Quantification of neuron types in the rodent hippocampal formation by data mining and numerical optimization

Area of Science:

• Neuroscience
• Computational Biology
• Cellular Neuroscience

Background:

• Establishing a comprehensive brain cell census requires quantifying distinct neuron types and their population sizes within specific anatomical regions.
• While the rodent hippocampal formation has 122 identified neuron types documented on Hippocampome.org, their relative abundances are largely unquantified.

Purpose of the Study:

• To quantitatively estimate the population sizes of all 122 neuron types within the rodent hippocampal formation.
• To provide reliable numerical ranges for each neuron type based on literature mining and numerical optimization.

Main Methods:

• Literature mining of existing neuroscience research to gather data on neuron counts.
• Numerical optimization techniques to estimate neuron population sizes across 26 subregions of the hippocampus.
• Sensitivity analysis to determine reliable numerical ranges for each neuron type.

Main Results:

• Quantitative estimates for the number of neurons in each of the 122 Hippocampome.org types, categorized by neurotransmitter (glutamate or GABA) and axonal-dendritic patterns.
• Neuron counts reported for 26 subregions, including the dentate gyrus, Ammon's horn, subiculum, and entorhinal cortex.
• Analysis revealed that dendritic-targeting interneuron populations are independent of anatomical volume, a characteristic not shared by other neuronal classes.

Conclusions:

• This study provides the first quantitative estimates of neuron type abundances in the rodent hippocampal formation.
• The findings contribute essential data for building a brain cell census and understanding hippocampal organization.
• All data, code, and evidence are publicly available on Hippocampome.org to facilitate future research.