Glowing feet control the blood of seizures.

Commentary Astrocytes of the healthy brain fulfill an important homeo-static role to couple neuronal activity to cerebral blood flow, and thereby to adapt local cerebral blood flow to metabolic demands, a phenomenon termed neurovascular coupling (1, 2). Astrocytes react to neuronal activity by a rise in intracel-lular Ca 2+ , and it is the increase in Ca 2+ in the astrocytic endfeet that ensheath the microvasculature that triggers vascular responses in the arterioles. The physiological consequence is vasodilation exerted through a variety of mechanisms (1, 3). In epilepsy, the excessive discharge of neurons leads to an increase in metabolic demand that needs to be met by an increase in cerebral blood flow (4). If blood supply to an epilep-togenic focus is insufficient, diffuse neuronal injury may result. Therefore, neurovascular coupling plays an important role in limiting damage following a seizure. However, the underlying mechanisms of neurovascular coupling within the context of epilepsy remain understudied. The study by Gόmez-Gonzalo and colleagues was designed to assess whether neurovascular coupling, as extensively studied in the normal brain, is also operant during epileptiform discharges. Two seizure models were studied: rat cortical slices exposed to picrotoxin under zero Mg2+ conditions, and an in vi-tro model of intact isolated guinea pig brain made epileptic by arterial perfusion with bicuculline. Preparations were analyzed by a combination of patch clamp recordings and Ca 2+ imaging, while arteriole responses (vessel diameter) were determined by differential interference contrast (DIC) microscopy. In the slice preparation, the Ca 2+ signal from cortical neurons could be used to determine the onset of the epilepti-form discharge and to distinguish between ictal and interictal discharges. Of importance, the ictal, but not the interictal, discharges triggered a diffuse elevation of Ca 2+ in astrocytic endfeet, as evidenced by the temporal profile of neuronal discharges and astrocytic Ca 2+ responses, and by the colocal-ization of the Ca 2+-dye with an astrocyte-specific marker in perivascular structures. These findings, showing elevated Ca 2+ in astrocytic endfeet in response to ictal, but not to interictal, discharges were validated in the isolated brain preparation. How do arterioles respond to ictal and interictal discharg-es? If only ictal discharges elevate Ca 2+ in astrocytic endfeet, then only ictal discharges should regulate the tone of the ar-teriole wall. By simultaneous Ca 2+ and DIC imaging in cortical slices, Gόmez-Gonzalo and colleagues studied changes in the intraluminal diameters of arterioles in response to ictal and …