Project Summary
Gene therapy is an emerging treatment strategy for epilepsy that promises to dampen activity in specific
seizure related circuitry in order to prevent or lessen the intensity of seizures. Finding the appropriate target
for delivery represents a significant challenge for preclinical seizure models. In order to optimize delivery
parameters, multiple strategies, locations, and doses must be compared. We have developed a novel screening
tool that uses optogenetic intensity-response curves to precisely determine thresholds for population discharge
(aka. interictal spikes), the oPDT. Once this threshold is known, suprathreshold stimulus trains of varying
length can be used to determine an after discharge threshold, a measure of seizure susceptibility. These two
metrics can be collected in the same animals, compared, and tracked. Thresholds vary predictably with
behavioral state (sleep/wake), but are stable over time allowing for multiple within subject experiments. A
chronic multi-site array in hippocampus and connected structures allows for detection of network wide
stimulus responses and also continuous monitoring of normal activity. We propose to test and optimize two
promising gene therapy strategies using our optogenetic thresholding technique, in non-epileptic animals, in
order to assess therapeutic potential. Kv1.1 overexpression in neurons reduces excitability by raising the
functional threshold for activation and decreasing burst production. Kir4.1 overexpression in astrocytes
improves their ability to absorb extracellular K+, preventing K+ build up and the resulting ictogenesis. In Aim
1, we will locate effective target areas and optimize the dose of Kv1.1 in order to balance efficacy
with impairment of normal function. An AAV vector developed by our collaborator Edward Perez-Reyes
will be used to deliver Kv1.1. Baseline activity, the oPDT, and the oADT will be tracked over time with multiple
measurements taken before expression occurs (<2 weeks), while expression builds (2-6 weeks), and when
expression levels stabilize (>6 weeks). Changes in these metrics over time will reveal important information
about the circuit level effects of Kv1.1 overexpression and its viability as a treatment for epilepsy. In Aim 2, we
will determine if Kir4.1 overexpression in astrocytes is sufficient to reduce seizure
suseptability. An AAV vector specific for astrocytes (using the GFAP promoter), will be used to overexpress
Kir4.1. Success in these experiments will help to identify potential targets for therapeutic intervention, assess
the therapeutic window, and provide critical clues about the nature of population discharge and seizure
generation.
