The effects of traumatic brain injury on inhibition in the hippocampus and dentate gyrus

Thomas M. Reeves, Bruce G Lyeth, Linda L. Phillips, Robert J. Hamm, John T. Povlishock

Research output: Contribution to journalArticle

83 Scopus citations

Abstract

Changes in inhibitory neuronal functioning may contribute to morbidity following traumatic brain injury (TBI). Evoked responses to orthodromic paired-pulse stimulation were examined in the hippocampus and dentate gyms at 2 and 15 days following lateral fluid percussion TBI in adult rats. The relative strength of inhibition was estimated by measuring evoked paired pulses in three afferent systems: the CA3 commissural input to the CA1 region of the hippocampus; the entorhinal cortical input to the ipsilateral CA1 area (temporoammonic system); and the entorhinal input to the ipsilateral dentate gyms (perforant path). In addition to quantitative electrophysiological estimates of inhibitory efficacy, levels of γ-aminobutyric acid (GABA) were qualitatively examined with immunohistochemical techniques. Effects of TBI on paired-pulse responses were pathway-specific, and dependent on time postinjury. At 2 days following TBI, inhibition of population spikes was significantly reduced in the CA3 commissural input to CA1, which contrasted with injury-induced increases in inhibition in the dentate gyrus seen at both 2 and 15 days postinjury. Low-level stimulation, subthreshold for population spikes, also revealed changes in paired-pulse facilitation of field extracellular postsynaptic potentials (fEPSPs), which depended on fiber pathway and time postinjury. Significant injury-induced electrophysiological changes were almost entirely confined to the hemisphere ipsilateral to injury. Intensity of GABA immunobinding exhibited a regional association with electrophysiological indices of inhibition, with the most pronounced increases in GABA levels and inhibition found in the dentate gyms. TBI- induced effects showed a regional pattern within the hippocampus which corresponds closely to inhibitory changes reported to follow ischemia and kindling. This degree of similarity in outcome following dissimilar injuries may indicate common mechanisms in the nervous system response to injury.

Original languageEnglish (US)
Pages (from-to)119-132
Number of pages14
JournalBrain Research
Volume757
Issue number1
DOIs
StatePublished - May 16 1997
Externally publishedYes

Keywords

  • γ-Aminobutyric acid
  • Dentate gyms
  • Hippocampus
  • Paired-pulse inhibition
  • Rat
  • Traumatic brain injury

ASJC Scopus subject areas

  • Neuroscience(all)

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