Interruption of the middle cerebral artery in 10-day-old rat alters normal development of distal collaterals.

Pial surface arterioles join rami of the anterior and middle cerebral arteries (MCA) in 10-day-old normal Wistar rats. Normally, the anastomosing branches differentiate into small-diameter vessels with significantly greater tortuosity (length) by 56 days of age. After interruption of th e MCA in 10-day-old rats, large-diameter, relatively straight collaterals were observed 46 or 90-110 days later. Evidently altered hemodynamic factors, as the result of MCA interruption, prevent the development of a normal pattern of arterioles and augment the development of an anomalous pattern of collaterals in young Wistar rats.