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Status Epilepticus Induced Spontaneous Dentate Gyrus Spikes: In Vivo Current Source Density Analysis.

Flynn SP, Barriere S, Barrier S, Scott RC, Lenck-Santini PP, Holmes GL - PLoS ONE (2015)

Bottom Line: DS frequency was significantly increased in pilocarpine-treated animals compared to controls.DS were associated with an increase in multiunit activity in the granule cell layer, but no change in CA1.These results suggest that following SE there is an increase in DS activity, potentially arising from hyperexcitability along the hippocampal-entorhinal pathway or within the dentate gyrus itself.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurological Sciences, University of Vermont College of Medicine, Burlington, VT, United States of America.

ABSTRACT
The dentate gyrus is considered to function as an inhibitory gate limiting excitatory input to the hippocampus. Following status epilepticus (SE), this gating function is reduced and granule cells become hyper-excitable. Dentate spikes (DS) are large amplitude potentials observed in the dentate gyrus (DG) of normal animals. DS are associated with membrane depolarization of granule cells, increased activity of hilar interneurons and suppression of CA3 and CA1 pyramidal cell firing. Therefore, DS could act as an anti-excitatory mechanism. Because of the altered gating function of the dentate gyrus following SE, we sought to investigate how DS are affected following pilocarpine-induced SE. Two weeks following lithium-pilocarpine SE induction, hippocampal EEG was recorded in male Sprague-Dawley rats with 16-channel silicon probes under urethane anesthesia. Probes were placed dorso-ventrally to encompass either CA1-CA3 or CA1-DG layers. Large amplitude spikes were detected from EEG recordings and subject to current source density analysis. Probe placement was verified histologically to evaluate the anatomical localization of current sinks and the origin of DS. In 9 of 11 pilocarpine-treated animals and two controls, DS were confirmed with large current sinks in the molecular layer of the dentate gyrus. DS frequency was significantly increased in pilocarpine-treated animals compared to controls. Additionally, in pilocarpine-treated animals, DS displayed current sinks in the outer, middle and/or inner molecular layers. However, there was no difference in the frequency of events when comparing between layers. This suggests that following SE, DS can be generated by input from medial and lateral entorhinal cortex, or within the dentate gyrus. DS were associated with an increase in multiunit activity in the granule cell layer, but no change in CA1. These results suggest that following SE there is an increase in DS activity, potentially arising from hyperexcitability along the hippocampal-entorhinal pathway or within the dentate gyrus itself.

No MeSH data available.


Related in: MedlinePlus

Simultaneous recoding of field activity in the CA1-dentate gyrus axis of dorsal hippocampus.For simplicity, every other trace is shown (16 total recording sites, 100 μm contact intervals). A) A typical dentate spike was depicted in the traces shown, characterized by a large amplitude, highly contoured event with a positive going waveform in the dentate gyrus. The CA1 pyramidal cell layer was located near trace 3 and the dentate granule cell layer was located near trace 9. B) An example recording depicting a characteristic response to a angular bundle stimulation. The silicon probe was located in a similar orientation to the recording shown in panel A. The CA1 pyramidal cell layer was located near trace 3 and the dentate granule cell layer was located between traces 9 and 11.
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pone.0132630.g001: Simultaneous recoding of field activity in the CA1-dentate gyrus axis of dorsal hippocampus.For simplicity, every other trace is shown (16 total recording sites, 100 μm contact intervals). A) A typical dentate spike was depicted in the traces shown, characterized by a large amplitude, highly contoured event with a positive going waveform in the dentate gyrus. The CA1 pyramidal cell layer was located near trace 3 and the dentate granule cell layer was located near trace 9. B) An example recording depicting a characteristic response to a angular bundle stimulation. The silicon probe was located in a similar orientation to the recording shown in panel A. The CA1 pyramidal cell layer was located near trace 3 and the dentate granule cell layer was located between traces 9 and 11.

Mentions: Spontaneous interictal events were detected from EEG recordings based on threshold values set for each individual recording. All recordings were acquired with the Cheetah32 analog signal recording system interfaced with Cheetah 5 data acquisition software (NeuraLynx, Bozeman, Montana). EEG was reviewed offline utilizing NeuroExplorer software (Nex Technologies, Madison, AL). CSD plots were generated using custom software in MATLAB to localize current sinks and sources across the recoded regions. All recordings across the 16-channels of the silicon probe were processed utilizing the same parameters. EEG traces were filtered with a 1 Hz high pass and 1 kHz low pass filter. Location of the recording channels within the hippocampus was determined based on a combination of three different approaches: 1) the presence of action potentials in recording sites located at the vicinity of a cell layer; 2) histological verification of the probe track identified by the DiI trace under fluorescent microscopy; 3) CSDs induced by the stimulation of the angular bundle in some animals (Fig 1B).


Status Epilepticus Induced Spontaneous Dentate Gyrus Spikes: In Vivo Current Source Density Analysis.

Flynn SP, Barriere S, Barrier S, Scott RC, Lenck-Santini PP, Holmes GL - PLoS ONE (2015)

Simultaneous recoding of field activity in the CA1-dentate gyrus axis of dorsal hippocampus.For simplicity, every other trace is shown (16 total recording sites, 100 μm contact intervals). A) A typical dentate spike was depicted in the traces shown, characterized by a large amplitude, highly contoured event with a positive going waveform in the dentate gyrus. The CA1 pyramidal cell layer was located near trace 3 and the dentate granule cell layer was located near trace 9. B) An example recording depicting a characteristic response to a angular bundle stimulation. The silicon probe was located in a similar orientation to the recording shown in panel A. The CA1 pyramidal cell layer was located near trace 3 and the dentate granule cell layer was located between traces 9 and 11.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4492740&req=5

pone.0132630.g001: Simultaneous recoding of field activity in the CA1-dentate gyrus axis of dorsal hippocampus.For simplicity, every other trace is shown (16 total recording sites, 100 μm contact intervals). A) A typical dentate spike was depicted in the traces shown, characterized by a large amplitude, highly contoured event with a positive going waveform in the dentate gyrus. The CA1 pyramidal cell layer was located near trace 3 and the dentate granule cell layer was located near trace 9. B) An example recording depicting a characteristic response to a angular bundle stimulation. The silicon probe was located in a similar orientation to the recording shown in panel A. The CA1 pyramidal cell layer was located near trace 3 and the dentate granule cell layer was located between traces 9 and 11.
Mentions: Spontaneous interictal events were detected from EEG recordings based on threshold values set for each individual recording. All recordings were acquired with the Cheetah32 analog signal recording system interfaced with Cheetah 5 data acquisition software (NeuraLynx, Bozeman, Montana). EEG was reviewed offline utilizing NeuroExplorer software (Nex Technologies, Madison, AL). CSD plots were generated using custom software in MATLAB to localize current sinks and sources across the recoded regions. All recordings across the 16-channels of the silicon probe were processed utilizing the same parameters. EEG traces were filtered with a 1 Hz high pass and 1 kHz low pass filter. Location of the recording channels within the hippocampus was determined based on a combination of three different approaches: 1) the presence of action potentials in recording sites located at the vicinity of a cell layer; 2) histological verification of the probe track identified by the DiI trace under fluorescent microscopy; 3) CSDs induced by the stimulation of the angular bundle in some animals (Fig 1B).

Bottom Line: DS frequency was significantly increased in pilocarpine-treated animals compared to controls.DS were associated with an increase in multiunit activity in the granule cell layer, but no change in CA1.These results suggest that following SE there is an increase in DS activity, potentially arising from hyperexcitability along the hippocampal-entorhinal pathway or within the dentate gyrus itself.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurological Sciences, University of Vermont College of Medicine, Burlington, VT, United States of America.

ABSTRACT
The dentate gyrus is considered to function as an inhibitory gate limiting excitatory input to the hippocampus. Following status epilepticus (SE), this gating function is reduced and granule cells become hyper-excitable. Dentate spikes (DS) are large amplitude potentials observed in the dentate gyrus (DG) of normal animals. DS are associated with membrane depolarization of granule cells, increased activity of hilar interneurons and suppression of CA3 and CA1 pyramidal cell firing. Therefore, DS could act as an anti-excitatory mechanism. Because of the altered gating function of the dentate gyrus following SE, we sought to investigate how DS are affected following pilocarpine-induced SE. Two weeks following lithium-pilocarpine SE induction, hippocampal EEG was recorded in male Sprague-Dawley rats with 16-channel silicon probes under urethane anesthesia. Probes were placed dorso-ventrally to encompass either CA1-CA3 or CA1-DG layers. Large amplitude spikes were detected from EEG recordings and subject to current source density analysis. Probe placement was verified histologically to evaluate the anatomical localization of current sinks and the origin of DS. In 9 of 11 pilocarpine-treated animals and two controls, DS were confirmed with large current sinks in the molecular layer of the dentate gyrus. DS frequency was significantly increased in pilocarpine-treated animals compared to controls. Additionally, in pilocarpine-treated animals, DS displayed current sinks in the outer, middle and/or inner molecular layers. However, there was no difference in the frequency of events when comparing between layers. This suggests that following SE, DS can be generated by input from medial and lateral entorhinal cortex, or within the dentate gyrus. DS were associated with an increase in multiunit activity in the granule cell layer, but no change in CA1. These results suggest that following SE there is an increase in DS activity, potentially arising from hyperexcitability along the hippocampal-entorhinal pathway or within the dentate gyrus itself.

No MeSH data available.


Related in: MedlinePlus