Abstracts

Rationale: Approximately 1 in 26 Americans will experience seizures, with newborns and the elderly accounting for the majority of the burden. In humans and in rodent models, early-life seizures often lead to cognitive and behavioral deficits such as intellectual disability and autistic behavior, but it is not clear how or why this occurs. Currently, there are no therapeutic interventions to block the development of these deficits, in part because the link between seizures and cognitive deficits are unclear. Studies indicate that impaired spine maturation can lead to cognitive dysfunction – impairment including altered density and morphology of dendritic spines, small dendritic protrusions that are postsynaptic sites of excitatory synapses – and these impairments are also seen in multiple seizure models. We hypothesize that seizure activity in key periods of brain development alter the maturation of dendritic spines in age-specific ways, leading to improper synaptic refinement and connectivity, and thus altered cognitive development. Regulation of dendritic spine maturation may represent a potential target for treatments to prevent the development of cognitive deficits after early-life seizures if a balance can be found between treating all dendritic spines and treating only vulnerable spines. Methods: We determined the normal developmental pattern of spine maturation in hippocampal neurons cultured from embryonic day (E)18 rats. We used spine density and morphology as readouts of spine maturation levels (n=7-11 cells/age). We tested whether seizure-like activity would alter spine maturation in a developmentally-dependent manner, using an established cell culture model of seizure activity induction, exposure to magnesium (Mg2+)-depleted media, at different points in early development. We examined morphological readouts of spine maturation at multiple time points after seizure activity induction in E18+DIV10 and E18+DIV14 neurons (n=4-11 cells/group). Results: We found an expected developmental trajectory of dendritic spine density along the primary dendrites of cultured hippocampal neurons during the first three postnatal weeks, with a peak in spine density from DIV14-17 (p=0.0008). We found that seizure activity could alter spine morphology in a developmentally-dependent manner (trending towards an increase after seizure activity at DIV10, but significantly decreased after seizure activity at DIV14; p=0.02), and also that specific types of spines are preferentially affected over others. With zero Mg2+ treatment at DIV10, only stubby spines were affected, trending towards increased density (p=0.082), whereas zero Mg2+ at DIV14 decreased density of both stubby (p=0.017) and mushroom spines (trending, p=0.093). Conclusions: Our results highlight the importance of treatments that take into account the specific developmental period in which the original insult occurred. Further, vulnerability variation correlated with spine classifications raises the possibility of finding more specific molecular targets, narrowing the effects of treatments to only the most vulnerable spine populations. Funding: Center for Chronic Diseases of AgingPCOM Department of Research