The rat epithalamus. I. Correlative scanning-transmission electron microscopy of supraependymal nerves

Light and electron microscopic immunocytochemical study on the innervation of the pineal gland of the tree shrew (Tupaia glis), with special reference to peptidergic synaptic junctions with pinealocytes

Conventional and immunocytochemical, light- and electron-microscopic studies on the innervation of the pineal gland of the tree shrew (Tupaia glis) were made. Neuropeptide Y (NPY)-immunoreactive fibers, which were abundantly distributed in the gland, disappeared almost completely after superior cervical ganglionectomy, suggesting that these fibers are mostly postganglionic sympathetic fibers. By contrast, tyrosine hydroxylase (TH)-immunoreactive fibers, which were less numerous than NPY-fibers, remained in considerable numbers in ganglionectomized animals, indicating the innervation of TH-positive fibers from extrasympathetic sources. Bundles of substance P (SP)- or calcitonin gene-related peptide (CGRP)-immunoreactive fibers, entering the gland at its distal end, were left intact after ganglionectomy. SP-fibers were numerous, but CGRP-fibers were scarce in the gland. SP-immunoreactive fibers were myelinated and nonmyelinated, and were regarded as peripheral fibers because of the presence of a Schwann cell sheath. NPY- and SP-immunoreactive fibers and endings were mainly localized in the pineal parenchyma. NPY-immunoreactive endings synapsed frequently, and SP-positive ones did less frequently, with the cell bodies of pinealocytes. The results suggest that NPY and SP directly control the activity of pinealocytes. Sections stained for myelin showed that thick and less thick bundles of myelinated fibers entered the gland by way of the habenular and posterior commissures, respectively. Under the electron microscope, the bundles were found to contain also unmyelinated fibers. A considerable number of nerve endings synapsing with the cell bodies of pinealocytes remained in ganglionectomized animals; these endings were not immunoreactive for TH or SP. Such synaptic endings may be the terminals of commissural fibers.

Scanning electron microscopy of central nervous system cerebrospinal-fluid-contacting surfaces: a bibliography (1963-1995)

This bibliography is compiled to assist in locating papers related to the application of scanning electron microscopy (SEM) to cerebrospinal-fluid-contacting surfaces in vertebrates. The use of SEM by neuroscientists has continued apace since the publication of the first bibliography in 1980. SEM studies now include more than 50 species of vertebrates and range from cyclostomes to humans; they encompass development from embryo to senescence and concern both normal and pathologic morphology. Although remarkable strides have been made toward a greater understanding of many aspects of the structure and function of cerebrospinal-fluid-contacting surfaces, many significant problems await the judicious application of scanning electron microscopy.

Supraependymal cell clusters in the rat hypothalamus

The fine structure of supraependymal cell clusters of the median eminence was studied with TEM. The cluster cells were identified on the basis of ultrastructure and histochemical determination of glial fibrillar acidic protein (GFA). The phagocytic properties were also studied by means of intraventricular injections of HRP. Neurons, neuroglia cells and degenerating ependyma- and glial cells were found. The extrusion of degenerating infundibular elements into the ventricle is a constant phenomenon but its precise localization and intensity are variable. The close proximity of the clusters to capillary loops is stressed. Because of the broken ependyma at the neck of the cluster, the permeability of the infundibular lining for HRP is increased. Clusters may be seen as sites lacking a brain--CSF barrier.

Effects of monosodium glutamate on the development of intraventricular axons in the rat hypothalamus

The development of intraventricular axons in the infundibular recess of the young rat was investigated by correlative scanning and transmission electron microscopy (SEM-TEM). From the fourth through the fifteenth day of life such axons increase steadily in number. During subsequent weeks their number gradually decreases. In animals given monosodium glutamate on the fourth postnatal day there is widespread neuronal necrosis in the arcuate nucleus, and the development of intraventricular axons is greatly reduced. These findings suggest that the axons originate from the neurons of the arcuate nucleus.

Neural elements associated with the subcommissural organ of the brush-tailed possum (Trichosurus vulpecula)

By means of various techniques and on the basis of a large sampling of the brush-tailed possum, Trichosurus vulpecula, a detailed description is given of the morphology of the neural elements associated with the subcommissural organ (SCO) and the leptomeninges on the dorsal surface of the midbrain. It is shown that the SCO of the possum is richly innervated, the nerves reaching the cerebral aqueduct by passing through the organ; there is, however, no evidence of a neural link between the SCO and the pineal gland. No typical axo-glandular synapses were found; however, many axo-glandular synaptoid junctions between axons and secretory cells of the SCO were demonstrable within the parenchyma of the SCO and on the aqueductal surface of the organ. The possible functional implications of the findings are: (1) The secretory activity of the SCO may be modified by nerves associated with it; this is in accord with some recently published experimental studies. (2) The nerves that innervate the SCO may also be responsible for ciliary activity on the aqueductal surface of the SCO, thus directing the apical secretory product of the SCO and debris flowing caudally in the cerebrospinal fluid into the poorly ciliated median groove where Reissner's fibre is found.

Regional surface changes during the development of the telencephalic choroid plexus in the chick. A scanning-electron microscopic study

The surface morphology of the developing chick telencephalic choroid plexus (TCP) was examined by scanning electron and light microscopy. A blunt evagination develops rostro-cranially to the foramen of Monro on the medial telencephalic septum. The pseudostratified TCP epithelium differs in its surface morphology from that of the surrounding ependyma. Subsequently the TCP becomes elongated and branches. On the 9th embryonic day (ED) the pseudostratified epithelium progressively becomes high columnar epithelium in a distal to proximal direction along the branches of the TCP. The apical poles of the high columnar epithelial cells protrude into the ventricular lumen. Later, additional branches sprout at the base of the TCP, which then resembles a tree with a bush growing at its roots. Before the time of hatching, the high columnar epithelium changes to low columnar epithelium again in a distal to proximal direction. The surface of the TCP becomes flatter, in the process of which the number of cilia per unit surface area is reduced. On the developing TCP the epiplexus cells vary in shape, depending upon their functional state. It is proposed that not only the morphological but also the functional differentiation of the TCP proceeds in a distal to proximal direction along the branches of the choroid plexus. The surface differentiation of the TCP has a more regular character than that of the diencephalic CP (DCP), described previously, which seems to be influenced in its development by other anatomical structures.

CSF-contacting pinealocytes in the pineal recess of the Mongolian gerbil: a correlative scanning and transmission electron microscope study

The pineal recess of the Mongolian gerbil was studied using correlative scanning and transmission electron microscopy. The surface of the pineal recess can be subdivided into three distinct zones: (1) central, (2) transitional, and (3) peripheral. In the gerbil, the deep pineal gland is located deep to the central and transitional zones. The ependyma of the peripheral zone is densely ciliated and resembles that of the main ventricular lining. Ependymal cells of the transitional zone are sparsely ciliated but possess numerous microvilli on their apical surfaces. Supraependymal neurons were identified in the transitional zones. These cells appear to make a synaptic-like contact with the underlying ependymal cells. Of the three zones, the central zone demonstrated the greatest amount of morphological variability. Although a number of supraependymal structures could be identified in the central zone, the most remarkable feature was the presence of protruding cells that possessed no significant surface features. Employing correlative transmission electron microscopy, the protruding cells were shown to be CSF-contacting pinealocytes. The number of CSF-contacting pinealocytes present in the central zone varied from one cell to large clusters that covered the entire zone. The results of this investigation demonstrate the presence of a direct contact and the potential for interaction between the deep pineal gland and the CSF of the pineal recess in the gerbil.

Supraependymal cell clusters in the rat brain

The histological patterns of supraependymal cell clusters (CC) in rats of different ages (untreated, androgenized, and treated with monosodium glutamate) were investigated with light (LM)-, scanning- and transmission electron microscopy (SEM, TEM). These clusters were a frequent but not a constant finding. In 18 day- and older embryos, CC were always found in the recess of the olfactory bulb immediately prior to its obliteration. All other CC appear in the infundibular recess between the 3rd and the 6th postnatal day. Independent of age, all cell clusters exhibit small aggregates of subependymal tissue protruding through the ependyma. Both neurons (light cells) and neuroglia (dark cells) were found in the CC. By use of SEM, in the region of the infundibular recess it is possible to distinguish four forms of supraependymal cell clusters according to localization, size, number of cells, and presence of intraventricular axons. CC may be 1) receptors or have an additional secretory function; 2) Manifestations of a pathological type of reaction of the ventricular wall; 3) possible excrescences of the neural matrix, or 4) modifications of the ventricular wall in relation to the obliteration of the ventricular recesses. The first two interpretations are not tenable based on the present observations.

The suprahabenular recess in the rat: a quantitative study of ciliated cells, supraependymal cells and some specific features of supraependymal fibres

Using light microscopy, scanning and transmission electron microscopy, an extensive quantitative analysis of ciliated ependymal cells, supraependymal cells and supraependymal fibres in the suprahabenular recess of twenty-two adult Wistar rats was carried out. In addition, six animals were used to determine the origin of supraependymal fibres and their relationship to ependyma. The findings were as follows: ciliated cells-mean 3.32 +/- 0.26 per 1000 micron 2 (range 0-10); supraependymal cells-5.91 +/- 1.37 per recess (range 2-16). Average number of cilia per cell in different animals ranged from 31 to 33. Sex did not influence the density of ciliated ependyma or supraependymal cells. Evidence was obtained that some supraependymal fibres are closely associated with aberrant commissural fibres. The supraependymal fibres enter the suprahabenular recess and form gap junctions, and other types of junctions, with subjacent ependyma.

The armadillo infundibulum: correlative histochemistry, scanning and transmission electron microscopy of the ventricular surface

The ependymal and supraependymal cells of the armadillo infundibulum (INF) were investigated by correlative histochemistry, scanning and transmission electron microscopy. Eighteen armadillos (8 adult females, 6 adult males, 2 immature females and 2 immature males) were examined. The following supraependymal elements were observed: (a) individual pleiomorphic cells made up of neurons, macrophages, and astrocytic-glial cells; (b) numerous spherical blebs of various sizes occurring singly or in clusters; (c) axons, traversing the surface alone or in association with macrophages and other SEC; (d) multicellular clusters containing SEC, macrophages, axons and other cell types. There were neurosecretory axons or blebs on and below the ependymal cell layer and a unique arrangement of multipolar cells and their processes, traversing the INF floor for several millimeters. The presence of neurosecretory axons at the INF ventricular surface, spherical blebs and SEC in contact with one another via long filaments or vast networks of smaller axons on the surface and numerous macrophages in close apposition to possible metabolic and transport sites give evidence of organized activity in a regulatory system.

Serotonergic intraventricular axons in the habenular region. Phagocytosis after induced degeneration

Both intracerebroventricular injection of 5,7-dihydroxytryptamine and electrolytical midbrain-raphe lesions in rats induce degeneration of supraependymal axons (SEAs) normally occurring in large numbers upon the ependyma of the medial habenular nucleus and habenular commissure. It is concluded that the intraventricular axon plexus in the epithalamic region is comprised of serotonergic (5-HT) fibers originating in the dorsal and/or median raphe nuclei. Besides the elimination of SEAs, conspicious features were a marked reduction in the number of cilia, degenerative signs in the habenular ependyma, and the emergence of large numbers of supraependymal macrophages, being most probably involved in phagocytosis of the axonal debris. It is suggested that the nucleus habenulae medialis is influenced serotonergically by the midbrain raphe via (1) a direct projection upon its neurons and (2) an indirect projection by way of the intraventricular axon plexus. The origin of intraventricular macrophages is discussed in relation to recent data in the literature.

Electron microscopic demonstration of a supraependymal cluster of neuronal cells and processes in the hamster third ventricle

A supraependymal cluster of neuronal cells and processes consistently present on the floor of the hamster third ventricle was identified and characterized by means of correlative scanning (SEM) and transmission (TEM) electron microscopy. SEM revealed each cluster to be ovoid with the majority of its surface covered by dome-shaped protrusions and fine beaded fibers. A number of processes traveling individually or in groups also entered or exited from the cluster at its base. As these processes passed over the ventricular surface, they contributed to an extensive network on the floor and ventral aspect of the ventricular wall. Some processes terminated on the ependymal surface in bulbous endings while others penetrated the ependyma. The neuronal nature of these clusters and their associated processes was confirmed at the TEM level. The dome-shaped protrusions visible on the surface of the cluster in SEM corresponded to apical surfaces of neurons confined to the peripheral aspect of a core of loosely arranged processes. These cells exhibited a prominent nucleolus, stacks of rough endoplasmic reticulum (RER), polyribosomes, Golgi cisternae, mitochondria and microtubules (MT) and gave rise to dendritic processes which extended into the core. These dendrites gave off branches at acute angles and contained polyribosomes, single cisternae of RER and evenly spaced MT. Other profiles of processes within the core shared these characteristics, suggesting that they also were branches of the peripheral cells. Axons present within the core and on the cluster's surface exhibited vesicle-filled varicosities which frequently established synaptic contact with the peripheral cells and their processes. The presence of an intraventricular cluster of neurons which potentially communicates with centers extrinsic to the ventricle may have important implications in the hypothesized role of cerebrospinal fluid and tanycytic ependyma in the neuroendocrine regulation of anterior pituitary function.