Vascular patterns of the rat hippocampal formation.

Little is known of the course and distribution of blood vessels supplying and draining the hippozampus. Such information could be of value in designing and evaluating lesion and ablation experiments and may reflect spatial properties of neurons. This study mapped the distribution of major arteries and veins of the rat hippocampal formation. Arteries and veins of adult female Wistar rats anesthetized with sodium pentobarbital were injected with silicone rubber. Double injections to demonstrate both arteries and veins in the same animal were with India ink and a fluorescent material. Arterial supply to the hippocampus was via transverse hippocampal arteries that stemmed from the longitudinal hippocampal artery, a branch of the posterior cerebral artery. Internal transverse hippocampal arteries located in the hippocampal fissure supplied small, short branches to the adjacent blade of the fascia dentata, part of the area dentata, and CA3 fields. Other branches of the longitudinal artery supplied the remaining blade of the fascia and area dentata, subicular fields, and entorhinal structures. Internal transverse hippocampal veins located in the hippocampal fissure alternated in position with the arteries and appeared to be paired with, and to drain fields supplied by, the internal transverse arteries. Deep transverse hippocampal veins, unaccompanied by arteries, received branches in the intraventricular alveus and adjacent stratum oriens of CA3. The transverse veins drained into longitudinal vessels or the basal vein. Although transversely directed arteries and veins may suggest a hippocampal lamellar neuronal organization, microvascular fields must be mapped before claims are made for a totally segmental vascular architecture in the hippocampus.