Neurovascular coupling (NVC) is defined as a local increase in cerebral blood flow in response to neuronal activity, it forms the basis of functional brain imaging and is altered during epilepsy. Because astrocytic calcium signaling (Ca2+) has been involved in the response of parenchymal vessels, this study investigates the role of this pathway during epilepsy. We exploit 4-Aminopyridine (4-AP) induced epileptic seizures to show that absolute Ca2+ concentration in astrocytic endfeet correlates with the changes in diameter of parenchymal vessels during neural activity in vivo. A two-photon laser scanning fluorescence lifetime microscopy was developed to simultaneously monitor free Ca2+ concentration in astrocytic endfeet with the calcium-sensitive indicator Oregon Green 488 BAPTA-1 (OGB-1) and the diameter of parenchymal vessels in the somatosensory cortex of mice following 4-AP injection. Our results reveal that the resting Ca2+ concentration in glial cells was spatially heterogeneous and that resting Ca2+ concentration in somatic regions was significantly higher than in endfoot regions. Moreover, following 4-AP injection in the somatosensory cortex of mice, we observed increases of Ca2+ in astrocytic endfeet associated with vasodilation of parenchymal vessels for each individual ictal event in the epileptic focus. However, vasodilation was seen to be inhibited by increase in absolute resting Ca2+ concentration. Our results suggest a role for baseline astrocytic Ca2+ concentration in vasodilation.
Cong Zhang, Maryam Tabatabaei, Samuel Bélanger, Hélène Girouard, Mohammad Moeini, Xuecong Lu, and Frédéric Lesage, "In vivo measurement of astrocytic endfoot Ca2+ and parenchymal vessel responses during 4-AP induced epilepsy using two-photon fluorescence lifetime microscopy," Proc. SPIE 10498, Multiphoton Microscopy in the Biomedical Sciences XVIII, 104980X (Presented at SPIE BiOS: January 29, 2018; Published: 23 February 2018); https://doi.org/10.1117/12.2290579.
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