Development of a noradrenergic neuron-selective AAV vector and its application to the brain-wide axonal mapping

Abstract

The locus coeruleus (LC) is the main source of noradrenaline (NA) in the brain and involved in various brain functions including arousal, cognitive and emotional regulation. Recent accumulating evidence shows that individual LC-NA neurons send segregated efferent projections in a target-specific manner; however, it is still controversial whether LC-NA neurons have fully target-specific or more global projection patterns. To identify their axonal wiring at mesoscale level, we developed a novel adeno-associated viral (AAV) vector for NA neuron-selective gene expression and conducted whole-brain mapping of LC-NA axons using the block-FAce Serial microscopy Tomography (FAST). By local injection of the AAVs to the LC, we observed 92% of cells labeled with fluorescent proteins were tyrosine hydroxylase-positive. Using an axon-targeting fluorescent protein and retrograde AAV, we found that ventral hippocampus-projecting LC-NA neurons send dense projection to the dorsal hippocampus and some collaterals to the wide cortical area. These results suggest that although LC-NA neurons have dense projection in a target-specific manner, they may globally transmit NA and regulate multiple brain regions via collaterals. These findings and the AAV vectors will contribute to more precise understanding of complex organization of LC-NA systems.