Abstract
SummarySynaptic scaling is a key homeostatic plasticity mechanism and is thought to be involved in the regulation of cortical activity levels. Here we investigated the spatial scale of homeostatic changes in spine size following sensory deprivation in a subset of inhibitory (layer 2/3 GAD65-positive) and excitatory (layer 5 Thy1-positive) neurons in mouse visual cortex. Using repeated in vivo two-photon imaging, we find that increases in spine size are tumor necrosis factor alpha (TNF-α) dependent and thus are likely associated with synaptic scaling. Rather than occurring at all spines, the observed increases in spine size are spatially localized to a subset of dendritic branches and are correlated with the degree of recent local spine loss within that branch. Using simulations, we show that such a compartmentalized form of synaptic scaling has computational benefits over cell-wide scaling for information processing within the cell.
Highlights
Following a reduction in activity resulting from sensory deprivation, excitatory synapses have been shown to strengthen, which is thought to facilitate the restoration of activity levels (Hengen et al, 2013, 2016; Keck et al, 2013; Wallace and Bear, 2004)
We focus on layer 5 excitatory cells, as we have previously reported that they exhibit spine size increases following sensory deprivation (Keck et al, 2013), whereas in layer 2/3 excitatory cells, we have previously found no evidence for either net increases in spine size or synaptic scaling in adult animals (Barnes et al, 2015)
We still observed a range of spine size changes similar to what we measured in control animals (Figures S1I–S1L), we found that the net in vivo spine size increases were blocked in both inhibitory (Figures 1D, S1I, and S1J) and excitatory (Figures 1E, S1K, and S1L) neurons in deprived animals that were injected with the tumor necrosis factor alpha (TNF-a) inhibitor, suggesting that the net increases in spine size reflect a synaptic scaling-like process
Summary
Following a reduction in activity resulting from sensory deprivation, excitatory synapses have been shown to strengthen, which is thought to facilitate the restoration of activity levels (Hengen et al, 2013, 2016; Keck et al, 2013; Wallace and Bear, 2004). Studies in reduced preparations have demonstrated that synaptic scaling can be locally induced in dendritic branches (Sutton et al, 2006) and that AMPARs can be synthesized locally within branches (Ju et al, 2004). These studies suggest that scaling could be implemented independently within dendritic branches (Yu and Goda, 2009), consistent with the idea that the dendritic branch is a fundamental computational unit for the processing of neural information (Branco and Ha€usser, 2010; Poirazi et al, 2003)
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