Quantitative analysis of dopamine receptor messages in the mouse cochlea

Dopamine receptor isoforms were examined in the cochlea of the CBA(J) mouse by RT-PCR analysis and nucleotide sequencing, utilizing primers specific for known dopamine receptor isoforms. Cochlear cDNA sequences corresponding to dopamine D(2(long)) and D₃ receptors were amplified, whereas those representing D(1A), D(1B), D(2(short)), and D₄ were not detected. Utilizing quantitative competitive PCR analysis, relative levels of dopamine receptor transcripts were found to be 0.002, 0.014, 0.016, and 1.000 for D(2(long)) cochlea, D₃ cochlea, D₃ brain, and D(2(long)) brain, respectively. In the context of previously published findings, the current work provides key quantitative evidence necessary to establish that dopamine is a neurotransmitter in the auditory inner ear.