Microvascularization of the cerebellum in the turtle, Pseudemys scripta elegans (Reptilia). A scanning electron microscope study of microvascular corrosion casts, including stereological measurements.

Cerebellar blood supply and microvascular patterns were studied in 12 freshwater turtles Pseudemys scripta elegans by scanning electron microscopy (SEM) of microvascular corrosion casts and histology. Vascular densities were estimated by point counting methods from casts and thin sections (7 microns). Short A2-arterioles and recurrent branches from A3-arterioles supply the capillary bed of the molecular layer, while V2 and V3 venules drain it. The Purkinje cell layer is supplied by horizontal branches ("parallel arteries") of A4 and A3 arterioles, which capillarize toward the granular and molecular layers. V2, V3 and V4 venules drain the areas supplied by A3 arterioles. The deep granular and subependymal layers are supplied by A4 arterioles, those adjacent to the Purkinje cell layer also by A3 arterioles. The areas supplied by A4 arterioles drain via V4 venules. The granular and Purkinje cell layers taken together have an estimated vascular density of 4.1%, while in the molecular layer this value is 3.3%. Our findings largely confirm published data from Testudo geometrica and Pseudemys scripta elegans with respect to gross supply and drainage. The microvascular patterns are similar to those of the human cerebellar cortex, particularly the basic patterns of intracortical arterioles and venules. The molecular layer, like that in the human brain, has a circulatory bed largely independent of that of the Purkinje cell and granular layers. In contrast to the human brain, a cerebellar pial capillary network is present in the brain of the turtle.