A possible role for gap junctions in generation of very fast EEG oscillations preceding the onset of, and perhaps initiating, seizures.
OBJECTIVE
We propose an experimentally and clinically testable hypothesis, concerning the origin of very fast (> approximately 70 Hz) EEG oscillations that sometimes precede the onset of focal seizures. These oscillations are important, as they may play a causal role in the initiation of seizures.


METHODS
Subdural EEG recordings were obtained from children with focal cortical dysplasias and intractable seizures. Intra- and extracellular recordings were performed in rat hippocampal slices, with induction of population activity, as follows: (a) bath-applied tetramethylamine (an intracellular alkalinizing agent, that opens gap junctions); (b) bath-applied carbachol, a cholinergic agonist; and (c) focal pressure ejection of hypertonic K+ solution. Detailed network simulations were performed, the better to understand the cellular mechanisms underlying oscillations. A major feature of the simulations was inclusion of axon-axon gap junctions between principal neurons, as supported by recent experimental data.


RESULTS
Very fast oscillations were found in children before seizure onset, but also superimposed on bursts during the seizure, and on interictal bursts. In slice experiments, very fast oscillations had previously been seen on interictal-like bursts; we now show such oscillations before, between, and after epileptiform bursts. Very fast oscillations were also seen superimposed on gamma (30-70 Hz) oscillations induced by carbachol or hypertonic K+, and in the latter case, very fast oscillations became continuous when chemical synapses were blocked. Simulations replicate these data, when axonal gap junctions are included.


CONCLUSIONS
Electrical coupling between principal neurons, perhaps via axonal gap junctions, could underlie very fast population oscillations, in seizure-prone brain, but possibly also in normal brain. The anticonvulsant potential of gap-junction blockers such as carbenoxolone, now in clinical use for treatment of ulcer disease, should be considered.
Department of Pharmacology, University of Birmingham School of Medicine, Vincent Drive, Edgbaston, Birmingham B15 2TT, UK. r.d.traub@bham.ac.uk
R D
RD
Traub
M A
MA
Whittington
E H
EH
Buhl
F E
FE
LeBeau
A
A
Bibbig
S
S
Boyd
H
H
Cross
T
T
Baldeweg
D000818:Animals; D001369:Axons / Q000502:physiology; D001921:Brain / Q000166:cytology / Q000503:physiopathology*; D002229:Carbenoxolone / Q000494:pharmacology / Q000627:therapeutic use; D004567:Electrodes, Implanted; D004569:Electroencephalography / Q000706:statistics & numerical data*; D017629:Gap Junctions / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D051379:Mice; D008807:Mice, Inbred BALB C; D008839:Microelectrodes; D009474:Neurons / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D012640:Seizures / Q000175:diagnosis* / Q000209:etiology / Q000503:physiopathology; D013355:Subdural Space; D014743:Videotape Recording
D002229:Carbenoxolone