Dynamic changes in astrocyte free Ca 2+ regulate synaptic signaling and local blood flow. Although astrocytes are poised to integrate signals from synapses and the vasculature to perform their functional roles, it remains unclear what dictates astrocyte responses during neurovascular coupling under realistic conditions. We examined peri-arteriole and peri-capillary astrocytes in the barrel cortex of active mice in response to sensory stimulation or volitional behaviors. We observed an AMPA and NMDA receptor-dependent elevation in astrocyte endfoot Ca 2+ that followed functional hyperemia onset. This delayed astrocyte Ca 2+ signal was dependent on the animal's action at the time of measurement as well as a neurovascular pathway that linked to endothelial-derived nitric oxide. A similar elevation in endfoot Ca 2+ was evoked using vascular chemogenetics or optogenetics, and opto-stimulated dilation recruited the same nitric oxide pathway as functional hyperemia. These data show that behavioral state and microvasculature influence astrocyte Ca 2+ in active mice.

No abstract

Astrocytes support the energy demands of synaptic transmission and plasticity. Enduring changes in synaptic efficacy are highly sensitive to stress, yet whether changes to astrocyte bioenergetic control of synapses contributes to stress-impaired plasticity is unclear. Here we show in mice that stress constrains the shuttling of glucose and lactate through astrocyte networks, creating a barrier for neuronal access to an astrocytic energy reservoir in the hippocampus and neocortex, compromising long-term potentiation. Impairing astrocytic delivery of energy substrates by reducing astrocyte gap junction coupling with dominant negative connexin 43 or by disrupting lactate efflux was sufficient to mimic the effects of stress on long-term potentiation. Furthermore, direct restoration of the astrocyte lactate supply alone rescued stress-impaired synaptic plasticity, which was blocked by inhibiting neural lactate uptake. This gating of synaptic plasticity in stress by astrocytic metabolic networks indicates a broader role of astrocyte bioenergetics in determining how experiencedependent information is controlled.

Highlights d Arteriole tone increases astrocyte endfoot Ca 2+ via TRPV4 channels to engage COX-1 d COX-1 generates feedback dilators to limit the extent of constriction d Astrocytic COX-1 constrains ultra-slow arteriole oscillations in slice and in vivo d Clamping astrocyte Ca 2+ in vivo decreases cerebral vasomotion

Functional hyperemia occurs when enhanced neuronal activity signals to increase local cerebral blood flow (CBF) to satisfy regional energy demand. Ca2+ elevation in astrocytes can drive arteriole dilation to increase CBF, yet affirmative evidence for the necessity of astrocytes in functional hyperemia in vivo is lacking. In awake mice, we discovered that functional hyperemia is bimodal with a distinct early and late component whereby arteriole dilation progresses as sensory stimulation is sustained. Clamping astrocyte Ca2+ signaling in vivo by expressing a plasma membrane Ca2+ ATPase (CalEx) reduces sustained but not brief sensory-evoked arteriole dilation. Elevating astrocyte free Ca2+ using chemogenetics selectively augments sustained hyperemia. Antagonizing NMDA-receptors or epoxyeicosatrienoic acid production reduces only the late component of functional hyperemia, leaving brief increases in CBF to sensory stimulation intact. We propose that a fundamental role of astrocyte Ca2+ is to amplify functional hyperemia when neuronal activation is prolonged.

The original version of the Supplementary Information associated with this Article contained an error in the Supplementary Data 2 file, which arose during manuscript preparation. The values in column D were sorted in descending order, but columns A-C were not reordered accordingly. The HTML has been updated to include the correct Supplementary Data 2 file.

Brain requires increased local cerebral blood flow (CBF) for as long as necessary during neuronal activation to match O2 and glucose supply with demand – termed functional hyperemia. Ca2+ elevation in astrocytes can drive arteriole dilation to increase CBF, yet affirmative evidence for the necessity of astrocytes in functional hyperemia in vivo is lacking. In awake and active mice, we discovered that functional hyperemia is bimodal with a distinct early and late component whereby arteriole dilation progresses as sensory stimulation is sustained. Clamping astrocyte Ca2+ signaling in vivo by expressing a high-affinity plasma membrane Ca2+ ATPase (CalEx) reduces sustained but not brief sensory-evoked arteriole dilation. Reciprocally, elevating astrocyte free Ca2+ using chemogenetics selectively augments sustained but not brief hyperemia. Neither locomotion, arousal, nor changes in neuronal signaling account for the selective effect of astrocyte Ca2+ on the late phase of the CBF response. Antagonizing NMDA receptors or epoxyeicosatrienoic acid production reduces only the late component of functional hyperemia, leaving brief increases in CBF to sensory stimulation intact. We propose that a fundamental role of astrocyte Ca2+ is to amplify functional hyperemia when neuronal activation is prolonged.

There has been a clear movement in recent years towards the adoption of more naturalistic experimental regimes for the study of behavior and its underlying neural architecture. Here we provide a protocol that allows experimenters working with mice, to mimic a looming and advancing predatory threat from the sky. This approach is easy to implement and can be combined with sophisticated neural recordings that allow access to real-time activity during behavior. This approach offers another option in a battery of tests that allow for a more comprehensive understanding of defensive behaviors.