Abstract 244 Perinatal Brain Injury: Patterns and Mechanisms Platform, Tuesday, 5/4

The aim of this study is to determine if subplate neurons are among cells injured in a rodent model of preterm hypoxic ischemic brain injury. Preterm hypoxic ischemic brain injury in the human infant involves excitotoxic injury, and leads to periventricular leukomalacia; a pattern of injury localized to the intermediate zone of neocortex. The intermediate zone contains oligodendroglial precursors, as well as subplate neurons. Subplate neurons have been shown to be important for normal cortical development, and their involvement in periventricular leukomalacia could explain many of the clinical consequences of preterm brain injury, including abnormal visual development. Subplate neurons undergo cell death during normal development.

To specifically identify subplate neurons, we employed bromodeoxyuridine (BrdU) birthdating. Injections of BrdU were given at the time of subplate neuron generation (E12.5 in rat), and subplate neurons were visualized in the neonatal rat with immunohistochemistry employing anti-BrdU monoclonal antibodies. Dying cells were identified using terminal transferase mediated dUTP nick end labeling (TUNEL), and with bisbenzamide nuclear counterstaining. Simultaneous staining with BrdU immunohistochemistry and TUNEL labeling identified double positive, dying subplate neurons. The P0 rat model of preterm hypoxic ischemic brain injury involves unilateral carotid ligation with subsequent global hypoxia using 8% oxygen. A control group of sham operated pups (hypoxia alone) were compared to pups with unilateral carotid ligation (hypoxia ischemia) at 4, 12, 24 and 48 hours post injury. We observed a pattern of bilateral, symmetric TUNEL signal in hippocampal region CA1, enterorhinal cortex, thalamus and striatum beginning as early as 4 hours post manipulation and peaking at 12 hours in both hypoxia alone and hypoxia ischemia groups. A pattern of TUNEL positive cells ipsilateral to the carotid ligation was noted only in the hypoxia ischemia group beginning after 12 hours. Double positive, dying subplate neurons could be identified in both groups, but were frequently observed in the ipsilateral intermediate zone of the hypoxia ischemia group.

We conclude that subplate neurons are among the cells injured in this rodent model of preterm hypoxic ischemic brain injury. Hypoxia alone may account for the early symmetric injury observed in both sham operated and focal ischemia groups.