NEURONAL CELL LOSS IN THE CA3 SUBFIELD OF THE HIPPOCAMPUS FOLLOWING CORTICAL CONTUSION UTILIZING THE OPTICAL DISECTOR METHOD FOR CELL COUNTING

Unilateral cortical contusion in the rat results in cell loss in both the cortex and hippocampus, Pharmacological intervention with growth f actors or excitatory neurotransmitter antagonists may reduce cell loss and improve neurological outcome, The window of opportunity for such intervention remains unclear because a detailed temporal analysis of n euronal loss has not been performed in the rodent cortical contusion m odel, To elucidate the time course of hippocampal CA3 neuronal death e nsuing cortical contusion, we employed the optical disector method for assessing the total number of CA3 neurons at 1 and 6 hours, 1, 2, 10, and 30 days following injury, This stereological technique allows rep orting of total cell numbers within a given region and is unaffected b y change in the volume of the structure or cell size, A rapid and sign ificant reduction in neurons/mm(3) in the ipsilateral CA3 field was ob served by 1 h following trauma, However, a significant increase in neu rons/mm(3) was seen at 30 days postinjury, This surprising finding is a result of CA3 volume shrinkage and redistribution of CA3 neurons, Ut ilization of the optical disector reveals that regardless of an increa se in neurons/mm(3) at 30 days following injury, CA3 cell loss reaches 41% of control animals by 1 day posttrauma and remains near that leve l at all subsequent time points examined. It is estimated that there a re about 156,000 neurons in the CA3 region in control animals, By 1 h following cortical contusion the cell population decreases to 93,000 n eurons indicating a very rapid cell loss, This suggests a window of le ss than 24 h for pharmacological intervention in order to save CA3 neu rons following cortical contusion.