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The Journal of Neuroscience, November 15, 1999, 19(22):10053-10064
Assessment of Inhibition and Epileptiform Activity in the Septal
Dentate Gyrus of Freely Behaving Rats During the First Week After
Kainate Treatment
Jennifer L.
Hellier,
Peter R.
Patrylo,
Ping
Dou,
Michelle
Nett,
Gregory M.
Rose, and
F.
Edward
Dudek
Department of Anatomy and Neurobiology, Colorado State University,
Fort Collins, Colorado 80523
Mossy fiber reorganization has been hypothesized to restore
inhibition months after kainate-induced status epilepticus. The time
course of recovery of inhibition after kainate treatment, however, is
not well established. We tested the hypothesis that if inhibition is
decreased after kainate treatment, it is restored within the first week
when little or no mossy fiber reorganization has occurred. Chronic
in vivo recordings of the septal dentate gyrus were
performed in rats before and 1, 4, and 7-8 d after kainate (multiple
injections of 5 mg/kg, i.p.; n = 17) or saline (n = 11) treatment. Single and paired-pulse stimuli
were used to assess synaptic inhibition. The first day after kainate
treatment, only a fraction of rats showed multiple population spikes
(35%), prolonged field postsynaptic potentials (76%), and loss of
paired-pulse inhibition (29%) to perforant path stimulation. Thus,
inhibition was reduced in only some of the kainate-treated rats. By
7-8 d after treatment, nearly all kainate-treated rats showed partial or full recovery in these response characteristics. Histological analysis indicated that kainate-treated rats had a significant decrease
in the number of hilar neurons compared to controls, but Timm staining
showed little to no mossy fiber reorganization. These results suggest
that a decrease in synaptic inhibition in the septal dentate gyrus is
not a prerequisite for epileptogenesis and that most of the recovery of
inhibition occurs before robust Timm staining in the inner molecular layer.
Key words:
freely behaving; in vivo; epilepsy; seizure; kainic acid; hippocampus; mossy fiber reorganization; neuronal loss
Copyright © 1999 Society for Neuroscience 0270-6474/99/192210053-12$05.00/0
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