The c-Fos transcription factor in the auditory pathway of the juvenile rat: Effects of acoustic deprivation and repetitive stimulation

The expression of the inducible transcription factors (ITF) c-Fos and JunB was investigated in the dorsal cochlear nucleus (DCN), ventral cochlear nucleus (VCN) and inferior colliculus (IC) of juvenile and adult rats following deprivation and repetitive stimulation paradigms using 8 kHz tone bursts at 5 min duration and 70 dB, 90 dB or 120 dB sound pressure level (SPL). (1) During postnatal development without stimulation, c-Fos is absent in DCN and VCN from postnatal day (P) 12 to adulthood, but shows a strong expression in the IC which declines during maturation. A similar decrease was also seen in the pens. (2) Between P15 and P35 stimulation of rats with 8 kHz for 5 min at 70 dB SPL evoked expression of c-Fos in a moderate number of cells of DCN, VCN and IC. Higher sound pressure levels increased the number of c-Fos immunoreactive neurons as studied at P21. (3) Deprivation of acoustic stimulation up to P21 reduced the expression of c-Fos when rats were stimulated with 90 dB immediately after the restoration of acoustic input. In contrast to 90 dB SPL, c-Fos immunoreactivity (LR) did not significantly differ between deprived and normal rats following application of 120 dB SPL at P21. Stimulation at P28, i.e., 7 days after the end of the deprivation, evoked an increase of c-Fos only in the IC compared to otherwise normally stimulated rats. At P35, effects of the former deprivation on the c-Fos expression were not longer detectable. (4) In a repetitive stimulation paradigm, 8 kHz tone bursts 5 min in duration were applied each second day between P23 and P35 or each day between P29 and P35. When compared with acutely stimulated rats at P35, both repetitive acoustic stimulation protocols reduced the c-Fos immunoreactivity by 50%-75% in the DCN, VCN and IC. In adult 4-month-old rats, repetitive stimulation did not reduce the c-Fos immunoreactivity from its moderate levels as compared with acute stimulation. (5) In some experiments, we studied also the expression of the JunB protein. JunB paralleled the expression of c-Fos following single acoustic stimulation, but was expressed in a substantially lower number of cells. In contrast to c-Fos, however, repetitive stimulation as described in section 4 did not evoke a decrease of JunB in the lower acoustic pathway. (C) 1997 Elsevier Science B.V.