title: A Novel Focal Seizure Pattern Generated in Superficial Layers of the Olfactory Cortex.
abstract: Seizure patterns identified in focal epilepsies caused by diverse etiologies 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 presurgical 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. 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. SLE 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, which are characterized by unmyelinated axons and perisynaptic astroglial envelopes. This 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 fibers 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.
authors.affiliation: Unit of Epileptology.
authors.forename: Laura
authors.initials: L
authors.lastname: Uva
authors.affiliation: Unit of Neuropathology, and.
authors.forename: Stefania
authors.initials: S
authors.lastname: Saccucci
authors.affiliation: Unit of Clinical Neurophysiology, Fondazione Istituto Neurologico Carlo Besta, 20133 Milano, Italy, and.
authors.forename: Maia
authors.initials: M
authors.lastname: Chikhladze
authors.affiliation: Claudio Munari Epilepsy Surgery Center, Ospedale Niguarda Ca' Granda, 20162 Milano, Italy.
authors.forename: Laura
authors.initials: L
authors.lastname: Tassi
authors.affiliation: Unit of Epileptology.
authors.forename: Vadym
authors.initials: V
authors.lastname: Gnatkovsky
authors.affiliation: Unit of Epileptology.
authors.forename: Gloria
authors.identifier: 0000-0002-0119-8085
authors.initials: G
authors.lastname: Milesi
authors.affiliation: Unit of Neuropathology, and.
authors.forename: Michela
authors.initials: M
authors.lastname: Morbin
authors.affiliation: Unit of Epileptology, marco.decurtis@istituto-besta.it.
authors.forename: Marco
authors.initials: M
authors.lastname: de Curtis
mesh_terms: D000818:Animals; D001683:Biological Clocks; D058256:Brain Waves; D005260:Female; D006168:Guinea Pigs; D009415:Nerve Net / Q000503:physiopathology*; D066194:Olfactory Cortex / Q000503:physiopathology*; D011188:Potassium / Q000378:metabolism; D012640:Seizures / Q000503:physiopathology*; D011984:Sensory Receptor Cells
chemical_list: D011188:Potassium
keywords: 4-aminopyridine; extracellular potassium; human intracerebral EEG recordings; in vitro guinea pig brain