A novel focal seizure pattern generated in superficial layers of the olfactory cortex.

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A novel focal seizure pattern generated in superficial layers of the olfactory cortex.

J Neurosci. 2017 Mar 06;:

Authors: Uva L, Saccucci S, Chikhladze M, Tassi L, Gnatkovsky V, Milesi G, Morbin M, de Curtis M

Abstract
Seizure patterns identified in focal epilepsies caused by diverse aetiologies are likely due to different pathogenic mechanisms. We describe here a novel region-specific focal seizure pattern that mimics seizure activity observed in a subpopulation of patients submitted to pre-surgical monitoring with intracerebral electrodes. Distinctive seizure-like events (SLEs) are induced in the olfactory regions by acute treatment of both tangential brain slices and the isolated guinea-pig brain with the potassium channel blocker 4-aminopyridine. The analysis of field potentials, intracellular activities and extracellular potassium changes demonstrates that SLEs in the piriform cortex initiate in the superficial layer 1 lacking principal neurons with an activity-dependent increase of extracellular potassium. SLEs progression (but not onset) does not require the participation of synaptic transmission and is mediated by diffusion of potassium to deep cortical layers. The novel seizure pattern here described is not observed in other cortical regions; it is proposed to rely on the peculiar organization of the superficial piriform cortex layers, characterized by unmyelinated axons and peri-synaptic astroglial envelopes.The study reveals a sequence of ictogenic events in the olfactory cortex that were never described before in other cortical structures, and supports the notion that altered potassium homeostasis and unmyelinated fibres may represent a potential vehicle for focal ictogenesis.SIGNIFICANCE STATEMENTWe describe a novel seizure pattern peculiar of the olfactory cortex that resembles focal seizures with low-voltage fast activity at onset observed in humans. The findings suggest that network mechanisms responsible for seizure onset can be region-specific.

PMID: 28264979 [PubMed - as supplied by publisher]

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