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Rats with confirmed temporal lobe epilepsy have impaired pattern separation behavior on 8 arm radial maze

  • Author(s): Ramezani, Ario Dustin
  • Advisor(s): Leutgeb, Jill
  • et al.

Episodic memories are a unique subtype of memory that encode the when, the where, and the what. The dentate gyrus within the hippocampus is vital for mediating pattern separation: the brain’s distinct ability to distinguish very similar memories from one another. Epilepsy, a disease characterized by hyper-excitation of neuronal circuits, is correlated with neuronal reorganization of the dentate gyrus. Previous studies from our lab have demonstrated that rats induced with chronic temporal lobe epilepsy through a low-dose kainate model have impaired behavioral performance on an 8 arm radial maze that tests for pattern separation. In this project, we asked whether these behavioral deficits were a precursor to, or a result of, chronic epileptogenesis. We introduced a 24-hour video monitoring system, which allowed us to review recorded video of induced animals in a vivarium to observe and score seizures. This data was then compared to the data collected from behavioral trials and we found that in the adjacent condition of the 8 arm radial maze (pattern separation condition), those with confirmed epilepsy had a statistically significant increase in trials necessary to reach criterion when compared to the control group. Their performance was comparable to a dentate gyrus lesion group, which controlled for inhibited pattern separation function. In the non-adjacent 8 arm radial maze condition, there was no significant difference in performance between groups since this condition is not dentate gyrus-dependent. Holistically, we conclude that chronic epileptogenesis results in impaired pattern separation behavior. Histological analysis of Timm stained tissue further supports that mossy fiber sprouting is positively correlated with impaired pattern separation behavior.

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