Cochlear frequency-place map in adult chickens: Intracellular biocytin labeling

A cochlear frequency-place map was developed for adult chickens by labeling cochlear ganglion neurons with biocytin and correlating the location of each labeled fiber along the basilar papilla with the characteristic frequency of the unit's tuning curve. Labeled fibers showed little or no branching within the sensory epithelium and most fibers appeared to terminate on a single hair cell along the neural side of the basilar papilla. The CFs of the labeled neurons ranged from 353 Hz to 3145 Hz and the location of the labeled neurons ranged from 30.1% to 74.4% of the total distance from the apex of the papilla. CFs increased in an orderly manner from the apex towards the base of the papilla. The cochlear frequency map for adult chickens was similar to that estimated from previous cochlear lesion studies carried out on 30 day old chicks, although the predicted frequencies in the adults were slightly higher in some regions of the basilar papilla than in 30 day old animals. However, previous maps developed in younger animals (≤21 days) using lesion or labeling data predict significantly lower frequencies for a given location than in adult animals particularly in the basal half of the cochlea.