Recurrent Excitation and Epileptiform Activity in the Hippocampal CA3 and CA1 Subregions of Immature and Mature Rats
Abstract number :
2.016
Submission category :
Year :
2001
Submission ID :
2007
Source :
www.aesnet.org
Presentation date :
12/1/2001 12:00:00 AM
Published date :
Dec 1, 2001, 06:00 AM
Authors :
L-R. Shao, M.D., Department of Anatomy and Neurobiology, Colorado State University, Fort Collins, CO; F.E. Dudek, Ph.D., Department of Anatomy and Neurobiology, Colorado State University, Fort Collins, CO
RATIONALE: Recurrent excitation via local excitatory circuits contribute to epileptiform activity. These local circuits differ across regions within the hippocampus and are thought to change during development. The present study compared their electrophysiological manifestations in the CA3 and CA1 regions from immature (9-25 d) and mature (90-120 d) rats.
METHODS: Hippocampal slices were prepared from immature and mature rats. The CA3 and CA1 subregions were isolated by knife cut. Simultaneous whole-cell patch-clamp and extracellular field recordings were used to register spontaneous activity and evoked responses in both regions.
RESULTS: All immature CA3 neurons (n=14) exhibited large high-frequency spontaneous excitatory postsynaptic currents (sEPSCs) or potentials (sEPSPs). Most immature slices (11 of 14) developed spontaneous synchronized network bursts when inhibition was suppressed by bicuculline, and typically showed a paroxysmal depolarization shift (PDS) followed by afterdischarges. Synaptic stimulations evoked similar bursts in an all-or-none manner. Most mature CA3 neurons (11 of 12) also had sEPSCs, but their frequency was lower and amplitude was smaller. Only half of the mature slices (6 of 13) developed network bursts in bicuculline, and these bursts only contained a PDS without afterdischarges. In CA1, only 7 of 22 immature neurons and 5 of 18 mature neurons exhibited sEPSCs or sEPSPs, which were small and infrequent. Two of the immature and none of the mature slices developed short (100-200 ms) network bursts in bicuculline.
CONCLUSIONS: These data support the hypothesis that immature CA3 neurons are more densely connected and thus have a high propensity for epileptiform activity. During subsequent development, the number of connections and the propensity for epileptiform activity appear to decline. CA1 neurons appear to have fewer excitatory interconnections, and these circuits appear not to change during development and are less likely to generate network bursts in bicuculline.
Support: NS 16683