Synaptic Connections From Multiple Subfields Contribute to Granule Cell Hyperexcitability in Hippocampal Slice Cultures

• Published in: Journal of neurophysiology Vol. 84; no. 6; pp. 2918 - 2932
• Main Authors: Bausch, Suzanne B, McNamara, James O
• Format: Journal Article
• Language: English
• Published: United States Am Phys Soc 01-12-2000
• Subjects: Action Potentials - drug effects; Animals; Animals, Newborn; Cells, Cultured; Epilepsy, Temporal Lobe - physiopathology; Excitatory Postsynaptic Potentials - drug effects; GABA Antagonists - pharmacology; GABA-A Receptor Antagonists; Glutamic Acid - metabolism; Hippocampus - cytology; Hippocampus - drug effects; Hippocampus - physiology; In Vitro Techniques; Male; Neural Pathways - physiology; Neural Pathways - surgery; Neurons - cytology; Neurons - drug effects; Neurons - physiology; Patch-Clamp Techniques; Rats; Rats, Sprague-Dawley; Reaction Time - drug effects; Receptors, AMPA - antagonists & inhibitors; Receptors, N-Methyl-D-Aspartate - antagonists & inhibitors; Seizures - physiopathology; Synapses - drug effects; Synapses - physiology; Synaptic Transmission - drug effects; Synaptic Transmission - physiology; Time
• ISSN: 0022-3077; 1522-1598
• DOI: 10.1152/jn.2000.84.6.2918

  1 Department of Medicine (Neurology),
  2 Department of Neurobiology, and
  3 Department of Pharmacology and Molecular Cancer
Biology, Duke University Medical Center, Durham, North Carolina 27710
Bausch, Suzanne B. and
James O. McNamara.
Synaptic Connections From Multiple Subfields Contribute to
Granule Cell Hyperexcitability in Hippocampal Slice Cultures. J. Neurophysiol. 84: 2918-2932, 2000. Limbic status epilepticus and preparation of
hippocampal slice cultures both produce cell loss and denervation. This
commonality led us to hypothesize that morphological and physiological
alterations in hippocampal slice cultures may be similar to those
observed in human limbic epilepsy and animal models. To test this
hypothesis, we performed electrophysiological and morphological
analyses in long-term ( postnatal day 11; 40-60 days
in vitro) organotypic hippocampal slice cultures. Electrophysiological
analyses of dentate granule cell excitability revealed that granule
cells in slice cultures were hyperexcitable compared with acute slices
from normal rats. In physiological buffer, spontaneous electrographic
granule cell seizures were seen in 22% of cultures; in the presence of a GABA A receptor antagonist, seizures were
documented in 75% of cultures. Hilar stimulation evoked postsynaptic
potentials (PSPs) and multiple population spikes in the granule cell
layer, which were eliminated by glutamate receptor antagonists,
demonstrating the requirement for excitatory synaptic transmission. By
contrast, under identical recording conditions, acute hippocampal
slices isolated from normal rats exhibited a lack of seizures, and
hilar stimulation evoked an isolated population spike without PSPs. To
examine the possibility that newly formed excitatory synaptic connections to the dentate gyrus contribute to granule cell
hyperexcitability in slice cultures, anatomical labeling and
electrophysiological recordings following knife cuts were performed.
Anatomical labeling of individual dentate granule, CA3 and CA1
pyramidal cells with neurobiotin illustrated the presence of axonal
projections that may provide reciprocal excitatory synaptic connections
among these regions and contribute to granule cell hyperexcitability.
Knife cuts severing connections between CA1 and the dentate gyrus/CA3c region reduced but did not abolish hilar-evoked excitatory PSPs, suggesting the presence of newly formed, functional synaptic
connections to the granule cells from CA1 and CA3 as well as from
neurons intrinsic to the dentate gyrus. Many of the
electrophysiological and morphological abnormalities reported here for
long-term hippocampal slice cultures bear striking similarities to both
human and in vivo models, making this in vitro model a simple, powerful
system to begin to elucidate the molecular and cellular mechanisms
underlying synaptic rearrangements and epileptogenesis.