Light, scanning and transmission electron microscopy study of fish cerebellar capillaries

Samples of teleost cerebellar cortex (Arius Spixii and Salmo Trout) fixed by immersion and vascular perfusion techniques were processed for light microscopy, SEM and TEM. SEM fractographs of endothelial cell nuclear, organelle and peripheral cytoplasmic zones have been compared with their corresponding TEM images. A simultaneous three-dimensional view of the luminal surface of endothelial cells at the nuclear zone, and inner details of heterochromatin structure was obtained. Chained micropinocytotic vesicles and deep cytoplasmic invaginations were observed. Surface connected micropinocytotic vesicles or vacuoles show stomas open to the luminal surface. Clear and dense endothelial micropinocytotic vesicles and vacuoles were observed at TEM level. The dense plasma substance can be used as an endogenous electron dense tracer for permeability studies. At SEM level the rough endoplasmic reticulum appears as a trabecular continuous system. The endothelial cytosol exhibits a smooth, glass surface appearance. The endothelial luminal surface changes its aspect according to the fixation procedure. The SEM and TEM aspect of endothelial junctions further supports their role as the morphological counterpart of blood-brain barrier. The basement membrane exhibited a homogeneous matrix and short or long neuropilar projections. Clear perivascular astrocytes with anastomotic processes form the main framework of perivascular neuropile. Like the peripheral endothelial cytoplasm, they exhibited dense and clear micropinocytotic vesicles and vacuoles, providing evidence for their transport function between capillaries and neighbouring brain parenchyma. The SEM appearance of their outer surface further supports their barrier function.