Early network activity propagates bidirectionally between hippocampus and cortex.

Area of Science:

• Neuroscience
• Developmental Biology
• Computational Neuroscience

Background:

• Spontaneous neuronal activity is crucial for refining brain connections during early development.
• In the neonatal mouse neocortex, activity waves originate from the septal nucleus and piriform cortex.

Purpose of the Study:

• To investigate the hippocampus's role as a potential source of neocortical spontaneous activity waves.
• To understand the mechanisms governing wave propagation from the hippocampus to the neocortex.

Main Methods:

• High-speed calcium imaging in parasagittal mouse brain slices.
• Pharmacological manipulation of GABAergic and glutamatergic neurotransmission.
• Electrical stimulation of brain regions.

Main Results:

• The hippocampus can initiate spontaneous activity waves that propagate into the neocortex.
• GABAergic transmission is necessary for wave propagation into the neocortex, while glutamatergic transmission is essential for hippocampal wave generation.
• Hippocampal waves can trigger astrocytic calcium waves, increasing their likelihood of neocortical propagation.
• The hippocampus and piriform cortex act as pacemakers due to intrinsic circuit properties.

Conclusions:

• The hippocampus is an additional source of neocortical spontaneous activity waves.
• Neurotransmitter systems and astrocytic interactions modulate wave propagation.
• Intrinsic properties of brain regions dictate their pacemaker function in early brain development.