A double-label study of efferent projections to the cochlea of the chicken, Gallus domesticus.

Intracochlear bilateral injection of the fluorescent retrograde markers fast blue and diamidino yellow was used to identify the brainstem location of the olivocochlear efferents in the domestic chicken. The overall distribution pattern of neurones was similar to that of recent studies using horseradish peroxidase as the retrograde tracer, although the number of labelled neurones was significantly greater than previously reported. The average number of labelled neurones projecting to any one cochlea was 242, with roughly equal numbers located ipsilaterally or contralaterally. After bilateral injection of the two tracers, no double-labelled neurones were detected.