Identification of gene expression profiles in rat ears with cDNA microarrays

The physiological processes of hearing implicate thousands of molecules acting in harmony; however, their identities are only partially understood. We used cDNA microarrays containing 1,176 genes to identify >150 genes expressed in rat middle and inner ear tissue. Expressed genes covered several gene families and biological pathways, many of which have previously not been described. Transcription factor genes that were expressed included inhibitors of DNA binding protein (Id). These were localized to the spiral ganglion, organ of Corti and stria vascularis, and they are possibly involved in neurogenesis and angiogenesis. Transcriptional factors that were highly expressed included Gax (homeobox) and I-kappaB, which inhibit cellular proliferation. Their presence suggests that inhibitory programs for cell proliferation are enforced in the ear. Ion channel genes that were expressed included voltage-dependent L-type calcium channels (LTCC) and proton-gated cation channels (PGCC). Genes involved in neurotransmitter production and release included glutamic acid decarboxylase (GAD1). Genes involved in postsynaptic inhibition included neuropeptide Y5 receptors (NPY5) and GAD1. Due to the existence of receptors and/or enzymes involved in their biochemical synthesis, neurotransmitters associated with these might include serotonin, glutamide, acetylcholine, gamma-aminobutyric acid (GABA), neurotensin, and dopamine.