Manganese Dynamics in Mouse Brain After Systemic MnCl(2) Administration for Activation-Induced Manganese-Enhanced MRI

Activation-induced manganese-enhanced MRI (AIM-MRI) is an attractive tool for non-invasively mapping whole brain activities. Manganese ions (Mn(2+)) enter and accumulate in active neurons via calcium channels. Mn(2+) shortens the longitudinal relaxation time (T1) of H(+), and the longitudinal relaxation rate R1 (1/T1) is proportional to Mn(2+) concentration. Thus, AIM-MRI can map neural activities throughout the brain by assessing the R1 map. However, AIM-MRI is still not widely used, partially due to insufficient information regarding Mn(2+) dynamics in the brain. To resolve this issue, we conducted a longitudinal study looking at manganese dynamics after systemic administration of MnCl(2) by AIM-MRI with quantitative analysis. In the ventricle, Mn(2+) increased rapidly within 1 h, remained high for 3 h, and returned to near control levels by 24 h after administration. Microdialysis showed that extracellular Mn returned to control levels by 4 h after administration, indicating a high concentration of extracellular Mn(2+) lasts at least about 3 h after administration. In the brain parenchyma, Mn(2+) increased slowly, peaked 24–48 h after administration, and returned to control level by 5 days after a single administration and by 2 weeks after a double administration with a 24-h interval. These time courses suggest that AIM-MRI records neural activity 1–3 h after MnCl(2) administration, an appropriate timing of the MRI scan is in the range of 24–48 h following systemic administration, and at least an interval of 5 days or a couple of weeks for single or double administrations, respectively, is needed for a repeat AIM-MRI experiment.