Fine structure of ependymal cells in the median eminence of the frog and mouse revealed by freeze-etching

Impact of Ploidy Change on Secondary Metabolites and Photochemical Efficiency in Solanum Bulbocastanum

Plants are well known for producing a wide diversity of natural compounds and several strategies have been proposed to enhance their production. Among them, somatic chromosome doubling may represent an effective and inexpensive method. The objective of the current study was to investigate the effect of polyploidization on the leaf metabolic profile and content of tetraploids produced from a wild diploid (2n=2x=24) potato species, Solanum bulbocastanum Dun. Photochemical efficiency of tetraploids was also analyzed. Results from HPLC-DAD and LC/MS analyses provided evidence that tetraploid genotypes displayed either a similar or a lower phenylpropanoids, tryptophan, tyrosine and α-chaconine content compared with the diploid parent. Similarly, no significant differences were found among genotypes both for measures of gas and for chlorophyll fluorescence, except for non-photochemical quenching (NPQ). Steroidal saponins content revealed superiority of some tetraploids with respect to the diploid parent, suggesting perturbations in the mechanism regulating the biosynthesis of such compounds following polyploidization. Lack of superiority may be attributed to the time required for adjustment, adaptation and evolution after the genomic shock induced by polyploidization, as well as the fact that an optimum ploidy level for each species may be crucial. Our results suggest that polyploidization as a strategy to enhance metabolite production cannot be generalized.

Relationship between orthogonal arrays of particles and tight junctions as demonstrated in cells of the ventricular wall of the rat brain

Ependymal cells in the ventricular wall and in several circumventricular organs of the rat were compared by means of freeze-fracturing. In principle, tight junctions and orthogonal arrays of particles (OAP) do not coexist in the cells bordering the ventricular wall: (1) Ordinary ependymal cells of the rat possess OAP and are devoid of tight junctions. (2) Epithelial cells of the rat choroid plexus are connected by tight junctions; OAP are lacking here. In some cases, however, tight junctions and OAP coexist in the same cell. In the boundary zone between choroid plexus and ependyma of the rat, the density of OAP is very low, whereas the tight junctions are well developed. In the subfornical and the subcommissural organ (SCO) of the rat both structures are poorly developed; in the SCO they occur segregated in different membranous areas. An overview of the literature confirms that tight junctions and OAP mostly exclude each other. The possibility that in astrocytes and ependymal cells tight junctions may have been replaced by OAP during phylogeny is briefly discussed.

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.

Tight junctions in the ependyma of the spinal cord of the urodele Pleurodeles waltlii

The ependymal junction pattern in the spinal cord of postmetamorphic ribbed newts has been studied, using transmission electron microscopy of ultrathin sections of normal animals and of animals perfused through the IVth ventricle with lanthanum. Contrary to what has been observed in mammalian CNS, the ependyma of the urodelan spinal cord is furnished with tight junctions that seal the luminal border of the terminal bars. These occludens junctions are made up of two to seven punctate fusions of the plasma membranes. Lanthanum tracer remains restricted inside the lumen of the central canal, being stopped at the first punctate fusion on its way through the intercellular clefts. Beyond this point, the extracellular space contains no tracer material. Besides tight junctions, intermediate, desmosomal and gap junctions are also present. Gap junctions and desmosomes are not present in CSF-contacting neurons. It is suggested that ependyma with occluding junctions (special ependyma) overlay the regions of the CNS where the ependymal cells significantly modify the composition of both intercellular and cerebrospinal fluids, through secretory, transporting and permeability control activities.

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.

The rhombencephalic recess in the rat. A light and electron microscopic study

The rhombencephalic recess, an ependymal organ, has been studied for the first time by light- and electron microscopy. It is situated mediosagitally on the floor of the rhomboid fossa at the level of the colliculus facialis. The recess and the superimposed tissue are built up by tanycytes, their apices being connected by tight junctions. HRP, injected into the c.s.f., does not penetrate into the intercellular clefts of the recess area. The recess area reveals a certain autonomy regarding its supply with arteries and capillaries. A blood-brain barrier exists, but shows slight leakage in circumscribed areas as a result of intense transendothelial vesicular transport. The organization of the recess area is compared with that of other ependymal organs, especially circumventricular organs.