THE SITE OF ACTION OF NEURONAL ACIDIC FIBROBLAST GROWTH-FACTOR IS THEORGAN OF CORTI OF THE RAT COCHLEA

Here we show that the mature cochlear neurons are a rich source of aci dic fibroblast growth factor (aFGF), which is expressed in the neurona l circuitry consisting of afferent and efferent innervation. The site of action of neuronal aFGF is likely to reside in the organ of Corti, where one of the four known FGF receptor (FGFR) tyrosine kinases-namel y, FGFR-3 mRNA-is expressed, Following acoustic overstimulation, known to cause damage to the organ of Corti, a rapid up-regulation of FGFR- 3 is evident in this sensory epithelium, at both mRNA and protein leve ls. The present results provide in vivo evidence for aFGF being a sens ory neuron-derived, anterogradely transported factor that may exert tr ophic effects on a peripheral target tissue, In this sensory system, a FGF, rather than being a neurotrophic factor, seems to promote mainten ance of the integrity of the organ of Corti. In addition, aFGF, releas ed from the traumatized nerve endings, may be one of the first signals initiating protective recovery and repair processes following damagin g auditory stimuli.