Figure 2.

Major cerebral arteries of the human (left) and rat (right), and their potential collateral connection points. (A) Diagram representing the three major cerebral arteries of the human (left) and rat (right): anterior cerebral artery (ACA), middle cerebral artery (MCA), and posterior cerebral artery (PCA). Connection points between these three vessels, known as collateral vessels (examples marked in yellow) are potential locations for the redirection of blood flow from one major artery to another. (B) +0h animals (which received whisker stimulation immediately post-pMCAO) had intact structure and evoked functional response to whisker stimulation at 24 hours post-occlusion (representative functional imaging data and stained coronal brain slice showing normal function and lack of infarct shown at upper right). In addition, baseline level blood flow was observed within the branches of the occluded MCA 24 hours post–permanent MCA occlusion (post-pMCAO; after having dropped significantly in response to occlusion; see graph for quantification of blood flow drop following pMCAO and return following stimulation treatment). The question, based on our knowledge of collateral vessels and the return of blood flow and function in the protected +0h animals, was then, is collateral flow supporting this return and the protection observed? (C) +0h distal occlusion experiments, wherein stimulation was still delivered immediately post-occlusion, but the distal ends of MCA were occluded in addition to the standard base occlusion pMCAO. These animals no longer maintained functional cortical integrity and sustained infarct (arrow). These experiments demonstrate that patent distal branches of MCA are necessary for protective plasticity, suggesting collateral vessel blood flow as the mechanism for the protection observed in +0h animals. Data in panels B and C are from Lay and others (2010); used with permission of authors and publisher.