Abstract
Neurons in the supramammillary nucleus (SuM) of hypothalamus project densely to the dentate gyrus and the CA2/CA3a regions of the hippocampus. Although the SuM has been considered to modulate the hippocampal function, the interaction between the SuM and the hippocampus is still unclear in freely moving rats. We monitored the neuronal activity in both the SuM and the hippocampus in freely moving rats using c-Fos immunohistochemistry. We compared the numbers of c-Fos positive neurons in the SuM and the hippocampus of rats sacrificed after exploring in an open field for two hours (OF group) with those of rats sacrificed soon after leaving their home cages (HC group). In the SuM, the dentate gyrus, CA1 and CA3 of the OF group, a large number of c-Fos positive neurons were observed, although only few c-Fos positive neurons could be found in those of the HC group. The distribution maps of c-Fos positive neurons in the SuM revealed that most of c-Fos positive neurons were found in the medial part of the SuM. We compared the number of c-Fos positive neurons in the hippocampus of SuM lesioned rats (SuM group) with that of sham operated rats (Sham group) after exploring in an open field. In the dentate gyrus and CA3, the number of c-Fos positive neurons were significantly decreased in the SuM group compared with the Sham group. These results suggest that the neuronal activity in the hippocampus is enhanced by the neuronal activity in the SuM when rats are exploring. [Jpn J Physiol 54 Suppl:S189 (2004)]
