Selective Maturation of Temporal Dynamics of Intracortical Excitatory Transmission at the Critical Period Onset

• Temporal dynamics of intracortical excitatory synapses mature at critical period onset
• Dynamics of cortical inhibitory synapses and thalamocortical inputs are unchanged
• This selective modulation depends on early visual experience
• Ubiquitous reduction of presynaptic release underlies the selective modulation.

SummaryAlthough the developmental maturation of cortical inhibitory synapses is known to be a critical factor in gating the onset of critical period (CP) for experience-dependent cortical plasticity, how synaptic transmission dynamics of other cortical synapses are regulated during the transition to CP remains unknown. Here, by systematically examining various intracortical synapses within layer 4 of the mouse visual cortex, we demonstrate that synaptic temporal dynamics of intracortical excitatory synapses on principal cells (PCs) and inhibitory parvalbumin- or somatostatin-expressing cells are selectively regulated before the CP onset, whereas those of intracortical inhibitory synapses and long-range thalamocortical excitatory synapses remain unchanged. This selective maturation of synaptic dynamics results from a ubiquitous reduction of presynaptic release and is dependent on visual experience. These findings provide an additional essential circuit mechanism for regulating CP timing in the developing visual cortex.

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