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 sections, we evaluated immunoreactivity of 11 neurotrophic factors and their receptors in facial nuclei of human brain stems (4 normal cases, and 1 from a patient with facial palsy and synkinesis). In the normal subjects, positive immunoreactivity of the growth factor neurotrophin-4 and acidic fibroblast growth factor (aFGF) was observed in facial motor neurons, as was positive immunoreactivity against ret, the receptor shared by glial cell line-derived neurotrophic factor and neurturin. Immunoreactivity was moderate for the receptor trkB and strong for trkC. In the case of partial facial palsy, surviving cells failed to show immunoreactivity against neurotrophins. However, immunoreactivity of aFGF was up-regulated in both neuronal and non- neuronal cells in this patient. Results suggest that these trophic growth factors and their receptors may protect facial neurons from secondary degeneration and promote regrowth of the facial nerve after axotomy or injury.