Although subcortical regions send numerous efferent fibers to the hippocampus,their involvement in hippocampal functions has not been fully elucidated. The aim of this study was to determine the effect of the supramammillary nucleus(SuM)on the hippocampus. M ethods: Neurons within the SuM of rats were destroy ed by local injections of an excitotoxin, ibotenic acid, and the effects of the SuM-lesion on behaviors in an open field were investigated. Results: SuM lesions increased distance

more »

... movement time and latency to start grooming,while they decreased time spent grooming. SuM lesions had no effect 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 behavioral characteristics of hippocampal-lesioned rats of the previous reports,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 of this study show the involvement of the SuM in hippocampal function and in anxiety perceived in a novel environment.