Altered glutamate signaling in mouse model of familial hemiplegic migraine

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Project Summary/Abstract Migraine is a pervasive neurological disorder affecting 12-15% of the general populace in the U.S. and is highly invasive, if not debilitating, to sufferers of attacks. The neurophysiology that underlies migraine, though, is poorly understood. Premonitory symptoms and altered cortical evoked responses in migraineurs between attacks suggests persistent changes in brain network function that somehow give rise to migraine. The precedent aura that heralds the attack in up to one-third of migraineurs corresponds with cortical spreading depression (CSD), a wave of neural and glial depolarization within the cortex. Our understanding of CSD initiation rests on dysfunctional regulation of extracellular K+ and the excitatory neurotransmitter, glutamate. The purpose of this proposal is to elucidate mechanism of altered brain network function in migraine by studying a genetic form of the disorder, Familial Hemiplegic Migraine, type 2 (FHM2). FHM2 is a mutation of a sodium-potassium ATPase found in astrocytes in adults that drives clearance of glutamate following neural release. This clearance of glutamate is required to maintain the fidelity and staccato nature of neuron-to-neuron communication. The first aim of this proposal is to determine whether this decrease in glutamate clearance significantly alters the time course of neural glutamate signaling. The approach uses state of the art in vivo imaging of glutamate in real time as a living mouse carrying the FHM2 mutation is given a sensory stimulus. Results from this aim will show whether basic neural signaling is altered in the genetic form of migraine. The second aim of this proposal is to determine the effects of slowed glutamate clearance on synaptic activity and neural processing. Increasing the duration of glutamate in the extracellular space following neural release increases the ability of glutamate to act on post-synaptic receptors and the probability of recruiting neural responses. Simultaneous optical and electrical recordings of glutamate and neural activity will determine the effect of slowed glutamate clearance on neural processing. The results of this study will provide mechanistic evidence of persistent changes in brain network processing in migraine, shedding light on the pathophysiology that gives rise to migraine events.