Our lab currently focuses on two projects:
(1) Respiration and Generalized Epilepsies.
Spike-Wave Discharges (SWDs) are a common type of seizure in the Genetic Generalized Epilepsies (GGEs). Hyperventilation triggers SWDs in the overwhelming majority of patients with absence epilepsy, the most common form of pediatric GGE. We have recently developed a rodent epilepsy model wherein we can evoke a burst of SWDs with hyperventilation. Within 6 minutes of hyperventilation, SWD count increases by over 500%. We now leverage this model to gain unprecedented access to core seizure-generating mechanisms associated with SWDs.
By combining plethysmography, EEG and blood measurements in single animals, we show that SWD circuits appear critically sensitive to blood pH. First, we show that hypoxia, a condition that activates hyperventilation, robustly evokes rodent SWDs. Hypoxia-induced hyperventilation results in increased exhalation of CO2 and concomitant blood alkalization (i.e. respiratory alkalosis). We also show that hypoxia-evoked SWDs are abolished when atmospheric CO2 is elevated, thereby supporting the hypothesis that blood alkalization drives hyperventilation-evoked SWDs. Finally, we also show that optogenetic activation of hyperventilation during normal atmospheric conditions – an experimental procedure that reduces blood CO2 but increases O2 – also evokes SWDs. Thus, collectively our data show that SWDs appear to primarily covary with blood CO2.
We complement our plethysmography-EEG data with brain slice electrophysiology and calcium imaging. We focus our attention on the intralaminar nuclei of the thalamus because activity-dependent cell tagging approaches (i.e. cFos) consistently label cells within this region after hypoxia-induced hyperventilation. By using whole-cell patch clamp recording techniques we demonstrate that intralaminar thalamic cells produce depolarizing ionic currents during alkalized conditions.
(2) Energy and Neural Circuit Excitability.
Glucose is the primary fuel used by the brain. While alternative energy substrates can transiently sustain the brain’s needs during hypoglycemic episodes, glucose-sensing neurons within the brain nonetheless respond to diminishing energy supplies by altering their electrical behavior. This cellular response often has significant ramifications for the electrical activity patterns produced by neural networks assembled from those neurons. In this project, we aim to identify the mechanisms responsible for this heightened glucosensitivity in a brain structure known as the thalamus, and to determine how these mechanisms promote seizures.
Our multifaceted approach utilizes calcium imaging and electrophysiological techniques to test the general hypothesis that glucose directly modulates neural circuits in the thalamus to exacerbate seizures. Using our preliminary data as a launching point, we will begin by carrying out experiments designed to (1) directly measure glucose levels in the thalamus while concomitantly recording seizure activity, and (2) selectively modulate glucose handling in the thalamus and measure impact on seizures. Additionally, measurements of neuronal activity in the thalamus during control and fasted conditions will be achieved directly through in vivo calcium imaging approaches as well as by blood oxygenation level dependent (BOLD) signals acquired during functional MRI studies. Collectively, these experiments will establish the thalamus, a critical seizure-generating node in the brain, as a glucosensitive structure.