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Ectopic axonal firing in an epileptic cortical focus is not triggered by thalamocortical volleys during the interictal stage

Authors
Journal
Brain Research
0006-8993
Publisher
Elsevier
Publication Date
Volume
576
Issue
1
Identifiers
DOI: 10.1016/0006-8993(92)90628-m
Keywords
  • Epilepsy
  • Cobalt
  • Rat
  • Neocortex
  • Thalamocortical Neuron
  • Ectopic Axonal Action Potential
  • Collision Test
  • Antidromic

Abstract

Abstract The triggering of ectopic action potentials (APs) at axon terminals in a chronic epileptic cobalt focus was investigated in thalamocortical (TC) neurons of rats under urethane anesthesia. TC cells which were in register with an active epileptic aggregate discharged bursts of 2–11 APs. According to the rules of the collision test, we ascertained that bursts contained APs of ectopic and/or somatic origin. During a transient blockage of TC orthodromic discharges produced by raising the extracellular concentration of Mg 2+, ectopic bursts which were in close time relationship with the focal interictal electrocorticographic spikes persisted. These results demonstrate (i) the antidromic nature of identified ectopic APs and (ii) that, during the interictal stage, such axonal APs were not a consequence of TC discharges. The possible mechanisms for the triggering of ectopic axonal APs in the chronic cobalt focus are discussed.

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