Stability of neocortical synapses across sleep and wake states during the critical period in rats

Sleep is important for brain plasticity, but its exact function remains mysterious. An influential but controversial idea is that a crucial function of sleep is to drive widespread downscaling of excitatory synaptic strengths. Here, we used real-time sleep classification, ex vivo measurements of postsynaptic strength, and in vivo optogenetic monitoring of thalamocortical synaptic efficacy to ask whether sleep and wake states can constitutively drive changes in synaptic strength within the neocortex of juvenile rats. We found that miniature excitatory postsynaptic current amplitudes onto L4 and L2/3 pyramidal neurons were stable across sleep- and wake-dense epochs in both primary visual (V1) and prefrontal cortex (PFC). Further, chronic monitoring of thalamocortical synaptic efficacy in V1 of freely behaving animals revealed stable responses across even prolonged periods of natural sleep and wake. Together, these data demonstrate that sleep does not drive widespread downscaling of synaptic strengths during the highly plastic critical period in juvenile animals. Whether this remarkable stability across sleep and wake generalizes to the fully mature nervous system remains to be seen.


Sample-size estimation
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Replicates
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Animal numbers can be found in the figure legends. Outliers were not removed, however cells not meeting standard measures of quality were excluded (criteria described in Methods sections concerning data collection).

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Animals were randomly chosen for conditions in slice experiments (Fig 3). Data handling is described in Methods section (See mEPSC analysis and Post hoc semiautomated behavioral state scoring).
Significant programs used for data analysis and experimentation have been uploaded to GitHub (link provided in Code Availability section of Methods). Figure data is in the process of being uploaded to Figshare (https://figshare.com/projects/Cary_et_al_2021_Elife_Submission/95867). Additional processed data used in analysis will be added as well.