Mn²⁺ dynamics in manganese-enhanced MRI (MEMRI): Ca_v1.2 channel-mediated uptake and preferential accumulation in projection terminals

Manganese-enhanced magnetic resonance imaging (MEMRI) exploits the biophysical similarity of Ca²⁺ and Mn²⁺ to map the brain's activity in vivo. However, to what extent different Ca²⁺ channels contribute to the enhanced signal that MEMRI provides and how Mn²⁺ dynamics influence Mn²⁺ brain accumulation after systemic administration of MnCl₂ are not yet fully understood. Here, we demonstrate that mice lacking the L-type Ca²⁺ channel 1.2 (Ca_v1.2) in the CNS show approximately 50% less increase in MEMRI contrast after repeated systemic MnCl₂ injections, as compared to control mice. In contrast, genetic deletion of L-type Ca²⁺ channel 1.3 (Ca_v1.3) did not reduce signal. Brain structure- or cell type-specific deletion of Ca_v1.2 in combination with voxel-wise MEMRI analysis revealed a preferential accumulation of Mn²⁺ in projection terminals, which was confirmed by local MnCl₂ administration to defined brain areas. Taken together, we provide unequivocal evidence that Ca_v1.2 represents an important channel for neuronal Mn²⁺ influx after systemic injections. We also show that after neuronal uptake, Mn²⁺ preferentially accumulates in projection terminals.