Distribution of BDNF, NT-3 and NT-4 in the developing auditory brainstem

This study describes the developmental expression of three neurotrophins, b rain derived neurotrophic factor (BDNF), neurotrophin 3 (NT-3) and neurotro phin (NT-4) in the rat auditory brainstem using immunohistochemistry. At po stnatal day 0 (PND 0), neurotrophins expression was virtually absent from a ll auditory nuclei in the brainstem, even though some positive neurons were observed in the mesencephalic trigeminal nucleus at this age. However, BDN F, NT-3 and NT-4 positive neurons were observed in most brainstem auditory nuclei by PND 6. At the following stages, there was a general increase in t he intensity of the neurotrophins immunoreactivity and BDNF labeling was pa rticularly prominent in most cochlear nucleus neurons. A differential patte rn of staining emerged in cochlear nucleus subdivisions, with more intense staining present in the ventral part. The superior olivary complex nuclei f ollowed a similar pattern of BDNF staining compared to the cochlear nucleus . In the adult, BDNF heavily labeled most neurons of the superior olivary n uclei and moderately labeled neurons of the inferior colliculus (IC). NT-3 and NT-4 showed a similar pattern of staining in most auditory brainstem nu clei. The first staining was observed by PND 6 in some neuronal cell bodies . NT-3 and NT-4 immunoreactivity increased in the following stages and in t he adult moderate labelings were observed in most neurons of the cochlear n ucleus, the superior olivary nuclei and the IC. These results show that neurotrophins are expressed 1 week before the onset of hearing and the increase of their expressions correlate with the appear ance of sound-evoked activity in the system. The temporal distribution of n eurotrophins does not correlate with neuronal birth, axonal outgrowth or th e formation of connection in the auditory structures, suggesting a role pri marily in the maintenance and/or modulation of postnatal and adult function s. (C) 1999 ISDN. Published by Elsevier Science Ltd. All rights reserved.