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Epileptiform activity in hippocampal slice cultures exposed chronically to bicuculline: increased gap junctional function and expression
Author(s) -
Samoilova Marina,
Li Jianxue,
Pelletier Marc R.,
Wentlandt Kirsten,
Adamchik Yana,
Naus Christian C.,
Carlen Peter L.
Publication year - 2003
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.2003.01893.x
Subject(s) - carbenoxolone , connexin , gap junction , chemistry , bicuculline , hippocampal formation , medicine , connexin 32 , endocrinology , neuroscience , biology , intracellular , biochemistry , antagonist , receptor
Chronic (18 h) exposure of cultured hippocampal slices to the type‐A GABA receptor blocker, bicuculline methiodide (BMI) 10 μ m increased the levels of connexin 43 (Cx43) and connexin 32 (Cx32) mRNAs, but not connexin 26 and connexin 36, as demonstrated by RNase protection assays. The levels of Cx43 and Cx32 proteins in membrane fractions detected by western blotting were also significantly increased. Immunoblotting indicated that BMI also promoted a significant expression of the transcription protein c‐fos. The rate of fluorescence recovery after photobleaching, an index of gap junctional coupling, was also significantly increased, whereas it was blocked by the gap junctional blocker, carbenoxolone (100 μ m ). Extracellular recordings in CA1 stratum pyramidale, performed in BMI‐free solution, demonstrated that BMI‐exposed cultures possessed synaptic responses characteristic of epileptiform discharges: (i) significantly greater frequency of spontaneous epileptiform discharges, (ii) post‐synaptic potentials with multiple population spikes, and (iii) significantly longer duration of primary afterdischarges. Carbenoxolone (100 μ m ), but not its inactive analog, oleanolic acid (100 μ m ), reversibly inhibited spontaneous and evoked epileptiform discharges. The findings of BMI‐induced parallel increases in levels of gap junction expression and function, and the increase in epileptiform discharges, which were sensitive to gap junctional blockers, are consistent with the hypothesis that increased gap junctional communication plays an intrinsic role in the epileptogenic process.