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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

Pilocarpine-induced morphological changes.A) Reconstruction of silicon probe placement within a coronal section of the hippocampus. Scaled silicon probe outlines were superimposed on sections counterstained with DAPI. DiI tracks and multiunit activity guided probe alignment. B) No differences in the distance from stratum oriens in CA1 to the outer molecular layer of the inferior blade of the dentate gyrus were seen between control and pilocarpine animals. C) There was a significant decrease in the distance taken up by area CA1 in pilocarpine-treated animals measured from stratum oriens to the hippocampal fissure. D) Further analysis of CA1 demonstrated a significant decrease in stratum oriens and stratum radiatum in pilocarpine-treated animals, with no change to the pyramidal cell layer or stratum lacunosum-moleculare.
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pone.0132630.g002: Pilocarpine-induced morphological changes.A) Reconstruction of silicon probe placement within a coronal section of the hippocampus. Scaled silicon probe outlines were superimposed on sections counterstained with DAPI. DiI tracks and multiunit activity guided probe alignment. B) No differences in the distance from stratum oriens in CA1 to the outer molecular layer of the inferior blade of the dentate gyrus were seen between control and pilocarpine animals. C) There was a significant decrease in the distance taken up by area CA1 in pilocarpine-treated animals measured from stratum oriens to the hippocampal fissure. D) Further analysis of CA1 demonstrated a significant decrease in stratum oriens and stratum radiatum in pilocarpine-treated animals, with no change to the pyramidal cell layer or stratum lacunosum-moleculare.

Mentions: Following recording, animals were transcardially perfused with PSB followed by 4% paraformaldehyde. Brains were removed and post-fixed in 4% PFA for 24 hrs, then moved to 30% sucrose solution until saturated and then frozen and sectioned at 30 μm on a cryostat. Sections were counterstained with DAPI (1:1000) to verify cell layers in relationship to DiI probe tracks (Fig 2A). Additional animals were processed for Timm staining following completion of EEG recording. Timm staining was performed as follows [33]: Rats were perfused with normal saline followed by 200 ml of sodium sulfide, and 200 ml of 4% paraformaldehyde. Brains were removed, post-fixed in 4% PFA for 24 hrs, and placed in 30% sucrose until the brains sank. Coronal sections were taken along the extent of the hippocampus at 40 μm on a freezing cryostat. For Timm staining, sections were developed in a solution of 50% gum arabic (120 ml), 51% citric acid (10 ml), 47% sodium citrate (10 ml), hydroquinone, and silver nitrate for 45 min. After washing slides containing DiI labeling from electrode placements were washed in dH20 and then coverslip with Fluromount G. The remaining slides were dehydrated in alcohol, cleared in methyl salicylate and coversliped with Permount.


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)

Pilocarpine-induced morphological changes.A) Reconstruction of silicon probe placement within a coronal section of the hippocampus. Scaled silicon probe outlines were superimposed on sections counterstained with DAPI. DiI tracks and multiunit activity guided probe alignment. B) No differences in the distance from stratum oriens in CA1 to the outer molecular layer of the inferior blade of the dentate gyrus were seen between control and pilocarpine animals. C) There was a significant decrease in the distance taken up by area CA1 in pilocarpine-treated animals measured from stratum oriens to the hippocampal fissure. D) Further analysis of CA1 demonstrated a significant decrease in stratum oriens and stratum radiatum in pilocarpine-treated animals, with no change to the pyramidal cell layer or stratum lacunosum-moleculare.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0132630.g002: Pilocarpine-induced morphological changes.A) Reconstruction of silicon probe placement within a coronal section of the hippocampus. Scaled silicon probe outlines were superimposed on sections counterstained with DAPI. DiI tracks and multiunit activity guided probe alignment. B) No differences in the distance from stratum oriens in CA1 to the outer molecular layer of the inferior blade of the dentate gyrus were seen between control and pilocarpine animals. C) There was a significant decrease in the distance taken up by area CA1 in pilocarpine-treated animals measured from stratum oriens to the hippocampal fissure. D) Further analysis of CA1 demonstrated a significant decrease in stratum oriens and stratum radiatum in pilocarpine-treated animals, with no change to the pyramidal cell layer or stratum lacunosum-moleculare.
Mentions: Following recording, animals were transcardially perfused with PSB followed by 4% paraformaldehyde. Brains were removed and post-fixed in 4% PFA for 24 hrs, then moved to 30% sucrose solution until saturated and then frozen and sectioned at 30 μm on a cryostat. Sections were counterstained with DAPI (1:1000) to verify cell layers in relationship to DiI probe tracks (Fig 2A). Additional animals were processed for Timm staining following completion of EEG recording. Timm staining was performed as follows [33]: Rats were perfused with normal saline followed by 200 ml of sodium sulfide, and 200 ml of 4% paraformaldehyde. Brains were removed, post-fixed in 4% PFA for 24 hrs, and placed in 30% sucrose until the brains sank. Coronal sections were taken along the extent of the hippocampus at 40 μm on a freezing cryostat. For Timm staining, sections were developed in a solution of 50% gum arabic (120 ml), 51% citric acid (10 ml), 47% sodium citrate (10 ml), hydroquinone, and silver nitrate for 45 min. After washing slides containing DiI labeling from electrode placements were washed in dH20 and then coverslip with Fluromount G. The remaining slides were dehydrated in alcohol, cleared in methyl salicylate and coversliped with Permount.

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