Abstracts

 Spreading depolarization (SD) is a massive self-regenerative wave of near-complete cellular depolarization, which spontaneously occurs in various epilepsy mouse models. In clinical studies, cortical SDs have been associated with various neurological deficits in brain injury patients, and cerebral blood flow (CBF) deficit during SD is considered as a deleterious mechanism of SD. However, most of the CBF responses during SD were studied in injured brain or SD evoked in anesthetized animals. It is not well understood how SD affects cerebral circulation in awake epilepsy mouse cortex. In the present study, we characterized CBF responses using laser speckle contrast imaging (LSCI) in head-restrained mouse cortex using heterozygous Scn8a gain-of-function (GoF) mutant mice which carry a patient-derived missense mutation (N1768D/+).

Awake head restrained mouse is restrained on the running wheel while cortical EEG, EMG, and nasal respiration were simultaneously monitored. CBF is evaluated using LSCI based on time domain contrast. SD was evoked by intraperitoneal injection of PTZ at subconvulsive dosage.

 In Scn8a^D/+ mice, PTZ at 20-40mg/kg triggered a bilateral SD similar to those detected in chronic DC-band EEG recording, while no spontaneous SD could be detected during our monitoring sessions. In LSCI, SD was detected as a bilateral synchronous wave of hyperfusion, followed by a transient recovery and prolonged hour-lasting hypoperfusion. SD was often accompanied by brief tonic spasms that coincided with apnea and abrupt CBF decrease.  In WT control, PTZ injection at a higher dosage (40-60 mg/kg) triggered SD associated with similar cortical hypoperfusion but was often unilateral and never accompanied by paroxysmal tonic spasm, suggesting the Scn8a^D/+ GOF mutation modifies the downstream excitability of SD.

Our study revealed a prolonged hypoperfusion effect of cortical SD in awake epileptic mice. Such hypoperfusion by spontaneous interictal SD may contribute to neurological deficits independently of seizures.