Cortical Somatostatin Innervation Follows a Unique Experience-Independent Developmental Trajectory.

Area of Science:

• Neuroscience
• Developmental Biology
• Synaptic Plasticity

Background:

• Inhibitory synapse development is crucial for regulating plasticity but remains poorly understood, especially for dendritic synapses.
• Somatostatin (SST)-expressing neurons form key inhibitory synapses on dendrites, which are difficult to study without specific molecular tags.

Purpose of the Study:

• To investigate the developmental trajectory of SST innervation in the mouse visual cortex.
• To determine the influence of visual experience on SST synapse formation and maturation.

Main Methods:

• Utilized a genetic synapse labeling strategy combined with epitope-preserving magnified analysis of proteome (eMAP).
• Employed tissue expansion and clearing techniques to visualize SST innervation at high resolution in male and female mice.

Main Results:

• SST bouton formation occurs simultaneously across cortical layers, without net pruning, unlike excitatory synapses.
• SST synapse formation peaks post-eye opening, coinciding with critical period plasticity, but is independent of visual experience.
• Excitatory and non-SST inhibitory synapses show experience-dependent development, contrasting with SST innervation.

Conclusions:

• SST cortical innervation follows a unique developmental path, independent of sensory input.
• The developmental timing of SST innervation is optimized to regulate fundamental processes in cortical circuit maturation.
• These findings offer new insights into the integration of influential SST neurons into developing cortical circuitry.