Aim : Although subcortical regions send numerous efferent fibers to the hippocampus, their involvement
in hippocampal functions has not been fu11y elucidated. The aim of this study was to determine the
efTect of the supram ammillary nucleus (SuM) on the hippocampus. Methods : Neurons within the SuM
of rats were destroyed by local injections of an excitotoxin, ibotenic acid, and the efTects of the
SuM-lesion on behaviors in an open field were investigated. Results: SuM lesions increased distance
traveled, movement time and latency to start grooming, while they decreased time spent grooming. SuM
lesions had no efTect on rearing frequency or immobility time. Conclusion : Prolonged exploration and
decrease in the total time spent grooming observed in the SuM-lesioned rats were consistent with the
beh avi oral characteri stics of hippocamp al -lesioned rats of the previ ous report s, suggesting that the SuM
is involved in the establishment of spatial memory by hippocampus during the initial exploration of a
novel environment. In addition, the reduction of grooming in the SuM-lesioned animal suggests that
SuM may be involved in emotion, such as anxiety. The results ofthis study show the involvement ofthe
SuM in hippocampal function and in anxiety perceived in anovel environment
