Distribution of ischemic neuronal damage in the dorsal hippocampus of rat

Selective neuronal death was investigated in dorsal hippocampus of rats subjected to 30 min of four-vessel occlusion (4VO) and recirculation times of 3, 8, 24, 48, and 72 h. Anatomical orientation was achieved in different subsectors by use of histochemical techniques for the enzyme acetylcholinesterase (AChE) and for heavy metals (Timm-stain). A systematic study of subsectors was performed in different section levels from mid-dorsal levels to the septal pole of the hippocampus. In the hilus of the dentate gyrus, there was early neuronal injury accompanied by microvacuolation of the neuropil. Delayed neuronal death occurred in sector CA1 in parallel to CA2 damage. The use of the Timm-stain allowed the first direct documentation of involvement of CA2 in ischemic injury. The CA3 sector was largely spared from lesions at mid-dorsal levels. At the septal extreme, however, there were lesions of CA3 pyramidal cells, and also portions of the dentate gyrus granule cells were affected. These findings demonstrate that all areas of the hippocampus can be involved in ischemic injury, depending on their position along the temporoseptal axis of the hippocampal formation.