Bicarbonate-dependent depolarizing potentials in pyramidal cells and interneurons during epileptiform activity.
Experimental and theoretical evidence indicates that GABAergic neurotransmission is fundamental for the synchronization of neuronal activity. In particular, the role of GABA in epileptiform activity has received increased attention due to, among others, the fact that the GABA-mediated potentials can be depolarizing, and hence excitatory, in some circumstances. Evidence is presented here that bicarbonate efflux via GABAA receptors in interneurons and pyramidal cells of the CA1 hippocampal area contribute to depolarizing GABAA-mediated potentials in an in vitro nonpharmacological seizure-like model of status epilepticus. Seizure-like and interictal activity was evoked in rat horizontal hippocampal slices using a superfusing solution with low magnesium concentration (0.5-0.9 mm). Whole-cell recordings from stratum oriens-alveus interneurons and CA1 pyramidal cells revealed that, during epileptiform activity, some GABAA-mediated potentials were depolarizing, and were suppressed by the carbonic anhydrase inhibitor ethoxyzolamide as well as by the GABAA-receptor antagonist bicuculline. These observations indicate that the depolarizing potentials observed during epileptiform activity reflect both glutamatergic and GABAA-receptor-mediated activity, and adds further support for the important role of GABAergic interneurons in promoting long-range synchronization.
Perez Velazquez
Jose L
JL
Hospital for Sick Children, Division of Neurology, room 6535 Hill Wing, University of Toronto, 555 University Avenue, Toronto, Ontario M5G1X8, Canada. jose-luis-perez-velazquez@sickkids.ca
D000818:Animals; D000831:Animals, Newborn; D001639:Bicarbonates / Q000494:pharmacology*; D001640:Bicuculline / Q000031:analogs & derivatives* / Q000494:pharmacology; D002257:Carbonic Anhydrase Inhibitors / Q000494:pharmacology; D004195:Disease Models, Animal; D004558:Electric Stimulation; D004827:Epilepsy / Q000139:chemically induced / Q000473:pathology*; D005016:Ethoxzolamide / Q000494:pharmacology; D005071:Evoked Potentials / Q000187:drug effects / Q000502:physiology; D018756:GABA Antagonists / Q000494:pharmacology; D066298:In Vitro Techniques; D007395:Interneurons / Q000187:drug effects* / Q000502:physiology; D008274:Magnesium / Q000008:administration & dosage; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009433:Neural Inhibition; D018408:Patch-Clamp Techniques / Q000379:methods; D017966:Pyramidal Cells / Q000187:drug effects* / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar
D001639:Bicarbonates; D002257:Carbonic Anhydrase Inhibitors; D018756:GABA Antagonists; C017069:bicuculline methiodide; D008274:Magnesium; D001640:Bicuculline; D005016:Ethoxzolamide