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Hewapathirane, Sesath - Abstract

The immature brain is exceptionally epileptogenic with the highest incidence of seizures in humans occurring during the first years of life. While these seizures occur during critical periods of synaptogenesis and neuronal growth, little is known of the impact of neonatal seizures on brain circuit development.

We have developed and characterized a novel model system designed specifically to examine effects of experimentally induced seizures on the growth of neurons within the intact developing brain. This model system involves pentylenetetrazol (PTZ)-induced seizures in the albino Xenopus laevis tadpole and in vivo multiphoton time-lapse imaging of individual immature neurons fluorescently labeled by single-cell electroporation. Bath application of PTZ elicits reproducible behavioural and electrographic seizures that cease upon washout of PTZ or by application of anticonvulsants. PTZ-induced seizure activity is highly comparable to that observed in commonly utilized mammalian seizure models, as revealed by detailed analysis of behavioural seizures, extracellular electrophysiological recording in vivo, and imaging of neuronal network dynamics in vivo using Calcium-sensitive fluorescent indicators.

Rapid time-lapse imaging of individual developing neurons within un-anaesthetized immobilized tadpoles during seizures revealed that dendritic filopodia -dynamic ultrastructural processes involved in dendrite growth -are significantly less motile and have a significantly higher retraction rate as compared to controls. Protracted imaging of the entire dendritic arbor over 8 hours revealed that prolonged seizures impede overall dendritic arbor growth, and that sustained seizure activity leads to retraction of existing dendritic branches. Collectively, these results strongly suggest that seizures impede neuronal growth within the developing brain. Our findings are particularly important given that the observed anatomical changes likely affect neuronal function and connectivity. Future directions include identifying the molecular signals underlying the observed changes, and examining seizure-induced effects on synapse formation.

International Award Winners: Inskip, J., Mikhail, D., Mills, P., Ramer, L., Simonette, G., Yiu, J., Zwicker, J., Chen, S.,  Faradaji, F., Gaudet, A.,
National Award Winners: Beirnes, K., Bundon, A., Hume, A., Lige, S., Schiarti, V.