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Lookup NU author(s): Dr Alistair Jenkins,
Professor Roger Whittaker,
Dr Ian Schofield,
Dr Gavin Clowry,
Professor Mark Cunningham
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Fast ripples (FRs) are network oscillations, defined variously as having frequencies of > 150 to > 250 Hz, with a controversial mechanism. FRs appear to indicate a propensity of cortical tissue to originate seizures. Here, we demonstrate field oscillations, at up to 400 Hz, in spontaneously epileptic human cortical tissue in vitro, and present a network model that could explain FRs themselves, and their relation to 'ordinary' (slower) ripples. We performed network simulations with model pyramidal neurons, having axons electrically coupled. Ripples (< 250 Hz) were favored when conduction of action potentials, axon to axon, was reliable. Whereas ripple population activity was periodic, firing of individual axons varied in relative phase. A switch from ripples to FRs took place when an ectopic spike occurred in a cell coupled to another cell, itself multiply coupled to others. Propagation could then start in one direction only, a condition suitable for re-entry. The resulting oscillations were > 250 Hz, were sustained or interrupted, and had little jitter in the firing of individual axons. The form of model FR was similar to spontaneously occurring FRs in excised human epileptic tissue. In vitro, FRs were suppressed by a gap junction blocker. Our data suggest that a given network can produce ripples, FRs, or both, via gap junctions, and that FRs are favored by clusters of axonal gap junctions. If axonal gap junctions indeed occur in epileptic tissue, and are mediated by connexin 26 (recently shown to mediate coupling between immature neocortical pyramidal cells), then this prediction is testable.
Author(s): Simon A, Traub RD, Vladimirov N, Jenkins A, Nicholson C, Whittaker RG, Schofield I, Clowry GJ, Cunningham MO, Whittington MA
Publication type: Article
Publication status: Published
Journal: European Journal of Neuroscience
Print publication date: 01/01/2014
ISSN (print): 0953-816X
ISSN (electronic): 1460-9568
Publisher: Wiley-Blackwell Publishing Ltd.
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