Abstract
Neurons in the cochlear nucleus (CN) receive primary auditory signals from the spiral ganglion neurons in the inner ear and transmit secondary signals to the higher auditory neurons in the medulla and thalamus. Little is known about the mechanisms how the CN neurons grow their fibers and find the higher order neurons during development. We report here that growth of fibers from the CN neurons changed dependence on BDNF in a few days after the birth. CNs were dissected from embryonic and newborn rats and cultured them in Neurobasal Medium (Gibco). Monolayer,culture of embryonic rat CN neurons represented two types of neurons, large long-axon neurons and small bipolar ones. Neurotrophins (NGF, BDNF or NT3) caused little changes in the growth of these neurons. Explants of small sections from embryonic CNs in collagen matrix extended thousands of thin fibers without addition of neurotrophins in the growth medium. By contrast, explants of CNs from day5 and day8 extended fibers in a BDNF-dependent manner. Only short fibers were grown when NGF or NT3 were added to the medium. Altogether, CN neurons changed their neurotrophin dependence, from no-dependence to BDNF-dependence, in a short period after the birth. [Jpn J Physiol 55 Suppl:S170 (2005)]
