Cellular Mechanisms of Temporal Lobe Epilepsy in Vitro studies in Animal Models

Deepak, S (2014) Cellular Mechanisms of Temporal Lobe Epilepsy in Vitro studies in Animal Models. Doctoral thesis, The Tamilnadu Dr. M.G.R. Medical University, Chennai.

Full text not available from this repository.


Epilepsy is classically defined as “a transient occurrence of signs and/or symptoms due to abnormal excessive or synchronous activity in the brain”. It is one of the most prevalent neurological disorder affecting over 50 million individuals worldwide, of which almost 80% are found in developing nations (WHO fact sheet, 2012). In India, over 10 million people have been estimated to suffer from Epilepsy. Apart from its severe debilitating effects, epilepsy also imposes a substantial economic burden with WHO estimating the cost of epilepsy care per person in India to almost 88% of the average income per capita. INTRODUCTION: Temporal Lobe Epilepsy (TLE) is the most common and most medically refractory form of human epilepsy. In India, over 1 million people suffer from medically refractory epilepsy. Although surgical interventions have been adopted as an effective strategy to treat medically refractory epilepsy, less than 200 epilepsy surgeries are performed per year in India with over 500,000 potential candidates. This clearly depicts the magnitude of this problem in our country and highlights the lack of effective alternate treatment strategies. AIMS: The primary aim of this thesis is to study the interactions between the CA3 and CA1 subfields of the hippocampus during epileptogenesis and gamma frequency synchronization using extracellular field potential recordings. OBJECTIVES: 1. To study network interactions between CA3 and CA1 during high K+ induced epileptogenesis. 2. To identify and characterize pathological gamma frequency synchronization that may precede or accompany epileptiform discharges in CA3 and CA1. 3. To suppress and/or modulate gamma synchronization in the CA3 - CA1 networks using oxytocin. MATERIAL AND METHODS: The study was reviewed and approved by the Institutional Review Board and Institutional Animal Ethics Committee of Christian Medical College (Ref: IRB Min. No. 7128). Brain slice preparation: Wistar rats (4-8weeks old) of both sexes were used for the study. Experiments were carried on horizontal slices of the ventral hippocampus extracted from both hemispheres. The rats were deeply anaesthetized using isofluorane, decapitated, brain dissected out quickly and placed in ice -cold (1-3°C) artificial cerebrospinal fluid (aCSF). The aCSF used during slice preparation contained 110mM Sucrose, 60mM NaCl, 3mM KCl, 0.5mM CaCl2, 7mM MgSO4, 26mM NaHCO3, 1.25mM NaH2PO4, 5mM glucose. The aCSF was equilibrated thoroughly with dissolved Carbogen (95% O2 / 5% CO2) and had a pH of 7.4 and osmolarity of 290 - 300mOsm. The hemispheres were cut along a horizontal plane tilted by a 10°angle in a posterosuperior -anteroinferior plane (87) (Fig. 2) . 450μM thick slices of the ventral hippocampus were cut using a vibrotome (VF-200, Precisionary instruments, USA). The slices did not include EC. Typically 8-10 slices were made from an animal and all the slices were given a 10 digit alphanumeric code for later identification. CONCLUSIONS: To summarize our key findings, 1. Prolonged incubation in high [K+]o condition leads to the development of gamma bursts in CA1 which characteristically consists of spike discharges at 30 40Hz. 2. Anatomical and pharmacological isolation of CA1 increased the frequency at which gamma bursts occurred, thus showing the independent and highly rhythmic nature of these bursts. 3. Gamma bursts are primarily GABA - ergic in nature and are strongly attenuated by GABAA receptor blocker BMI. 4. Similar to BMI, application of oxytocin and bumetanide strongly attenuate the gamma bursts. These results suggest that a compromised Cl - homeostasis could possibly underlie gamma bursts generation. FUTURE SCOPE OF THE STUDY: The primary finding of this dissertation is the generation of gamma bursts in CA1. We have described the properties of these bursts and the putative mechanisms that underlie CA1 gamma bursts. However, this study has its limitations. In our study, we have not included the EC in our slice preparation and therefore the effect of EC inputs on CA1 gamma bursts has not been studied. The direct projection from EC to CA1 via the TA pathway and the projections from CA1 back to EC are believed to form a short reverberating loop which aggravate seizures generated by EC (28). Moreover, Ang [et al.] have shown a 10 fold increase in the strength of TA projections in temporal lobe epilepsy (10). Epileptiform activity in this loop is controlled by interictal discharges from CA3 (95). Loss of CA3 inputs on CA1 might therefore expose CA1 directly to EC generated seizures and can also lead to the development of seizures in CA1(37). Thus future studies should be aimed at studying the effect of direct projections of EC on CA1 gamma bursts. Additionally, we have studied the gamma bursts using extracellular field recordings. Precise identification and characterization of individual CA1 neurons that participate in gamma burst generation might help us understand this phenomenon better. This would also allow us to study the effect of oxytocin on gamma bursts precisely and may also shed light on the putative mechanisms through which these effects are exerted.

Item Type: Thesis (Doctoral)
Uncontrolled Keywords: Cellular Mechanisms, Temporal Lobe Epilepsy (TLE), In Vitro studies, Animal Models.
Subjects: MEDICAL > Neurology
Depositing User: Subramani R
Date Deposited: 18 Jan 2022 07:39
Last Modified: 18 Jan 2022 07:39
URI: http://repository-tnmgrmu.ac.in/id/eprint/19005

Actions (login required)

View Item View Item