Increased dendritic excitability in hippocampal ca1 in vivo in the kainic acid model of temporal lobe epilepsy: a study using current source density analysis.
We used kainic acid in rats as an animal model of temporal lobe epilepsy, and studied the synaptic transmission in hippocampal subfield CA1 of urethane-anesthetized rats in vivo. Dendritic currents were revealed by field potential mapping, using a single micropipette or a 16-channel silicon probe, followed by current source density analysis. We found that the population excitatory postsynaptic potentials in the basal dendrites and distal apical dendrites of CA1 were increased in kainate-treated as compared with control rats following paired-pulse, but not single-pulse, stimulation of CA3b or medial perforant path. In contrast, the trisynaptic midapical dendritic response in CA1 following medial perforant path stimulation was decreased in kainate-treated as compared with control rats. Increased coupling between excitatory postsynaptic potential and the population spike in CA1 was found after kainate seizures. Short-latency, presumably monosynaptic CA1 population spikes following medial perforant path stimulation was found in kainate-treated but not control rats. An enhancement of dendritic excitability was evidenced by population spikes that invaded into or originated from the distal apical dendrites of CA1 in kainate-treated but not control rats. Reverberation of hippocampo-entorhinal activity was evidenced by recurrent excitation of CA1 following CA3b stimulation in kainate-treated but not control rats. Blockade of inhibition by intraventricularly administered bicuculline induced excitatory potentials in CA1 that were stronger and more prolonged in kainate-treated than control rats. The bicuculline-induced excitation was mainly blocked by non-N-methyl-D-aspartate receptor antagonists. We conclude that kainate seizures induced disinhibition in CA1 that unveiled excitation at the basal and distal apical dendrites, resulting in enhancement of the direct entorhinal cortex to CA1 input and reverberations via the hippocampo-entorhinal loop. These changes in the output of the hippocampus from CA1 are likely detrimental to the behavioral functions of the hippocampus and they may contribute to increased seizure susceptibility after kainate seizures.
Wu
K
K
Department of Clinical Neurological Sciences, University of Western Ontario, London, ON, Canada N6A 5A5.
Leung
L S
LS
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D001640:Bicuculline / Q000494:pharmacology; D003712:Dendrites / Q000502:physiology*; D004195:Disease Models, Animal; D004558:Electric Stimulation; D018728:Entorhinal Cortex / Q000166:cytology / Q000503:physiopathology; D004833:Epilepsy, Temporal Lobe / Q000139:chemically induced / Q000473:pathology / Q000503:physiopathology*; D018690:Excitatory Amino Acid Agonists; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology; D018756:GABA Antagonists / Q000494:pharmacology; D006624:Hippocampus / Q000166:cytology / Q000503:physiopathology*; D007608:Kainic Acid; D008297:Male; D009433:Neural Inhibition / Q000502:physiology; D009434:Neural Pathways; D019580:Perforant Pathway / Q000166:cytology / Q000503:physiopathology; D051381:Rats; D020318:Rats, Long-Evans; D017470:Receptors, Glutamate / Q000502:physiology; D016194:Receptors, N-Methyl-D-Aspartate / Q000502:physiology
D018690:Excitatory Amino Acid Agonists; D018756:GABA Antagonists; D017470:Receptors, Glutamate; D016194:Receptors, N-Methyl-D-Aspartate; D007608:Kainic Acid; D001640:Bicuculline