Optical measurement of microvascular oxygenation and blood flow responses in awake mouse cortex during functional activation
İkbal Şencan, Tatiana Esipova, Kıvılcım Kılıç, Baoqiang Li, Michèle Desjardins, Mohammad A Yaseen, Hui Wang, Jason E Porter, Sreekanth Kura, Buyin Fu, Timothy W Secomb, David A Boas, Sergei A Vinogradov, Anna Devor, Sava Sakadžić
Abstract
The cerebral cortex has a number of conserved morphological and functional characteristics across brain regions and species. Among them, the laminar differences in microvascular density and mitochondrial cytochrome c oxidase staining suggest potential laminar variability in the baseline O 2 metabolism and/or laminar variability in both O 2 demand and hemodynamic response. Here, we investigate the laminar profile of stimulus-induced intravascular partial pressure of O 2 (pO2) transients to stimulus-induced neuronal activation in fully awake mice using two-photon phosphorescence lifetime microscopy. Our results demonstrate that stimulus-induced changes in intravascular pO 2 are conserved across cortical layers I–IV, suggesting a tightly controlled neurovascular response to provide adequate O 2 supply across cortical depth. In addition, we observed a larger change in venular O 2 saturation (ΔsO 2 ) compared to arterioles, a gradual increase in venular ΔsO 2 response towards the cortical surface, and absence of the intravascular “initial dip” previously reported under anesthesia. This study paves the way for quantification of layer-specific cerebral O 2 metabolic responses, facilitating investigation of brain energetics in health and disease and informed interpretation of laminar blood oxygen level dependent functional magnetic resonance imaging signals.