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.

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.

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.

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.

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.

Micromorphology of the third ventricular ependyma and infundibular recess in the mud-eel Amphipnous cuchia (Ham.).

Ependymal cells of varied size and shape including tanycytes with long basal processes are encountered both in the third ventricle and infundibular recess of A. cuchia. The basal processes of the tanycytes may be branched or unbranched and often lie in contact with each other or even from loose bundles. They also terminate on, or maintain close contact with the neurons of the nucleus lateralis tuberis, blood vessels, axonal tract of the nucleus preopticus and other neuronal elements. Golgi-Cox technique is apparently selective in its impregnation of both neurons and tanycytes. Prominent apical processes of some cells project into the ventricle. Some supraependymal cellular elements have their entire cell body projecting into the ventricle. The ependymal cells react positively to alkaline phosphatase and ascorbic acid tests.

Histological and histochemical study of the caudal neurosecretory system of the freshwater teleost Ompok bimaculatus (Bloch) with a note on its response to hypophysectomy and osmotic stress.

The caudal neurosecretory system in well developed in Ompok bimaculatus. It extends from 8th to the last caudal vertebra. In the last vertebra the spinal cord forms a distinct, lobate and highly vascular ventral urophysis where the neurosecretory fibers have perivascular endings forming a neurohaemal organ. In the anterior segment near the 8th preterminal vertebra the Dahlgren cells are large and sparsely distributed. In the posterior segment close to the urophysis they are small and densely arranged. The neurosecretory material (NSM) has affinity for acid stains but reacts negatively to Gomori's stain or to a reagent demonstrating SS/SH group. The Dahlgren cells have high RNA content in the cytoplasm indicating active protein synthesis. Histological evidence suggests that the caudal neurosecretory system of this species did not respond to hypertonic osmotic stress. However, immersion in deionized water is accompanied by hypertrophy of Dahlgren cells and depletion of NSM from the caudal neurosecretory system. Hypophysectomy results in initial hypertrophy of the Dahlgren cells followed by atrophic changes and depletion of NSM. Ninety days after hypophysectomy this system gradually reverts to normal.

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.

[Morphological studies of the matrix in human hypothalamus]. / Morphologische Untersuchungen der Matrix im Bereich des Hypothalamus beim Menschen.

The variations of matrix and ependyma in the hypothalamus was histologicaly investigated in 120 human brains of both sexes from the 13 week old fetuses up to the end of the first year of postnatal life. The plane of cuts were in the region of the anterior hypothalamic nucleus, of the ventromedial nucleus, and the arcuate nucleus. We have found that the exhaustion of the matrix begins in the 14 week old embryo in the anterior and medial hypothalamus. A subependymale zone is present in these areas in the 17 week old embryo and exists up to 23 week. The one-cell-layer ependyma appears in the anterior are of the ventromedial nucleus at first in the 24 week week old embryo. After this the ependyma appears from the 25 to the 28 week old embryo in the regions of the anterior hypothalamic nucleus and the other areas of the ventromedial nucleus. In the immediate surrounding of the arcuate nucleus we observed the first alterations in the 15 week old embryo. The exhaustion of matrix is a continuous process up to the 23rd week. The boundary of the third ventricle remained to be a multilayer and in all stages of development cells were found, which reach into the lumen. Only after birth the multilayer boundary was reduced. At the end of the first year of postnatal life the one-layer ependyma was developed at a few sites. We could not find any significant variations of matrix exhaustion in the different sexes.

[Changes in the subcommissural organ of white rats with age]. / Vozrastnye izmeneniia subkomissural'nogo organa belykh krys

Histological and histochemical methods were applied to the study of 82 male rats of different age (newborn, 1-, 2-, 5-, and 17-month-old). Microstructure of the subcomissural organ (SCO) was investigated; the height of its ependyma was measured. In rats at all the age groups studied ependymocytes secreted substances of glucoproteid nature; a moderate content of RNA persisted in the cells, and also a high activity of non-specific esterases. Secretory activity of ependymocytes increased with the growth of the animals, remaining high in adult rats; it fell in the old animals. Age changes of the SCO consisted in the reduction of the height of the ependyma, of the number of cell layers in it and atrophy of the villi.