Layer-specific generation and propagation of seizures in slices of developing neocortex: role of excitatory GABAergic...

Area of Science:

• Neuroscience
• Epilepsy Research
• Neonatal Neurology

Background:

• The neonatal period is a critical window for seizure susceptibility.
• Neocortical networks play a central role in infantile epilepsies.
• Understanding seizure generation mechanisms in immature brains is crucial.

Purpose of the Study:

• To investigate the transition from interictal seizures (IISs) to ictal seizures (ISs) in immature neocortical networks.
• To elucidate the roles of different neuronal layers and cell types in seizure generation and propagation.
• To explore the involvement of excitatory GABA and NKCC1 transporters in neonatal seizures.

Main Methods:

• Application of 4-aminopyridine (4-AP) to immature (P6-P9) rat neocortical slices.
• Cell-attached recordings to monitor neuronal activity (action potentials).
• Single N-methyl-d-aspartate (NMDA) channel recordings to measure cell resting potential (Em).
• Administration of bumetanide, a NKCC1 co-transporter antagonist.

Main Results:

• 4-AP induced layer-specific IISs in immature neocortical slices, which transformed into ISs.
• Transition to ISs correlated with gradual Em depolarization of L2/3 and L5/6 pyramidal neurons, increasing excitability.
• Deep layer (L5/6) neurons initiated IISs, propagating to superficial layers (L2/3) via interneurons.
• Bumetanide inhibited IIS generation and prevented their transformation to ISs, suggesting excitatory GABA contributes to epilepsy.

Conclusions:

• Deep layer neurons are more susceptible to seizures than superficial ones during development.
• The transition from IISs to ISs involves enhanced excitability of pyramidal neurons due to Em depolarization.
• Inhibition of NKCC1 by bumetanide offers a potential therapeutic strategy for neonatal seizures by targeting excitatory GABA effects.