Traumatic Brain Injury Alters the Molecular Fingerprint of TUNEL-Positive Cortical Neurons In Vivo: A Single-Cell Analysis

The cerebral cortex is selectively vulnerable to cell death after traumatic brain injury (TBI). We hypothesized that the ratio of mRNAs encoding proteins important for cell survival and/or cell death is altered in individual damaged neurons after injury that may contribute to the cell's fate. To investigate this possibility, we used amplified antisense mRNA (aRNA) amplification to examine the relative abundance of 31 selected candidate mRNAs in individual cortical neurons with fragmented DNA at 12 or 24 hr after lateral fluid percussion brain injury in anesthetized rats. Only pyramidal neurons characterized by nuclear terminal deoxynucleotidyl transferase-mediated biotinylated dUTP nick end labeling (TUNEL) reactivity with little cytoplasmic staining were analyzed. For controls, non-TUNEL-positive neurons from the cortex of sham-injured animals were obtained and subjected to aRNA amplification. At 12 hr after injury, injured neurons exhibited a decrease in the relative abundance of specific mRNAs including those encoding for endogenous neuroprotective proteins. By 24 hr after injury, many of the mRNAs altered at 12 hr after injury had returned to baseline (sham-injured) levels except for increases in caspase-2 and bax mRNAs. These data suggest that TBI induces a temporal and selective alteration in the gene expression profiles or "molecular fingerprints" of TUNEL-positive neurons in the cerebral cortex. These patterns of gene expression may provide information about the molecular basis of cell death in this region after TBI and may suggest multiple avenues for therapeutic intervention.