Evidence that catecholamines are not the afferent transmitter in the cochlea.

Beta-receptor blocking agents (practolol, propranolol) and alpha-receptor blocking agents (phenoxybenzamine, phentolamine), when applied intracochlearly do not eliminate the afferetn discharges or compound action potential of the cochlear nerve. Under the assumption that the drugs used reach the synaptic site, it is therefore concluded that these drugs do not interfere with afferent synaptic transmission. Phentolamine,, however, has a toxic effect upon the cochlea independent from the synaptic process. Local application of catecholamines does not increase spontaneous activity of single fibres of the cochlear nerve. These findings show that catecholamines are not likely to be the afferent transmitter.