Astrocytic endfoot Ca²⁺ correlates with parenchymal vessel responses during 4-AP induced epilepsy: An in vivo two-photon lifetime microscopy study

Abstract

Neurovascular coupling (NVC) underlying the local increase in blood flow during neural activity forms the basis of functional brain imaging and is altered in epilepsy. Because astrocytic calcium (Ca²⁺) signaling is involved in NVC, this study investigates the role of this pathway in epilepsy. Here, we exploit 4-AP induced epileptic events to show that absolute Ca²⁺ concentration in cortical astrocyte endfeet in vivo correlates with the diameter of precapillary arterioles during neural activity. We simultaneously monitored free Ca²⁺ concentration in astrocytic endfeet with the Ca²⁺-sensitive indicator OGB-1 and diameter of adjacent arterioles in the somatosensory cortex of adult mice by two-photon fluorescence lifetime measurements following 4-AP injection. Our results reveal that, regardless of the mechanism by which astrocytic endfoot Ca²⁺ was elevated during epileptic events, increases in Ca²⁺ associated with vasodilation for each individual ictal event in the focus. In the remote area, increases in Ca²⁺ correlated with vasoconstriction at the onset of seizure and vasodilation during the later part of the seizure. Furthermore, a slow increase in absolute Ca²⁺ with time following multiple seizures was observed, which in turn, correlated with a trend of arteriolar constriction both at the epileptic focus and remote areas.