Changes in mIPSCs and sIPSCs after kainate treatment: evidence for loss of inhibitory input to dentate granule cells and possible compensatory responses.
How inhibition is altered after status epilepticus and the role of inhibition during epileptogenesis remain unsettled issues. The present study examined acute (4-7 days) and chronic (>3 mo) changes of GABA(A) receptor-mediated inhibitory synaptic input to dentate granule cells after kainate-induced status epilepticus. Whole cell patch-clamp techniques were used to record spontaneous and miniature inhibitory postsynaptic currents (sIPSCs and mIPSCs) in the presence of 6,7-dinitroquinoxaline-2,3-dione and dl-2-amino-5-phosphonopentanoic acid to block glutamatergic excitatory synaptic transmission. In both groups, mean sIPSC frequency of dentate granule cells from the saline- and kainate-treated rats was not significantly different. However, mIPSC frequency from the kainate-treated rats of both groups was approximately 30% lower than that of the respective saline controls. The mean amplitude of sIPSCs and mIPSCs from kainate-treated rats was not reduced in either the acute or chronic groups. The mean 10-90% rise time of IPSCs was not altered in kainate-treated rats, but the decay time constant was slightly longer than in controls, and the charge transfer 4-7 days after kainate treatment was significantly larger. The similar reduction of mIPSC frequency (i.e., approximately 30%) in the two groups of kainate-treated rats suggests a decreased inhibitory input to dentate granule cells (presumably due to a partial loss of inhibitory interneurons that innervate them) without recovery during epileptogenesis. The lack of effect on sIPSC frequency and the decreased mIPSC frequency in both groups suggests a possible compensatory increase in firing rate of interneurons, which may involve a hypothetical reduction of inhibitory input to the remaining interneurons.
Shao
Li-Rong
LR
Department of Biomedical Sciences, Anatomy and Neurobiology Section, Colorado State University, Fort Collins, CO 80523, USA.
Dudek
F Edward
FE
D000704:Analysis of Variance; D000779:Anesthetics, Local / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D001640:Bicuculline / Q000494:pharmacology; D018891:Dentate Gyrus / Q000166:cytology*; D004347:Drug Interactions; D005071:Evoked Potentials / Q000187:drug effects* / Q000502:physiology; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology*; D018756:GABA Antagonists / Q000494:pharmacology; D066298:In Vitro Techniques; D007608:Kainic Acid / Q000494:pharmacology*; D008297:Male; D009433:Neural Inhibition / Q000187:drug effects*; D009474:Neurons / Q000145:classification / Q000187:drug effects* / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011930:Reaction Time / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D009435:Synaptic Transmission / Q000187:drug effects* / Q000502:physiology; D013779:Tetrodotoxin / Q000494:pharmacology; D013997:Time Factors
D000779:Anesthetics, Local; D018690:Excitatory Amino Acid Agonists; D018756:GABA Antagonists; D013779:Tetrodotoxin; D007608:Kainic Acid; D001640:Bicuculline