CA3 NEURONAL DEGENERATION FOLLOWS CHRONIC ENTORHINAL CORTEX LESIONS

Entorhinal cortex lesions are a common experimental paradigm to study memory function and neural plasticity after hippocampal deafferentatio n, The long term consequences of such lesions are of particular intere st both in the context of these models and because pathological change s of Alzheimer's disease destroy entorhinal cortex projection neurons. We used stereological counting techniques to assess the structural in tegrity of the hippocampal formation 0.5-28 months after entorhinal le sion in the rhesus monkey. Surprisingly, 18-28 months after lesion the number of CA3 neurons was decreased by 57%, while neuron numbers in o ther subfields did not change. These results suggest that delayed tran ssynaptic neural degeneration can occur long after brain injury.