Authors :
Presenting Author: Matthew Stern, PhD – Emory University
Eric Cole, PhD – Emory University School of Medicine
Claire-Anne Gutenkust, PhD – Emory University
Jenny Yang, PhD – Georgia State University
Ken Berglund, PhD – Emory University
Robert Gross, MD, PhD – Robert Wood Johnson School of Medicine
Rationale:
Cortical spreading depolarization (CSD) have been observed to follow seizures in both animal models and humans, and induced CSD has been demonstrated to arrest seizures. As our understanding of this termination mechanism is incomplete, defining intracellular differences between seizures and CSD could offer insight to this end. In particular, neurons exhibit a dramatic increase in cytosolic calcium during CSD that greatly exceeds the rise during seizures, which may be integral to this termination. Thus, we sought to define the calcium homeostatic mechanisms distinguishing these events.
Methods:
To examine the subcellular compartmental changes occurring with calcium storage and release, we developed a calcium indicator co-expression paradigm to enable simultaneous recording of the cytosol and endoplasmic reticulum (ER), the largest store of intracellular calcium. Using AAV delivery, we pan-neuronally expressed our constructs in mouse cortex and performed awake intravital two-photon calcium imaging with simultaneous EEG and DC recordings. We employed this approach during repeated pentylenetetrazol-induced seizures and during CSD induced using high frequency cortical electrical stimulation.
Results:
We observed CSD as a slow propagating post-ictal cytosolic calcium wave with a concomitant depletion of ER calcium. While we noted pre-ictal spike-wave discharges and seizure onset to also demonstrate abrupt rises in cytosolic calcium, the ER calcium store remained stable during these events. Additionally, we failed to observe a comparable depletion of ER calcium post-ictally in seizures not followed by a CSD. When considering the relative timing of these organellular calcium changes during CSD we determined they were spatiotemporal consistent with a calcium-induced calcium release (CICR). We also found electrically induced CSD to be marked by the same spatiotemporal cytosolic and ER calcium dynamics. We further confirmed that both seizure associated and electrically induced CSD suppressed post-ictal epileptiform activity in our models.
Conclusions:
These findings suggest that calcium homeostatic dysregulation is a distinguishing feature between seizures and CSD, although further investigation is needed to determine the necessity of CICR in CSD and its seizure suppressive effect. If CICR proves to be mechanistically involved, this could offer new therapeutic targets, such as through mimicking an anti-seizure effect of CSD, while avoiding a widespread CSD phenomena and its ensuing pathologic effects.
Funding: NIH NINDS F31NS115479 (MAS); NIH OD S10OD021773 (KB); NIH NINDS R21NS112948 (REG); Mirowski Family Foundation (REG)