Identification of New Neuronal Types in the Hippocampal Formation of Mouse Brains Based on Morphology

Abstract

Hippocampome.org is a knowledge base characterizing neuronal types of the circuitry of the hippocampal formation of rodents, based on morphology, molecular markers, connectivity, and physiology. One of the project's main set of goals is to thoroughly cover all available data on rodent neurons in the hippocampus, identify their types, and be a publicly available resource for rodent neuronal type-related information. Using the reconstructions of mouse neurons generated by the Janelia MouseLight Project, we identified the locations of the somatic, axonal, and dendritic points with respect to the layers of the subregions of the hippocampal formation and matched them with the neuron types from Hippocampome.org. Using a purely algorithmic approach, we did not find any neurons showing the same axonal-dendritic patterns as the types that had been already identified by Hippocampome.org. However, we believe this to be a limitation of the methodology, as a visual inspection of several dentate gyrus neurons revealed them to be DG Granule cells. Our algorithmic technique also uncovered four potential new neuron types, where a neuron type is formally defined by Hippocampome.org as two or more neurons with matching axonal-dendritic patterns. These four new neuron types, each with their soma in the dentate gyrus, will be considered for addition to the knowledge base.