Repeated mild shaking of neonates induces transient cerebral microhemorrhages and anxiety-related behavior in adult rats

Growing evidence suggests that neonatal cerebral microhemorrhages (MHs) are implicated in neuropsychiatric diseases in adults. Although animal studies have identified the progression of the underlying mechanisms of MHs, few studies have investigated the histopathology and behavioral outcomes. In this study, we created an experimental rat model of MHs using a new experimental device for repeated mild shaking brain injury (SBI) in the neonatal period and examined temporal changes in MHs using susceptibility weighted imaging (SWI) and iron histochemistry. SWI demonstrated transient MHs in the gray matter of the cerebral cortex and hippocampus in injured rats. Iron histochemical staining demonstrated leakage of iron and iron-positive cells surrounding MHs. This staining pattern lasted for a long time and continued after disappearance of hemorrhagic signals on SWI. These data suggested the presence of iron-associated gray matter injury after MHs. In the open field test, these injured rats showed anxiety-related behavior as adults. This model may be useful for exploring the underlying mechanisms of changes that occur after MHs and the behavioral outcomes of repeated mild SBI in early development.