Histological evidence for cholinergic alteration in the hippocampus following entorhinal cortex lesion

The initial stage of Alzheimer's disease is characterized by neuropathological alteration in the entorhinal cortex. To model one aspect of the neurodegeneration observed and to investigate anatomical changes of the hippocampus associated with unilateral entorhinal cortex lesion, excitotoxin ibotenic acid was used to produce selective unilateral neuronal loss in rat entorhinal cortex. Histological and morphometrical analyses confirmed excitotoxic lesion of the entorhinal cortex after 3 months and showed a decrease of acetylcholinesterase-stained fibers in the stratum moleculare of the dentate gyrus and the stratum radiatum of the CA3 field. This study demonstrates the importance of the entorhinal cortex in the hippocampal cholinegic function which appears to be important to memory and learning, and raises the possibility that memory deficit in Alzheimer's disease may be associated with partial neuronal loss in the entorhinal cortex.