Structural and spatial organisation of brain parenchymal vessels in the lizard, Podarcis sicula: a light, transmission and scanning electron microscopy study

The structure and 3-dimensional pattern of the intraparenchymal microvessel s in the brain of the lizard, Podarcis sicula, were studied by a combinatio n of light and transmission electron microscopy as well as scanning electro n microscopy of vascular corrosion casts. The angioarchitecture pattern con sists of narrow hairpin-shayed microvascular loops of different length orig inating from the meningeal surface. In each loop, descending and ascending vessels are closely apposed to one another throughout their length and are connected by a narrow U-shaped terminal loop at their tips. The 2 limbs of the vessel pairs show a slightly different diameter but lack other structur al differences. While some paired vessels give rise to a secondary hairpin- shaped loop with 2 possible branching patterns, there are no anastomotic in traparenchymal connections with analogous neighbouring structures. The cere bral vascular pattern of Podarcis sicula resembles that found in a few repr esentatives of other vertebrate classes. All cerebral vessels structurally appear to be capillaries. Also the observations carried out on semithin and thin sections strongly support the capillary loop model in the Podarcis br ain vasculature and, in accordance with studies carried out on various vert ebrates. the general submicroscopic features of the brain capillary wall su ggest the presence of an endothelial type blood-brain barrier.