Unbalanced Peptidergic Inhibition in Superficial Neocortex Underlies Spike and Wave Seizure Activity

Area of Science:

• Neuroscience
• Epileptology
• Computational Neuroscience

Background:

• Slow spike and wave discharges (0.5-4 Hz) are characteristic of various epilepsies and are linked to thalamocortical axis dysfunction.
• While thalamic mechanisms are well-described, a separate cortical generator for these discharges remains to be fully elucidated.

Purpose of the Study:

• To investigate a separate generator for spike and wave discharges within neocortical local circuits.
• To elucidate the specific cellular and molecular mechanisms underlying the generation of these epileptiform discharges in rats.

Main Methods:

• Utilized electrophysiological recordings in rat neocortex to analyze background delta rhythms and spike and wave discharges.
• Investigated the role of neuromodulatory systems, including nicotinic acetylcholine and serotonin (5HT3A) receptors, in regulating cortical interneurons.
• Examined the involvement of neuropeptides, specifically neuropeptide Y (NPY) and vasoactive intestinal peptide (VIP), in modulating local circuit inhibition and disinhibition.

Main Results:

• Identified a neocortical generator for spike and wave discharges originating from a sleep-associated delta rhythm.
• Demonstrated that loss of tonic neuromodulatory excitation to 5HT3-immunopositive interneurons slows and amplifies the delta rhythm into the 'wave' component.
• Showed that spike and wave discharges result from impaired fast inhibition and increased slow inhibition in superficial cortical layers, driven by reduced NPY and increased VIP signaling.

Conclusions:

• Aberrant neuropeptide corelease in neocortical local circuits can precipitate spike and wave discharges, suggesting a novel mechanism for epilepsy.
• Blockade of NPY Y1 receptors induced spike and wave discharges, while VIP receptor blockade nearly abolished them, highlighting their opposing roles.
• These findings challenge the solely thalamic origin of spike and wave discharges, proposing a significant contribution from local cortical circuit dynamics.