Dissecting the Entorhinal-Hippocampal Circuitry

Abstract

The hippocampus, in conjunction with the entorhinal cortex, performs an indispensable function in the formation and retrieval of memories, thus rendering it one of the most extensively studied components of the brain, both in terms of function and structure. However, the quantification of these structural connections remains largely uncharted territory. Furthermore, there is a lack of insight regarding the parallel connections in the trisynaptic circuits. In light of these considerations, the objective was to ascertain the efficacy of various quantification methodologies in order to formulate a semi-quantitative approach to the number of connections between the entorhinal cortex and the dentate gyrus. In addition, the second objective was to ascertain the presence of any entorhinal cortex layer II neurons that project to both the dentate gyrus and CA3. In order to accomplish this objective, a combination of viral tracing and immunofluorescence techniques was utilised. It was determined through the application of these techniques that the quantification of entorhinal-dentate connections required tracers of a more refined nature than those employed in standard AAVs and pseudorabies viruses. Additionally, the confirmation was made that neurons within the entorhinal cortex project concurrently to both the dentate gyrus and CA3. These findings could assist in establishing a baseline for future investigations into the role of the hippocampus in pattern separation and completion, as well as the development of more precise computer models.