Serial monitoring of endogenous neuroblast migration by cellular MRI

Endogenous neural progenitor cell migration in vivo can be monitored using MRI-based cell tracking. The current protocol is that micron sized iron oxide particles (MPIOs) are injected into the lateral ventricle proximal to the neural stem cell niche in the brain. MPIOs are endocytosed and incorporated into the neural progenitor cell population, making them visible by gradient echo MRI. Here this new method is extended to serially quantify cell migration. Initially, in vivo cell labeling methodologies were optimized, as high susceptibility effects from the MPIOs generate substantial signal loss around the injection site, masking early migratory events. Then, using improved labeling conditions, a longitudinal study was conducted over two weeks to quantify the migration of labeled progenitor cells toward the olfactory bulb (OB). By 3 days following injection, we calculated 0.26% of the volume of the OB containing labeled cells. By 8days, this volume nearly doubled to 0.49% and plateaued. These MRI results are in accordance with our data on iron quantification from the OB and with those from purely immunohistochemical studies.