Abstract
Regulation of AMPA receptor (AMPAR) expression is central to synaptic plasticity and brain function, but how these changes occur in vivo remains elusive. Here, we developed a method to longitudinally monitor the expression of synaptic AMPARs across multiple cortical layers in awake mice using two-photon imaging. We observed that baseline AMPAR expression in individual spines is highly dynamic with more dynamics in primary visual cortex (V1) layer 2/3 (L2/3) neurons than V1 L5 neurons. Visual deprivation through binocular enucleation induces a synapse-specific and depth-dependent change of synaptic AMPARs in V1 L2/3 neurons, wherein deep synapses are potentiated more than superficial synapses. The increase is specific to L2/3 neurons and absent on apical dendrites of L5 neurons, and is dependent on expression of the AMPAR-binding protein GRIP1. Our study demonstrates that specific neuronal connections, across cortical layers and even within individual neurons, respond uniquely to changes in sensory experience.
Highlights
Neuronal circuits in the brain are subject to synaptic plasticity mechanisms induced by sensory experience (Ko et al, 2013) and learning (Chen et al, 2015; Peters et al, 2017) while exhibiting a critical ability to maintain network activity within a normal operating range during perturbations such as sensory deprivation (Hengen et al, 2016; Turrigiano, 2012)
To track AMPA receptors (AMPARs) and spine dynamics in layer 2/3 (L2/3) neurons of V1 in awake mice, we employed in utero electroporation to transfect L2/3 pyramidal neurons with the GluA1 AMPAR subunit tagged with Super Ecliptic pHluorin (SEP), a pH-sensitive form of green fluorescent protein, myc-GluA2 AMPAR subunit, and dsRed2 as previously described (Makino and Malinow, 2011; Suresh and Dunaevsky, 2017; Zhang et al, 2015; Figure 1; Figure 1—figure supplement 1)
We found a high correlation between spine intensity of SEP-GluA1 and glutamate uncaging-evoked excitatory postsynaptic current amplitude (Figure 1C,D), suggesting that spine enrichment of SEP-GluA1 largely reflects postsynaptic strength
Summary
Neuronal circuits in the brain are subject to synaptic plasticity mechanisms induced by sensory experience (Ko et al, 2013) and learning (Chen et al, 2015; Peters et al, 2017) while exhibiting a critical ability to maintain network activity within a normal operating range during perturbations such as sensory deprivation (Hengen et al, 2016; Turrigiano, 2012). The molecular mechanisms underlying this homeostatic regulation of neuronal activity in vivo have not been much investigated. Whether these homeostatic mechanisms occur homogenously across the individual neuron or are specific to individual dendritic compartments remains elusive. One of the major forms of homeostatic regulation of neuronal activity involves the modulation of AMPAR expression at synapses and this has been extensively characterized in vitro and ex vivo (Desai et al, 2002; Goel et al, 2006; Goel and Lee, 2007; O’Brien et al, 1998; Turrigiano, 2012; Turrigiano et al, 1998), where chronic visual deprivation induces up-regulation of synaptic AMPARs in the primary visual cortex (V1). Whether sensory-deprivation-induced homeostatic regulation of AMPAR trafficking occurs in vivo is unknown
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