Layer I ectopias and increased excitability in murine neocortex.

Area of Science:

• Neuroscience
• Developmental Neuroscience
• Epileptology

Background:

• Cortical dysplasias are linked to epilepsy and cognitive deficits in humans.
• Existing animal models often involve global disruptions or lesions, leaving the impact of small malformations unclear.
• Layer I ectopias, small neuronal misplacements, are found in humans with cognitive issues and in mice with behavioral deficits.

Purpose of the Study:

• To investigate if small, spontaneous neocortical malformations (ectopias) increase seizure susceptibility and brain excitability.
• To determine if single-layer I ectopias are associated with heightened cortical excitability in vitro and in vivo.

Main Methods:

• Extracellular recordings from brain slices to assess neuronal excitability.
• Utilizing the GABA(A) receptor antagonist bicuculline to induce epileptiform activity.
• In vivo testing using the convulsant pentylenetetrazole in mice with and without ectopias.

Main Results:

• Slices with single-layer I ectopias exhibited epileptiform activity at lower bicuculline concentrations compared to controls.
• Removal of ectopias did not restore normal excitability, indicating the source is not within the malformation itself.
• Mice with ectopias showed increased sensitivity to pentylenetetrazole, suggesting heightened in vivo seizure susceptibility.

Conclusions:

• Focal layer I malformations increase cortical excitability.
• Even small, spontaneous cortical dysplasias are associated with increased excitability both in vitro and in vivo.
• These findings suggest a potential mechanism linking minor neocortical malformations to neurological dysfunction.