Physiological changes in chronic epileptic rats are prominent in superficial layers of the medial entorhinal area

Epilepsia. 2005;46 Suppl 5:72-81. doi: 10.1111/j.1528-1167.2005.01012.x.

Abstract

Purpose: We investigated whether the functional network properties of the medial entorhinal area (MEA) of the entorhinal cortex were altered in a rat model of chronic epilepsy that is characterized by extensive cell loss in MEA layer III.

Methods: Responses were evoked in the entorhinal cortex by electrical stimulation of the subiculum in anesthetized chronic epileptic rats, 2-4 months after status epilepticus, induced by systemic kainate (KA) injections. Laminar field potentials were measured using a 16-channel silicon probe that covered all six layers of the MEA; an estimate of the local transmembrane currents was made using current source density analysis.

Results: Double-pulse stimulation of the subiculum evoked responses in deep and superficial layers of the MEA in control and KA rats. A current sink in layer I and at the border of layer I and II that was induced by antidromic activation of MEA-II, was much more prominent in KA rats with extensive neuronal loss in MEA-III than in control rats or KA rats with minor MEA-III loss. Furthermore, KA rats that displayed MEA-III loss presented a series of oscillations induced by subicular stimulation in the beta/gamma-frequency range (20-100 Hz), which were confined to superficial layers of MEA. These oscillations were never observed in control rats or KA rats with minor MEA-III loss.

Conclusions: These results indicate that the observed alterations in the superficial MEA responses to subiculum stimulation and the occurrence of beta/gamma-oscillations are related phenomena, which are a consequence of altered and impaired inhibition within these MEA layers in chronic epileptic rats.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Count
  • Cell Death / physiology
  • Chronic Disease
  • Disease Models, Animal
  • Electric Stimulation
  • Entorhinal Cortex / pathology
  • Entorhinal Cortex / physiology
  • Entorhinal Cortex / physiopathology*
  • Epilepsy / chemically induced
  • Epilepsy / physiopathology*
  • Evoked Potentials / physiology
  • Hippocampus / pathology
  • Hippocampus / physiology
  • Hippocampus / physiopathology
  • Kainic Acid
  • Male
  • Neural Pathways / physiology
  • Neurons / physiology*
  • Rats
  • Rats, Sprague-Dawley

Substances

  • Kainic Acid