Expression of c-Fos protein in medial septum/diagonal band of Broca and CA3 region, associated with the temporary inactivation of the supramammillary area

•Cell activity in the medial septum/diagonal band of Broca and CA3 region of the hippocampus was studied when the SuM area was inactivated.•It was noted that the temporary inactivation of the SuM area by microinjections of tetrodotoxin, produces hyperactivity in the medial septum/diagonal band of Broca and hypoactivity in the CA3 region of the hippocampus.•These data suggested that information input to CA3 region of the hippocampus by the SuM area is especially important for good memory/spatial learning functioning.

The supramammillary (SuM) area is part of the diencephalic nuclei comprising the mammillary bodies, and is a key structure in the memory and spatial learning processes. It is a critical region in the modulation/generation of hippocampal theta rhythm. In addition, many papers have recently shown a clear involvement of this structure in the processes of spatial learning and memory in animal models, although it is still not known how it modulates spatial navigation and response emotional.The aim of the present research was to study the effect of the temporary inactivation of the SuM area on synaptic plasticity of crucial structures in the formation of spatial memory and emotional response.Sprague–Dawley rats were asigned in three groups: a control group where the animals were not subjected to any treatment, and two groups where the rats received microinjections of tetrodotoxin (TTX) in the SuM area (5 ng diluted in 0.5 μl of saline) or saline (0.5 μl). The microinjections were administered 90 min before the perfusion. Later, cellular activity in medial septum/diagonal band of Broca (MS/DBB) and CA3 region of the dorsal hippocampus was assessed, by measuring the immediate early gene c-fos.The results show a clear hiperactivity cellular in medial septum/diagonal band of Broca and a clear hypoactivity cellular in the CA3 region of the hippocampus when there was a functional inactivation of the SuM area. It suggests that the SuM area seems to be part of the connection and information input pathways to CA3 region of the hippocampal formation, key for proper functioning in spatial memory and emotional response.