Mossy Fiber Sprouting Research Articles

Silencing MicroRNA-134 Alleviates Hippocampal Damage and Occurrence of Spontaneous Seizures After Intraventricular Kainic Acid-Induced Status Epilepticus in Rats.

Epilepsy is a disorder of abnormal brain activity typified by spontaneous and recurrent seizures. MicroRNAs (miRNAs) are short non-coding RNAs, critical for the post-transcriptional regulation of gene expression. MiRNA dysregulation has previously been implicated in the induction of epilepsy. In this study, we examined the effect of silencing miR-134 against status epilepticus (SE). Our results showed that level of miR-134 was significantly up-regulated in rat brain after Kainic acid (KA)-induced SE. TUNEL staining showed that silencing miR-134 alleviated seizure-induced neuronal apoptosis in the CA3 subfield of the hippocampus. Western blot showed that a miR-134 antagonist suppressed lesion-induced endoplasmic reticulum (ER) stress and apoptosis related expression of CHOP, Bim and Cytochrome C, while facilitated the expression of CREB at 24 h post KA-induced lesion in the hippocampus. Consistently, silencing miR-134 significantly diminished loss of CA3 pyramidal neurons using Nissl staining as well as reducing aberrant mossy fiber sprouting (MFS) in a rat epileptic model. In addition, the results of EEG and behavior analyses showed seizures were alleviated by miR-134 antagonist in our experimental models. These results suggest that silencing miR-134 modulates the epileptic phenotype by upregulating its target gene, CREB. This in turn attenuates oxidative and ER stress, inhibits apoptosis, and decreases MFS long term. This indicates that silencing miR-134 might be a promising intervention for the treatment of epilepsy.

Lacosamide modulates collapsin response mediator protein 2 and inhibits mossy fiber sprouting after kainic acid-induced status epilepticus.

Mossy fiber sprouting (MFS) and neuronal loss are important pathological features of chronic epilepsy closely related to the development of spontaneous recurrent seizures. However, the pathological mechanism of MFS remains unclear. Collapsin response mediator protein 2 (CRMP2) is a cytoplasmic protein highly expressed in the nervous system and is involved in axon/dendrite specification and axonal growth. It is possibly associated with the development of MFS. Lacosamide (LCM), a novel antiepileptic drug, was recently found to inhibit the CRMP2-mediated neurite outgrowth. Therefore, we studied the relationships between LCM, CRMP2, and MFS, seeking potential therapeutic targets for epileptogenesis and a better understanding of the mechanism of action of LCM. We used kainic acid to induce status epilepticus in an animal model and examined the resultant changes in protein expression by Western blot and changes in histology by specific staining for cell death and MFS. Our results showed that the expression level of CRMP2 was elevated and the expression level of phosphorylated CRMP2 (p-CRMP2) was reduced following status epilepticus. Administration of LCM not only reversed this effect but also suppressed spontaneous recurrent seizures and reduced MFS and loss of hippocampal neurons. This study reveals that, in addition to its antiseizure efficacy, LCM has a neuroprotective effect and inhibits the development of epilepsy. CRMP2 is possibly involved in the mechanism by which LCM suppresses MFS and is expected to be a new therapeutic target for treating epileptogenesis.

Zinc/CaMK II Associated-Mitophagy Signaling Contributed to Hippocampal Mossy Fiber Sprouting and Cognitive Deficits Following Neonatal Seizures and Its Regulation by Chronic Leptin Treatment.

The role of leptin in the pathogenesis of epilepsy is getting more and more attention in clinical and basic research. Although there are data indicating neuroprotective effects of elevated serum/brain leptin levels following acute seizures, no study to date has dealt with the impact of chronic leptin treatment on long-term brain injury following developmental seizures. The aim of this study was to evaluate whether chronic leptin treatment may have neuroprotective effects on cognitive and hippocampal mossy fiber sprouting following flurothyl-induced recurrent neonatal seizures and whether these effects are mediated by the zinc/CaMKII-associated mitophagy signaling pathway. Forty Sprague-Dawley rats (postnatal day 6, P6) were randomly assigned into two groups: neonatal seizure group and control group. At P13, they were further divided into control group, seizure group (RS), control + leptin (leptin, i.p., 2 mg/kg/day for 10 days), seizure+leptin group (RS+Leptin, 2mg/kg/day, i.p., for 10 consecutive days). Morris water maze test was performed during P27-P32. Subsequently, Timm staining and Western blotting were used to detect the mossy fiber sprouting and protein levels in hippocampus. Flurothyl-induced seizures (RS group) significantly down-regulated mitophagy markers PINK, Drp1, PHB, and memory marker CaMK II alpha while up-regulating zinc transporters ZnT3, ZnT4, ZIP7, and autophagy execution molecular cathepsin-E, which were paralleled with hippocampal aberrant mossy fiber sprouting and cognitive dysfunction. However, these changes were restored by chronic leptin treatment (RS+Leptin group). The results showed that leptin had neuroprotective effect on hippocampal pathological damage and cognitive deficits induced by neonatal seizures and suggested that Zinc/CaMK II associated-mitophagy signaling pathway in hippocampus may be a new target of leptin's neuroprotection, with potential value of translational medicine.

Anterior nucleus of thalamus stimulation inhibited abnormal mossy fiber sprouting in kainic acid-induced epileptic rats

BackgroundDeep brain stimulation (DBS) of the anterior nucleus of the thalamus (ANT) has demonstrated antiepileptic efficacy, especially for mesial temporal lobe epilepsy (MTLE). Mossy fiber sprouting (MFS) is involved in the pathogenesis of MTLE, and Sema-3A and GAP-43 are pivotal regulators of MFS. This study investigated the effects of ANT-DBS on MFS and expression levels of Sema-3A and GAP-43 as a possible mechanism for seizure suppression. MethodsAdult male Sprague-Dawley rats were randomly divided into four groups: (1) control (saline injection), (2) KA (kainic acid injection), (3) KA + Sham-DBS (electrode implantation without stimulation), and (4) KA + DBS (electrode implantation with stimulation). Video electroencephalography (EEG) was used to ensure model establishment and monitor seizure frequency, latency, and severity (Racine stage). Chronic ANT stimulation was conducted for 35 days in the KA + DBS group, and MFS compared to the other groups by quantitative Timm staining. Sema-3A and GAP-43 expression levels in the hippocampal formation were evaluated in all groups with western blot. ResultsThe latency period was significantly prolonged and spontaneous seizure frequency reduced in the KA + DBS group compared to KA and KA + Sham-DBS groups. Staining scores for MFS in CA3 and dentate gyrus (DG) were significantly lower in the KA + DBS group. The KA + DBS group also exhibited decreased GAP-43 expression and increased Sema-3A expression compared to KA and KA + Sham-DBS groups. ConclusionThese results suggest that ANT-DBS extends the latent period following epileptogenic stimulation by impeding MFS through modulation of GAP-43 and Sema-3A expression.

UCH-L1 inhibition aggravates mossy fiber sprouting in the pentylenetetrazole kindling model

Mossy fiber sprouting (MFS) is a pathological phenomenon that is commonly observed in epilepsy, and plentiful data reveal that abnormal phosphorylated modification of tau protein plays a critical role in MSF by the regulation of microtubule dynamics and axonal transport. Ubiquitin C-terminal hydrolase L1 (UCH-L1), a proteasomal deubiquitinating enzyme, has been proved to be associated with tau aggregation through mediating degradation of ubiquitinated and hyperphosphorylated tau. Thus, this study aimed to determine the expression of UCH-L1 in the rat hippocampus during the pentylenetetrazole (PTZ)-induced process and to demonstrate the possible correlation with MFS in epileptogenesis. Seizures were established by intraperitoneal injection of PTZ and LDN-57444 was used to inhibit the hydrolase activity of UCH-L1. We used western blot, immunofluorescence, immunoprecipitation, and timm staining to detect phosphorylated modification of tau and MSF. The results presented that LDN-57444 induced the deteriorated severity of seizures, increased phosphorylation of tau and increased distribution of Timm granules in both the supragranular region of the dentate gyrus (DG) and the stratum pyramidale of CA3 subfield. Our results suggest that UCH-L1 may be associated with hippocampal MSF followed the epileptogenesis through mediating phosphorylation of tau. UCH-L1 may be a potential and novel therapeutic target to limit epileptogenesis.

The Molecular and Cellular Mechanisms of Axon Guidance in Mossy Fiber Sprouting.

The question of whether mossy fiber sprouting is epileptogenic has not been resolved; both sprouting-induced recurrent excitatory and inhibitory circuit hypotheses have been experimentally (but not fully) supported. Therefore, whether mossy fiber sprouting is a potential therapeutic target for epilepsy remains under debate. Moreover, the axon guidance mechanisms of mossy fiber sprouting have attracted the interest of neuroscientists. Sprouting of mossy fibers exhibits several uncommon axonal growth features in the basically non-plastic adult brain. For example, robust branching of axonal collaterals arises from pre-existing primary mossy fiber axons. Understanding the branching mechanisms in adulthood may contribute to axonal regeneration therapies in neuroregenerative medicine in which robust axonal re-growth is essential. Additionally, because granule cells are produced throughout life in the neurogenic dentate gyrus, it is interesting to examine whether the mossy fibers of newly generated granule cells follow the pre-existing trajectories of sprouted mossy fibers in the epileptic brain. Understanding these axon guidance mechanisms may contribute to neuron transplantation therapies, for which the incorporation of transplanted neurons into pre-existing neural circuits is essential. Thus, clarifying the axon guidance mechanisms of mossy fiber sprouting could lead to an understanding of central nervous system (CNS) network reorganization and plasticity. Here, we review the molecular and cellular mechanisms of axon guidance in mossy fiber sprouting by discussing mainly in vitro studies.

Signaling Pathways and Cellular Mechanisms Regulating Mossy Fiber Sprouting in the Development of Epilepsy.

The sprouting of hippocampal dentate granule cell axons, termed mossy fibers, into the dentate inner molecular layer is one of the most consistent findings in tissue from patients with mesial temporal lobe epilepsy. Decades of research in animal models have revealed that mossy fiber sprouting creates de novo recurrent excitatory connections in the hippocampus, fueling speculation that the pathology may drive temporal lobe epileptogenesis. Conducting definitive experiments to test this hypothesis, however, has been challenging due to the difficulty of dissociating this sprouting from the many other changes occurring during epileptogenesis. The field has been largely driven, therefore, by correlative data. Recently, the development of powerful transgenic mouse technologies and the discovery of novel drug targets has provided new tools to assess the role of mossy fiber sprouting in epilepsy. We can now selectively manipulate hippocampal granule cells in rodent epilepsy models, providing new insights into the granule cell subpopulations that participate in mossy fiber sprouting. The cellular pathways regulating this sprouting are also coming to light, providing new targets for pharmacological intervention. Surprisingly, many investigators have found that blocking mossy fiber sprouting has no effect on seizure occurrence, while seizure frequency can be reduced by treatments that have no effect on this sprouting. These results raise new questions about the role of mossy fiber sprouting in epilepsy. Here, we will review these findings with particular regard to the contributions of new granule cells to mossy fiber sprouting and the regulation of this sprouting by the mTOR signaling pathway.

Ablation of aberrant neurogenesis fails to attenuate cognitive deficit of chronically epileptic mice

Pilocarpine-induced acute seizures strongly induce aberrant hippocampal neurogenesis, characterized by increased proliferation of neural progenitors and abnormal integrations of newly generated granule cells − hilar ectopic granule cells (EGCs), mossy fibre sprouting (MFS), and hilar basal dendrites (HBDs), which may disturb hippocampal neuronal circuits and thus contribute to cognitive impairment in temporal lobe epilepsy (TLE) patients and animal models. Previous studies via ablating hippocampal neurogenesis after acute seizures produced inconsistent results regarding the development of long-term cognitive impairment. Furthermore, a sufficient decrease of subsequent abnormal integrations in chronically epileptic hippocampus was not well-established in these studies. Therefore, the link between seizure-induced aberrant hippocampal neurogenesis and cognitive decline associated with epilepsy is still in need to be clarified. In this study, the mice were injected with methylazoxymethanol acetate (MAM) both before and after pilocarpine-induced status epilepticus (SE) to achieve an overall ablation of newborn cells contributing to the pathological recruitment. In addition, a protracted time point was chosen for behavioral testing considering it takes a fairly long time for newborn granule cells to adequately develop abnormal integrations, especially MFS. Although an overall reduction of abnormal integrations, including EGCs, MFS and HBDs was confirmed following the ablation regime, the performance of ablated and non-ablated mice in the Morris Water Maze (MWM) task did not differ. The current findings therefore provide novel evidences that ablation of neurogenesis with an overall decrease of abnormal integrations cannot attenuate subsequent cognitive impairment at least in the model used in this study.

Intravenous infusion of mesenchymal stem cells reduces epileptogenesis in a rat model of status epilepticus

ObjectiveStatus epilepticus (SE) causes neuronal cell death, aberrant mossy fiber sprouting (MFS), and cognitive deteriorations. The present study tested the hypothesis that systemically infused mesenchymal stem cells (MSCs) reduce epileptogenesis by inhibiting neuronal cell death and suppressing aberrant MFS, leading to cognitive function preservation in a rat model of epilepsy. MethodsSE was induced using the lithium-pilocarpine injection model. The seizure frequency was scored using a video-monitoring system and the Morris water maze test was carried out to evaluate cognitive function. Comparisons were made between MSCs- and vehicle-infused rats. Immunohistochemical staining was performed to detect Green fluorescent protein (GFP)+ MSCs and to quantify the number of GAD67+ and NeuN+ neurons in the hippocampus. Manganese-enhanced magnetic resonance imaging (MEMRI) and Timm staining were also performed to assess the MFS. ResultsMSC infusion inhibited epileptogenesis and preserved cognitive function after SE. The infused GFP+ MSCs were accumulated in the hippocampus and were associated with the preservation of GAD67+ and NeuN+ hippocampal neurons. Furthermore, the MSC infusion suppressed the aberrant MFS in the hippocampus as evidenced by MEMRI and Timm staining. ConclusionsThis study demonstrated that the intravenous infusion of MSCs mitigated epileptogenesis, thus advancing MSCs as an effective approach for epilepsy in clinical practice.

Stress and Corticosteroids Aggravate Morphological Changes in the Dentate Gyrus after Early-Life Experimental Febrile Seizures in Mice.

Stress is the most frequently self-reported seizure precipitant in patients with epilepsy. Moreover, a relation between ear stress and epilepsy has been suggested. Although ear stress and stress hormones are known to influence seizure threshold in rodents, effects on the development of epilepsy (epileptogenesis) are still unclear. Therefore, we studied the consequences of ear corticosteroid exposure for epileptogenesis, under highly controlled conditions in an animal model. Experimental febrile seizures (eFS) were elicited in 10-day-old mice by warm-air induced hyperthermia, while a control group was exposed to a normothermic condition. In the following 2 weeks, mice received either seven corticosterone or vehicle injections or were left undisturbed. Specific measures indicative for epileptogenesis were examined at 25 days of age and compared with vehicle injected or untreated mice. We examined structural [neurogenesis, dendritic morphology, and mossy fiber sprouting (MFS)] and functional (glutamatergic postsynaptic currents and long-term potentiation) plasticity in the dentate gyrus (DG). We found that differences in DG morphology induced by eFS were aggravated by repetitive (mildly stressful) vehicle injections and corticosterone exposure. In the injected groups, eFS were associated with decreases in neurogenesis, and increases in cell proliferation, dendritic length, and spine density. No group differences were found in MFS. Despite these changes in DG morphology, no effects of eFS were found on functional plasticity. We conclude that corticosterone exposure during early epileptogenesis elicited by eFS aggravates morphological, but not functional, changes in the DG, which partly supports the hypothesis that ear stress stimulates epileptogenesis.

Different mossy fiber sprouting patterns in ILAE hippocampal sclerosis types

ObjectiveHippocampal sclerosis (HS) is the most prevalent pathology in temporal lobe epilepsy (TLE) characterized by segmental neuronal cell loss in the cornu ammonis (CA) 1–4. In addition, migration of granule cells and reorganization of their axons is observed, known as granule cell dispersion (GCD) and mossy fiber sprouting (MFS). The loss of mossy fibers` (MF) target cells in CA4 and CA3 was considered to be causative for MFS. The ILAE HS (International League Against Epilepsy) classification identifies three subtypes with different cell loss patterns in CA1-4. We studied the relation of ILAE HS subtypes to GCD and MFS to corroborate clinico-pathological subgroups in a large retrospective single-center series. Material and methodsHippocampal specimen of 319 patients were screened, 214 could be used for analysis. Immunohistochemical stainings for semi-quantitative analysis of neuronal cell loss (NeuN) and MFS (synaptoporin) were performed. Presurgical data were available from patient files and seizure outcome was classified according to Engel score after surgery. ResultsIn 39 patients (18%) no neuronal cell loss (ILAE no-HS), no GCD and no MFS was observed. In 154 patients (72%) severe neuronal cell loss was seen in CA1, CA4 and CA3 (ILAE HS 1, typical HS); in addition extensive GCD and MFS was observed. In 17 patients (8%) cell loss was seen predominantly in CA1 (ILAE HS 2); despite different cell loss pattern these hippocampi also showed GCD and MFS. In 4 patients (2%) cell loss was predominately detected in CA3 and CA4 (ILAE HS type 3), consecutively GCD and MFS were observed. Longer epilepsy duration and younger age at surgery was more often associated with ILAE HS 2 and febrile convulsions were completely absent in ILAE no-HS. Yet, seizure onset, age at initial precipitating injury and postsurgical seizure outcome did not show any significant association with ILAE HS subtypes. ConclusionGCD and MFS might develop independently from the neuronal cell loss of MF target cells.

Effect of eugenol on lithium-pilocarpine model of epilepsy: behavioral, histological, and molecular changes.

Objective(s):Epilepsy establishment gives rise to biochemical and morphological changes in the hippocampus. Oxidative stress, morphological changes, and mossy fiber sprouting (MFS) in the hippocampus underpin the epilepsy establishment. Eugenol is the main component of the essential oil extracted from cloves with the potential to modulate neuronal excitability. Therefore, we investigated the effect of eugenol on convulsive behavior, oxidative stress, and histological changes of the hippocampus in lithium-pilocarpine model of epilepsy.Materials and Methods:Male Wistar rats weighing 220–250 g were divided into 4 groups; Control, Pilocarpine, Eugenol-Pilocarpine, and Eugenol. Oxidative stress markers were assayed by a biochemical method. Nissl and Timm staining were used to show neuronal survival and MFS, respectively. Behavioral convulsions were evaluated using the modified Racine scale.Results:Eugenol decreased seizure stage and duration as well as mortality. Neuronal numbers were preserved by eugenol treatment in epileptic animals, while eugenol alone reduced the number by itself in all hippocampal sub-regions including DG, CA3, and CA1. Furthermore, eugenol alone increased MDA, GPx and SOD markers, while it increased MDA not only in combined treatment with pilocarpine but also in pilocarpine-treated animals. In contrast to MFS enhancement in naïve animals, eugenol partially reversed the MFS enhancement induced by pilocarpine.Conclusion:Eugenol could prevent behavioral convulsions and show neuroprotective effects through increasing neuronal survival probably by decreasing MFS and increasing the GPx antioxidant marker.

Reduced abnormal integration of adult-generated granule cells does not attenuate spontaneous recurrent seizures in mice

Epileptic seizures lead to aberrant hippocampal neurogenesis, including increased proliferation of neural progenitors and abnormal integrations of newly generated granule cells – hilar ectopic granule cells (EGCs), mossy fiber sprouting (MFS), and hilar basal dendrites (HBDs). Previous results from ablating hippocampal neurogenesis after acute seizures have been controversial with regards to the development of spontaneous recurrent seizures (SRSs). While ablation of hippocampal newborn cells was effective, a sufficient decrease of subsequent abnormal integrations in chronically epileptic hippocampus was not well-established in these studies. Evaluations of the role of aberrant neurogenesis in epileptogenesis were therefore inconclusive. In this study, we ablated the hippocampal neurogenesis by methylazoxymethanol acetate (MAM) treatment both before and after pilocarpine induced status epilepticus (SE). We found that an overall ablation of newborn granule cells and a protracted delay after the cell ablation are required to eliminate subsequent abnormal integrations, including EGCs, MSF and HBDs. However, there were no alterations in frequency, duration and severity of chronic seizures were demonstrated following this regime. The current findings provide novel evidences that an overall decrease of abnormal integrations via cell ablation cannot exert significant effects on the development of SRSs at least in the model used in this study.

Effects of embryonic lead exposure on motor function and balance ability in offspring rats and possible mechanisms

To explore the effects of embryonic lead exposure on motor function and balance ability in offspring rats and the possible mechanisms. An animal model of embryonic lead exposure was prepared with the use of pregnant Sprague-Dawley rats freely drinking 0.1% (low-dose group, LG) or 0.2% (high-dose group, HG) lead acetate solution. A normal control group (NG) was also set. The male offspring rats of these pregnant rats were included in the study, consisting of 12 rats in the NG group, 10 rats in the LG group, and 9 rats in the HG group. The offspring rats' motor function and balance ability were evaluated using body turning test and coat hanger test. Eight rats were randomly selected from each group, and immunohistochemistry and Timm's staining were employed to measure the expression of c-Fos and mossy fiber sprouting (MFS) in the hippocampus. The HG group had a significantly longer body turning time than the NG and LG groups (P<0.05), and the LG group had a significantly longer body turning time than the NG group (P<0.05). The HG group had a significantly lower score of balance ability than the NG and LG groups (P<0.05), and the LG group had a significantly lower score of balance ability than the NG group (P<0.05). The area percentage of c-Fos-positive neurons in the hippocampal CA1 region was significantly higher in the HG group than in the other two groups (P<0.05), and it was significantly higher in the LG group than in the NG group (P<0.05). The semi-quantitative scores of MFS in the hippocampal CA3 region and dentate gyrus were significantly higher in the HG group than in the other two groups (P<0.05), and they were significantly higher in the LG group than in the NG group (P<0.05). Embryonic lead exposure could impair the offspring rats' motor function and balance ability. These changes may be related to increased c-Fos expression in the hippocampal CA3 region and abnormal MFS in the hippocampal CA3 region and dentate gyrus.

Berberine ameliorates intrahippocampal kainate-induced status epilepticus and consequent epileptogenic process in the rat: Underlying mechanisms.

Status epilepticus (SE) is a life-threatening neurologic condition, instigating epileptogenesis to transform normal brain to an epileptic condition. SE is followed by spontaneous recurrent seizures (SRS) and final development of temporal lobe epilepsy (TLE) that is resistant to treatment. Neuroprotective strategies are increasingly put forward as a promising therapy to prevent and/or manage epileptic conditions. In this study, we investigated whether berberis alkaloid, i.e. berberine (BBR), could ameliorate intrahippocampal kainate-induced SE and its consequent epileptogenic process and to explore some underlying mechanisms. BBR was daily administered at doses of 25 or 50mg/kg. Results showed that BBR treatment of kainate-microinjected rats at a dose of 50mg/kg lowered the incidence of SE and SRS. It also significantly restored hippocampal level of reactive oxygen species (ROS), glutathione (GSH), nuclear factor (erythroid-derived 2)-like 2 (Nrf2), activity of catalase and caspase 3, nuclear factor-<kappa>B (NF-κB), toll-like receptor 4 (TLR4), tumor necrosis factor α (TNFα), interleukin-1β (IL-1β), neural cell adhesion molecule (NCAM), glial fibrillary acidic protein (GFAP), cathepsin D, and heme oxygenase 1 (HO-1). Additionally, BBR protected against hippocampal CA3 neuronal loss and prevented development of aberrant mossy fiber sprouting (MFS) as an essential element of chronic epileptogenic circuit. These data suggest that BBR could mitigate SE and SRS in intrahippocampal kainate model of epilepsy and exert neuroprotective effect and its influence is mainly mediated via suppression of oxidative stress, neuroinflammation, and possibly apoptosis.

The Role of 5-HTR6 in Mossy Fiber Sprouting: Activating Fyn and p-ERK1/2 in Pilocarpine-Induced Chronic Epileptic Rats

Objective: Our primary objective is to verify whether 5-HTR6 is involved in the development of mossy fiber sprouting (MFS), and to determine how the progression of MFS is affected by 5-HTR6. Methods: A total of 90 male adult Sprague-Dawley rats were allocated into either the control group (n=36) or the epileptic group (n=54). Status epilepticus (SE) of rats was induced by the intraperitoneal (i.p.) injection of LiCl-pilocarpine. We conducted our experiments in two stages. The first stage involves equally dividing 36 epileptic rats into three groups with treatments of none, 5-HTR6 antagonist SB-27104 (SB) and vehicle DMSO. Then behavior and electroencephalogram (EEG) of rats were monitored by video-EEG. The second stage involves dividing 126 epileptic rats into seven groups with treatments of none, 10% DMSO, SB (100 µg/kg), Fyn antagonist PP₂ (50 µg/kg), p-ERK1/2 antagonist PD-98059 (30 µg/kg), SB (100 µg/ kg) + PP₂ (50 µg/kg); SB (100 µg/kg) + PD-98059 (30 µg/kg). We also treated 18 rats in the control group of the first stage with 100 µg/kg 5-HTR6 agonist WAY-181187 (WAY). MFS of rats was detected through the approach of Timm’s staining. Finally, expressions of 5-HTR6, Fyn, p-ERK1/2 and GAP-3 were qualified and semi-quantified via western blotting or RT-PCR. Results: Induction of SE could stimulate formation of MFS and increased GAP-43 expressions. Expressions of 5-HTR6, Fyn and p-ERK1/2 were also up-regulated with increasing time after establishment of SE models. The development of MFS was remarkably inhibited by SB, PP₂ and PD. Compared to the single antagonist, such an inhibitory effect was enhanced by SB+PD or SB+PP. Moreover, treatment of healthy rats with WAY would contribute to up-regulated Fyn and p-ERK1/2 expressions, as well as development of MFS (P < 0.05). Suppression of Fyn triggered a down-regulating trend of p-ERK1/2 (P < 0.05), however, suppressed p-ERK1/2 did not have such a significant effect on Fyn expression. Conclusion: HTR6 may affect the progression of MFS by activating both p-ERK1/2 and Fyn, which further modulate the expression of GAP-43.

Mossy Fiber Sprouting in the Epileptic Brain: Taking on the Lernaean Hydra.

Mossy Fiber Sprouting in the Epileptic Brain: Taking on the Lernaean Hydra.

Extent of mossy fiber sprouting in patients with mesiotemporal lobe epilepsy correlates with neuronal cell loss and granule cell dispersion

ObjectiveThe most frequent finding in temporal lobe epilepsy is hippocampal sclerosis, characterized by selective cell loss of hippocampal subregions CA1 and CA4 as well as mossy fiber sprouting (MFS) towards the supragranular region and granule cell dispersion. Although selective cell loss is well described, its impact on mossy fiber sprouting and granule cell dispersion remains unclear. Materials and methodsIn a single center series, we examined 319 human hippocampal specimens, collected in a 15-years period. Hippocampal specimens were stained for neuronal loss, granule cell dispersion (Wyler scale I–IV, Neu-N, HE) and mossy fiber sprouting (synaptoporin-immunohistochemistry). For seizure outcome Engel score I–IV was applied. ResultsIn Wyler I and II specimens, mossy fibers were found along their natural projection exclusively in CA4 and CA3. In Wyler III and IV, sprouting of mossy fibers into the molecular layer and a decrease of mossy fibers in CA4 and CA3 was detected. Mean granule cell dispersion was extended from 121μm to 185μm and correlated with Wyler III-IV as well as mossy fiber sprouting into the molecular layer. Wyler grade, mossy fiber sprouting and granule cell dispersion correlated with longer epilepsy duration, late surgery and higher preoperative seizure frequency. Parameters analyzed above did not correlate with postoperative seizure outcome. DiscussionMossy fiber sprouting might be a compensatory phenomenon of cell death of the target neurons in CA4 and CA3 in Wyler III–IV. Axonal reorganization of granule cells is accompanied by their migration and is correlated with the severity of cell loss and epilepsy duration.

Lentiviral Vector-Induced Overexpression of RGMa in the Hippocampus Suppresses Seizures and Mossy Fiber Sprouting.

Repulsive guidance molecule a (RGMa) is a membrane-bound protein that inhibits axon outgrowth in the central nervous system. Temporal lobe epilepsy (TLE) is a common neurological disorder characterized by recurrent spontaneous seizures. To explore the role of RGMa in epilepsy, we investigated the expression of RGMa in patients with TLE, pilocarpine-induced rat model, and pentylenetetrazol kindling model of epilepsy, and then we performed behavioral, histological, and electrophysiological analysis by lentivirus-mediated overexpression of RGMa in the hippocampus of animal model. We found that RGMa was significantly decreased in TLE patients and in experimental rats from 6h to 60days after pilocarpine-induced seizures. In two types of epileptic animal models, pilocarpine-induced model and pentylenetetrazol kindling model, overexpression of RGMa in the hippocampus of rats exerted seizure-suppressant effects. The reduced spontaneous seizures were accompanied by attenuation of hippocampal mossy fiber sprouting. In addition, overexpression of RGMa inhibited hyperexcitability of hippocampal neurons via suppressing NMDAR-mediated currents in Mg2+-free-induced organotypic slice model. Collectively, these results demonstrate that overexpression of RGMa could be an alternative strategy for epilepsy therapy.

Axonal plasticity of age-defined dentate granule cells in a rat model of mesial temporal lobe epilepsy

Dentate granule cell (DGC) mossy fiber sprouting (MFS) in mesial temporal lobe epilepsy (mTLE) is thought to underlie the creation of aberrant circuitry which promotes the generation or spread of spontaneous seizure activity. Understanding the extent to which populations of DGCs participate in this circuitry could help determine how it develops and potentially identify therapeutic targets for regulating aberrant network activity. In this study, we investigated how DGC birthdate influences participation in MFS and other aspects of axonal plasticity using the rat pilocarpine-induced status epilepticus (SE) model of mTLE. We injected a retrovirus (RV) carrying a synaptophysin-yellow fluorescent protein (syp-YFP) fusion construct to birthdate DGCs and brightly label their axon terminals, and compared DGCs born during the neonatal period with those generated in adulthood. We found that both neonatal and adult-born DGC populations participate, to a similar extent, in SE-induced MFS within the dentate gyrus inner molecular layer (IML). SE did not alter hilar MF bouton density compared to sham-treated controls, but adult-born DGC bouton density was greater in the IML than in the hilus after SE. Interestingly, we also observed MF axonal reorganization in area CA2 in epileptic rats, and these changes arose from DGCs generated both neonatally and in adulthood. These data indicate that both neonatal and adult-generated DGCs contribute to axonal reorganization in the rat pilocarpine mTLE model, and indicate a more complex relationship between DGC age and participation in seizure-related plasticity than was previously thought.