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Abstract:
Glutamate, a primary excitatory neurotransmitter, provides us key understanding of the signaling of neuron-glia-vessel network due to its roles in trans- and extrasynaptic transmission in synaptic release and propagation. Using virally expressed genetically encoded fluorescent reporter iGluSnFR for extracellular glutamate sensing and genetically encoded calcium indicator GCaMP6f for calcium sensing, we demonstrate iGluSnFR with a more rapid temporal features of sensory response than the evoked calcium signal detected by GCaMP6f (Fig. 1 A). iGluSnFR showed earlier onset time (~11 ms vs ~20ms) and time to peak response (~20 ms vs ~40 ms) when it is compared to GCaMP6f. Extracellular clearance following synaptic glutamate release evoked by multiply electrical forepaw stimuli (2mA, 1Hz,10s and 2 mA, 3Hz,10s) showed comparable signal-to-noise ratio with GCaMP6f (Fig. 1 B C). The temporal profile of extracellular glutamate might help deciphering the cellular mechanism underlying blood-oxygen-level-depended (BOLD) signal in the brain of rodents. Implemented together with functional magnetic resonance imaging (fMRI) and simultaneously two channel fiber-optic fluorescent recording, robust BOLD signal in response to electrical forepaw stimulation were observed in both iGluSnFR and GCaMP6f expressed somatosensory region (Fig.1 D). This combined method may lead to a better understanding of neurovascular coupling through the neuron-glia-vessel network in the animal brain.
