Development of Differential Sublaminar Feedforward Inhibitory Circuits in CA1 Hippocampus Requires Satb2

Area of Science:

• Neuroscience
• Cell Biology
• Developmental Biology

Background:

• CA1 pyramidal cells (PCs) exhibit radial organization (deep/superficial) influencing information processing.
• Superficial PCs have weaker feedforward inhibition from CA3 Schaffer collaterals due to fewer inhibitory synapses from parvalbumin (PV)-expressing interneurons.

Purpose of the Study:

• Investigate mechanisms of CA1 PC differentiation and inhibitory circuit development.
• Determine the role of the transcriptional regulator SATB2 in establishing superficial PC inhibitory connectivity.

Main Methods:

• Conditional knockout of Satb2 in Emx1 mice (both sexes) to study its function in PCs.
• Paired whole-cell recordings to assess synaptic connections between PCs and PV+ interneurons.
• Analysis of excitatory and inhibitory synaptic strength.

Main Results:

• Satb2 knockout in superficial PCs increased feedforward inhibition, matching deep PC levels in controls.
• Loss of Satb2 enhanced unitary inhibitory synaptic connections from PV+ interneurons to superficial PCs.
• Excitatory synaptic connections were unaffected; SATB2 suppresses PV+ interneuron synapse formation during development.

Conclusions:

• Early postnatal SATB2 expression in superficial PCs is essential for developing biased feedforward inhibition in the hippocampus.
• SATB2 regulates inhibitory synapse formation, not excitatory ones, during CA1 circuit development.