Postsynaptic contributions to hippocampal network hyperexcitability induced by chronic activity blockade in vivo

Cynthia D. Galvan, Jurgen H. Wenzel, Kelly Dineley, Trang T. Lam, Philip A. Schwartzkroin, J. David Sweatt, John W. Swann

Research output: Contribution to journalArticle

31 Citations (Scopus)

Abstract

Neuronal activity is thought to play an important role in refining patterns of synaptic connectivity during development and in the molecular maturation of synapses. In experiments reported here, a 2-week infusion of tetrodotoxin (TTX) into rat hippocampus beginning on postnatal day 12 produced abnormal synchronized network discharges in in vitro slices. Discharges recorded upon TTX washout were called 'minibursts', owing to their small amplitude. They were routinely recorded in area CA3 and abolished by CNQX, an AMPA receptor antagonist. Because recurrent excitatory axon collaterals remodel and glutamate receptor subunit composition changes after postnatal day 12, experiments examined possible TTX-induced alterations in recurrent excitation that could be responsible for network hyperexcitability. In biocytin-labelled pyramidal cells, recurrent axon arbors were neither longer nor more highly branched in the TTX infusion site compared with saline-infused controls. However, varicosity size and density were increased. Whereas most varicosities contained synaptophysin and synaptic vesicles, many were not adjacent to postsynaptic specializations, and thus failed to form anatomically identifiable synapses. An increased pattern of excitatory connectivity does not appear to explain network hyperexcitability. Quantitative immunoblots also indicated that presynaptic markers were unaltered in the TTX infusion site. However, the postsynaptic AMPA and NMDA receptorsubunits, GIuR1, NR1 and NR2B, were increased. In electrophysiological studies EPSPs recorded in slices from TTX-infused hippocampus had an enhanced sensitivity to the NR2B containing NMDA receptor antagonist, ifenprodil. Thus, increases in subunit protein result in alterations in the composition of synaptic NMDA receptors. Postsynaptic changes are likely to be the major contributors to the hippocampal network hyperexcitability and should enhance both excitatory synaptic efficacy and plasticity.

Original languageEnglish (US)
Pages (from-to)1861-1872
Number of pages12
JournalEuropean Journal of Neuroscience
Volume18
Issue number7
DOIs
StatePublished - Oct 2003
Externally publishedYes

Fingerprint

Tetrodotoxin
Synapses
Axons
Hippocampus
6-Cyano-7-nitroquinoxaline-2,3-dione
Synaptophysin
alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid
Neurotransmitter Receptor
Neuronal Plasticity
AMPA Receptors
Synaptic Vesicles
Pyramidal Cells
Excitatory Postsynaptic Potentials
Protein Subunits
Glutamate Receptors
N-Methylaspartate
N-Methyl-D-Aspartate Receptors

Keywords

  • AMPA
  • Axon remodelling
  • Hippocampus
  • NMDA
  • Rat
  • Synapse
  • Tetrodotoxin

ASJC Scopus subject areas

  • Neuroscience(all)

Cite this

Postsynaptic contributions to hippocampal network hyperexcitability induced by chronic activity blockade in vivo. / Galvan, Cynthia D.; Wenzel, Jurgen H.; Dineley, Kelly; Lam, Trang T.; Schwartzkroin, Philip A.; Sweatt, J. David; Swann, John W.

In: European Journal of Neuroscience, Vol. 18, No. 7, 10.2003, p. 1861-1872.

Research output: Contribution to journalArticle

Galvan, Cynthia D. ; Wenzel, Jurgen H. ; Dineley, Kelly ; Lam, Trang T. ; Schwartzkroin, Philip A. ; Sweatt, J. David ; Swann, John W. / Postsynaptic contributions to hippocampal network hyperexcitability induced by chronic activity blockade in vivo. In: European Journal of Neuroscience. 2003 ; Vol. 18, No. 7. pp. 1861-1872.
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