Journal of Neuroscience, Vol 3, 1373-1378, Copyright © 1983 by Society for Neuroscience
Frequency-specific projections of individual neurons in chick brainstem auditory nuclei
SR Young and EW Rubel
Nucleus magnocellularis and nucleus laminaris in the avian brainstem
contain second- and third-order auditory neurons thought to be homologous
to the mammalian anteroventral cochlear nucleus and medial superior olivary
nucleus, respectively. Nucleus laminaris in the chicken is a tonotopically
organized sheet of bipolar neurons; each of these neurons receives
spatially segregated bilateral innervation from the two magnocellular
nuclei. In the present study, this projection was studied at the single
cell level by analyzing the pattern of terminal arborizations of individual
horseradish peroxidase-filled axons. Reconstruction of the terminal
arborizations of nucleus magnocellularis axons revealed that each axon
forms an elongated band of endings, the long axis of which is parallel to
the physiologically defined isofrequency bands. Within a band, the
individual terminal collaterals form distinct patches separated by areas
without endings. We suggest that the elongated terminal fields provide the
basis of the tonotopic organization observed in nucleus laminaris and that
the trajectories of the ipsilateral and contralateral axons may provide
differential conduction delays that are important for binaural integration
of acoustic information.