Gradients of organic substances between fluid compartments of the cochlea.

We have previously demonstrated the presence of steep gradients of amino acids between cochlear endolymph and perilymph of scala vestibuli. However, only recently have we succeeded in developing a sampling technique which is capable of providing amino acid levels in scala tympani which are representative of the in vivo situation under physiological circumstances. This is achieved by sampling perilymph in a closed system, which precludes unphysiological contamination by CSF via the cochlear aqueduct. It is also shown that amino acids which exhibit very steep gradients between CSF and perilymph, such as glycine and alanine, can be used as endogenous markers to assess the degree of artifactual admixture of CSF when perilymph is sampled by conventional techniques in the open system. Moreover, pilot experiments indicate that net production of perilymph is very low when the cochlear aqueduct is blocked.