Using Manganese-Enhanced MRI (MEMRI) to Detect the Order of Neuronal Connections in the Olfactory Pathway at the Level of Specific Layers

Der-Yow Chen¹, Stephen J. Dodd, Daniel R. Glen, Ziad S. Saad, Alan P. Koretsky

MEMRI can be used for neuronal tracing in the brain. Here it is demonstrated that MEMRI identifies the laminar connections of the olfactory system and traces layer-specific inputs to olfactory cortices. MnCl₂ was injected into nostrils or the olfactory bulb of rats, and they were imaged with this MRI technique at several time points. The dynamic changes of Mn²⁺ enhancement could be characterized by the arrival latency into each specific region. The olfactory pathway from olfactory bulb to higher-order cortex was labeled in proper, known laminar order. Mn²⁺ enhancement into the orbitofrontal cortex predicts that connections from olfactory cortex innervate superficial layer of the orbitofrontal cortex. This is a connection that has not been previously mapped. Therefore, MEMRI neural tracing is specific at the level of cortical layers in the olfactory pathway.