Layer-specific generation and propagation of seizures in slices of developing neocortex: role of excitatory GABAergic synapses.
The neonatal period is critical for seizure susceptibility, and neocortical networks are central in infantile epilepsies. We report that application of 4-aminopyridine (4-AP) to immature (P6-P9) neocortical slices generates layer-specific interictal seizures (IISs) that transform after recurrent seizures to ictal seizures (ISs). During IISs, cell-attached recordings show action potentials in interneurons and pyramidal cells in L5/6 and interneurons but not pyramidal neurons in L2/3. However, L2/3 pyramidal neurons also fire during ISs. Using single N-methyl-d-aspartate (NMDA) channel recordings for measuring the cell resting potential (Em), we show that transition from IISs to ISs is associated with a gradual Em depolarization of L2/3 and L5/6 pyramidal neurons that enhances their excitability. Bumetanide, a NKCC1 co-transporter antagonist, inhibits generation of IISs and prevents their transformation to ISs, indicating the role excitatory GABA in epilepsies. Therefore deep layer neurons are more susceptible to seizures than superficial ones. The initiating phase of seizures is characterized by IISs generated in L5/6 and supported by activation of both L5/6 interneurons and pyramidal cells. IISs propagate to L2/3 via activation of L2/3 interneurons but not pyramidal cells, which are mostly quiescent at this phase. In superficial layers, a persistent increase in excitability of pyramidal neurons caused by Em depolarization is associated with a transition from largely confined GABAergic IIS to ictal events that entrain the entire neocortex.
Rheims
Sylvain
S
Institut de Neurobiologie de la Mediterranee, Institut National de la Santé et de la Recherche Médicale U901, Université de la Méditerranée, Marseille, France. sylvain.rheims@free.fr
Represa
Alfonso
A
Ben-Ari
Yehezkel
Y
Zilberter
Yuri
Y
D015761:4-Aminopyridine / Q000009:adverse effects*; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000344:Afferent Pathways / Q000502:physiology / Q000528:radiation effects; D000818:Animals; D000831:Animals, Newborn; D002034:Bumetanide / Q000494:pharmacology; D004307:Dose-Response Relationship, Radiation; D004558:Electric Stimulation / Q000379:methods; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D051379:Mice; D019579:Neocortex / Q000166:cytology / Q000254:growth & development*; D009474:Neurons / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D018377:Neurotransmitter Agents / Q000037:antagonists & inhibitors; D018408:Patch-Clamp Techniques / Q000379:methods; D026902:Potassium Channel Blockers / Q000009:adverse effects; D011930:Reaction Time / Q000187:drug effects; D012640:Seizures / Q000139:chemically induced / Q000503:physiopathology*; D049994:Sodium Potassium Chloride Symporter Inhibitors / Q000494:pharmacology; D013569:Synapses / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D018691:Excitatory Amino Acid Antagonists; D018377:Neurotransmitter Agents; D026902:Potassium Channel Blockers; D049994:Sodium Potassium Chloride Symporter Inhibitors; D002034:Bumetanide; D005680:gamma-Aminobutyric Acid; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D015761:4-Aminopyridine