Cochlear nucleus inputs to olivocochlear neurones revealed by combined anterograde and retrograde labelling in the guinea pig.

Injections of the fluorescent tracer, Fast blue (FB), into cochlear nucleus complex in guinea pig produced strong anterograde labelling of ascending projections from this nucleus. When combined with retrograde labelling of olivocochlear efferent neurones by intracochlear injection of a second fluorescent tracer, Diamidino yellow (DY), the synaptic terminals formed on these cells by projections from the cochlear nucleus could be identified. The results provide direct support for the notion that many of the ipsilateral-monaural cochlear efferents identified in physiological studies correspond to the olivocochlear neurones located in brainstem nuclei contralateral to their target cochlea.