Coexpression of neurotrophic growth factors and their receptors in human facial motor neurons

Neuronal development and maintenance of facial motor neurons is believed to be regulated by neurotrophic growth factors. Using celloidin-embedded sect ions, we evaluated immunoreactivity of ii neurotrophic factors and their re ceptors in facial nuclei of human brain stems (4 normal cases, and 1 from a patient with facial palsy and synkinesis). In the normal subjects, positiv e immunoreactivity of the growth factor neurotrophin-4 and acidic fibroblas t growth factor (aFGF) was observed in facial motor neurons, as was positiv e immunoreactivity against ret, the receptor shared by glial cell line-deri ved neurotrophic factor and neurturin. Immunoreactivity was moderate for th e receptor trkB and strong for trkC. In the case of partial facial palsy, s urviving cells failed to show immunoreactivity against neurotrophins. Howev er, immunoreactivity of aFGF was up-regulated in both neuronal and nonneuro nal cells in this patient. Results suggest that these trophic growth factor s and their receptors may protect facial neurons from secondary degeneratio n and promote regrowth of the facial nerve after axotomy or injury.