A developmental transition from early neural hyperexcitability in zebrafish

Early brain development is characterized by plastic phases that play a crucial role in the establishment of functional connectivity. However, this plasticity also renders the developing brain highly sensitive to perturbations. The dynamics of the transition of the immature brain from a hyperexcitable state to a relatively stable network remains poorly understood. Using a combination of brain-wide activity mapping, behavioural and molecular analysis in response to pentylenetetrazole (PTZ), a GABA _A receptor antagonist, we assessed neural hyperexcitability at different developmental stages in larval zebrafish and observed a distinct age-dependent trajectory. Specifically, we observed that early stages (4-6 dpf) exhibited high susceptibility to external perturbations, whereas by 9 dpf, both neural activity and behavioral responses were markedly attenuated. Further, upon chronic insult, rather than a cumulative increase in excitability, early life hyperexcitation events rendered the larvae resistant to subsequent induction. Put together, our work maps the temporal transition of the vertebrate brain from a state of hyperexcitability to a phase of relative resistance and has potential implications on understanding the progression of neurological conditions in the pediatric population.