To what extent are the retinal capillaries ensheathed by Müller cells? A stereological study in the tree shrew Tupaia belangeri

Abstract

The cellular ensheathment of capillaries in the 3 outer capillary layers of the central retina of the adult tree shrew Tupaia belangeri was studied quantitatively by transmission electron microscopy. Using a stereological approach, the relative surface of capillary basal lamina ensheathed by Mu$ ller cells and by nonmacroglial cells (collectively termed non-Mu$ ller cells) was estimated in 5 animals. The participation of Mu$ ller cells was distinctly different in the 3 capillary layers studied. In the outermost capillary layer 1, the mean (standard deviation) percentage surface coverage by non-Mu$ ller cell processes was 46n8 (15n3) %. Much less of the capillary basal lamina was ensheathed by non-Mu$ ller cells in capillary layers 2 and 3 (3n0 (2n1) % and 0n3 (0n3) % respectively). The observed total variation of the stereological estimates for the surface fraction of Mu$ ller cells (expressed as the between-subject coefficient of variation) was significantly higher in capillary layer 1 (28n8 %) compared with capillary layers 2 (2n2 %) and 3 (0n3 %). In capillary layer 1, the high observed total variation was due to a high biological variation among animals for the fractions of both Mu$ ller cell and non-Mu$ ller cell ensheathment. The rare occurrence of direct contacts between the capillary basal lamina and the perikarya of either microglial cells (capillary layer 3) or amacrine cells (capillary layer 2) corresponded well to the low stereological values obtained for the relative capillary surface ensheathed by non-Mu$ ller cells in these capillary layers. Previously, extensive and frequent contacts between the basal lamina of capillaries belonging to capillary layer 1 and horizontal cells had been observed in single sections. The present study quantitatively demonstrates a marked paucity of macroglial investment of capillaries located in capillary layer 1 of Tupaia. It can be concluded that horizontal cells ensheath most of the capillary surface not invested by Mu$ ller cells. In the retina of the adult tree shrew Tupaia belangeri, the basal lamina of capillaries located between the nerve fibre layer and the ganglion cell layer (capillary layer 4) is invested by the processes of Mu$ ller cells and by astrocytes which are absent from the outer parts of the retina. Retinal capillaries in the 3 outer capillary layers (capillary layers 1 to 3) are incompletely invested by the processes of Mu$ ller cells. To an extreme, the perikarya and the processes of horizontal cells abut on up to 90 % of the basal lamina of single capillary cross sections located between the outer

Glial and endothelial blood-retinal barrier responses to amyloid-β in the neural retina of the rat

“…However, this is not the case in all species. For example, in retinal capillary layer 1 (lying between the OPL and the INL) of the tree shrew ( Tupaia belangeri ) 46.8 ± 15.3% (mean ± SEM) of the relative surface of capillary basal lamina is ensheathed with neuronal horizontal cells (Ochs et al 2000); thus supporting the hypothesis that horizontal cells represent a cell type intermediate between neuronal and glial cells.…”

Relationship of the Optical Coherence Tomography Signal to Underlying Retinal Histology in the Tree Shrew (Tupaia belangeri)

“…Studies in chick 28 and swine 29 retinas support the present results, as the inner plexiform-inner nuclear layer histologic boundary is usually proximal to the LRP boundary T3a. The alignment of T3a with the border between amacrine and Müller cell somas may be explained by the known properties of Müller cell somas, which are more polygonal than either amacrine or bipolar cell somas [61][62][63] and so may alter the backscattering properties of the retina. In addition, the Müller cell density in tree shrew retina has been found to be similar to primate in central retina (both greater than 20,000 cells per mm 2 ), 63,64 so that Müller cells form a close-knit sublayer within the inner nuclear layer (Fig.…”

“…1 MathWorks). Ten sublaminae boundaries were identified in the histologic sections by using established anatomic criteria45,50,61,62 (Figs. 2, 3A)…”

Early development of the nervous system of the eutherian <i>Tupaia belangeri</i>

“…To define the scope of our findings more accurately, in a second step, an unbiased stereological method was used to determine the extent of basal lamina occupied by macroglial Müller cells and non-macroglial cells, respectively, in the three outer capillary layers of the central retina of adult Tupaia belangeri (Ochs et al, 2000). It turned out that the mean (standard deviation) percentage surface coverage by non-Müller cell processes was 46.8 (15.3) % (layer 1), 3.0 (2.1) % (layer 2), and 0.3 (0.3) % (layer 3).…”