Figure 6. BLEC ultrastructure revealed in TEM of adult brain meninges.
(A) and (B) TEM micrographs of tangential sections of the domed tectal surface revealed cells (BLEC) with large spherical inclusions in proximity to meningeal blood vessels (BV). Higher magnification shows that BLECs are not contained within the basement membrane (A’ and B’, arrowheads) of endothelial cells (E) and are separated from the vessels by other cellular processes (e.g. asterisk in A’). Putative Mato/FGP cells are indicated (FGP?). (C) and (D) Pericytes (P) maintain close contact with endothelial cells (E) and are found under the basement membrane (arrowheads). BLECs are only found in the meninges (C) and are absent near blood vessels in the neuropil (D) of the brain. (E) and (F) T/S sections of tectal (E) and latero-ventral telencephalic (F) meninges showing BLECs are present in the inner layer (IL) of the meningeal covering. BLEC, brain lymphatic endothelial cell; E, endothelial cell; FGP, fluorescent granular perithelial cell; P, pericyte; TJ, tight junction. Nomenclature of meningeal layers according to Momose et al. (1988): OL, outer layer; IML, intermediate layer; IL, inner layer, BL, basal lamina; GL, glia limitans.