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Reorganization of supramammillary-hippocampal pathways in the rat pilocarpine model of temporal lobe epilepsy: evidence for axon terminal sprouting.

Soussi R, Boulland JL, Bassot E, Bras H, Coulon P, Chaudhry FA, Storm-Mathisen J, Ferhat L, Esclapez M - Brain Struct Funct (2014)

Bottom Line: This hypothalamic nucleus, which provides major extracortical projections to the hippocampal formation, plays a key role in the regulation of several hippocampus-dependent activities, including theta rhythms, memory function and emotional behavior, such as stress and anxiety, functions that are known to be altered in MTLE.This reorganization, which starts during the latent period, is massive when animals become epileptic and continue to evolve during epilepsy.It is characterized by an aberrant distribution and an increased number of axon terminals from neurons of both lateral and medial regions of the SuM, invading the entire inner molecular layer of the DG.

View Article: PubMed Central - PubMed

Affiliation: INSERM, UMR 1106, Institut de Neurosciences des Systèmes - INS, 13385, Marseille, France.

ABSTRACT
In mesial temporal lobe epilepsy (MTLE), spontaneous seizures likely originate from a multi-structural epileptogenic zone, including several regions of the limbic system connected to the hippocampal formation. In this study, we investigate the structural connectivity between the supramammillary nucleus (SuM) and the dentate gyrus (DG) in the model of MTLE induced by pilocarpine in the rat. This hypothalamic nucleus, which provides major extracortical projections to the hippocampal formation, plays a key role in the regulation of several hippocampus-dependent activities, including theta rhythms, memory function and emotional behavior, such as stress and anxiety, functions that are known to be altered in MTLE. Our findings demonstrate a marked reorganization of DG afferents originating from the SuM in pilocarpine-treated rats. This reorganization, which starts during the latent period, is massive when animals become epileptic and continue to evolve during epilepsy. It is characterized by an aberrant distribution and an increased number of axon terminals from neurons of both lateral and medial regions of the SuM, invading the entire inner molecular layer of the DG. This reorganization, which reflects an axon terminal sprouting from SuM neurons, could contribute to trigger spontaneous seizures within an altered hippocampal intrinsic circuitry.

No MeSH data available.


Related in: MedlinePlus

Quantitative analysis of VGLUT2 and VGAT proteins. a, b Quantitative analysis of the mean densities of labeling for VGLUT2 only and for VGLUT2/VGAT performed for the dorsal and ventral DG, in two regions of interest drawn over the inner molecular layer (IML) and granule cell layer which included the supragranular layer (GCL/SGL) as illustrated in (b) of the suprapyramidal blade (Sup.bl). Measures were obtained from three controls (white rectangles) and three pilocarpine-treated rats at 4 months (gray rectangles). Statistically significant differences are indicated (*p < 0.05; **p < 0.01; ***p < 0.001; ANOVA test). Errors bars SEM
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Fig5: Quantitative analysis of VGLUT2 and VGAT proteins. a, b Quantitative analysis of the mean densities of labeling for VGLUT2 only and for VGLUT2/VGAT performed for the dorsal and ventral DG, in two regions of interest drawn over the inner molecular layer (IML) and granule cell layer which included the supragranular layer (GCL/SGL) as illustrated in (b) of the suprapyramidal blade (Sup.bl). Measures were obtained from three controls (white rectangles) and three pilocarpine-treated rats at 4 months (gray rectangles). Statistically significant differences are indicated (*p < 0.05; **p < 0.01; ***p < 0.001; ANOVA test). Errors bars SEM

Mentions: Quantification of bouton densities from BDA-tracing experiments does not allow comparative analysis between animals. Indeed, the number of BDA-labeled fibers and boutons may vary for each animal depending on tracer uptake efficiency by the neurons (amount of labeled cells). Therefore, in the DG, the densities of boutons, originating from SuML and SuMM neurons, were estimated by the densities of axon terminals displaying SuML and SuMM neurochemical phenotype, i.e., labeled for VGLUT2/VGAT and VGLUT2 only, respectively. The densities of VGLUT2/VGAT- and VGLUT2 only labeled terminals were assessed by the quantification of immunolabeling for VGLUT2/VGAT and VGLUT2 only, respectively. These analyses were performed on sections from both control (n = 3) and 4-month pilocarpine-treated (n = 3) rats. Single optical confocal images were acquired with Zeiss LSM 5 Pascal laser-scanning microscope and analyzed with the software provided by the microscope manufacturer (LSM 5 Examiner, Zeiss). All images were acquired from the suprapyramidal blade of the dorsal and ventral DG, using identical parameters for control and pilocarpine-treated animals. The densities of labeling for VGLUT2 only and for VGLUT2–VGAT were estimated by counting the number of positive pixels in each dentate gyrus (dorsal and ventral) and in two regions of interests (ROIs): (1) the granule cell layer (GCL) including the narrow zone superficial to the granule cells defined as the supragranular layer (SGL) and (2) the inner one-third of the molecular layer (IML) as illustrated in Fig. 5b. For each channel, an identical bottom threshold was applied throughout the analyses, and only the pixels with a value above this threshold were counted. When a pixel had a value above the threshold in both channels, it was counted as double positive. The number of counted pixels was reported to the area of the ROI so that the variable shapes of the ROIs drawn were not a source of bias. The average numbers of pixels representing the average labeling densities for VGLUT2 only and VGLUT2–VGAT (±SEM) were calculated in each ROI for each group of control and 4-month pilocarpine-treated rats. The data were analyzed statistically with a mixed model analysis of variance (ANOVA) and Student’s t test.


Reorganization of supramammillary-hippocampal pathways in the rat pilocarpine model of temporal lobe epilepsy: evidence for axon terminal sprouting.

Soussi R, Boulland JL, Bassot E, Bras H, Coulon P, Chaudhry FA, Storm-Mathisen J, Ferhat L, Esclapez M - Brain Struct Funct (2014)

Quantitative analysis of VGLUT2 and VGAT proteins. a, b Quantitative analysis of the mean densities of labeling for VGLUT2 only and for VGLUT2/VGAT performed for the dorsal and ventral DG, in two regions of interest drawn over the inner molecular layer (IML) and granule cell layer which included the supragranular layer (GCL/SGL) as illustrated in (b) of the suprapyramidal blade (Sup.bl). Measures were obtained from three controls (white rectangles) and three pilocarpine-treated rats at 4 months (gray rectangles). Statistically significant differences are indicated (*p < 0.05; **p < 0.01; ***p < 0.001; ANOVA test). Errors bars SEM
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Related In: Results  -  Collection

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Fig5: Quantitative analysis of VGLUT2 and VGAT proteins. a, b Quantitative analysis of the mean densities of labeling for VGLUT2 only and for VGLUT2/VGAT performed for the dorsal and ventral DG, in two regions of interest drawn over the inner molecular layer (IML) and granule cell layer which included the supragranular layer (GCL/SGL) as illustrated in (b) of the suprapyramidal blade (Sup.bl). Measures were obtained from three controls (white rectangles) and three pilocarpine-treated rats at 4 months (gray rectangles). Statistically significant differences are indicated (*p < 0.05; **p < 0.01; ***p < 0.001; ANOVA test). Errors bars SEM
Mentions: Quantification of bouton densities from BDA-tracing experiments does not allow comparative analysis between animals. Indeed, the number of BDA-labeled fibers and boutons may vary for each animal depending on tracer uptake efficiency by the neurons (amount of labeled cells). Therefore, in the DG, the densities of boutons, originating from SuML and SuMM neurons, were estimated by the densities of axon terminals displaying SuML and SuMM neurochemical phenotype, i.e., labeled for VGLUT2/VGAT and VGLUT2 only, respectively. The densities of VGLUT2/VGAT- and VGLUT2 only labeled terminals were assessed by the quantification of immunolabeling for VGLUT2/VGAT and VGLUT2 only, respectively. These analyses were performed on sections from both control (n = 3) and 4-month pilocarpine-treated (n = 3) rats. Single optical confocal images were acquired with Zeiss LSM 5 Pascal laser-scanning microscope and analyzed with the software provided by the microscope manufacturer (LSM 5 Examiner, Zeiss). All images were acquired from the suprapyramidal blade of the dorsal and ventral DG, using identical parameters for control and pilocarpine-treated animals. The densities of labeling for VGLUT2 only and for VGLUT2–VGAT were estimated by counting the number of positive pixels in each dentate gyrus (dorsal and ventral) and in two regions of interests (ROIs): (1) the granule cell layer (GCL) including the narrow zone superficial to the granule cells defined as the supragranular layer (SGL) and (2) the inner one-third of the molecular layer (IML) as illustrated in Fig. 5b. For each channel, an identical bottom threshold was applied throughout the analyses, and only the pixels with a value above this threshold were counted. When a pixel had a value above the threshold in both channels, it was counted as double positive. The number of counted pixels was reported to the area of the ROI so that the variable shapes of the ROIs drawn were not a source of bias. The average numbers of pixels representing the average labeling densities for VGLUT2 only and VGLUT2–VGAT (±SEM) were calculated in each ROI for each group of control and 4-month pilocarpine-treated rats. The data were analyzed statistically with a mixed model analysis of variance (ANOVA) and Student’s t test.

Bottom Line: This hypothalamic nucleus, which provides major extracortical projections to the hippocampal formation, plays a key role in the regulation of several hippocampus-dependent activities, including theta rhythms, memory function and emotional behavior, such as stress and anxiety, functions that are known to be altered in MTLE.This reorganization, which starts during the latent period, is massive when animals become epileptic and continue to evolve during epilepsy.It is characterized by an aberrant distribution and an increased number of axon terminals from neurons of both lateral and medial regions of the SuM, invading the entire inner molecular layer of the DG.

View Article: PubMed Central - PubMed

Affiliation: INSERM, UMR 1106, Institut de Neurosciences des Systèmes - INS, 13385, Marseille, France.

ABSTRACT
In mesial temporal lobe epilepsy (MTLE), spontaneous seizures likely originate from a multi-structural epileptogenic zone, including several regions of the limbic system connected to the hippocampal formation. In this study, we investigate the structural connectivity between the supramammillary nucleus (SuM) and the dentate gyrus (DG) in the model of MTLE induced by pilocarpine in the rat. This hypothalamic nucleus, which provides major extracortical projections to the hippocampal formation, plays a key role in the regulation of several hippocampus-dependent activities, including theta rhythms, memory function and emotional behavior, such as stress and anxiety, functions that are known to be altered in MTLE. Our findings demonstrate a marked reorganization of DG afferents originating from the SuM in pilocarpine-treated rats. This reorganization, which starts during the latent period, is massive when animals become epileptic and continue to evolve during epilepsy. It is characterized by an aberrant distribution and an increased number of axon terminals from neurons of both lateral and medial regions of the SuM, invading the entire inner molecular layer of the DG. This reorganization, which reflects an axon terminal sprouting from SuM neurons, could contribute to trigger spontaneous seizures within an altered hippocampal intrinsic circuitry.

No MeSH data available.


Related in: MedlinePlus