Cortical representation of olfactory bulb input revealed by retrograde mono-transsynaptic labeling

Abstract

In the mouse olfactory system, more than 1000 classes of olfactory receptor neurons(ORNs) each sends convergent axonal projections into a pair of specific glomeruli in the olfactory bulb (OB), creating a space map for odor detection. Mitral/tufted cells receive ORN inputs from individual glomeruli and project axons to the olfactory cortex. How the olfactory map in the OB is represented in the cortex is largely unknown. Here we combine a retrograde mono-transsynaptic labeling technique with mouse genetics such that we can precisely control spatial location, number and cell type of starter cortical neurons. We found that individual cortical neurons receive mitral cells representing multiple glomeruli, demonstrating a direct information convergence. Cortical neurons in highly restricted areas receive inputs from glomeruli that spread widely in the olfactory bulb. Quantitative analyses revealed that the space map in the OB is differentially represented in the anterior olfactory nucleus, amygdala and piriform cortex. Finally, our genetically regulable transsynaptic labeling method can be widely applied to mapping connections in many parts of the nervous system in mice.