Kim Annink

33 The pattern of Purkinje cell injury in neonates with HIE INTRODUCTION Hypoxic-ischemic encephalopathy (HIE) following perinatal asphyxia is the leading cause of mortality in term neonates with an incidence of 1.5 per 1000 term births (1,2). Therapeutic hypothermia is the current standard of care to reduce brain injury and additional treatment options are still limited (3). Besides high mortality rates, long-term neurodevelopmental disabilities such as cognitive, behavioral and attention impairments and motor dysfunction are still common in neonates with moderate or severe HIE (4–7). In the clinical setting, HIE is often characterized as cerebral injury (8). However, also cerebellar injury in neonates is being increasingly recognized as a contributor to neurodevelopmental outcome (9,10). For instance, cerebellar injury has been linked to motor deficits, as well as cognitive functioning, behavior, learning and emotional deficits (11,12). However, research about the association between behavioral problems and cerebellar injury in HIE remains sparse (9). In infants born extremely preterm (i.e. below 28 weeks of gestation) a clear association was found between early cerebellar injury and long-term behavioral problems (10,13). During the third trimester of pregnancy the cerebellum shows a rapid increase in growth, making the cerebellum especially vulnerable to insults that disturb normal development within this time period (e.g. hypoxia-ischemia) (14,15). Surprisingly, acute cerebellar injury is rarely detected on conventional clinical neuroimaging (e.g. T1-, T2-weighted and diffusion weighted magnetic resonance imaging (MRI) scans) (16,17). In contrast, on histopathological level, there is evidence that the cerebellum is injured after severe HIE in infants (18). Of the cerebellar neurons, the Purkinje cells (PCs) are known to be the most susceptible to hypoxic events, which is most likely due to their high metabolic activity and associated oxygen demand (19,20). Postmortem studies in human neonates with HIE on PCs are lacking, but in neonatal mouse models, pronounced reductions in PC number and morphological alterations of PCs in response to hypoxic-ischemia were indeed found (i.e. swelling, autolytic necrosis, cell shrinkage and dark cell degeneration) (24,25). Other animal studies on perinatal hypoxic-ischemia have also demonstrated increased microglia activation, myelination deficits and overall necrosis and apoptosis in the cerebellum (23–25). Whereas the cerebellar anatomy has been described as homogenous, its susceptibility to cellular damage has been shown to vary between cerebellar lobules. In murine 2