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 micr oscopy (SEM) of microvascular corrosion casts and histology. Vascular densities were estimated by point counting methods from casts and thin sections (7 mu m). 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 horizo ntal branches (''parallel arteries'') of A4 and A3 arterioles, which c apillarize toward the granular and molecular layers. V2, V3 and V4 ven ules drain the areas supplied by A3 arterioles. The deep granular and subependymal layers are supplied by A4 arterioles, those adjacent to t he Purkinje cell layer also by A3 arterioles. The areas supplied by A4 arterioles drain via V4 venules. The granular and Purkinje cell layer s taken together have an estimated vascular density of 4.1%, while in the molecular layer this value is 3.3%. Our findings largely confirm p ublished data from Testudo geometrica and Pseudemys scripta elegans wi th respect to gross supply and drainage. The microvascular patterns ar e similar to those of the human cerebellar cortex, particularly the ba sic patterns of intracortical arterioles and venules. The molecular la yer, like that in the human brain, has a circulatory bed largely indep endent of that of the Purkinje cell and granular layers. In contrast t o the human brain, a cerebellar pial capillary network is present in t he brain of the turtle.