The effects of MS/VDB lesions on behavioral despair and learning and memory

Abstract

The present study aimed to investigate the consequences of hippocampal denervation in terms of irreversible medial septal area lesioning on behavioral despair and navigational learning. To that purpose medial septum / vertical diagonal band of Broca (MS/VDB) lesions were achieved electrolytically or with 980-nm diode laser application in the rat brain. The animals were tested in forced swim test followed a week later by Morris water maze to assess behavioral despair and navigational ability respectively.Histochemical evaluation revealed lower acetylcholinesterase (AChE) content in the hippocampus of some of the lesioned animals compared to sham-operated control animals as a functional outcome of MS/VDB lesions. Animals with low AChE content in the hippocampus showed aggravated behavioral despair determined by augmented duration of immobility in the second swim test. On the other hand, the temporal learning acquisition in Morris water maze rather than total learning capability is affected by medial septal area lesions. Behavioral findings in the present study appear, not to be due to possible sensory-motor impairments of the lesioned animals since the latter did not differ from the sham-operated controls in the visible platform version of MWM task and open field activity test. Electrolytic lesions appear to be more efficient than laser lesions in terms of AChE decrease in the hippocampus.In conclusion, reduction of hippocampal AChE content via irreversible lesions of MS/VDB area aggravates behavioral despair but fails to induce learning impairments in rats.|Keywords: 980-nm diode laser, electrocoagulation, neurosurgery, acetylcholinesterase, forced swim test, Morris water maze.