Date of Award

1-1-2023

Document Type

Thesis

Degree Name

Medical Doctor (MD)

Department

Medicine

First Advisor

Hal Blumenfeld

Abstract

SINGLE NEURONAL FIRING DYNAMICS IN A MOUSE MODEL FOR ABSENCE SEIZURES

Waleed Khan1, Samiksha Chopra1, Xinyuan Zheng2, Shixin Liu1, Marcus Valcarce-Aspegren1, Lim-Anna Sieu1, Sarah Mcgill3, Cian Mccafferty4, Hal Blumenfeld1.1 Department of Neurology, Yale University, School of Medicine, New Haven, CT. 2 Department of Biomedical Engineering, Yale University, School of Medicine, New Haven, CT. 3 Department of Neuroscience, Yale University, School of Medicine, New Haven, CT. 4 Department of Anatomy and Neuroscience, University College Cork, Cork, Ireland.

Background: Absence seizures are generalized seizures that occur mostly in children and often manifest as staring spells. Absence seizures can often occur hundreds of times per day, severely compromising the quality of life of affected children. A recent study in a rat model of absence seizure found that there are differences in the activity of individual neurons during an absence seizure, which can be classified into four main types (sustained increase, sustained decrease, onset peak and no change). Our aim in this project is to investigate why these differences in activities exist and whether they can help us better understand the mechanism behind absence seizures by performing juxtacellular recordings on awake head fixed mice during absence seizures.

Methods: C3H/HeJ mice of age 6-11 weeks were implanted with tripolar electrodes at the frontal and parietal cortex, along with a ground electrode mid-cerebellum, under anesthesia, to obtain intracranial EEG recordings. Following a week of recovery, they were head-fixed, in an awake state, and EEG was recorded using an amplifier. An access craniotomy had already been created over the right barrel subfield, during electrode implantation, to obtain juxtacellular recording. A bleached silver wire, immersed in a neurobiotin solution, was placed in a glass electrode, of resistance 5-20MΩ, and introduced through the access craniotomy. The electrode was very slowly lowered until neuronal activity was observed. Current was clamped and the potential difference was measured using a MultiClamp 700B. Signals were digitized at a rate of 20kHz with an A/D converter and analyzed using Spike 2. A current of 600pA was passed in 2Hz pulses to entrain the neurons and label them with neurobiotin.

Results: A variety of different activities, during absence seizures, were observed from a total of 36 cortical neurons that were recorded. Like the rat model, there was a sudden decrease in activity 2-3s before seizure onset followed by a transient peak in activity at the start of the seizure; however, unlike the rat model there was no corresponding decrease in overall activity during the absence seizure. The same categories of neuronal activities found previously in the rat model were also observed in the C3H/HeJ mice, which include, sustained increase (neuronal activity is high throughout the seizure), sustained decrease (neuronal activity is low throughout the seizure), onset peak (neuronal activity peaks at the beginning of the seizure) and no change (neuronal activity remains the same), but these neuronal types differ in proportions compared to the rat model. Additionally, several of the neurons recorded from were successfully labelled with neurobiotin and recovered in histology.

Conclusions: The activity of individual neurons can vary during an absence seizure. These differences are not specific to one species and can be seen in mice as well as rats. These variations can be classified into distinct categories which are found in both species. There are also both similarities and differences in the overall neuronal firing pattern observed between the two species, suggesting that certain aspects of the neuronal response to absence seizures are conserved, and juxtacellular labelling can be an invaluable tool to investigate the underlying mechanism behind their patterns in the hope of potentially identifying targeted therapies in the future.

Comments

This thesis is restricted to Yale network users only. It will be made publicly available on 06/30/2025

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