ABSTRACT
Consciousness is lost within seconds upon cessation of cerebral blood flow. The brain cannot store oxygen, and interruption of oxidative phosphorylation is fatal within minutes. Yet only rudimentary knowledge exists regarding cortical partial oxygen tension (Po2) dynamics under physiological conditions. Here we introduce Green enhanced Nano-lantern (GeNL), a genetically encoded bioluminescent oxygen indicator for Po2 imaging. In awake behaving mice, we uncover the existence of spontaneous, spatially defined "hypoxic pockets" and demonstrate their linkage to the abrogation of local capillary flow. Exercise reduced the burden of hypoxic pockets by 52% compared with rest. The study provides insight into cortical oxygen dynamics in awake behaving animals and concurrently establishes a tool to delineate the importance of oxygen tension in physiological processes and neurological diseases.
Subject(s)
Cerebral Cortex , Cerebrovascular Circulation , Hypoxia, Brain , Luminescent Measurements , Oxygen Saturation , Oxygen , Animals , Mice , Cerebral Cortex/blood supply , Cerebral Cortex/diagnostic imaging , Cerebral Cortex/metabolism , Oxygen/blood , Oxygen/metabolism , Partial Pressure , Hypoxia, Brain/blood , Hypoxia, Brain/diagnostic imaging , Hypoxia, Brain/metabolism , Vasodilation , Luminescent Measurements/methods , Luciferases/genetics , Luciferases/metabolism , Recombinant Fusion Proteins/genetics , Recombinant Fusion Proteins/metabolism , Green Fluorescent Proteins/genetics , Green Fluorescent Proteins/metabolism , Hypercapnia/blood , Hypercapnia/diagnostic imaging , Hypercapnia/metabolismABSTRACT
Information transfer within neuronal circuits depends on the balance and recurrent activity of excitatory and inhibitory neurotransmission. Chloride (Cl-) is the major central nervous system (CNS) anion mediating inhibitory neurotransmission. Astrocytes are key homoeostatic glial cells populating the CNS, although the role of these cells in regulating excitatory-inhibitory balance remains unexplored. Here we show that astrocytes act as a dynamic Cl- reservoir regulating Cl- homoeostasis in the CNS. We found that intracellular chloride concentration ([Cl-]i) in astrocytes is high and stable during sleep. In awake mice astrocytic [Cl-]i is lower and exhibits large fluctuation in response to both sensory input and motor activity. Optogenetic manipulation of astrocytic [Cl-]i directly modulates neuronal activity during locomotion or whisker stimulation. Astrocytes thus serve as a dynamic source of extracellular Cl- available for GABAergic transmission in awake mice, which represents a mechanism for modulation of the inhibitory tone during sustained neuronal activity.
