Interneurons Differentially Contribute to Spontaneous Network Activity in the Developing Hippocampus Dependent on...

Area of Science:

• Neuroscience
• Developmental Biology
• Computational Neuroscience

Background:

• Spontaneously generated network activity is crucial for synaptic development in immature neural circuits.
• Giant depolarizing potentials (GDPs) are key network events in the developing rodent hippocampus.
• Interneurons, originating from the medial (MGE) or caudal (CGE) ganglionic eminences, contribute to GDPs, but their relative roles are unclear.

Purpose of the Study:

• To investigate the distinct contributions of MGE- and CGE-derived interneurons to GDP generation and network coordination in the neonatal mouse hippocampus.
• To compare the synaptic connectivity and targeting properties of MGE- and CGE-derived interneurons in the CA1 region.

Main Methods:

• Optogenetic inhibition of MGE- or CGE-derived interneurons in a region-specific manner in vitro.
• Dual whole-cell patch-clamp recordings in neonatal mouse hippocampus (CA1).
• Analysis of synaptic connections and network activity (GDPs) between CA1 and CA3 regions.

Main Results:

• MGE-derived interneurons preferentially and strongly contributed to GDP generation in the CA1 region.
• MGE interneurons exhibited higher synaptic connectivity with pyramidal cells compared to CGE interneurons.
• MGE interneurons primarily targeted perisomatic regions, while CGE interneurons targeted dendrites.
• Inhibition of MGE interneurons in CA1 suppressed GDPs in CA3, and vice versa, indicating coordinated network activity.

Conclusions:

• MGE-derived interneurons play a dominant role in generating and coordinating GDPs across the developing hippocampus.
• Their extensive synaptic connectivity and specific targeting properties enable MGE interneurons to control network activity.
• These findings reveal a critical function for MGE interneurons in establishing functional hippocampal circuitry.