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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

Comparison of neurochemical phenotypes for the ventral dentate gyrus afferents from the SuM between control (a–g) and epileptic pilocarpine-treated (h–n) rats, characterized by simultaneous labeling for BDA anterograde tracer (green), GAD65 (red) and VGLUT2 (blue) in coronal sections. a Image corresponding to a maximum intensity projection of a confocal slice z-stack (40 optical slices, spaced at 300 nm) showing labeling for BDA (green), GAD65 (red) and VGLUT2 (blue) in the ventral DG of a control rat. Axon terminals and fibers, originating from the SuM neurons, labeled for the BDA anterograde tracer (green) were distributed in the SGL and in the lower part of the IML. Numerous GAD65-containing terminals and VGLUT2-containing terminals were present in this region. b–d Images of the three different fluorophores used for the triple labeling, obtained by sequential acquisition of separate wavelength channels from a single confocal slice, in the SGL of the ventral DG demonstrated axon terminals labeled for BDA (b, green, arrows) containing GAD65 (c, red, arrows) and VGLUT2 (d, blue, arrows) and BDA-labeled terminals containing VGLUT2 only (d, blue, arrowheads). e Merge of b and c. f Merge of b and d. g Merge of b–d. Triple-labeled boutons for BDA, GAD65 and VGLUT2 (white, arrows) and double-labeled boutons for BDA and VGLUT2 (arrowheads) were surrounded by double-labeled terminals for GAD65 and VGLUT2 (purple) as well as single-labeled terminals for GAD65 (red) or VGLUT2 (blue). h Image corresponding to a maximum intensity projection of a confocal slice z-stack (40 optical slices, spaced at 300 nm) showing labeling for BDA (green), GAD65 (red) and VGLUT2 (blue) in the ventral DG of an epileptic rat at 2 months after pilocarpine injection. Axon terminals and fibers, originating from SuM neurons, labeled for the BDA anterograde tracer (green) displayed an aberrant distribution as compared to the control rat (a), many boutons and fibers being observed in the entire IML including the upper part. Numerous GAD65-containing terminals (red) and VGLUT2-containing terminals (blue) were also present in this entire region. i–k Images of the three different fluorophores used for the triple labeling, obtained by sequential acquisition of separate wavelength channels from a single confocal slice, in the IML of the ventral DG demonstrated that many of these ectopic BDA-labeled axon terminals (i, green, arrows) contained GAD65 (j, red, arrows) and VGLUT2 (k, blue, arrows) and some contained VGLUT2 only (i–k arrowhead). l Merge of i and j. m Merge of i and k. n Merge of i–k. Triple-labeled boutons for BDA, GAD65 and VGLUT2 (white, arrows) and double-labeled terminals for BDA and VGLUT2 (arrowhead) were surrounded by double-labeled terminals for GAD65 and VGLUT2 (purple) as well as single-labeled terminals for GAD65 (red). Ctrl control, Pilo 2months pilocarpine-treated rat at 2 months after status epilepticus. Scale bars 10 µm in a and h; 2 µm in b–g and i–n
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Fig4: Comparison of neurochemical phenotypes for the ventral dentate gyrus afferents from the SuM between control (a–g) and epileptic pilocarpine-treated (h–n) rats, characterized by simultaneous labeling for BDA anterograde tracer (green), GAD65 (red) and VGLUT2 (blue) in coronal sections. a Image corresponding to a maximum intensity projection of a confocal slice z-stack (40 optical slices, spaced at 300 nm) showing labeling for BDA (green), GAD65 (red) and VGLUT2 (blue) in the ventral DG of a control rat. Axon terminals and fibers, originating from the SuM neurons, labeled for the BDA anterograde tracer (green) were distributed in the SGL and in the lower part of the IML. Numerous GAD65-containing terminals and VGLUT2-containing terminals were present in this region. b–d Images of the three different fluorophores used for the triple labeling, obtained by sequential acquisition of separate wavelength channels from a single confocal slice, in the SGL of the ventral DG demonstrated axon terminals labeled for BDA (b, green, arrows) containing GAD65 (c, red, arrows) and VGLUT2 (d, blue, arrows) and BDA-labeled terminals containing VGLUT2 only (d, blue, arrowheads). e Merge of b and c. f Merge of b and d. g Merge of b–d. Triple-labeled boutons for BDA, GAD65 and VGLUT2 (white, arrows) and double-labeled boutons for BDA and VGLUT2 (arrowheads) were surrounded by double-labeled terminals for GAD65 and VGLUT2 (purple) as well as single-labeled terminals for GAD65 (red) or VGLUT2 (blue). h Image corresponding to a maximum intensity projection of a confocal slice z-stack (40 optical slices, spaced at 300 nm) showing labeling for BDA (green), GAD65 (red) and VGLUT2 (blue) in the ventral DG of an epileptic rat at 2 months after pilocarpine injection. Axon terminals and fibers, originating from SuM neurons, labeled for the BDA anterograde tracer (green) displayed an aberrant distribution as compared to the control rat (a), many boutons and fibers being observed in the entire IML including the upper part. Numerous GAD65-containing terminals (red) and VGLUT2-containing terminals (blue) were also present in this entire region. i–k Images of the three different fluorophores used for the triple labeling, obtained by sequential acquisition of separate wavelength channels from a single confocal slice, in the IML of the ventral DG demonstrated that many of these ectopic BDA-labeled axon terminals (i, green, arrows) contained GAD65 (j, red, arrows) and VGLUT2 (k, blue, arrows) and some contained VGLUT2 only (i–k arrowhead). l Merge of i and j. m Merge of i and k. n Merge of i–k. Triple-labeled boutons for BDA, GAD65 and VGLUT2 (white, arrows) and double-labeled terminals for BDA and VGLUT2 (arrowhead) were surrounded by double-labeled terminals for GAD65 and VGLUT2 (purple) as well as single-labeled terminals for GAD65 (red). Ctrl control, Pilo 2months pilocarpine-treated rat at 2 months after status epilepticus. Scale bars 10 µm in a and h; 2 µm in b–g and i–n

Mentions: Previous studies demonstrated in control rats the heterogeneity of SuM–DG pathways with two main projections originating from neurons in the SuML and the SuMM (Haglund et al. 1984; Vertes 1992; Maglóczky et al. 1994; Vertes and McKenna 2000) that can be identified based on their neurochemical content (Soussi et al. 2010). The axon terminals from the SuML that innervate the SGL of the dorsal DG and to a much lesser extent of the ventral DG contain markers of both glutamatergic (VGLUT2) and GABAergic (GAD65 and VGAT) neurotransmissions, whereas the axon terminals from the SuMM that innervate exclusively the IML contain VGLUT2 only. To assess the contribution of each pathway in the reorganization of the SuM–DG projections, triple immunofluorescence labeling for BDA, VGLUT2 and GAD65 were performed in the dorsal (Fig. 3) and ventral (Fig. 4) regions of the DG in epileptic and control rats.Fig. 3


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)

Comparison of neurochemical phenotypes for the ventral dentate gyrus afferents from the SuM between control (a–g) and epileptic pilocarpine-treated (h–n) rats, characterized by simultaneous labeling for BDA anterograde tracer (green), GAD65 (red) and VGLUT2 (blue) in coronal sections. a Image corresponding to a maximum intensity projection of a confocal slice z-stack (40 optical slices, spaced at 300 nm) showing labeling for BDA (green), GAD65 (red) and VGLUT2 (blue) in the ventral DG of a control rat. Axon terminals and fibers, originating from the SuM neurons, labeled for the BDA anterograde tracer (green) were distributed in the SGL and in the lower part of the IML. Numerous GAD65-containing terminals and VGLUT2-containing terminals were present in this region. b–d Images of the three different fluorophores used for the triple labeling, obtained by sequential acquisition of separate wavelength channels from a single confocal slice, in the SGL of the ventral DG demonstrated axon terminals labeled for BDA (b, green, arrows) containing GAD65 (c, red, arrows) and VGLUT2 (d, blue, arrows) and BDA-labeled terminals containing VGLUT2 only (d, blue, arrowheads). e Merge of b and c. f Merge of b and d. g Merge of b–d. Triple-labeled boutons for BDA, GAD65 and VGLUT2 (white, arrows) and double-labeled boutons for BDA and VGLUT2 (arrowheads) were surrounded by double-labeled terminals for GAD65 and VGLUT2 (purple) as well as single-labeled terminals for GAD65 (red) or VGLUT2 (blue). h Image corresponding to a maximum intensity projection of a confocal slice z-stack (40 optical slices, spaced at 300 nm) showing labeling for BDA (green), GAD65 (red) and VGLUT2 (blue) in the ventral DG of an epileptic rat at 2 months after pilocarpine injection. Axon terminals and fibers, originating from SuM neurons, labeled for the BDA anterograde tracer (green) displayed an aberrant distribution as compared to the control rat (a), many boutons and fibers being observed in the entire IML including the upper part. Numerous GAD65-containing terminals (red) and VGLUT2-containing terminals (blue) were also present in this entire region. i–k Images of the three different fluorophores used for the triple labeling, obtained by sequential acquisition of separate wavelength channels from a single confocal slice, in the IML of the ventral DG demonstrated that many of these ectopic BDA-labeled axon terminals (i, green, arrows) contained GAD65 (j, red, arrows) and VGLUT2 (k, blue, arrows) and some contained VGLUT2 only (i–k arrowhead). l Merge of i and j. m Merge of i and k. n Merge of i–k. Triple-labeled boutons for BDA, GAD65 and VGLUT2 (white, arrows) and double-labeled terminals for BDA and VGLUT2 (arrowhead) were surrounded by double-labeled terminals for GAD65 and VGLUT2 (purple) as well as single-labeled terminals for GAD65 (red). Ctrl control, Pilo 2months pilocarpine-treated rat at 2 months after status epilepticus. Scale bars 10 µm in a and h; 2 µm in b–g and i–n
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Fig4: Comparison of neurochemical phenotypes for the ventral dentate gyrus afferents from the SuM between control (a–g) and epileptic pilocarpine-treated (h–n) rats, characterized by simultaneous labeling for BDA anterograde tracer (green), GAD65 (red) and VGLUT2 (blue) in coronal sections. a Image corresponding to a maximum intensity projection of a confocal slice z-stack (40 optical slices, spaced at 300 nm) showing labeling for BDA (green), GAD65 (red) and VGLUT2 (blue) in the ventral DG of a control rat. Axon terminals and fibers, originating from the SuM neurons, labeled for the BDA anterograde tracer (green) were distributed in the SGL and in the lower part of the IML. Numerous GAD65-containing terminals and VGLUT2-containing terminals were present in this region. b–d Images of the three different fluorophores used for the triple labeling, obtained by sequential acquisition of separate wavelength channels from a single confocal slice, in the SGL of the ventral DG demonstrated axon terminals labeled for BDA (b, green, arrows) containing GAD65 (c, red, arrows) and VGLUT2 (d, blue, arrows) and BDA-labeled terminals containing VGLUT2 only (d, blue, arrowheads). e Merge of b and c. f Merge of b and d. g Merge of b–d. Triple-labeled boutons for BDA, GAD65 and VGLUT2 (white, arrows) and double-labeled boutons for BDA and VGLUT2 (arrowheads) were surrounded by double-labeled terminals for GAD65 and VGLUT2 (purple) as well as single-labeled terminals for GAD65 (red) or VGLUT2 (blue). h Image corresponding to a maximum intensity projection of a confocal slice z-stack (40 optical slices, spaced at 300 nm) showing labeling for BDA (green), GAD65 (red) and VGLUT2 (blue) in the ventral DG of an epileptic rat at 2 months after pilocarpine injection. Axon terminals and fibers, originating from SuM neurons, labeled for the BDA anterograde tracer (green) displayed an aberrant distribution as compared to the control rat (a), many boutons and fibers being observed in the entire IML including the upper part. Numerous GAD65-containing terminals (red) and VGLUT2-containing terminals (blue) were also present in this entire region. i–k Images of the three different fluorophores used for the triple labeling, obtained by sequential acquisition of separate wavelength channels from a single confocal slice, in the IML of the ventral DG demonstrated that many of these ectopic BDA-labeled axon terminals (i, green, arrows) contained GAD65 (j, red, arrows) and VGLUT2 (k, blue, arrows) and some contained VGLUT2 only (i–k arrowhead). l Merge of i and j. m Merge of i and k. n Merge of i–k. Triple-labeled boutons for BDA, GAD65 and VGLUT2 (white, arrows) and double-labeled terminals for BDA and VGLUT2 (arrowhead) were surrounded by double-labeled terminals for GAD65 and VGLUT2 (purple) as well as single-labeled terminals for GAD65 (red). Ctrl control, Pilo 2months pilocarpine-treated rat at 2 months after status epilepticus. Scale bars 10 µm in a and h; 2 µm in b–g and i–n
Mentions: Previous studies demonstrated in control rats the heterogeneity of SuM–DG pathways with two main projections originating from neurons in the SuML and the SuMM (Haglund et al. 1984; Vertes 1992; Maglóczky et al. 1994; Vertes and McKenna 2000) that can be identified based on their neurochemical content (Soussi et al. 2010). The axon terminals from the SuML that innervate the SGL of the dorsal DG and to a much lesser extent of the ventral DG contain markers of both glutamatergic (VGLUT2) and GABAergic (GAD65 and VGAT) neurotransmissions, whereas the axon terminals from the SuMM that innervate exclusively the IML contain VGLUT2 only. To assess the contribution of each pathway in the reorganization of the SuM–DG projections, triple immunofluorescence labeling for BDA, VGLUT2 and GAD65 were performed in the dorsal (Fig. 3) and ventral (Fig. 4) regions of the DG in epileptic and control rats.Fig. 3

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