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Published on: June 25, 2016
Presubiculum stimulation in vivo evokes distinct oscillations in superficial and deep entorhinal cortex layers in
Else A Tolner1, Fabian Kloosterman, Erwin A van Vliet
1Swammerdam Institute of Life Sciences, Center for Neuroscience, University of Amsterdam, Graduate School of Neurosciences, 1098 SM Amsterdam, The Netherlands.
Abstract:
The characteristic cell loss in layer III of the medial entorhinal area (MEA-III) in human mesial temporal lobe epilepsy is reproduced in the rat kainate model of the disease. To understand how this cell loss affects the functional properties of the MEA, we investigated whether projections from the presubiculum (prS), providing a main input to the MEA-III, are altered in this epileptic rat model. Injections of an anterograde tracer in the prS revealed bilateral projection fibers mainly to the MEA-III in both control and chronic epileptic rats. We further examined the prS-MEA circuitry using a 16-channel electrode probe covering the MEA in anesthetized control and chronic epileptic rats. With a second 16-channel probe, we recorded signals in the hippocampus. Current source density analysis indicated that, after prS double-pulse stimulation, afterdischarges in the form of oscillations (20-45 Hz) occurred that were confined to the superficial layers of the MEA in all epileptic rats displaying MEA-III neuronal loss. Slower oscillations (theta range) were occasionally observed in the deep MEA layers and the dentate gyrus. This kind of oscillation was never observed in control rats. We conclude that dynamical changes occur in an extensive network within the temporal lobe in epileptic rats, manifested as different kinds of oscillations, the characteristics of which depend on local properties of particular subareas. These findings emphasize the significance of the entorhinal cortex in temporal lobe epilepsy and suggest that the superficial cell layers could play an important role in distributing oscillatory activity.
Insights
Temporal lobe epilepsy in rats shows abnormal brain oscillations in the medial entorhinal area (MEA). These network changes, particularly in superficial MEA layers, highlight the entorhinal cortex's role in epilepsy.
Area of Science:
- Neuroscience
- Epilepsy Research
- Computational Neuroscience
Background:
- Mesial temporal lobe epilepsy (MTLE) is characterized by neuronal loss in the medial entorhinal area layer III (MEA-III).
- The rat kainate model replicates this MEA-III cell loss, offering a platform to study epilepsy-related network alterations.
Purpose of the Study:
- To investigate functional changes in the presubiculum-medial entorhinal area (prS-MEA) circuitry in an epileptic rat model.
- To determine how MEA-III cell loss impacts the functional properties of the medial entorhinal area.
Main Methods:
- Utilized an anterograde tracer injected into the presubiculum (prS) to map projections to the MEA.
- Employed multi-channel electrode probes to record neural activity in the MEA and hippocampus of control and epileptic rats.
- Performed current source density analysis following prS stimulation to examine evoked electrical activity.
Main Results:
- Confirmed bilateral prS projections to the MEA-III in both control and epileptic rats.
- Observed epilepsy-specific afterdischarges, manifesting as 20-45 Hz oscillations confined to superficial MEA layers in epileptic rats with MEA-III loss.
- Detected theta-range oscillations in deep MEA layers and dentate gyrus of epileptic rats, which were absent in controls.
Conclusions:
- Epileptic rats exhibit dynamic network changes within the temporal lobe, characterized by distinct oscillatory patterns.
- The observed oscillations are dependent on the local properties of specific brain subareas.
- The findings underscore the medial entorhinal cortex's critical role in temporal lobe epilepsy and suggest superficial MEA layers are key in distributing oscillatory activity.
