Brief excitotoxic insults cause a calpain-mediated increase in nuclear membrane permeability in neonatal neurons

Neuronal edema after excitotoxic brain insults results in neuronal injury and death. Osmotic and surgical interventions designed to mitigate edema yield poor clinical outcomes, highlighting the need to explore other mechanisms. Concurrent with neuronal swelling, excessive Ca(2+) loading can be deleterious but remains poorly investigated, especially during the neonatal period. We used in and ex vivo multiphoton Ca(2+) imaging to evaluate the relationship between cytotoxic edema and Ca(2+) load in neonatal GCaMP6-expressing neurons after different and brief excitotoxic insults. We report acute translocation of cytosolic GCaMP6s into the nucleus of neonatal neurons after various short excitotoxic insults quantified as the ratio of nuclear: cytosolic intensity (N/C ratio). The increase in the N/C ratio occurred independently of neuronal swelling. Transmission electron microscopy revealed that elevated N/C ratios correlated with increased nuclear pore size in neurons. Inhibiting calpains in and ex vivo prevented increased N/C ratios and decreased neuronal swelling. Our results demonstrate that brief excitotoxic injury can enlarge nuclear pores and dysregulate nuclear transport in neurons through a calpain-mediated mechanism during early brain development. Additionally, N/C ratio measurements can be used to detect acute neuronal injury in real-time.