Lipophilic Tracer DiI Used for Neuronal Tracing in the Fixed Hippocampal Formations of Mice

Both the hippocampus and the entorhinal cortex are involved in memory formation. It is thought that they work together to create a loop that is involved in the formation of long term memories. The entorhinal cortex sends projections to the CA1 field of the hippocampus and the CA1 field sends projections back to the entorhinal cortex. How exactly they communicate is unknown. In order to do electrophysiological studies it is necessary to know in which orientation to cut the brain to preserve the most connections between these two areas. Here we show that DiI crystal application can be used to successfully label known fiber paths from the dentate gyrus to the CA3 field. Then we begin with sagittal and horizontal slices of the brain to see how well connections between the CA1 field and the EC are preserved.