Noise and the RNA synthesis of the cochlea. Autoradiographic studies

In cochlear basal turns of 22 guinea pigs with autoradiography, grain density was measured after injection of 3H-cytidine. Following high initial nuclear labelling, a low incorporation in cytoplasm was observed, even after 24 hours. Synthesis of ribosomal RNA in the organ of Corti seems to be slow. Low grain densities in the whole cochlea presuppose a blood-lymph barrier to cytidine. After white noise (85 dB SPL, 12 hours) were seen a more rapid incorporation into nuclei and after 24 hours an increased labelling of cytoplasm of ganglion cells, fibrocytes and inner hair cells, less of outer hair cells. This might be induced by increased blood flow, concentration of the precursor in the lymphs, cell permeability of alterations of the cellular nucleotide pool. But a real stimulation of cochlear RNA synthesis seems to be the most likely. On comparing different turns, a peak in grain density was found over nuclei of the organ of Corti after 1 hour in the 2nd turn. After 24 hours, cytoplasmic labelling showed a decrease only in outer hair cells towards apical turns.