Effect of acoustic stress on glucocorticoid receptor mRNA in the cochlea of the guinea pig.

As a first step toward elucidating the mechanism underlying the therapeutic effect of glucocorticoids on acute noise-induced hearing loss, we used semiquantitative reverse transcription polymerase chain reaction to study the level of glucocorticoid receptor (GR) mRNA in the cochlea of the guinea pig after acoustic overstimulation. The cochleas were dissected and divided into three portions (lateral portion, medial portion and modiolus). In the lateral portion, the glucocorticoid receptor mRNA level was significantly decreased 2 h after exposure to a 120 dB SPL sound and both 2 and 6 h after exposure to a 130 dB SPL sound. To determine where in the cochlea the changes in glucocorticoid receptor mRNA levels occur, in situ hybridization histochemistry was performed with digoxigenin-labeled sense and antisense RNA probes complementary to guinea pig glucocorticoid receptor mRNA. Glucocorticoid receptor mRNA was demonstrated in the spiral ligament, stria vascularis, spiral limbus and spiral ganglion. Moreover, the glucocorticoid receptor mRNA level was decreased in the spiral ligament, especially in the spiral prominence of the basal turn, 2 h after exposure to the 130 dB SPL sound. These results could imply that the therapeutic effect of glucocorticoids in the cochlea might be mediated in the spiral ligament, particularly in the spiral prominence.