Effect of entorhinal cortex lesion on hippocampal cholinergic system in rat in operant learning task as studied by in vivo brain microdialysis.

An in vivo microdialysis method was used to study the cholinergic alteration of the hippocampus in entorhinal cortex-lesioned rats performing a positive reinforcement operant learning task. Rats with bilateral entorhinal cortex lesions were implanted with a dialysis probe into the hippocampal CA3 after ten learning sessions. After 7 days, the bilateral entorhinal cortex-lesioned rats showed impaired acquisition of positive reinforcement operant learning. The basal level of the acetylcholine efflux decreased within 30 min before the beginning of a learning session. The hippocampal acetylcholine efflux showed a significantly diminished increase and rapidly returned to the basal level during the 60 min after the beginning of a learning session. These results suggested that enorhinal cortex lesion may cause damage to the hippocampal cholinergic system with disruption of the entorhinal cortex-hippocampus relay passage.