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Christiaen E, Goossens MG, Descamps B, Delbeke J, Wadman W, Vonck K, Boon P, Raedt R, Vanhove C. White Matter Integrity in a Rat Model of Epileptogenesis: Structural Connectomics and Fixel-Based Analysis. Brain Connect 2021; 12:320-333. [PMID: 34155915 DOI: 10.1089/brain.2021.0026] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Introduction: Electrophysiological and neuroimaging studies have demonstrated that large-scale brain networks are affected during the development of epilepsy. These networks can be investigated by using diffusion magnetic resonance imaging (dMRI). The most commonly used model to analyze dMRI is diffusion tensor imaging (DTI). However, DTI metrics are not specific to microstructure or pathology and the DTI model does not take into account crossing fibers, which may lead to erroneous results. To overcome these limitations, a more advanced model based on multi-shell multi-tissue constrained spherical deconvolution was used in this study to perform tractography with more precise fiber orientation estimates and to assess changes in intra-axonal volume by using fixel-based analysis. Methods: dMRI images were acquired before and at several time points after induction of status epilepticus in the intraperitoneal kainic acid (IPKA) rat model of temporal lobe epilepsy. Tractography was performed, and fixel metrics were calculated in several white matter tracts. The tractogram was analyzed by using the graph theory. Results: Global degree, global and local efficiency were decreased in IPKA animals compared with controls during epileptogenesis. Nodal degree was decreased in the limbic system and default-mode network, mainly during early epileptogenesis. Further, fiber density (FD) and fiber-density-and-cross-section (FDC) were decreased in several white matter tracts. Discussion: These results indicate a decrease in overall structural connectivity, integration, and segregation and decreased structural connectivity in the limbic system and default-mode network. Decreased FD and FDC point to a decrease in intra-axonal volume fraction during epileptogenesis, which may be related to neuronal degeneration and gliosis. Impact statement To the best of our knowledge, this is the first longitudinal multi-shell diffusion magnetic resonance imaging study that combines whole-brain tractography and fixel-based analysis to investigate changes in structural brain connectivity and white matter integrity during epileptogenesis in a rat model of temporal lobe epilepsy. Our findings present better insights into how the topology of the structural brain network changes during epileptogenesis and how these changes are related to white matter integrity. This could improve the understanding of the basic mechanisms of epilepsy and aid the rational development of imaging biomarkers and epilepsy therapies.
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Affiliation(s)
- Emma Christiaen
- MEDISIP, Department of Electronics and Information Systems, Ghent University, Ghent, Belgium
| | | | - Benedicte Descamps
- MEDISIP, Department of Electronics and Information Systems, Ghent University, Ghent, Belgium
| | - Jean Delbeke
- 4Brain, Department of Head and Skin, Ghent University, Ghent, Belgium
| | - Wytse Wadman
- 4Brain, Department of Head and Skin, Ghent University, Ghent, Belgium
| | - Kristl Vonck
- 4Brain, Department of Head and Skin, Ghent University, Ghent, Belgium
| | - Paul Boon
- 4Brain, Department of Head and Skin, Ghent University, Ghent, Belgium
| | - Robrecht Raedt
- 4Brain, Department of Head and Skin, Ghent University, Ghent, Belgium
| | - Christian Vanhove
- MEDISIP, Department of Electronics and Information Systems, Ghent University, Ghent, Belgium
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Goossens MG, Boon P, Wadman W, Van den Haute C, Baekelandt V, Verstraete AG, Vonck K, Larsen LE, Sprengers M, Carrette E, Desloovere J, Meurs A, Delbeke J, Vanhove C, Raedt R. Long-term chemogenetic suppression of seizures in a multifocal rat model of temporal lobe epilepsy. Epilepsia 2021; 62:659-670. [PMID: 33570167 DOI: 10.1111/epi.16840] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2020] [Revised: 01/21/2021] [Accepted: 01/21/2021] [Indexed: 01/14/2023]
Abstract
OBJECTIVE One third of epilepsy patients do not become seizure-free using conventional medication. Therefore, there is a need for alternative treatments. Preclinical research using designer receptors exclusively activated by designer drugs (DREADDs) has demonstrated initial success in suppressing epileptic activity. Here, we evaluated whether long-term chemogenetic seizure suppression could be obtained in the intraperitoneal kainic acid rat model of temporal lobe epilepsy, when DREADDs were selectively expressed in excitatory hippocampal neurons. METHODS Epileptic male Sprague Dawley rats received unilateral hippocampal injections of adeno-associated viral vector encoding the inhibitory DREADD hM4D(Gi), preceded by a cell-specific promotor targeting excitatory neurons. The effect of clozapine-mediated DREADD activation on dentate gyrus evoked potentials and spontaneous electrographic seizures was evaluated. Animals were systemically treated with single (.1 mg/kg/24 h) or repeated (.1 mg/kg/6 h) injections of clozapine. In addition, long-term continuous release of clozapine and olanzapine (2.8 mg/kg/7 days) using implantable minipumps was evaluated. All treatments were administered during the chronic epileptic phase and between 1.5 and 13.5 months after viral transduction. RESULTS In the DREADD group, dentate gyrus evoked potentials were inhibited after clozapine treatment. Only in DREADD-expressing animals, clozapine reduced seizure frequency during the first 6 h postinjection. When administered repeatedly, seizures were suppressed during the entire day. Long-term treatment with clozapine and olanzapine both resulted in significant seizure-suppressing effects for multiple days. Histological analysis revealed DREADD expression in both hippocampi and some cortical regions. However, lesions were also detected at the site of vector injection. SIGNIFICANCE This study shows that inhibition of the hippocampus using chemogenetics results in potent seizure-suppressing effects in the intraperitoneal kainic acid rat model, even 1 year after viral transduction. Despite a need for further optimization, chemogenetic neuromodulation represents a promising treatment prospect for temporal lobe epilepsy.
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Affiliation(s)
| | - Paul Boon
- 4BRAIN, Department of Head and Skin, Ghent University, Ghent, Belgium
| | - Wytse Wadman
- 4BRAIN, Department of Head and Skin, Ghent University, Ghent, Belgium
| | - Chris Van den Haute
- Laboratory for Neurobiology and Gene Therapy, Center for Molecular Medicine and Leuven Brain Institute, KU Leuven, Leuven, Belgium.,Leuven Viral Vector Core, Center for Molecular Medicine, KU Leuven, Leuven, Belgium
| | - Veerle Baekelandt
- Laboratory for Neurobiology and Gene Therapy, Center for Molecular Medicine and Leuven Brain Institute, KU Leuven, Leuven, Belgium
| | - Alain G Verstraete
- Department of Diagnostic Sciences, Ghent University, Ghent, Belgium.,Department of Laboratory Medicine, Ghent University Hospital, Ghent, Belgium
| | - Kristl Vonck
- 4BRAIN, Department of Head and Skin, Ghent University, Ghent, Belgium
| | - Lars E Larsen
- 4BRAIN, Department of Head and Skin, Ghent University, Ghent, Belgium
| | - Mathieu Sprengers
- 4BRAIN, Department of Head and Skin, Ghent University, Ghent, Belgium
| | - Evelien Carrette
- 4BRAIN, Department of Head and Skin, Ghent University, Ghent, Belgium
| | - Jana Desloovere
- 4BRAIN, Department of Head and Skin, Ghent University, Ghent, Belgium
| | - Alfred Meurs
- 4BRAIN, Department of Head and Skin, Ghent University, Ghent, Belgium
| | - Jean Delbeke
- 4BRAIN, Department of Head and Skin, Ghent University, Ghent, Belgium
| | - Christian Vanhove
- IBiTech, Department of Electronics and Information Systems, Ghent University, Ghent, Belgium
| | - Robrecht Raedt
- 4BRAIN, Department of Head and Skin, Ghent University, Ghent, Belgium
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