Recovery of afferent function and synaptic strength in hippocampal CA1 following traumatic brain injury

Christopher M. Norris, Stephen W. Scheff

Research output: Contribution to journalArticlepeer-review

66 Scopus citations

Abstract

Cortical contusion injury can result in the partial loss of ipsilateral CA3 neurons within 48h, leading to a proportional reduction in the number of afferent fibers to CA1 stratum radiatum. While the loss of afferent input to CA1 exhibits a remarkable, albeit incomplete, recovery over the next few weeks, little is known about the functional status of presynaptic afferents during the depletion and recovery phases following injury. Here, we prepared hippocampal slices from adult Sprague Dawley rats at 2, 7, and 14 days after lateral cortical contusion injury and measured fiber volley (FV) amplitudes extracellularly in CA1 stratum radiatum. Field excitatory post-synaptic potentials (EPSPs) were also measured and plotted as a function of FV amplitude to assess relative synaptic strength of residual and/or regenerated synaptic contacts. At 2 days post-injury, FV amplitude and synaptic strength were markedly reduced in the ipsilateral, relative to the contralateral, hippocampus. FV amplitude in ipsilateral CA1 showed a complete recovery by 7 days, indicative of a post-injury sprouting response. Synaptic strength in ipsilateral CA1 also showed a dramatic recovery over this time; however, EPSP-to-FV curves remained slightly suppressed at both the 7 and 14 day time points. Despite these deficits, ipsilateral slices retained the capacity to express long-term potentiation, indicating that at least some mechanisms for synaptic plasticity remain intact, or are compensated for. These results are in agreement with anatomical evidence showing a profound deafferentation, followed by a remarkable re-enervation, of ipsilateral CA1 in the first few weeks after traumatic brain injury. Although plasticity mechanisms appear to remain intact, synaptic strength deficits in CA1 could limit information throughput in the hippocampus, leading to persistent memory dysfunction.

Original languageEnglish
Pages (from-to)2269-2278
Number of pages10
JournalJournal of Neurotrauma
Volume26
Issue number12
DOIs
StatePublished - Dec 1 2009

Keywords

  • Cortical contusion injury
  • Deafferentation
  • Excitatory postsynaptic potential
  • Fiber volley
  • Schaffer collaterals

ASJC Scopus subject areas

  • Clinical Neurology

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