Convergent Inhibitory Cortical Circuit Disruption Drives Genetically Distinct Absence Seizures

Area of Science:

• Neuroscience
• Epilepsy Research
• Cortical Circuitry

Background:

• Absence seizures are common in children, marked by consciousness lapses and EEG abnormalities.
• Thalamic changes are known, but the underlying cortical circuit defects driving spike-wave discharges (SWD) are unclear.

Purpose of the Study:

• Investigate cortical circuit abnormalities in absence epilepsy mouse models.
• Identify the specific neuronal subtypes and circuit motifs involved in SWD generation.
• Establish the causal relationship between identified circuit defects and seizure onset.

Main Methods:

• Utilized stargazer and tottering mouse models of absence epilepsy.
• Examined translaminar inhibitory circuits involving Layer 6 corticothalamic (L6 CT) neurons and Tac1+ Pvalb interneurons.
• Employed chemogenetics to disrupt specific circuit motifs in wild-type mice.

Main Results:

• Identified selective disruption of the L6 CT-Tac1+ Pvalb interneuron motif in both epilepsy models.
• Observed secondary collapse of Sst interneurons coinciding with seizure onset.
• Demonstrated that disrupting this motif alone induces seizures and Sst interneuron collapse in wild-type mice.

Conclusions:

• A sequential synaptic failure, a 'domino effect,' in translaminar inhibitory circuits underlies absence epilepsy.
• This identified cortical circuit pathology is a shared feature across different genetic models of absence epilepsy.
• The disrupted L6 CT-Tac1+ Pvalb circuit represents a convergent and causative target for therapeutic intervention.