Skip to Main Content
 

Global Search Box

 
 
 
 

Files

File List


Thomas Ladas PhD Dissertation.pdf (16.76 MB)

ETD Abstract Container

Abstract Header

An Optogenetic Approach to Induce Seizure Suppression

Ladas, Thomas P
http://rave.ohiolink.edu/etdc/view?acc_num=case1389054549

Abstract Details

2014, Doctor of Philosophy, Case Western Reserve University, Biomedical Engineering.
Epilepsy is a chronic neurological disorder characterized by recurrent, unprovoked seizures that can be debilitating and are often resistant to current pharmacologic therapies. Mesial temporal lobe epilepsy involving the hippocampus, in particular, does not respond well to medication and often necessitates surgical resection of an epileptic focus. Recently, deep brain stimulation has been shown to be an effective alternative to surgical therapies, although the optimal stimulus location and stimulation paradigm remain a subject of great debate. In this thesis work, optogenetic techniques were used to investigate the mechanisms of low-frequency stimulation (LFS) and high-frequency stimulation (HFS) paradigms to suppress hippocampal hyperactivity in a model of epilepsy. These stimulation paradigms have already been implemented clinically and have been shown to reduce disease burden, although the underlying mechanisms resulting in seizure suppression are poorly understood, limiting optimization of these techniques to maximize seizure suppression efficacy. In this study, low- and high-frequency optical stimulation with blue light was used to activate the cation channel channelrhodopsin-2 (ChR2) in both in vitro and in vivo experimental preparations. This optogenetic construct was expressed in mice under the control of specific promoters to drive expression in neurons (Thy1-ChR2) or selectively in GABA interneurons (VGAT-ChR2). The potassium channel blocker 4-aminopyridine (4-AP) was used to induce epileptiform activity, which was monitored by extracellular and intracellular recording techniques. Immunofluorescence and confocal microscopy were used to investigate the expression of optogenetic constructs in the hippocampus. We found that local and selective optical stimulation of neurons directly at low (1 Hz) and high (20Hz and 50Hz) frequencies could effectively reduce epileptiform activity in the hippocampus, demonstrating that the effect is not mediated by a glial mechanism or by activating afferent or passing fibers. Suppression of activity was seen when optically activating both pyramidal and GABA neurons, although epileptiform activity could effectively be suppressed even when only hippocampal interneurons were stimulated. Selective GABA interneuron activation at low frequencies caused entrainment and sculpting of epileptiform activity in a similar manner as did electrical stimulation, but through a GABAA-mediated mechanism. Optical stimulation at high frequencies reduced 4-AP-induced hyperactivity in a dose-dependent manner, with higher laser stimulation power producing increased suppression. Though continued stimulation at high frequencies exhibited suppression with break-through activity, we found that an intermittent stimulation paradigm could restore suppression efficacy. These results provide evidence that optogenetic techniques can be used to suppress seizure activity by low- and high-frequency neural activation. Further, these results indicate that GABA interneurons play an important role in shaping inter-ictal activity in the hippocampus by facilitating cell excitation during epileptogenic conditions, and that activating these neurons with the appropriate stimulation paradigm can effectively suppress hippocampal network hyperactivity. These findings will help in the understanding of DBS-mediated seizure suppression mechanisms that could direct the development of novel therapeutic strategies for clinical application.
Dominique Durand (Advisor)
Miklos Gratzl (Committee Member)
George Dubyak (Committee Member)
Kitti Kaiboriboon (Committee Member)
Luis Gonzalez-Reyes (Committee Member)
167 p.
Biomedical Engineering; Neurosciences
optogenetics; hippocampus; epilepsy; 4-AP; LFS; HFS; seizure suppression; GABA; interneuron

Recommended Citations

Citations

  • Ladas, T. P. (2014). An Optogenetic Approach to Induce Seizure Suppression [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1389054549

    APA Style (7th edition)

  • Ladas, Thomas. An Optogenetic Approach to Induce Seizure Suppression. 2014. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1389054549.

    MLA Style (8th edition)

  • Ladas, Thomas. "An Optogenetic Approach to Induce Seizure Suppression." Doctoral dissertation, Case Western Reserve University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1389054549

    Chicago Manual of Style (17th edition)

case1389054549
339
© 2013, all rights reserved.
This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.