Loss of hippocampal CA1 pyramidal neurons correlates with memory impairment in rats with ischemic or neurotoxin lesions.

Rats were trained for 20 days in a modified T maze to perform an invariant, tactile discrimination and a variable, delayed spatial discrimination, and then were exposed either to 30 min of transient forebrain ischemia or to low- or high-dose ibotenic acid to damage the dorsal hippocampus bilaterally. Only rats exposed to ischemia or high-dose ibotenic acid demonstrated impaired performance during 30 postoperative test days on both aspects of the task (p less than .05). Volume of hippocampal damage did not predict performance. However, the extent of CA1 pyramidal neuron loss correlated significantly with performance on the delayed spatial discrimination (p less than .01). Damage to the dentate gyrus and CA2-3 did not correlate with performance. These results support the view that the hippocampus, in particular the CA1 region, is crucial for certain types of memory performance.