Examining The Role of Corticothalamic Loops in the Prefrontal Cortex in Temporal Lobe Epilepsy - Abstract Epilepsy affects approximately three million U.S. adults with one-third of patients displaying inadequate seizure control with drug therapy alone. Temporal lobe epilepsy, where seizures originate in the temporal lobe and propagate to the thalamus and downstream cortical regions, is the most common type of drug-resistant epilepsy. Focal onset seizures originating in the amygdala or hippocampus propagate to the mediodorsal nucleus of the thalamus (MD) and spread to the prefrontal cortex (PFC). The MD is tightly connected with the medial PFC and its three subregions: Anterior Cingulate cortex, Prelimbic cortex (PrL), and Infralimbic cortex (IL). Each subregion contains 5 layers. Cortical pyramidal cells in layer 5 of the PrL and IL are highly interconnected with the MD – they receive direct input from the MD and send reciprocal input back to the MD, forming a loop. In this proposal, I will use the amygdala-kindling model of temporal lobe epilepsy in rats to characterize (1) how focal onset seizures affect MD-PFC loop and (2) how inhibition of the MD-PFC loop affects focal onset seizures. Our preliminary data suggests that this mutually excitatory loop may act as one route for distribution and spread of seizure activity. Chemogenetic inhibition of MD projections to the PrL as well as inhibition of layer 5/6 cells in the PrL and IL abolishes amygdala-kindled seizures. To characterize how temporal lobe epilepsy alters the circuitry of the PFC, I will use ex-vivo whole-cell patch clamp electrophysiology in kindled and sham-kindled rats to measure changes in intrinsic electrophysiology properties of pyramidal cells. To understand how PFC projections to the MD are selectively altered, I will use retrograde viral expression in the MD to focus on intrinsic properties of layer 5 MD-projecting cells. To understand how the MD-PFC loop is altered, I will use optogenetics in these same animals to measure synaptic properties and excitatory drive of MD projections onto of layer 5 MD- projecting cells. Since pyramidal cells in both layers 5 and 6 project to the MD, I will use chemogenetics in amygdala-kindled rats to identify how selectively inhibiting layers 5/6 pyramidal cells affects seizures. To determine involvement of PFC subregions in amygdala-kindled seizures, I will measure the degree of seizure suppression from inhibiting layer 5/6 pyramidal cells in either the PrL or IL. To determine involvement of cortical projections in amygdala-kindled seizures, I will measure the degree of seizure suppression from inhibiting MD- projecting cells in the PrL and IL. Through the course of these experiments, I will gain training and experience with slice electrophysiology, in vivo circuit manipulation, epilepsy models, which will prepare me for future bench- to-bedside research as a physician-scientist. I will comprehensively characterize physiological markers of epileptogenesis in downstream regions of temporal lobe epilepsy and identify how closed loop circuits between the thalamus and cortex are involved in temporal epilepsy. These findings will expand our map of epileptogenic networks and possible therapeutic targets for drug-resistant epilepsy.
