In primary visual cortex (V1), precise spatiotemporal neuronal responses are known to underlie visual
processing. Though neuronal roles in visual processing have been well studied, the role of non-neuronal cells,
particularly astrocytes, in cortical synapses and circuits remains poorly understood. Cortical astrocytes contact
and ensheathe nearly all excitatory synapses, creating discrete functional units consisting of a presynaptic input,
a postsynaptic spine and an astrocyte process. A crucial function of astrocytes is the active uptake of glutamate
from the synaptic cleft via transporters, particularly GLT1. We propose that astrocytes contribute fundamentally
to V1 circuits via GLT1 activity, actively shaping synaptic and neuronal response profiles. Focal Ca2+ transients
potentially related to synaptic glutamate uptake have recently been demonstrated within astrocyte processes,
and synaptic transmission shown to actively recruit astrocytic GLT1 to sites of synaptic activity. Novel high-
resolution imaging techniques, together with cell-specific markers, new optical probes, and genetically
engineered mice with specific temporal and spatial control of protein expression, enable us to analyze the
crosstalk between astrocyte and neuronal activity at unprecedented resolution in awake mice in vivo. We aim to
take advantage of the exquisite organization of visual inputs to V1 neurons to examine the interaction of Ca2+
microdomains, mitochondria and glutamate transporters in astrocyte processes, the functional contribution of
astrocyte transporters to neuronal synapses and circuits during visual processing, and the impact of altered
glutamate transport on the development and plasticity of V1 circuits. In Aim 1, we will examine astrocyte
microdomain Ca2+ responses to visual stimuli, including orientation-specific gratings and complex natural
images, their relationship to mitochondria, and how genetic or pharmacological reduction of GLT1 impacts the
specificity and reliability of astrocyte and cell-specific neuronal responses. In Aim 2, we will determine the
functional relationship between single dendritic spines and adjacent astrocytic processes using simultaneous
dual-wavelength imaging of astrocytes and neurons during visual stimulation. We will also determine how GLT1
reduction affects astrocytic process and neuronal spine responses and structures. In Aim 3, we will determine
the role of GLT1 in the development and plasticity of astrocyte responses and visual cortex circuits. We will
examine how germline reduction of GLT1 alters neuronal and astrocyte microdomain responses during normal
development and following monocular deprivation, along with the sharpening of orientation selectivity and the
binocular matching of orientation preference. Our overarching goal is to critically examine the hypothesis that
astrocytes and their transporters are integral functional partners with neurons in the function and development
of cortical circuits. As such, an understanding of normal and abnormal function in a host of neurodevelopmental
and neurodegenerative disorders will require incorporating the role of astrocytes.