reaction represents an internal control so that the intensity of the activity dependent gene can be compared unambiguously with the control and the treated samples pcr ready to go beads from amersham pharmacia were used in order to ensure a standardization of the pcr conditions and to reduce contamination during pipetting finally the pcr products were analyzed in a 2 agarose gel which was visualized using an ethidium bromide stain and densitometric analysis using an alpha imager 2200 from biometra the intensity of the amplified activity dependent gene was normalized for each reaction to the level of the coamplified gapdh the amplification conditions for arc bdnf c fos and gapdh were for the initial denaturation phase of 94 u00b0 c for three minutes 30 cycles each of one minute of denaturation 94 u00b0 c one minute of annealing 54 u00b0 c 1 5 minutes of extension 72 u00b0 c and a final extension phase of ten minutes at 72 u00b0 c the pcr fragments were cloned and sequenced as described previously the anesthesia of the animals and the abr screening was carried out as described previously cf knipper m et al 2000 loc cit schimmang t et al 2003 lack of bdnf and trkb signalling in the postnatal cochlea leads to a spatial reshaping of innervation along the tonotopic axis and hearing loss development 130 pages 4741 to 4750 as described above salicylate was administered locally in the niche of the round window to female rats of approximately the same weight in order to preclude any post traumatic effects on the expression of the activity dependent genes in the cochlear neurons the individuals used were exclusively those showing no change.