NEUROTROPHIN-4 NEUROTROPHIN-5 IS A TROPHIC FACTOR FOR MAMMALIAN FACIAL MOTOR-NEURONS

The survival of developing motor neurons depends on factors secreted from skeletal muscles and from cells within the central nervous system. Although several members of the nerve growth factor protein family [neurotrophins (NTs)] are able to maintain developing rat motor neurons in vitro, only the brain-derived neurotrophic factor has been shown to have significant effects on the survival of motor neurons in vivo. In the present study, we demonstrate that NT-4/5 also prevents injury-induced death of facial motor neurons in neonatal rats. Furthermore, facial motor neurons express a functional receptor for NT-4/5, whereas mRNA-encoding NT-4/5 can be detected in their environment throughout embryonic and postnatal life. Thus, both NT-4/5 and brain-derived neurotrophic factor may be physiological survival factors for facial motor neurons and may serve as therapeutic agents for motor neuron disease.