In vivo detection of excitotoxicity by manganese-enhanced MRI: comparison with physiological stimulation.

Manganese-enhanced MRI (MEMRI) is a powerful technique for the in vivo monitoring of brain function in animals. Manganese enters into cells through calcium channels, i.e., voltage-gated calcium channels and activated glutamate receptors (e.g., N-methyl-D-aspartate receptors). N-methyl-D-aspartate receptors are activated both in normal physiological and pathophysiological conditions. Consistent with these mechanisms, we showed that in the olfactory bulb, the MEMRI signal strongly increases when excitotoxic mechanisms are induced by an administration of a N-methyl-D-aspartate receptor agonist, quinolinate. We found that the intensity of the MEMRI signal in excitotoxic conditions is similar to the odor-evoked signal in normal physiological conditions. Finally, we showed that the dynamics of the MEMRI signal are determined by the early phase of manganese in the olfactory bulb. Overall, these data show that, in addition to physiological studies, MEMRI can be used as an in vivo method to follow-up the dynamics of excitotoxic events.