Epileptiform activity in hippocampal slice cultures exposed chronically to bicuculline: increased gap junctional function and expression

• Published in: Journal of neurochemistry Vol. 86; no. 3; pp. 687 - 699
• Main Authors: Samoilova, Marina, Li, Jianxue, Pelletier, Marc R., Wentlandt, Kirsten, Adamchik, Yana, Naus, Christian C., Carlen, Peter L.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Science Ltd 01.08.2003; Blackwell
• Subjects: Animals; bicuculline; Bicuculline - analogs & derivatives; Biological and medical sciences; carbenoxolone; Carbenoxolone - pharmacology; Connexin 26; Connexin 43 - genetics; Connexin 43 - metabolism; connexins; Connexins - genetics; Connexins - metabolism; Cyclic AMP Response Element-Binding Protein - metabolism; Degenerative and inherited degenerative diseases of the nervous system. Leukodystrophies. Prion diseases; Electric Stimulation; epilepsy; Epilepsy - chemically induced; Epilepsy - physiopathology; Fluorescence Recovery After Photobleaching; GABA Antagonists; gap junction; Gap Junction beta-1 Protein; Gap Junctions - drug effects; Gap Junctions - physiology; Gene Expression - drug effects; Hippocampus - drug effects; Hippocampus - metabolism; Hippocampus - physiopathology; In Vitro Techniques; Male; Medical sciences; Nerve Tissue Proteins - metabolism; Neurology; Octanols - pharmacology; Patch-Clamp Techniques; Proto-Oncogene Proteins c-fos - biosynthesis; Rats; Rats, Wistar; RNA, Messenger - metabolism; Time Factors; Nervous system diseases; Membrane protein; Rat; Epilepsy; Rodentia; Cell junction; Gene expression; Gap junction; Cerebral disorder; Carbenoxolone; Connexin; Vertebrata; Mammalia; Epileptiform discharge; Animal; Central nervous system disease; Gabaergic receptor A; Hippocampus
• ISSN: 0022-3042; 1471-4159
• DOI: 10.1046/j.1471-4159.2003.01893.x

Chronic (18 h) exposure of cultured hippocampal slices to the type‐A GABA receptor blocker, bicuculline methiodide (BMI) 10 μm 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 μm). 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 μm), but not its inactive analog, oleanolic acid (100 μm), 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.