Influence of Optogenetic Modulation and Convulsant Drugs on Neuronal Activity

Neuronal cultures derived from primary or stem cells are essential tools for assessing the effects of novel drugs, particularly those that modulate neuronal excitability, prior to clinical studies. These cultures also serve as models for common neurological disorders such as epilepsy, raising important questions: can in-vitro cultures capture seizure-like dynamics, can optogenetics be used to modulate activity in this setting, and can drugs be identified that modulate or induce hyperexcitability? Electrophysiological techniques, including multielectrode arrays (MEA), have been used to quantify responses such as spike rate changes to drugs like 4-aminopyridine (4-AP) or kainic acid. However, these analyses often fail to capture the full complexity of drug effects. Reports are inconsistent, with some studies showing increased activity and others decreasing activity over time, highlighting discrepancies between in-vitro and in-vivo observations. To address these limitations, this dissertation introduces a novel method for analyzing inter-spike interval (ISI) dynamics, which accounts not only for the mean effect of the intervention, but rather takes into account the local temporal features of the dynamics. We validated this approach in ten experimental groups, including chemical interventions with 4-AP in two doses, optogenetic stimulation of neurons expressing ArchT (inhibitory opsin) or ChR2 (excitatory opsin), and combinations of chemical and optical stimulation. Our ISI-based analysis revealed treatment-specific alterations in firing patterns, including clear dose-dependent effects. These results demonstrate the sensitivity and versatility of our method in capturing complex responses from the neuronal network. Beyond methodological advances, the findings contribute to the broader discussion of seizure modeling in culture, activity modulation through optogenetics, and drug-based activity suppression, thereby informing future studies in neuropharmacology and disease modeling.