IMAGING NEURONAL DEVELOPMENT WITH MAGNETIC-RESONANCE-IMAGING (NMR) MICROSCOPY

An ideal technique for following the development of the vertebrate ner vous system would allow cells to be followed at the resolution of ligh t microscopy at depths of several millimeters into the tissue. This wo uld permit critical events to be followed at cellular or sub-cellular resolution even deep within the developing organism. To date, no techn ique has emerged with all of the needed properties. Light microscopy c an follow a cell and its descendants after they have been labeled by e ither the infection of embryonic cells with a recombinant retrovirus o r the microinjection of individual precursor cells with enzymes or flu orescent dyes. However, light microscopy cannot image events deeper th an a few hundred micrometers within an embryo due to light scattering and aberrations in the objective lenses and other optics. Magnetic res onance imaging (MRI) does not suffer from these limitations, routinely being used to image in 3 dimensions through specimens as large as adu lt humans. However, it is relatively slow and, as implemented to date, it cannot routinely achieve cellular resolution. Here, we present our attempts to meet the technical challenges posed by in vivo MRI micros copy. As an example of both the progress and the future challenges, we present images of cells within the developing frog embryo over a seve ral day time course.