FIBER OUTGROWTH AND PATHFINDING IN THE DEVELOPING AUDITORY BRAIN-STEM

In order to study the initial outgrowth of cochlear nucleus fibers, th e lipophilic carbocyanine dye DiI was used to label these neurites in rats at E13 and E15. At E13, prior to leaving the ventricular zone, co chlear neurons have already extended axons along the marginal edge of the hindbrain and a few fibers have reached the midline. By E15, many more fibers have entered the midline region and some appear to contact glial cells at the midline. Based on axon trajectory and growth cone morphology it does not appear likely that there are significant interm ediate decision points for trapezoid body fibers at these early stages of development. Contact between growth cones and glial cells at the m idline is consistent with these cells playing a role in providing guid ance cues for developing auditory fibers.