GABAA-current rundown of temporal lobe epilepsy is associated with repetitive activation of GABAA “phasic” receptors
- Eleonora Palma*,†,‡,
- Cristina Roseti*,
- Francesca Maiolino*,
- Sergio Fucile*,†,
- Katiuscia Martinello†,
- Manuela Mazzuferi§,
- Eleonora Aronica¶,
- Mario Manfredi†,
- Vincenzo Esposito†,
- Gianpaolo Cantore†,
- Ricardo Miledi‡,‖,**,
- Michele Simonato§, and
- Fabrizio Eusebi*,†
- *Dipartimento di Fisiologia Umana e Farmacologia-Centro di Eccellenza Biologia e Medicina Molecolare, Universita' di Roma “Sapienza,” Piazzale A. Moro 5, I00185 Rome, Italy;
- †Neuromed-Istituto di Ricovero e Cura a Carattere Scientifico, Via Atinese 18, I-86077 Isernia, Italy;
- ¶Department of (Neuro) Pathology, Academic Medical Center, University of Amsterdam, 1105 AZ, Amsterdam, The Netherlands;
- §Dipartimento di Medicina Clinica e Sperimentale, Sezione di Farmacologia and Istituto Nazionale di Neuroscienze, Università di Ferrara, 44100 Ferrara, Italy;
- ‖Instituto de Neurobiología, Campus Universidad Nacional Autónoma de México-Juriquilla, AP1-1141, Querétaro, Mexico; and
- **Department of Neurobiology and Behavior, University of California, Irvine, CA 92697-4550
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Contributed by Ricardo Miledi, November 9, 2007 (received for review October 1, 2007)
Abstract
A study was made of the “rundown” of GABAA receptors, microtransplanted to Xenopus oocytes from surgically resected brain tissues of patients afflicted with drug-resistant human mesial temporal lobe epilepsy (mTLE). Cell membranes, isolated from mTLE neocortex specimens, were injected into frog oocytes that rapidly incorporated functional GABAA receptors. Upon repetitive activation with GABA (1 mM), “epileptic” GABAA receptors exhibited a GABAA-current (I GABA) rundown that was significantly enhanced by Zn2+ (≤250 μM), and practically abolished by the high-affinity GABAA receptor inverse agonist SR95531 (gabazine; 2.5–25 μM). Conversely, I GABA generated by “control” GABAA receptors microtransplanted from nonepileptic temporal lobe, lesional TLE, or authoptic disease-free tissues remained stable during repetitive stimulation, even in oocytes treated with Zn2+. We conclude that rundown of mTLE epileptic receptors depends on the presence of “phasic GABAA receptors” that have low sensitivity to antagonism by Zn2+. Additionally, we found that GABAA receptors, microtransplanted from the cerebral cortex of adult rats exhibiting recurrent seizures, caused by pilocarpine-induced status epilepticus, showed greater rundown than control tissue, an event also occurring in patch-clamped rat pyramidal neurons. Rundown of epileptic rat receptors resembled that of human mTLE receptors, being enhanced by Zn2+ (40 μM) and sensitive to the antiepileptic agent levetiracetam, the neurotrophin brain-derived neurotrophic factor, and the phosphatase blocker okadaic acid. Our findings point to the rundown of GABAA receptors as a hallmark of TLE and suggest that modulating tonic and phasic mTLE GABAA receptor activity may represent a useful therapeutic approach to the disease.
Footnotes
- ‡To whom correspondence may be addressed. E-mail: eleonora.palma{at}uniroma1.it or rmiledi{at}uci.edu
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Author contributions: E.P., R.M., M.S., and F.E. designed research; E.P., C.R., F.M., S.F., K.M., and V.E. performed research; M. Mazzuferi, E.A., M. Manfredi, V.E., G.C., and M.S. contributed new reagents/analytic tools; E.P., C.R., F.M., S.F., and K.M. analyzed data; and E.P., R.M., M.S., and F.E. wrote the paper.
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The authors declare no conflict of interest.
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This article contains supporting information online at www.pnas.org/cgi/content/full/0710522105/DC1.
- © 2007 by The National Academy of Sciences of the USA
