Cochlear efferent neurons projecting to both ears in the chicken, Gallus domesticus

Different retrograde neuroanatomical tracers were injected into each cochlea of adult chicken. The number of cells labeled in the cochlear efferent cell group found bilaterally within the caudal pontine reticular formation depended upon the tracer, with True Blue and Fluoro Gold yielding maximal average counts of 332 efferent neurons per injection. Double labeling of less than 1% of these cells was possible with the combination of True Blue and Diamidino Yellow. Thus the contribution of efferent neurons with axon collaterals projecting to both ears is not fundamentally different in birds and other vertebrates.