Neuronal injury and loss after traumatic brain injury: time course and regional variability.

We have examined regional neuronal injury after traumatic brain injury using Fluoro-Jade, an acidic dye that exhibits a marked affinity for both the degenerating neuronal cell body and its processes and have determined the extent to which early injury corresponds to regional patterns of neuronal loss. Rats (n=45) were subjected to lateral fluid percussion brain injury and euthanized at 3 h to 28 days post injury. Complementary Fluoro-Jade, silver impregnation methods and TUNEL were used to assess neuronal injury. Neuronal loss was evaluated in sections immunostained for NeuN, a neuronal specific nuclear protein. Overt neuronal cell loss was evident by 7 days post injury in the cortex, hippocampus and thalamus. Injured neurons were apparent in the ipsilateral cortex bordering the impact site, hippocampus (CA1 and dentate), thalamus, and vermis of the cerebellum as early as 3 h post injury. Degenerating neurons were maximal by 1 and 3 days in the cortex and hippocampus, by 3 and 7 days in the cerebellum, and by 7 days in the thalamus. The regional distribution of Fluoro-Jade-labeled neurons corresponded to a similar pattern of silver and TUNEL staining. Together, these findings demonstrate a regionally specific temporal pattern of neuronal injury that results in overt neuronal cell loss within both cortical and subcortical regions.