Cell death in the rat hippocampus in a model of prenatal brain injury: time course and expression of death-related proteins

Survival rates have increased dramatically for very premature (gestational week 24–28) infants. However, many of these infants grow up to have profound cognitive, motor and behavioral impairments due to brain damage. We have developed a novel model of prenatal infant gray matter injury. During the neonatal period, GABA is an excitatory neurotransmitter. GABA A receptor activation results in chloride efflux and membrane depolarization sufficient to open L-type voltage sensitive calcium channels. Our model involves excessive GABA A receptor activation in the newborn rat, with damage due to the resultant excessive calcium influx, not GABA A receptor activation itself. A common feature among numerous insult pathologies in the neonatal brain is an elevation in the intracellular levels of calcium. The goals of the present study were: 1) to document the time course and amount of cell death (both apoptotic and necrotic), and 2) to investigate the effect of GABA A receptor activation on the time course and expression of three cell death-related proteins (caspase-9, bax and bcl-2) in our model of prenatal brain injury. The magnitude of cell death, using TdT-mediated dUTP nick end labelingand Cresyl Violet to quantify the incidence of apoptotic and necrotic cells, was region dependent (CA1>CA2/3>dentate gyrus) and persisted for at least 5 days following insult. There was a relative increase in the amount of bax to bcl-2 protein, and increased protein levels of caspase-9, indicative of cell death. These findings are consistent with mechanisms of cell death seen in other types of early brain insult, and highlight a conserved cascade of events leading to cell death in the developing brain.