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 < .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 < .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.