Time-Course of Changes in Astrocyte Endfeet Damage in the Hippocampus Following Experimental Ischemia and Reperfusion Injury

Background: Astrocyte endfeet (AEF) serves as a key element of the blood-brain barrier and is important for the survival and maintenance of neuronal function. However, the immunohistochemical and ultrastructural changes of AEF in the CA1 and CA3 areas of the hippocampus over time following cerebral ischemia-reperfusion (IR) injury have not been well elucidated. Objectives: We investigated chronological changes in AEF in the gerbil hippocampal CA1 area from 3 h to 10 days following transient forebrain ischemia (TFI), and examined their association with neuronal death and tissue repair following IR injury. Changes in the CA3 area were also examined at 10 days post-TFI for comparative purposes. Methods: Neuronal death was confirmed using histochemistry, immunohistochemistry, and histofluorescence. Changes in AEF were examined by double immunofluorescence with glial fibrillary acidic protein (GFAP) and glucose transporter 1 (GLUT1), and by transmission electron microscopy (TEM) for ultrastructural changes. Results: Significant TFI-induced neuronal death occurred in the CA1 area on day 5 following IR injury and persisted until 10 days after TFI, while no neuronal death (or loss) was found in the CA3 area after TFI. Looking at TFI-induced changes in AEF, at 3 and 6 h after TFI, GFAP-immunoreactive (+) AEF in the CA1 area appeared swollen and harbored enlarged, dark mitochondria, and the swelling was reduced by 1-day post-TFI. On 2 and 5 days following TFI, GFAP+ AEF were markedly enlarged and fragmented, containing shrunken mitochondria, vacuolations, and sparse organelles. Ten days post-TFI, the ends of GFAP+ astrocytic processes extended to microvessels, appeared edematous, and were filled with cellular debris. In the CA3 area, AEF was slightly dilated at 10 days after TFI. These findings indicate that damage to or disruption of AEF in the CA1 area occurs in the early phase after 5-min TFI but is rarely observed in the CA3 area. Conclusion: Taken together, damage to or disruption of AEF following ischemic insults may be strongly linked to neuronal death/loss.