The functional significance of gap junction channels in the epileptogenicity and seizure susceptibility of juvenile rats.
OBJECTIVE
The functional significance of gap-junction (GJ) channels in seizure susceptibility and induction and maintenance of seizures in the developing rat brain was investigated on the 4-aminopyridine (4-AP) in vivo epilepsy model.


METHODS
In electrophysiological experiments, GJs were manipulated with a blocker or opener before induction or at the active epileptic foci between postnatal days 9 and 28 (P9-28). Semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) amplification was used to measure the levels of connexin (Cx) 26, 32, 36, and 43 mRNAs at the untreated cortex or epileptic foci.


RESULTS
The basic electrocorticogram (ECoG) and Cx messenger RNA (mRNA) expression patterns exhibited characteristic maturation; the 4-AP-induced epileptiform activity correlated well with these changes. Cx mRNA expressions were significantly upregulated around P16 (except for Cx26). The Cx26, 36, and 43 gene inducibility was highest around P16 and then declined significantly. In the youngest animals, the GJ opener induced rhythmic synchronous cortical activity. On maturation, the seizures became focalized and periodic; the discharges accelerated their amplitude and frequency increase. A transient decrease (P13-14) and then increase (P15-16) in seizure susceptibility were followed by a tendency to periodicity and focalization.


CONCLUSIONS
The study suggests that GJ communication is involved in rhythm genesis and synchronization of cortical activity and may enhance the epileptogenicity of the developing brain.
Gajda
Zita
Z
Department of Comparative Physiology, University of Szeged, Szeged, Hungary.
Hermesz
Edit
E
Gyengési
Erika
E
Szupera
Zoltán
Z
Szente
Magdolna
M
D015761:4-Aminopyridine; D000818:Animals; D000831:Animals, Newborn; D002229:Carbenoxolone / Q000494:pharmacology; D017630:Connexins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology*; D003344:Cortical Synchronization / Q000187:drug effects; D004195:Disease Models, Animal; D004198:Disease Susceptibility / Q000378:metabolism / Q000503:physiopathology; D004569:Electroencephalography / Q000187:drug effects / Q000706:statistics & numerical data; D004827:Epilepsy / Q000139:chemically induced / Q000378:metabolism / Q000503:physiopathology; D005260:Female; D017629:Gap Junctions / Q000235:genetics / Q000378:metabolism* / Q000502:physiology*; D015870:Gene Expression / Q000187:drug effects; D008297:Male; D008744:Methylamines / Q000494:pharmacology; D019579:Neocortex / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012640:Seizures / Q000139:chemically induced* / Q000378:metabolism* / Q000503:physiopathology
D017630:Connexins; D008744:Methylamines; D012333:RNA, Messenger; D015761:4-Aminopyridine; C023336:trimethylamine; D002229:Carbenoxolone