IMMUNOHISTOCHEMICAL ALTERATIONS OF FIBRONECTIN DURING THE FORMATION AND PROLIFERATIVE REPAIR OF EXPERIMENTAL CEREBRAL ANEURYSMS IN RATS

Background and Purpose To determine whether distributional changes of fibronectin, a factor promoting wound healing, occur during the formation and repair of cerebral saccular aneurysms, we performed immunohistochemical analyses in experimental aneurysms. Methods Cerebral aneurysms were induced in rats by both the ligation of the unilateral common carotid artery and induced hypertension. Intimal proliferation in aneurysmal walls was induced by the ligation of the preserved common carotid artery 3 months after the first operation. The distribution of fibronectin was examined by immunohistochemistry in anterior cerebral artery-olfactory artery bifurcations under the following three conditions: normal bifurcations in control rats, early aneurysmal lesions during the aneurysm induction, and aneurysmal lesions dth intimal proliferation. Furthermore, the immunohistochemical distributions of type I and IV collagens were examined to evaluate the specificity of fibronectin immunoreactivity. Results In the normal bifurcations, fibronectin was positive in the subintimal space, the surrounding area of the medial smooth muscle cells, and the adventitial fibrous tissue. In early aneurysmal lesions, linear staining of fibronectin and type I and IV collagens in the subendothelial space disappeared with the loss of the internal elastic lamina. In the intimal proliferation of early aneurysmal lesions, fibronectin was strongly immunostained in the subendothelial space and diffusely immunostained in the widened extracellular space surrounding proliferated cells. In contrast, the stainings of type I and IV collagens were sparse or negative. Conclusions Although the present findings regarding dynamic changes of fibronectin distribution do not prove any causality in the process of aneurysm formation and repair, these immunohistochemical changes may constitute the crucial sequela of intimal endothelial damage and its subsequent recovery in cerebral aneurysms.