In vivo Tracing of the Ascending Vagal Projections to the Brain with Manganese Enhanced Magnetic Resonance Imaging

Abstract

The vagus nerve is the primary neural pathway that mediates the interactions between the brain and visceral organs. However, it is incompletely understood how the vagus nerve ascends bodily signals to the brain. Here, we explored manganese-enhanced magnetic resonance imaging (MEMRI) for in vivo tracing of vagal nerve projections to the brainstem and assessing their functional dependence on cervical vagus nerve stimulation. Manganese chloride solution was injected into either the left or right nodose ganglion. T1-weighted MRI at 12 or 24 hours following the injection showed that vagal afferent neurons inside the nodose ganglion could uptake and transport manganese ions, as a surrogate of calcium ions, to the nucleus tractus solitarius in the brainstem ipsilateral to the injection side, showing about 19 to 24% contrast enhancement. Four hours of vagus nerve stimulation further promoted nerve activity and resulted in greater contrast enhancement of 40 to 43%. These results demonstrate the feasibility of using MEMRI for structural and functional assessment of vagal afferents and their influences on brain activity.