Glial cell line-derived neurotrophic factor (GDNF) and its receptor complex are expressed in the auditory nerve of the mature rat cochlea

Glial cell line-derived neurotrophic factor (GDNF) is a survival factor for many neuronal cell types which signals through a heterodimer receptor cons isting of GDNF-family receptor alpha 1 (GFR alpha -1) and Ret (rearranged d uring transformation). GDNF expression has previously been reported in the inner hair cells of the rat cochlea, with expression of GFR alpha -1 but no t Ret in the cell bodies of the auditory nerve (spiral ganglion cells), usi ng in situ hybridization. The present study used reverse transcription-poly merase chain reaction (RT-PCR), and immunocytochemistry to examine GDNF, GF R alpha -1 and Ret in the adult rat auditory nerve. Semi-quantitative RT-PC R showed expression of GDNF and the two receptor components, GFR alpha -1 a nd Ret, in the modiolar subfraction of the cochlea containing spiral gangli on cells. A shorter mRNA splice variant for GDNF was also detected. Immunoc ytochemistry showed immunostaining in the modiolus for GDNF, GFR alpha -1 a nd Ret that was confined to spiral ganglion cells. When RT-PCR expression l evels were compared to the expression in the substantia nigra, GFR alpha -1 expression levels were similar, Ret mRNA was lower in the modiolus and GDN F expression was higher in the modiolus. However, when GDNF was further ass essed using Western blot, while GDNF protein was found in the modiolus it w as at lowe cr levels than in substantia nigra tissue. These results demonst rate that GDNF and both of its receptor components are found in spiral gang lion cells of the adult rat cochlea. Along with the previous report of GDNF in inner hair cells, these new results provide a basis for the role of GDN F as a survival factor for the auditory nerve, as suggested by previous stu dies. (C) 2001 Published by Elsevier Science B.V.