DNA microarray analysis on frequency tuning and tonotopical organization in the mouse cochlea

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To understand the mechanism of frequency tuning and tonotopical organization in the mouse cochlea, we characterized mRNA expression in the apical and basal parts of the mouse cochlea with a DNA microarray analysis.DNA microarray analysis revealed that the mRNA expression of 184 out of 19801 genes on the DNA chip was more than three times up-regulated in the apical part of the mouse cochlea and that the mRNA expression of 181 out of 19801 genes on the DNA chip was more than three times up-regulated in the basal part. Further study by using a real-time PCR technique confirmed that the expressions of Slc4al (Cl-HC03 exchanger) was up-regulated by 3.12 times in the apical part and that the expressions of six genes including Gabt1 (GABA receptor β1), Nstr2 (Neurotensin receptor), and Tac1 (Substance P) were up-regulated more than three times in the basal part.DNA microarray analysis focusing on the efferent neurotransmission via acetylcholine receptors (AChR) and GABA receptors (GABAR) demonstrated that the mRNA expression of AChR subunits was almost comparable in the apical and basal parts of the mouse cochlea while the mRNA expression of GABAR subunits was not always even in both parts. The mRNA expressions of subunits γ3,θ,δ, and ρ were almost equal in both parts. However, the expressions of β1,β2,γ1, and γ2 were more than two times up-regulated in the basal part of the mouse cochlea.These results indicate that the location/place-specific mRNA expression in hair cells and spiral ganglion cells in the mouse cochlea might determine the frequency tuning and tonotopical organization.