Drug-resistant Temporal Lobe Epilepsy Suppressed by Inhibiting the Entorhinal Cortex in the Mouse
通過抑制小鼠的內嗅皮層治療耐藥性顳葉癲癇
Student thesis: Doctoral Thesis
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Award date | 6 Jan 2021 |
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Permanent Link | https://scholars.cityu.edu.hk/en/theses/theses(549a5e16-8fa3-40e7-970d-22f3eec833c7).html |
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Abstract
Epilepsy is a group of long-term neurological disorders characterized by spontaneous recurrent seizures. Epileptic seizure causes unconsciousness and changes in body movements, body function, and sensation awareness. Epileptic seizure affects over 50 million people worldwide, and up to 70% of patients with epilepsy are able to live seizure-free if they are properly diagnosed and treated. It is generally agreed that epileptic seizures are caused by hyper-excitability, synchronization, and sudden abnormal discharge of neurons. The excitation/inhibition imbalance of the neuronal network leads to epilepsy development. After the formation of epileptic foci, the excitatory and inhibitory balance of the brain changes dynamically. Reducing the excitatory connections or enhancing the inhibitory circuits in the brain of patients could reduce the onset of spontaneous seizure attacks.
Most seizures involve the neocortex and hippocampus, regions that are associated with neuronal plasticity. Cholecystokinin (CCK) from the entorhinal cortex enables neural plasticity in the neocortex. CCK is the most abundant neuropeptide in the central nervous system, which participates in many processes and functions of the brain. Our previous studies showed that high frequency stimulation (HFS)-induced long-term potentiation (LTP) was blocked by the infusion of CCK B receptor antagonist (L365,260) in vitro (Chen X, et al., 2019).
In the present study, we found that HFS-induced LTP was fully blocked by the application of CCK B receptor antagonist (YM022) in C57BL/6 mice cortical brain slices. We speculated that YM022 could be a potential therapeutic agent for temporal lobe epilepsy (TLE). For behavioral analysis, we developed the chronic TLE mice model by intra-hippocampal kainic acid (KA) injection. In these mice models, the frequency of spontaneous recurrent seizures was reduced significantly after a single YM022 infusion (i.p.).
Next, we adopted the same experimental design using another CCK B receptor antagonist (YF476). Our results demonstrated that LTP induced with HFS was fully blocked by the application of YF476 in C57BL/6 mice cortical brain slices. In the behavioral analysis, the number of spontaneous seizures decreased significantly by a single infusion of YF476 (i.p.). To study the long-term anti-epileptic effects of this molecule, the mice were injected with YF476 twice per day for one week. Our results showed that the YF476 treatment reduced the number of spontaneous seizures in the chronic TLE mouse model.
We used the common clinical anti-epileptic drugs (AEDs; phenytoin, and valproate) as the positive control. LTP induced with HFS was entirely blocked by the application of phenytoin or valproate in C57BL/6 mice in vitro. Further, a single injection of phenytoin produced a similar anti-ictogenic effect as the CCK B receptor antagonist.
Taken together, the present findings imply that the application of KA in the hippocampus temporally activates the temporal lobe, possibly facilitating CCK release in the brain. By injecting the CCK B receptor antagonist, further enhancement of the excitatory circuitry can be blocked.
We observed that LTP induced by HFS was obvious in wild-type animals (129S) but not in CCK-AR/BR-KO mice. The number of spontaneous seizures differed between different strains of mice in the KA-induced chronic TLE models. Among the three mice strains (C57BL/6, CCK-CreER, and CCK-AR/BR-KO), CCK-AR/BR-KO mice showed the least number of recurrent spontaneous seizures. In addition, we found that treatment with phenytoin for one week did not significantly reduce the severity of seizures in the CCK-AR/BR-KO chronic TLE model.
Our data indicated that CCK-AR/BR-KO mice might be resistant to treatment with the current AEDs. Thus, we wondered whether there could be another treatment strategy for the CCK-AR/BR-KO chronic TLE model. It is well known that the entorhinal cortex is a part of the medial temporal lobe or hippocampal memory system and constitutes the major gateway between the hippocampal formation and the neocortex. We hypothesized that suppression of the entorhinal cortex might play an important role in reducing the onset and propagation of recurrent spontaneous seizures in these mice.
We used pharmacological and chemogenetic methods to verify the involvement of the entorhinal cortex in TLE. CCK-AR/BR-KO mice were used in this study. We employed the classical KA-induced TLE model and injected the adeno-associated virus (AAV8-hSyn-hM4Di-mCherry) into the entorhinal cortex bilaterally. Results indicated that chemogenetic suppression of the entorhinal cortex alleviated the severity of seizure onset in chronic epileptic models. Our study provides insight into the role of the entorhinal cortex in the treatment of TLE.
Most seizures involve the neocortex and hippocampus, regions that are associated with neuronal plasticity. Cholecystokinin (CCK) from the entorhinal cortex enables neural plasticity in the neocortex. CCK is the most abundant neuropeptide in the central nervous system, which participates in many processes and functions of the brain. Our previous studies showed that high frequency stimulation (HFS)-induced long-term potentiation (LTP) was blocked by the infusion of CCK B receptor antagonist (L365,260) in vitro (Chen X, et al., 2019).
In the present study, we found that HFS-induced LTP was fully blocked by the application of CCK B receptor antagonist (YM022) in C57BL/6 mice cortical brain slices. We speculated that YM022 could be a potential therapeutic agent for temporal lobe epilepsy (TLE). For behavioral analysis, we developed the chronic TLE mice model by intra-hippocampal kainic acid (KA) injection. In these mice models, the frequency of spontaneous recurrent seizures was reduced significantly after a single YM022 infusion (i.p.).
Next, we adopted the same experimental design using another CCK B receptor antagonist (YF476). Our results demonstrated that LTP induced with HFS was fully blocked by the application of YF476 in C57BL/6 mice cortical brain slices. In the behavioral analysis, the number of spontaneous seizures decreased significantly by a single infusion of YF476 (i.p.). To study the long-term anti-epileptic effects of this molecule, the mice were injected with YF476 twice per day for one week. Our results showed that the YF476 treatment reduced the number of spontaneous seizures in the chronic TLE mouse model.
We used the common clinical anti-epileptic drugs (AEDs; phenytoin, and valproate) as the positive control. LTP induced with HFS was entirely blocked by the application of phenytoin or valproate in C57BL/6 mice in vitro. Further, a single injection of phenytoin produced a similar anti-ictogenic effect as the CCK B receptor antagonist.
Taken together, the present findings imply that the application of KA in the hippocampus temporally activates the temporal lobe, possibly facilitating CCK release in the brain. By injecting the CCK B receptor antagonist, further enhancement of the excitatory circuitry can be blocked.
We observed that LTP induced by HFS was obvious in wild-type animals (129S) but not in CCK-AR/BR-KO mice. The number of spontaneous seizures differed between different strains of mice in the KA-induced chronic TLE models. Among the three mice strains (C57BL/6, CCK-CreER, and CCK-AR/BR-KO), CCK-AR/BR-KO mice showed the least number of recurrent spontaneous seizures. In addition, we found that treatment with phenytoin for one week did not significantly reduce the severity of seizures in the CCK-AR/BR-KO chronic TLE model.
Our data indicated that CCK-AR/BR-KO mice might be resistant to treatment with the current AEDs. Thus, we wondered whether there could be another treatment strategy for the CCK-AR/BR-KO chronic TLE model. It is well known that the entorhinal cortex is a part of the medial temporal lobe or hippocampal memory system and constitutes the major gateway between the hippocampal formation and the neocortex. We hypothesized that suppression of the entorhinal cortex might play an important role in reducing the onset and propagation of recurrent spontaneous seizures in these mice.
We used pharmacological and chemogenetic methods to verify the involvement of the entorhinal cortex in TLE. CCK-AR/BR-KO mice were used in this study. We employed the classical KA-induced TLE model and injected the adeno-associated virus (AAV8-hSyn-hM4Di-mCherry) into the entorhinal cortex bilaterally. Results indicated that chemogenetic suppression of the entorhinal cortex alleviated the severity of seizure onset in chronic epileptic models. Our study provides insight into the role of the entorhinal cortex in the treatment of TLE.
- Temporal lobe epilepsy, Seizure, Excitatory, Long-term potentiation, Cholecystokinin, CCK B receptor antagonist, Entorhinal cortex, Chemogenetic suppression