junctions are observed between 5-HT nerve terminals and ependymal cells but no true synapses. The function of these nerves is not known. They do not appear to regulate ciliary movement, but might influence the shape of ependymal cells.

Pineal innervation of the third ventricular ependyma in the teleost, Puntius sophore (Ham.)

In the teleost Puntius sophore a well defined pineal tract intersects the posterior commissure at right angles and enters the ependymal layer in the roof of the third ventricle. In the ependymal layer it gives out varying number of branches which are in morphological contact with the component cells. Few branches apparently project into the third ventricles also. Further, EM studies would confirm the site of their constituent axonal endings. Such a direct pineal pathway projecting into the ependyma and third ventricle may be of great functional importance.

The distribution of orthogonal arrays in the freeze-fractured rat median eminence

The distribution of orthogonal arrays of particles and their relationships to gap and tight junctions have been studied in the glia of the freeze-fractured rat median eminence (ME). These rectilinear clusters of intramembrane particles are thought to represent trans-membrane channels for ions or metabolites, and were found to be densely packed on the membranous laminations of the pial-glial limitans. Additionally, arrays were found to be present on all of the perivascular glial end-feet examined. Two classes of end-feet were distinguished by their relative densities of orthogonal arrays. End-feet displaying low densities of arrays occurred more frequently in the internal zone, while end-feet displaying high densities occurred more often in the external zone. Similar distinctions based on array density could be made in membranes from other regions of the cell as well. Cross-fractures revealing the cytoplasm underlying these membranes often exposed lipid inclusion bodies, suggesting that membranes containing few arrays belong to tanycytes (or to 'astrocyte-like tanycytes'). The distribution of arrays appeared to be unrelated to the distribution of gap junctions in the membranes of astrocytes and tanycytes (and 'astrocyte-like tanycytes') of the ME, appearing near to and far from gap junctions with approximately equal frequency. Orthogonal arrays were absent from glial membranes near synaptic profiles in the ME. Arrays were also absent from the microvillous membranes of the apical surfaces of ependymal cells, from the cytoplasmic protrusions into the CSF of tanycytes, and from the vicinity of the tight and complex junctions linking the tanycyte and ependymal cell lateral membranes near their apical poles. These results suggest that there is a gradient of array density for most glia of the ME, increasing from the ventricular to the pial surface.

[Postnatal histogenesis of the ependymal layer of the human spinal cord and its organogenetic transformation]

The structure and histochemistry of the ependymal layer in the spinal cord were studied light optically and electron microscopically at the age of birth up to 96 years in 200 persons of both sex died from various trauma. At 18-20 years of age in the lumbar part (L1-L5), as a result of the subependymal cells proliferation, an abundantly innervated and vascularized intraspinal organ is formed, which has the connective tissue stroma and ectoglial parenchyma. The parenchymal cells are rich in active oxidoreductases and phosphatases, with a well represented granular endoplasmic reticulum, mitochondria, laminar complex and electron opaque inclusions in them, their dynamic changes being connected with the production of Gomori-positive secretion. Certain changes are mentioned in the development of the organ: the initial, early, completed formation and the period of involution.

[Types of 3d cerebral ventricle ependyma in sheep and their localization using segment analysis]

Attention was focused to the determination of the topographical locality of different ependyma types and determination of their extent by the method of segment analysis. Brain samples of five sheep of the Slovak Merino breed were studied. Excised brains were transversally cut into segments from the frontal pole at 5mm intervals. The eighth, ninth and tenth slices were cast in paraffin and were cut in simultaneous series at 300 microns intervals, the cutting thickness being 10 microns. The paraffin slices were stained with haematoxylin-eosine, Gömöri's chromium haematoxylin, and by the aldehyde fuchsine method after Gömöri. Nine types of ependymal epithelium of the third cerebral ventricle were observed, according to the kind and arrangement of cells. Remarkable differences were found in the occurrence of the types of cells and in their arrangement in the ependyma at the level of the arch of the side walls and bottom of the ventricle within each segment and within the extent of the studied transversal cuts. From the viewpoint of the regulation of hypophysial functions, a significant difference exists in the structure and organization of ependyma at the locality of recessus supraopticus, recessus infundibularis and recessus mammillaris. The results of our study are in agreement with findings in laboratory animals and enrich our previous findings.

The hypothalamic 'tuberoinfundibular' system of the rat as demonstrated by horseradish peroxidase (HRP) microiontophoresis

Microiontophoresis of horseradish peroxidase (20%) into the median eminence of the rat has allowed visualization of perikarya and axon projections of the tuberoinfundibular system after retrograde transport. Cells projecting to the median eminence were found in the periventricular regions of the hypothalamus and were particularly pronounced in dorsal portions of the rostral arcuate nucleus, the medial division of the paraventricular nucleus, and within the anterior periventricular nucleus. Labeling of perikarya within the ventromedial nucleus was rarely found. No labeling by HRP was found within cells of the dorsomedial, anterior, suprachiasmatic, preoptic, lateral hypothalamic nuclei or within the septal and amygdaloid nuclei. Axons from identifiably cells were located within the periventricular neuropil and contained within the baso-lateral portions of the hypothalamic-hypophysial tract.

Cerebrospinal fluid contacting and supraependymal mesencephalic trigeminal cells in the blue and mako sharks. A scanning electron microscopic study

Scanning electron microscopic observations reveal cerebrospinal fluid contacting and supraependymal cell bodies of the mesencephalic trigeminal (Mes V) nucleus in adult specimens of mako and blue sharks, but not in very young specimens of the smooth dogfish shark. Possible functional roles are discussed in terms of participation of cerebrospinal fluid contacting Mes V cells in a neuroendocrine regulatory system. Comparisons are made with light microscopic observations of the relationship of Mes V cells with the ventricular wall. General features of the scanning electron microscopic appearance of the roof of the ventricle of the optic tectum in sharks are described and compared to similar general features found in the third ventricle of a variety of vertebrates.

The significance of the evolution of the cerebrospinal fluid system

A study of the comparative morphology of the cerebrospinal fluid (CSF) system has been made in amphioxus, lamprey, dogfish, goldfish, lungfish, frog, salamander, turtle, pigeon, and mouse. Using mainly intracardiac fixation and a careful histological technique, serial sections have been obtained of the brain in situ surrounded by its various membranes and the skull. The ventricular system, the roof of the hindbrain, the meninges and subarachnoid space, the ependyma with its various derivatives, including the choroid plexuses and paraphysis, and the relationship between the various CSF compartments and the cerebrovascular system have all been compared in these animals. The hypothesis has been derived that the CSF system is primarily developed to maintain the chemical environment necessary to the function of the cells of the central nervous system, including the neuroendocrine pathways.

The filum terminale of the frog spinal cord, a non transformed preparation: I. Morphology and uptake of gamma-aminobutyric acid

The filum terminale of the frog spinal cord is a rather pure glial cell preparation, largely devoid of neuronal elements. gamma-Aminobutyric acid (GABA) is taken up by the frog filum terminale (FT) via a Na+-dependent, ouabain-inhibited, saturable high affinity transport system with a Km of 2.7 x 10(5) M. The rate of the FT GABA uptake is significantly greater than the velocities observed in the spinal cord. In fact, the Vmax increases caudally beyond the level of the last root, and is maximal in the FT per se. beta-Alanine is a competitive inhibitor of the FT high affinity transport system for GABA (Ki 11.1 x 10(-5) M). In addition to GABA, the FT also takes up beta-alanine, glycine, glutamate and aspartate at rates significantly higher than those shown by the spinal cord of the frog. Light and electron microscope level radioautography clearly shows that GABA uptake occurs primarily in the glial cells and also in ependymal cells present in the FT. In that the FT contains few ependymal cells and a large number of glia, it is fair to state that most of the GABA accumulated by the FT reflects the glial transport of this amino acid. Unlike the adult frog, the spinal cord of the tadpole does not show any regional differences in the rate of GABA transport during early development. However, during later developmental stages, the rates of GABA transport increase in the caudal portion of the tadpole cord as compared to the more rostral areas. Close to metamorphosis, the terminal portion of the tadpole cord, which is destined to become the filum terminals of the frog, accumulates GABA at rates not greatly different from those observed in the FT of the adult frog. Therefore, the tadpole spinal cord is a useful preparation in which to study the dynamic properties of normal non-transformed glia as influenced by a changing neuronal population, whereas the frog FT is a unique preparation for the study of some properties of normal glia largely in the absence of neurons.

The morphology of extrachoroidal ependyma overlying gray and white matter in the rabbit lateral ventricle

A morphologic investigation of ependyma over gray matter (caudate nucleus) and over periventricular white matter (tapetum) of the rabbit lateral ventricle was undertaken prior to evaluation of morphological changes which occur with experimental hydrocephalus. Ependymal cells over the caudate nucleus are cuboidal and heavily ciliated. Numerous microvilli cover the cell surface. The lateral margins are straight and interdigitations between adjacent ependymal cells are absent. Ependymal cells over white matter are squamous. Nonciliated as well as ciliated cells contribute to the epithelial lining. Microvilli are present at the cell surface but tend to aggregate near the cellular borders. The lateral margins are convoluted and complex interdigitations are present between adjacent cells. Morphologic differences between ependymal cells over the caudate nucleus and those over periventricular white matter may help to explain the differential response to hydrocephalus observed in these two regions of the lateral ventricle.

Variability in maps of identified neurons in the sea lamprey spinal cord examined by a wholemount technique

A technique is described for preparing toluidine blue-stained wholemounts of lamprey spinal cords. By this technique virtually all the neurons in the spinal cord can be studied with respect to their soma size and shape, their primary dendrites, and sometimes secondary dendrites and proximal portions of the axon. Several cell types previously studied physiologically and described by others in cross section are described in wholemounts. These are dorsal cells, giant interneurons, edge cells and lateral cells. In addition, several unique cell types are noted in wholemount which were previously unremarked upon. These include obliquely oriented bipolar cells, trident-shaped cells located mostly in the rostral two-thirds of the spinal gray column, and small neurons with cell bodies in the dorsal and ventral axon tracts. Edge cells, which had previously been described as having large cell bodies close to the lateral edge of the lateral axon tracts with large medially oriented dendrites, are shown to be quite heterogeneous in size, location of soma and dendritic tree configuration. By use of the wholemount technique, 4 spinal cords of large sea lamprey larvae, close to transformation, were mapped for lateral cells, giant interneurons and dorsal cells. Considerable variability was noted in numbers and locations of these cells. The possible significance of this finding for the development of the vertebrate nervous system is discussed.