Vascular dilation modulates brain haematoma expansion in larval zebrafish

Intracerebral haemorrhage (ICH) is a severe form of stroke with high morbidity and mortality rates. For survivors, acute haematoma expansion strongly determines neurological outcome. Although blood pressure reduction is widely investigated as a strategy to limit haematoma growth, the haemodynamic mechanisms regulating haemorrhage development remain poorly understood. Zebrafish provide a tractable in vivo model to study cerebrovascular biology and spontaneous ICH, yet the contribution of vascular regulation to haemorrhage onset and expansion has not been explored in this species. Here, we investigated whether pharmacological modulation of vascular dilation influences ICH development in zebrafish larvae. We first characterised vascular changes during the developmental window in which spontaneous ICH occurs and observed increased heart rate and progressive reductions in arterial diameter between 2 and 3 days post-fertilisation, suggesting increased vascular resistance. We then tested whether vasoconstriction promotes haemorrhage using angiotensin II, which induced systemic and cerebrovascular vasoconstriction but did not increase ICH incidence or haematoma size in two independent ICH models. In contrast, pharmacological vasodilation using sodium nitroprusside or isoproterenol significantly reduced haematoma size in a high-incidence model of atorvastatin-induced ICH. Live imaging of cerebral blood flow revealed that vasodilation was associated with the confinement of red blood cells around affected vessels rather than dispersing into the brain ventricles. Together, these findings indicate that vascular dilation modulates haemorrhage progression in zebrafish ICH and establish this model as a platform to investigate haemodynamic mechanisms regulating haematoma expansion.