Two-photon fluorescence imaging of visually evoked glutamate release using IGluSnFr in the mouse visual system

Abstract

Neurons within the central nervous system communicate by releasing neurotransmitter at synapses. While electrophysiological recording and calcium imaging allow quantitative measurements of neuronal activation pre- and postsynaptically, a recently developed tool, iGluSnFR, permits direct measurements of neurotransmitter release from one neuron onto another. By visualizing neurotransmitter release, iGluSnFR allows innovative, quantitative studies in at least three major areas. First, by resolving synaptic release locally on dendrites, iGluSnFR enables efficient studies of the spatial organization of synaptic input. Second, by reporting the transmitted signal, rather than the pre- or postsynaptic neuronal response, iGluSnFR can help identify specific contributions from presynaptic release vs. postsynaptic receptor mechanisms during synaptic plasticity. Third, by reporting the presence of neurotransmitter in the extracellular space, iGluSnFR permits new studies of the transporter mechanisms responsible for the removal of neurotransmitter following synaptic release and changes in these mechanisms during neurological disease. In this chapter we describe how to target iGluSnFR expression to select neuron populations and how to measure stimulus-evoked iGluSnFR responses using two-photon fluorescence (2P) microscopic imaging.