Pyramidal cells accumulate chloride at seizure onset.
Seizures are thought to originate from a failure of inhibition to quell hyperactive neural circuits, but the nature of this failure remains unknown. Here we combine high-speed two-photon imaging with electrophysiological recordings to directly evaluate the interaction between populations of interneurons and principal cells during the onset of seizure-like activity in mouse hippocampal slices. Both calcium imaging and dual patch clamp recordings reveal that in vitro seizure-like events (SLEs) are preceded by pre-ictal bursts of activity in which interneurons predominate. Corresponding changes in intracellular chloride concentration were observed in pyramidal cells using the chloride indicator Clomeleon. These changes were measurable at SLE onset and became very large during the SLE. Pharmacological manipulation of GABAergic transmission, either by blocking GABA(A) receptors or by hyperpolarizing the GABA(A) reversal potential, converted SLEs to short interictal-like bursts. Together, our results support a model in which pre-ictal GABA(A) receptor-mediated chloride influx shifts E(GABA) to produce a positive feedback loop that contributes to the initiation of seizure activity.
Department of Neurology, Massachusetts General Hospital, 114 16th St. #2600, Charlestown, MA 02129, USA. lillis.kyle@mgh.harvard.edu
Kyle P
KP
Lillis
Mark A
MA
Kramer
Jerome
J
Mertz
Kevin J
KJ
Staley
John A
JA
White
D015761:4-Aminopyridine / Q000494:pharmacology; D000086:Acetazolamide / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D000927:Anticonvulsants / Q000494:pharmacology; D002712:Chlorides / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005071:Evoked Potentials / Q000187:drug effects / Q000502:physiology; D018682:GABA Agents / Q000494:pharmacology; D005968:Glutamate Decarboxylase / Q000235:genetics / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000235:genetics; D006624:Hippocampus / Q000166:cytology*; D006863:Hydrogen-Ion Concentration; D007395:Interneurons / Q000187:drug effects / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009433:Neural Inhibition / Q000502:physiology; D009924:Organ Culture Techniques; D026902:Potassium Channel Blockers / Q000494:pharmacology; D017966:Pyramidal Cells / Q000187:drug effects / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics
D000927:Anticonvulsants; D002712:Chlorides; D018682:GABA Agents; D026902:Potassium Channel Blockers; D011993:Recombinant Fusion Proteins; C415371:clomeleon; D049452:Green Fluorescent Proteins; D015761:4-Aminopyridine; D005968:Glutamate Decarboxylase; C402565:glutamate decarboxylase 1; D000086:Acetazolamide