Role of the subcommissural organ in the pathogenesis of congenital hydrocephalus in the HTx rat.

The present investigation was designed to clarify the role of the subcommissural organ (SCO) in the pathogenesis of hydrocephalus occurring in the HTx rat. The brains of non-affected and hydrocephalic HTx rats from embryonic day 15 (E15) to postnatal day 10 (PN10) were processed for electron microscopy, lectin binding and immunocytochemistry by using a series of antibodies. Cerebrospinal fluid (CSF) samples of non-affected and hydrocephalic HTx rats were collected at PN1, PN7 and PN30 and analysed by one- and two-dimensional electrophoresis, immunoblotting and nanoLC-ESI-MS/MS. A distinct malformation of the SCO is present as early as E15. Since stenosis of the Sylvius aqueduct (SA) occurs at E18 and dilation of the lateral ventricles starts at E19, the malformation of the SCO clearly precedes the onset of hydrocephalus. In the affected rats, the cephalic and caudal thirds of the SCO showed high secretory activity with all methods used, whereas the middle third showed no signs of secretion. At E18, the middle non-secretory third of the SCO progressively fused with the ventral wall of SA, resulting in marked aqueduct stenosis and severe hydrocephalus. The abnormal development of the SCO resulted in the permanent absence of Reissner's fibre (RF) and led to changes in the protein composition of the CSF. Since the SCO is the source of a large mass of sialilated glycoproteins that form the RF and of those that remain CSF-soluble, we hypothesize that the absence of this large mass of negatively charged molecules from the SA domain results in SA stenosis and impairs the bulk flow of CSF through the aqueduct.

Morphological and behavioral changes in the pathogenesis of a novel mouse model of communicating hydrocephalus.

The Ro1 model of hydrocephalus represents an excellent model for studying the pathogenesis of hydrocephalus due to its complete penetrance and inducibility, enabling the investigation of the earliest cellular and histological changes in hydrocephalus prior to overt pathology. Hematoxylin and eosin staining, immunofluorescence and electron microscopy were used to characterize the histopathological events of hydrocephalus in this model. Additionally, a broad battery of behavioral tests was used to investigate behavioral changes in the Ro1 model of hydrocephalus. The earliest histological changes observed in this model were ventriculomegaly and disorganization of the ependymal lining of the aqueduct of Sylvius, which occurred concomitantly. Ventriculomegaly led to thinning of the ependyma, which was associated with periventricular edema and areas of the ventricular wall void of cilia and microvilli. Ependymal denudation was subsequent to severe ventriculomegaly, suggesting that it is an effect, rather than a cause, of hydrocephalus in the Ro1 model. Additionally, there was no closure of the aqueduct of Sylvius or any blockages within the ventricular system, even with severe ventriculomegaly, suggesting that the Ro1 model represents a model of communicating hydrocephalus. Interestingly, even with severe ventriculomegaly, there were no behavioral changes, suggesting that the brain is able to compensate for the structural changes that occur in the pathogenesis of hydrocephalus if the disorder progresses at a sufficiently slow rate.

Cellular mechanisms involved in the stenosis and obliteration of the cerebral aqueduct of hyh mutant mice developing congenital hydrocephalus.

Two phases may be recognized in the development of congenital hydrocephalus in the hyh mutant mouse. During embryonic life the detachment of the ventral ependyma is followed by a moderate hydrocephalus. During the first postnatal week the cerebral aqueduct becomes obliterated and a severe hydrocephalus develops. The aim of the present investigation was to elucidate the cellular phenomena occurring at the site of aqueduct obliteration and the probable participation of the subcommissural organ in this process. Electron microscopy, immunocytochemistry, and lectin histochemistry were used to investigate the aqueduct of normal and hydrocephalic hyh mice from embryonic day 14 (E-14) to postnatal day 7 (PN-7). In the normal hyh mouse, the aqueduct is an irregularly shaped cavity with 3 distinct regions (rostral, middle, and caudal) lined by various types of ependyma. In the hydrocephalic mouse, these 3 regions behave differently; the rostral end becomes stenosed, the middle third dilates, and the caudal end obliterates. The findings indicate that the following sequence of events lead to hydrocephalus: 1) denudation of the ventral ependyma (embryonic life); 2) denudation of dorsal ependyma and failure of the subcommissural organ to form Reissner fiber (first postnatal week); 3) obliteration of distal end of aqueduct; and 4) severe hydrocephalus. No evidence was obtained that NCAM is involved in the detachment of ependymal cells. The process of ependymal denudation would involve alterations of the surface sialoglycoproteins of the ependymal cells and the interaction of the latter with macrophages.

Severe hydrocephalus in L1-deficient mice.

The neural adhesion molecule L1, a member of the immunoglobulin superfamily of cell recognition molecules, performs important functions in the developing and adult nervous system. This view is confirmed by the fact that mutations in the human L1 gene cause a severe neurological disease, termed CRASH (acronym for: corpus callosum hypoplasia, retardation, adducted thumbs, spastic paraplegia, and hydrocephalus). X-linked hydrocephalus is certainly the most prominent symptom of CRASH syndrome. Mouse mutants deficient in L1 also develop enlarged ventricles. Here, we report that ventricular dilation in L1-deficient mice is not correlated with stenosis of the aqueduct of Sylvius nor with ultrastructural abnormalities of ependymal cells lining the lateral ventricles or the aqueduct. However, a few L1 mutant mice displayed severe hydrocephalus, characterized by a significant enlargement of the skull and an almost complete atrophy of the cerebral cortex. The aqueduct of these severely affected animals was completely closed. Since mutant animals from two independently generated L1-deficient mouse lines displayed a similar phenotype, we consider severe hydrocephalus as a specific consequence of L1-deficiency. However, results of the present study also indicate that severe hydrocephalus represents a secondary rather than a primary defect of the L1 mutation; our combined data suggest that deformations of the brain as a result of massively enlarged ventricles secondarily cause stenosis of the aqueduct and subsequently high pressure hydrocephalus.

Scanning electron microscopy of the floor of the fourth ventricle in rats subjected to graded impact injury to the sensorimotor cortex.

OBJECT: Respiratory dysfunction including apnea frequently follows head injury in humans. The purpose of this study was to identify any structural alterations in the region of brainstem respiratory nuclei that might account for immediate postinjury respiratory abnormalities in anesthetized experimental animals. METHODS: Using scanning electron microscopy, the authors examined the floor of the fourth ventricle in injured rats after a piston strike to the sensorimotor cortex that depressed the dura 1, 2, or 4 mm. The rats were killed within minutes of injury. Cortical impact depths measuring either 1 or 2 mm (eight rats) produced no respiratory abnormalities, and the structural integrity of the ependymal lining of the ventricular floor in these animals was not compromised. Thirteen rats were subjected to impact to a 4-mm depth and 10 of these exhibited immediate temporary or permanent apnea. The medullae of nine of these rats were studied using scanning electron microscopy, and the fourth ventricular floors of all nine rats showed tears. Four rats that exhibited immediate, permanent apnea had tears in the caudal fourth ventricle floor near the obex, whereas five rats with no or only transient apnea had tears located more anteriorly, near the aqueduct or laterally. Changes in cerebrospinal fluid flow or pressure dynamics may have caused these tears. Light microscopy, focused near the area postrema, revealed a shearing defect through the ependyma of the fourth ventricular floor into the subjacent neuropil with a disruption of axonal pathways. CONCLUSIONS: Respiratory neuronal network components lying within 2 mm of the area postrema may well have been disrupted by the caudal tears producing permanent apnea. A similar phenomenon could account for the transient or permanent postinjury apnea seen in humans with severe head injury.

[The effect of hypo- and hypermagnetic fields on the motor activity of the ciliary apparatus of the ependymal cells]. / Izuchenie vliianiia gipo- i gipermagnitnogo polei na dvigatel'nuiu aktivnost' resnitchatogo apparata épendimnykh kletok.

The effect of vertical component of geomagnetic field on ciliate apparatus of ependymal cells in newborn rats in culture has been studied. It has been shown that hypo- and hypermagnetic fields retard the motor activity of ciliary apparatus up to full stoppage with cell swelling.

A scanning and transmission electron microscopic analysis of the cerebral aqueduct in the rabbit.

An examination of the surface of the cerebral aqueduct with the scanning electron microscope revealed that the walls of the cerebral aqueduct were so heavily ciliated that most of the ependymal surface was obscured, yet certain specialized supraependymal structures could be discerned lying on (or embedded within) this matt of cilia. These structures were determined by transmission electron microscopy and Golgi analysis to be either macrophages, supraependymal neurons, dendrites from medial periaqueductal gray neurons, or axons of unknown origin. Some axons, which were found to contain vesicles, appeared to make synaptic contacts with ependymal cells. Using the transmission electron microscope, the ependymal lining was found to consist of two different cell types: normal ependymal cells and tanycytes which have a long tapering basal process that was observed to contact blood vessels or, more rarely, seemed to terminate in relation to neuronal elements. While there have been previous reports on the structure of the third and lateral ventricles in other species, there are limited reports in the rabbit. The present report is not only the first description for the rabbit, but it is the first complete scanning and transmission electron microscopic analysis of the cerebral aqueduct in any species.

[Serotoninergic nerve fibers in the area of the substantia grisea and the ependyma of the cerebral aqueduct]. / Serotoninergicheskie nervnye volokna v zone serogo veshchestva i épendimy vodoprovoda mozga.

An electron microscopic study of the midbrain gravy with the help of degeneration caused by serotonin-like neurotoxin 5,7-dihydroxytryptamine has shown that serotonergic terminals are responsible for the innervation of dendrites, neuron bodies and ependyma cells of the cerebral aqueduct. The detection of light, dark with prevailing fine transparent or large granular synaptic vesicles as well as vacuole degeneration evidences of the existence of several sources of serotonergic innervation of the central gray substance. Continuous damage of perivascular astrocytes of the central gray by neurotoxin allows a suggestion to be made that they are also the object of serotonergic innervation. Immunomorphological data on the presence of serotoninergic neurons in the cerebral gray are confirmed.

The ependyma of goat. II. Ependymal lining of the lateral ventricles, mesencephalic canal, and fourth ventricle: scanning electron microscopic study.

The ependymal surface of the lateral cerebral ventricle, mesencephalic canal, and IVth ventricle of 13 male and female goats were studied by means of scanning electron microscopy. The lateral cerebral ventricle was covered mostly with thin cilia that might have club-like terminations on nucleus caudatus, the wide "naked" places with bleb-like protrusions occurred in the transition to cornu temporale during anestrous cycle. The ependymal surface of mesencephalic canal of female goats during anestrus was covered with abundant spherical protrusions. No other changes that could be related to the sexual differences were found.

Scanning electron microscopy of transitory subependymal cysts in the developing midbrain of postnatal rats.

Transitory cystic cavities, associated with the subependymal region of the aqueduct in the midbrain of postnatal rats aged 1-15 days, were studied by light and scanning electron microscopy. The walls of these cysts, as observed in scanning electron microscopy, were lined by a dense feltwork of nerve fibres. Two types of cells were identified in the cysts: smaller glioblasts and larger amoeboid microglial cells. The glioblasts were characterized by a smoother cell body with radiating long processes. The amoeboid microglial cells showed blebs and pseudopodia on their surface. They either adhered to the walls or floated freely in the lumen. It is postulated that the formation of the subependymal cysts in the developing brain resulted following the cleavage or breakdown of the nervous tissue due to the expansion of the aqueduct and the brain as a whole. The amoeboid microglial cells in the cysts were probably derived from the extravasated blood monocytes in response to the physical damage ensuing during the formation of the cysts.

[Regional characteristics of ventricular surfaces of the brain in aging and in senile dementia (aqueduct of Sylvius)]. / Regiona'lnye osobennosti zheludochkovykh poverkhnostei golovnogo mozga pri starenii i seni'lnoi dementsii (si'lviev vodoprovod).

Electron scanning microscopy was applied to investigate the surfaces within the human brain ventricular system in order to establish their age-related changes. The brains were studied in different age groups and in patients with senile dementia. The changes of ependymal surfaces were manifested in the loss of ependymal cell's cilia and microvilli. These changes were marked in dementia patients. Two types of age-related changes were detected in aqueductal surface ependymal cells but its lumen was never narrowed.

Morphological aspects of the development of hydrocephalus in a mouse mutant (SUMS/NP).

The SUMS/NP is a mouse mutant with a recessive gene for congenital hydrocephalus. The condition is detectable outwardly at 3 days after birth and affected animals die soon after weaning. The heads of fetuses from 14 to 20 days gestation and at 1, 4, 5, 12 and 18 days after birth have been sectioned for light microscopy and the volume of the lateral ventricles measured in all but the three oldest ages. At 16 days gestation and earlier all fetuses had a relatively large lateral ventricle volume. Hydrocephalus was first detected from volume measurements at 18 days gestation and generally became progressively more severe with age. Hydrocephalic animals, in addition to lateral and third ventricle dilatation, always showed a reduction in the cross-sectional area of the cerebral aqueduct or a total absence of the aqueduct. All hydrocephalics, with the exception of two fetuses, also had cystic cavitation of the forebrain around the lateral ventricles. Electron microscopy of animals with a reduced aqueduct showed the ventral part to be absent in hydrocephalics.

Ependymal foldings and other related ependymal structures in the cerebral aqueduct and fourth ventricle of man.

The ependymal lining of the cerebral aqueduct and fourth ventricle of 100 normal humans was studied with the light microscope. Ependymal foldings with normal morphology and a constant distribution pattern were detected in all. The most common sites were the median sulcus and sulcus limitans in the fourth ventricle, and the ventral and lateral walls in the cerebral aqueduct. Rows, islands and rosettes of ependymal cells embedded in normal subependyma were present in 25/82 adults (30%) and in 3/18 children (16%) in a similar distribution pattern as that of the ependymal foldings. We illustrate these normal structures which probably result from fusion between the walls of the ependymal foldings and distinguish them from granular ependymitis and postmortem artifact.

Morphological features of the surface of the subcommissural organ and aqueduct in the red necked wallaby (Wallabia rufogrisea).

The subcommissural organ and aqueduct of the red necked wallaby were examined using scanning electron microscopy. The surface of the subcommissural organ was similar to that of the possum brain and was superficially similar to that of the rat. However, on close examination, the apical protrusions composing the eutherian subcommissural organ were not present and tight clusters of microvilli were noted instead. Caudal to the subcommissural organ and on each side of the mesocoelic recess there were ciliated paramedian folds. These have been described in the possum but have not been noted in any eutherian mammalian brain. It is believed that these structures are peculiar to marsupial brains. Zones B and C (caudal to the subcommissural organ) represent a superior convex bulge into the aqueduct and then a concavity in the roof of the aqueduct, respectively. Both zones had sparsely ciliated ependyma, the cell surfaces being covered by microvilli. The most caudal zone, C, was much wider and longer than zone B. A line of cells in the roof of the aqueduct similar to zone C has been observed in eutherian mammalian brains in which a dorsal dilation is present. Furthermore, a ridge of long thin ependymal cells has been noted in the roof of the mesencephalon in prenatal rats as early as 16 days of gestation. It is postulated that this region is a circumventricular organ present in ontogeny in all mammals, persisting into the adult only in those with a dorsal dilation in the aqueduct.

[Anatomic demonstration of axon collaterals of the periaqueductal gray formation and the ventrobasal thalamic nuclei of both sides]. / Dimostrazione anatomica di collaterali assoniche dalla formazione grigia periacqueduttale (GPA) ai nuclei talamici VPM dei due lati.

In 4 adult cats the left and right thalamic nucleus VPM have been injected with fluorescent substances, Evans Blue and Fast Blue in order to ascertain whether PAG cells send bifurcated axons to the thalamic nuclei of both sides. The results confirm previous studies on the PAG-VPM connections performed in this laboratory by using HRP technique, and demonstrate, within the PAG, the presence of a good number of double-labeled cells (stained by both E.B. and F.B.) intermingled with single-labeled cells, stained either by E.B. or F.B. The double-labeled cells might represent the anatomical substrate of a possible bilateral analgesic mechanism in the trigeminal region.

Specialized ependymal ridges in the cerebral aqueduct of the rat.

Novel paired ependymal ridges (EPRS) have been identified in the ventrolateral wall of the cerebral aqueduct of the rat. Scanning electron microscopic techniques revealed that the dorsolateral and ventromedial ridges differ from each other in surface morphology. Using the PAP immunohistochemical technique, the EPRS demonstrate a dense innervation of both serotonin and LH-RH fibers when compared to the surrounding midbrain periaqueductal gray and the "non-ridge" ependyma of the aqueduct. Each ridge is composed of a single layer of ependymal cells with a central core of subependymal cells and numerous blood vessels. Ependymal cells resembling tanycytes extend between the lumen of the aqueduct and the subependymal capillaries. It is suggested that the EPRS may serve as sites for the release of neurochemicals into the cerebrospinal fluid.

Experimental obstructive hydrocephalus in the rat: a scanning electron microscopic study.

Hydrocephalus was induced in 12-day old rats by the cisternal infusion of a concentrated kaolin suspension. The animals were killed at day 20 and the ependymal lining of all the ventricles prepared for scanning electron microscopy. The dilation of the ventricles was moderate to gross in all cases. The ependyma of the lateral ventricles was similar in both control and experimental animals. Ependymal damage was present in six out of the twelve hydrocephalic rats. Two had fibres visible on the ependymal surface. Four had tears covered with small round cells, believed to be responsible for the repair of the ependyma. The third ventricle, cerebral aqueduct and fourth ventricle enlarged by incorporating folds of ependyma, present in control animals, into the ventricular walls. The circumventricular organs present in the third and fourth ventricles were not damaged by the dilation of the ventricles, even in severe hydrocephalus.