THE EFFECTS OF AMPA-INDUCED LESIONS OF THE MEDIAL SEPTUM AND VERTICALLIMB NUCLEUS OF THE DIAGONAL BAND OF BROCA ON SPATIAL DELAYED-NONMATCHING-TO-SAMPLE AND SPATIAL-LEARNING IN THE WATER MAZE

These experiments investigated in the rat the impact on spatial delaye d non-matching to sample and on acquisition of the Morris water maze o f (i) AMPA-induced lesions of the medial septal nucleus, which produce d a marked reduction of hippocampal choline acetyltransferase activity and acetylcholine levels (measured using in vivo dialysis) together w ith lesser reductions in cholinergic markers in the cingulate cortex a nd (ii) similar AMPA-induced lesions of the vertical limb nucleus of t he diagonal band of Broca (vDB), which produced more marked reductions in cholinergic markers in the cingulate cortex than in the hippocampu s. Medial septal lesions produced a delay-dependent deficit in spatial working memory, while lesions of the vDB resulted in a delay-independ ent performance deficit. In addition, rats with vDB lesions adopted bi ased response strategies during the imposition of long delays. Neither lesion significantly affected the acquisition of a spatial reference memory task, the Morris water maze, The results are discussed in terms of cholinergic- and GABAergic-dependent functions of the hippocampal formation and cingulate cortex in spatial short-term and reference mem ory.