One in 26 people develop epilepsy and in these temporal lobe epilepsy (TLE) is common. Many patients display a pattern of neuron loss called hippocampal sclerosis. Seizures usually start in the hippocampus but underlying mechanisms remain unclear. One possibility is insufficient inhibition of dentate granule cells. Normally parvalbumin‐immunoreactive (PV) interneurons strongly inhibit granule cells. Humans with TLE display loss of PV interneurons in the dentate gyrus but questions persist. To address this, we evaluated PV interneuron and bouton numbers in California sea lions (
- Award ID(s):
- 1828327
- NSF-PAR ID:
- 10218442
- Date Published:
- Journal Name:
- Bioprotocol
- Volume:
- 10
- Issue:
- 4
- ISSN:
- 2331-8325
- Page Range / eLocation ID:
- e3533
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Zalophus californianus -
null (Ed.)The dentate gyrus (DG) is a region of the adult rodent brain that undergoes continuous neurogenesis. Seizures and loss or dysfunction of GABAergic synapses onto adult-born dentate granule cells (GCs) alter their dendritic growth and migration, resulting in dysmorphic and hyperexcitable GCs. Additionally, transplants of fetal GABAergic interneurons in the DG of mice with temporal lobe epilepsy (TLE) result in seizure suppression, but it is unknown whether increasing interneurons with these transplants restores GABAergic innervation to adult-born GCs. Here we address this question by retroviral birth-dating GCs at different times up to 12 weeks after pilocarpine-induced TLE in adult mice. ChR2-EYFP-expressing MGE-derived GABAergic interneurons from E13.5 mouse embryos were transplanted into the DG of the TLE mice and GCs with transplant-derived inhibitory post-synaptic currents were identified by patch-clamp electrophysiology and optogenetic interrogation. Putative synaptic sites between GCs and GABAergic transplants were also confirmed by intracellular biocytin staining, immunohistochemistry, and confocal imaging. 3D reconstructions of dendritic arbors and quantitative morphometric analyses were carried out in >150 adult-born GCs. GABAergic inputs from transplanted interneurons correlated with markedly shorter GC dendrites, compared to GCs that were not innervated by the transplants. Moreover, these effects were confined to distal dendritic branches and a short time window of 6-8 weeks. The effects were independent of seizures as they were also observed in naïve mice with MGE transplants. These findings are consistent with the hypothesis that increased inhibitory currents over a smaller dendritic arbor in adult-born GCs may reduce their excitability and lead to seizure suppression.more » « less
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null (Ed.)GABAergic interneuron dysfunction has been implicated in temporal lobe epilepsy (TLE), autism, and schizophrenia. Inhibitory interneuron progenitors transplanted into the hippocampus of rodents with TLE provide varying degrees of seizure suppression. We investigated whether human embryonic stem cell (hESC)-derived interneuron progenitors (hESNPs) could differentiate, correct hippocampal-dependent spatial memory deficits, and suppress seizures in a pilocarpine-induced TLE mouse model. We found that transplanted ventralized hESNPs differentiated into mature GABAergic interneurons and became electrophysiologically active with mature firing patterns. Some mice developed hESNP-derived tumor-like NSC clusters. Mice with transplants showed significant improvement in the Morris water maze test, but transplants did not suppress seizures. The limited effects of the human GABAergic interneuron progenitor grafts may be due to cell type heterogeneity within the transplants.more » « less
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Summary Objective Seizures develop in 80% of patients with anti–
N ‐methyl‐d ‐aspartate receptor (NMDAR) encephalitis, and these represent a major cause of morbidity and mortality. Anti‐NMDAR antibodies have been linked to memory loss in encephalitis; however, their role in seizures has not been established. We determined whether anti‐NMDAR antibodies from autoimmune encephalitis patients are pathogenic for seizures.Methods We performed continuous intracerebroventricular infusion of cerebrospinal fluid (CSF) or purified immunoglobulin (IgG) from the CSF of patients with anti‐NMDAR encephalitis or polyclonal rabbit anti‐NMDAR IgG, in male C57BL/6 mice. Seizure status during a 2‐week treatment was assessed with video‐electroencephalography. We assessed memory, anxiety‐related behavior, and motor function at the end of treatment and assessed the extent of neuronal damage and gliosis in the CA1 region of hippocampus. We also performed whole‐cell patch recordings from the CA1 pyramidal neurons in hippocampal slices of mice with seizures.
Results Prolonged exposure to rabbit anti‐NMDAR IgG, patient CSF, or human IgG purified from the CSF of patients with encephalitis induced seizures in 33 of 36 mice. The median number of seizures recorded in 2 weeks was 13, 39, and 35 per mouse in these groups, respectively. We observed only 18 brief nonconvulsive seizures in 11 of 29 control mice (median seizure count of 0) infused with vehicle (n = 4), normal CSF obtained from patients with noninflammatory central nervous system (CNS) conditions (n = 12), polyclonal rabbit IgG (n = 7), albumin (n = 3), and normal human IgG (n = 3). We did not observe memory deficits, anxiety‐related behavior, or motor impairment measured at 2 weeks in animals treated with CSF from affected patients or rabbit IgG. Furthermore, there was no evidence of hippocampal cell loss or astrocyte proliferation in the same mice.
Significance Our findings indicate that autoantibodies can induce seizures in anti‐NMDAR encephalitis and offer a model for testing novel therapies for refractory autoimmune seizures.
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Abstract Objective Cognitive impairment often impacts quality of life in epilepsy even if seizures are controlled. Word‐finding difficulty is particularly prevalent and often attributed to etiological (static, baseline) circuit alterations. We sought to determine whether interictal discharges convey significant superimposed contributions to word‐finding difficulty in patients, and if so, through which cognitive mechanism(s).
Methods Twenty‐three patients undergoing intracranial monitoring for drug‐resistant epilepsy participated in multiple tasks involving word production (auditory naming, short‐term verbal free recall, repetition) to probe word‐finding difficulty across different cognitive domains. We compared behavioral performance between trials with versus without interictal discharges across six major brain areas and adjusted for intersubject differences using mixed‐effects models. We also evaluated for subjective word‐finding difficulties through retrospective chart review.
Results Subjective word‐finding difficulty was reported by the majority (79%) of studied patients preoperatively. During intracranial recordings, interictal epileptiform discharges (IEDs) in the medial temporal lobe were associated with long‐term lexicosemantic memory impairments as indexed by auditory naming (
p = .009), in addition to their established impact on short‐term verbal memory as indexed by free recall (p = .004). Interictal discharges involving the lateral temporal cortex and lateral frontal cortex were associated with delayed reaction time in the auditory naming task (p = .016 andp = .018), as well as phonological working memory impairments as indexed by repetition reaction time (p = .002). Effects of IEDs across anatomical regions were strongly dependent on their precise timing within the task.Significance IEDs appear to act through multiple cognitive mechanisms to form a convergent basis for the debilitating clinical word‐finding difficulty reported by patients with epilepsy. This was particularly notable for medial temporal spikes, which are quite common in adult focal epilepsy. In parallel with the treatment of seizures, the modulation of interictal discharges through emerging pharmacological means and neurostimulation approaches may be an opportunity to help address devastating memory and language impairments in epilepsy.
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.21769/BioProtoc.3533
