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 deafferentation. The long term consequences of such lesions are of particular interest both in the context of these models and because pathological changes of Alzheimer's disease destroy entorhinal cortex projection neurons. We used stereological counting techniques to assess the structural integrity of the hippocampal formation 0.5-28 months after entorhinal lesion in the rhesus monkey. Surprisingly, 18-28 months after lesion the number of CA3 neurons was decreased by 57%, while neuron numbers in other subfields did not change. These results suggest that delayed transsynaptic neural degeneration can occur long after brain injury.