Manganese Accumulation for Genetically Induced Contrast (MAGIC) MRI in the brain across species
Mapping the mesoscale architecture of neural circuits is essential for understanding brain function, yet high-resolution anatomical tracing remains largely dependent on fluorescent reporters that require terminal histology. Here, we present Manganese Accumulation for Genetically Inducible Contrast (MAGIC) MRI, a gene expression reporter system based on the metal ion transporter Zip14 (Slc39a14) which enables noninvasive, in vivo neural tracing. In rodents, viral delivery of Zip14 enables both anterograde and retrograde tracing of cortico-thalamic and basal ganglia circuits. Mechanistic validation via laser ablation-inductively coupled plasma-time-of-flight-mass spectrometry (LA-ICP-TOF-MS) confirmed that MRI contrast changes are driven by specific Mn2+ accumulation. This permitted high-resolution visualization of neural populations and projections using clinical standard MRI sequences without supplementary contrast agents. However, addition of systemic Mn2+ further increased the signal by a factor of 2-5 fold. To facilitate objective, high-throughput analysis, we developed a fully automated pipeline for voxel-wise anomaly detection that accurately identifies and quantifies MAGIC enhanced regions in individual subjects. Finally, it is demonstrated that MAGIC is translatable to the large mammalian brain, providing the first functional demonstration of an MRI-visible reporter in the rhesus macaque. By enabling the non-invasive monitoring of neural connectivity across species, MAGIC provides a versatile, longitudinal tool for studying structural plasticity and circuit organization in the living brain.