DEVELOPMENTAL-CHANGES IN GROWTH-FACTORS RELEASED BY THE EMBRYONIC INNER-EAR

Recent studies have demonstrated a role for neurotrophins in regulatin g the survival of developing auditory and vestibular neurons. However, the developmental time-course for neurotrophin production and release by inner ear tissues has not been defined. In the present study, neur otrophin-like activity was evaluated from culture medium conditioned b y early-or midembryonic stage inner ears. Examination of the proteinac eous properties of conditioned medium revealed a developmental change in growth factor release by the inner ear. Neurotrophin-like molecules were not detected in medium conditioned by early stage otocysts. In c ontrast, neurotrophin-like bioactivity was detected in medium conditio ned by middevelopmental stage inner ears. Western blot analysis reveal ed that NT-3 was released by the rat inner ear at midstages of inner e ar development. ELISA measurements revealed that both NT-3 and BDNF ar e produced by the middevelopmental stage inner ear, and that NT-3 prot ein levels are higher than BDNF levels. These results suggest that the re are developmental changes in the release of growth factors by the i nner ear. (C) 1998 Academic Press.