Upregulation of glial cell line-derived neurotrophic factor (GDNF) in the rat cochlea following noise

There are endogenous intracellular mechanisms that provide cells with prote ction from stress, as well as repair from damage. These pathways often invo lve stress proteins and neurotrophic factors. The present study used Wester n blot analysis to examine changes in glial cell line-derived neurotrophic factor (GDNF) following noise overstimulation. A noise exposure was utilize d which causes a temporary threshold shift and has been previously shown to upregulate heat shock protein 72 in the rat cochlea. This noise exposure a lso provides protection from a second noise exposure that would otherwise c ause a permanent threshold shift. Experimental animals were assessed 2, 4, 8 and 12 h after cessation of noise exposure. Control animals received the same treatment except for the noise exposure and were assessed at the 8 h t ime point. A moderate expression of GDNF was observed in the normal cochlea . No significant change in GDNF levels was observed at 2 or 4 h following n oise overstimulation. However, a significant increase was found at 8 h. At 12 h following noise overstimulation, GDNF levels were no longer significan tly elevated from normal. These results suggest that GDNF is involved in th e endogenous stress response in the cochlea and are consistent with the pro tection that exogenously applied GDNF has been shown to provide. (C) 2000 E lsevier Science B.V. All rights reserved.