HPLC detection of dopamine and noradrenaline in the cochlea of adult and developing rats.
The presence and postnatal development of dopamine (DA) and noradrenaline (NA) in the rat cochlea were detected by high-performance liquid chromatography coupled with electrochemical detection. Cochlear DA content rose gradually after birth. Conversely, NA concentrations rose rapidly between postnatal day 1 and 8; then, up to day 30, it increased more slowly. On day 30, both DA and NA levels were around 5 times higher than on day 1. In the adult rat cochlea, NA mean content was 234 +/- 22.2 pg/mg protein, while DA mean content was 23.6 +/- 1.1 pg/mg protein. Adrenaline was always undetectable. The present study is the first report describing directly the presence of DA in the rat cochlea. DA might serve as one of the lateral efferent neurotransmitters, whereas NA probably acts as a neurotransmitter of the sympathetic cochlear innervation. Nevertheless, their influences on the cochlear physiology, either in adulthood or during development are still a matter of discussion.